Scholarly article on topic 'A search for pair production of new light bosons decaying into muons'

A search for pair production of new light bosons decaying into muons Academic research paper on "Physical sciences"

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Physics Letters B
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{LHC / CMS / Muon / NMSSM / "Hidden sectors" / "Dark matter"}

Abstract of research paper on Physical sciences, author of scientific article —

Abstract A search for the pair production of new light bosons, each decaying into a pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7  fb − 1 collected in proton–proton collisions at center-of-mass energy of s = 8  TeV . No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-to-minimal supersymmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime.

Academic research paper on topic "A search for pair production of new light bosons decaying into muons"

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Physics Letters B

www.elsevier.com/locate/physletb

A search for pair production of new light bosons decaying into muons ^

CMS Collaboration *

CERN, Switzerland

CrossMark

A R T I C L E I N F 0

Article history:

Received 31 May 2015

Received in revised form 20 October 2015

Accepted 25 October 2015

Available online 3 November 2015

Editor: M. Doser

Keywords:

Hidden sectors

Dark matter

A B S T R A C T

A search for the pair production of new light bosons, each decaying into a pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7 fb-1 collected in proton-proton collisions at center-of-mass energy of -,/s = 8 TeV. No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-to-minimal super-symmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime.

© 2015 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.

1. Introduction

In July 2012 the ATLAS and CMS Collaborations at the CERN LHC announced the discovery of a particle [1-3] with properties consistent with the standard model (SM) Higgs boson [4-7]. Direct measurements of the production and decay rates of the new particle, using SM decay channels, have so far played a key role in determining whether or not it is indeed consistent with the SM predictions. However, substantially increasing the precision of these measurements will require further data. Searches for Higgs bosons through production mechanisms not predicted by the SM, or decay modes involving particles not included in the SM, provide a complementary approach and have the advantage of probing specific types of new physics models with the existing data.

This letter presents a search for the pair production of new light bosons (denoted as 'a') decaying to pairs of isolated, oppositely charged muons (dimuons). One production mechanism for these new bosons is in the decay chain of a Higgs boson h, which can be SM-like or not: h ^ 2a + X ^ 4i + X, where X denotes possible additional particles from cascade decays of the Higgs boson. A range of new physics scenarios predict this decay topology, including the next-to-minimal supersymmetric standard model (NMSSM) [8] and models with hidden (or dark) sectors [9-11].

* E-mail address: cms-publication-committee-chair@cern.ch.

The NMSSM is an extension of the minimal supersymmet-ric standard model (MSSM) [12,13] that includes an additional gauge singlet field. It resolves the so-called i problem [14] and significantly reduces the amount of fine tuning required in the MSSM [15]. The NMSSM Higgs sector consists of three CP-even neutral Higgs bosons h12,3, two CP-odd neutral Higgs bosons a12 and a pair of charged Higgs bosons h±. The h1 and h2 can decay via h1>2 ^ 2a1, where either the h1 or h2 can be the boson observed at 125 GeV. The a1 boson can be light and couple weakly to SM particles with a coupling to fermions proportional to the fermion mass. Therefore it can have a substantial branching fraction B(a1 ^ ¡i+i~) if its mass is within the range 2m^ < ma1 < 2mT [16,17] (benchmark model 1 in this letter). A search for final states containing muon pairs provides sensitivity to models of this form.

Supersymmetry (SUSY) models with dark sectors (dark SUSY) offer an explanation for the excess in the ratio of the positron flux to the combined flux of positrons and electrons observed by the satellite experiments [18-20] in primary cosmic rays as well as predict cold dark matter with a scale of O(1 TeV). A simple realization of these models includes a new U(1)D symmetry (the subscript "D" stands for "Dark") which is broken and gives rise to massive dark photons (denoted as yD). Kinetic mixing of the new U(1)D with the SM hypercharge U(1)Y provides a small mixing between yD and the SM photon which allows yD to decay to SM particles [21]. Depending on the value s of the kinetic mixing, the yD may also be long-lived. The lack of an antiproton to proton ratio excess of the magnitude similar to the positron excess in the mea-

http://dx.doi.org/10.1016/j.physletb.2015.10.067

0370-2693/© 2015 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.

surements of the cosmic ray spectrum constrains the mass of yD to be less than twice the mass of the proton [22]. If the hidden sector directly or indirectly interacts with the Higgs field, a number of possible scenarios may be realized. One such scenario, denoted in this letter as benchmark model 2, is a model of SUSY where the SM-like Higgs boson can decay via h ^ 2n1, where n1 is the lightest neutralino in the visible (as opposed to hidden) part of the SUSY spectrum. The n1 can decay via n1 ^ nD + yD, where nD is a dark neutralino that escapes detection. Assuming that yD can only decay to SM particles, the branching fraction B(yD ^ fi+ can be as large as 45%, depending on the mass of yD [11].

Previous searches for pair production of new light bosons decaying into dimuons were performed at the Tevatron [23] and the LHC [24,25]. Searches for associated production of the light CP-odd scalar bosons have been performed at e+e- colliders [26,27] and the Tevatron [28]. Direct a1 production has been studied at the LHC [29], but this is heavily suppressed by the typically very weak couplings of the new bosons to SM particles. The constraints on the allowed NMSSM parameter space are driven by the measurements of relic density by WMAP [30] and more recently by PLANCK [31], while specifically for the Higgs sector the most relevant measurements come from LEP [32-37], LHC measurements of the SM-like Higgs properties, and direct searches for h ^ aa [25]. In the framework of dark SUSY, experimental searches for dark photons have focused on their production at the end of SUSY cascades at the Tevatron [38-40] and the LHC [41,42]. Searches at a range of low energy e+e- colliders (KLOE [43], BaBar [44]), heavy-ion colliders (PHENIX [45]), fixed-target experiments (APEX [46], A1 at MAMI [47], HADES [48]), as well as cosmological measurements [49-51] and others [52-56] provide constraints on complementary regions of the available parameter space.

Results are presented in this Letter in the context of the two benchmark scenarios discussed earlier, one in the context of NMSSM and another one in the framework of dark SUSY scenarios. However, the search has been designed to be independent of the details of these two specific models, and the results can be interpreted in the context of other models predicting the production of the same final states. Compared to the previous version [25], the present analysis has been redesigned to be sensitive to signatures with the intermediate bosons traversing a nonnegligible distance before decaying into a pair of muons. Such signatures can be realized in dark SUSY models if the mixing of the dark photon with its SM counterpart is sufficiently weak. In addition, the present analysis uses a dataset four times larger than the previous analysis, and at a higher center-of-mass energy, further extending the reach for signatures with prompt muons.

2. The CMS detector

This search is based on a data sample corresponding to an integrated luminosity of 20.7 fb-1 of proton-proton collisions at a center-of-mass energy = 8 TeV, recorded by the CMS detector in 2012. The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter, and a brass and scintillator hadron calorimeter, each composed of a barrel and two endcap sections. Muons are measured in gas-ionization detectors embedded in the steel flux-return yoke outside the solenoid. Extensive forward calorimetry complements the coverage provided by the barrel and endcap detectors. Muons are measured in the pseudorapidity range |nl < 2.4, with detection planes made using three technologies: drift tubes, cathode strip chambers, and resistive plate chambers. Matching muon candidates to tracks measured in the silicon tracker results in an accurate measurement of the transverse momentum (pT). As an

example, for muons with pT < 10 GeV the relative pT resolution is found to be 0.8%-3.0% (depending on |nl) and for muons with 20 < pT < 100 GeV it is 1.3-2.0% in the barrel and better than 6% in the endcaps [57]. A more detailed description of the CMS detector, together with definitions of the coordinate system used and the relevant kinematic variables, can be found in [58].

3. Data selection

The data were collected with an online trigger selecting events containing at least two muon candidates, one with pT > 17 GeV and another with pT > 8 GeV. In this analysis offline muon candidates are defined as particle-flow (PF) muons [57]. The PF reconstruction algorithm combines information from all CMS sub-detectors to identify and reconstruct individual particles, such as electrons, photons, hadrons or muons.

Events are further selected by requiring at least four offline muon candidates with pT > 8 GeV and |nl < 2.4 that form two oppositely charged pairs. At least one of these muons must additionally satisfy the requirement of pT > 17 GeV and |nl < 0.9, which ensures that the trigger efficiency is high and independent of the event topology, including effects related to overlaps of nearby muon trajectories. Tracks associated with a pair of opposite-charge muon candidates are fit for a common vertex using a Kalman filter algorithm [59]. If the vertex is reconstructed, a muon pair is combined into a dimuon system if its invariant mass measured at the common vertex < 5 GeV and the vertex fit prob-

ability Pv > 1%. Muon pairs failing these requirements

are still retained for the analysis if at the point of closest approach of the two trajectories they are within ARQi+, /x-) =

yW+ - )2 + - ^^-)2 < 0.01, where are the az-imuthal angles in radians. This recovery step is designed to compensate for the reduced efficiency of the vertex selection for dimuons in which the two muon tracks are nearly parallel to each other, therefore a good efficiency is maintained for dimuon masses down to the 2m^ threshold (0.2114 GeV). For dimuons in which this is the case the point of closest approach is selected as the vertex position, with the additional selection requirement that the distance between the tracks be < 0.5 mm. The dimuon kinematic variables are measured at the dimuon vertex position. There is no restriction on the number of ungrouped additional muons. Both dimuons are required to have at least one hit in the first layer of the barrel or endcaps of the pixel detector, and this defines an effective "fiducial" region. This requirement, along with the muon pT and |n| criteria, ensures high trigger (>96%), reconstruction, and selection efficiencies, with a greatly reduced dependence on the pT, n, or opening angle between the muons.

The projected z coordinate of the dimuon system at the point of the closest approach to the beam line (zis reconstructed using the dimuon momentum. The requirement |z1w - z2^| < 1 mm is imposed to ensure that both dimuons are consistent with the same pp interaction; no explicit requirements are made on the impact parameter or the z coordinate at the point of closest approach to the beam line of the individual reconstructed muons to preserve sensitivity to signatures with displaced muons.

To suppress background events in which the muons are produced in the decay of heavy quarks (and thus appear in jets), the dimuons are required to be isolated from other event activity using the criterion Isum < 2 GeV. The isolation parameter /sum is defined as the scalar sum of the pT of charged tracks with pT > 0.5 GeV within a cone of size AR = 0.4 centered on the momentum vector of the dimuon system, excluding the tracks corresponding to the two muon candidates. The tracks used in the calculation of Isum must also have a z coordinate at the point of closest approach to the beam line that lies within 1 mm of z^. The Isum selection

Table 1

Event selection efficiencies esim(mhj, ma1 ) and esim(m№, cryD), as obtained from simulation, the geometric and kinematic acceptances agen(mh,, ma1 ) and agen(myD, ctyD),

calculated using only generator-level information, and their ratios (with statistical uncertainties), for a few representative NMSSM and dark SUSY benchmark samples. The experimental data-to-simulation scale factor (6data/fsim, described later) is not applied.

mhl [GeV] 90 125 125

mai [GeV] 2 0.5 3.55

esim [%] 11.0 ± 0.1 21.1 ± 0.1 17.3 ± 0.1

agen [%] 15.9 ± 0.1 32.0 ± 0.1 26.3 ± 0.1

esim/«gen 0.69 ± 0.01 0.66 ± 0.01 0.66 ± 0.01

mYD [GeV] 0.25 1.0

ctyd [mm] 0 0.5 2 0 0.5 2

esim [%] 8.85 ± 0.12 1.76 ± 0.05 0.23 ± 0.03 6.13 ± 0.23 4.73 ± 0.07 1.15 ± 0.04

agen [%] 14.32 ± 0.14 2.7 ± 0.06 0.31 ± 0.03 8.89 ± 0.28 6.98 ± 0.09 1.68 ± 0.05

esim/agen 0.62 ± 0.01 0.65 ± 0.02 0.74 ± 0.13 0.69 ± 0.03 0.68 ± 0.01 0.68 ± 0.03

suppresses the contamination from bb production by about a factor of 40, as estimated using a bb enriched control sample with one dimuon recoiling off a jet containing an unpaired muon, while rejecting less than 20% of events with the signal topology.

The invariant mass m1^ always refers to the dimuon containing a muon with pT > 17 GeV and |nl < 0.9. For events with both dimuon systems containing such a muon, the assignment of m1n and m2ii is random for compatibility with the background modeling schema described in Section 5. The invariant masses of both reconstructed dimuons are required to be compatible within the detector resolution, specifically |m1w — m2/l/l| < 0.13 GeV + 0.065 (m1n + m2ii)/2, which defines a diagonal signal region in the plane of the invariant masses of the two dimuons. The numerical parameters in the requirement correspond to at least five times the size of the core resolution in the dimuon mass.

4. Signal modeling

The results from this analysis are designed to be model independent, but are also presented in the context of the two benchmark models introduced earlier. NMSSM simulation samples for benchmark model 1 are generated with pythia 6.4.26 [60], using MSSM Higgs boson production via gluon fusion gg ^ H°mssm, with the Higgs bosons decaying via H0MSSM ^ 2Amssm. The masses of the MSSM bosons H0MSSM and A0MSSM are set to the desired values for the h1 mass and a1 mass of the NMSSM bosons, respectively. The mass of H0MSSM is in the range 90-150 GeV (mass below 90 GeV is excluded by LEP [37]) and the mass of AMSSM is in range 0.25-3.55 GeV. Both AMSSM bosons are forced to decay promptly to a pair of muons. Dark SUSY simulation samples for benchmark model 2 are generated with MadGraph 4.5.2 [61] using SM Higgs boson production via gluon fusion gg ^ hSM, with mhSM = 125 GeV. The Bridge program [62] is used to force the Higgs bosons to undergo a non-SM decay to a pair of neutrali-nos, each of which decays via n1 ^ nD + yD, where mn1 = 10 GeV, mnD = 1 GeV, which is representative of the type of models considered [42]. Dark photons are generated with m№ in the range 0.25-2.0 GeV and a decay length cxyD in the range of 0-20 mm. Each of the two dark photons is forced to decay to two muons, while both dark neutralinos escape detection. The narrow-width approximation is imposed by setting the widths of the dark photons to a small value (10—3 GeV).

All benchmark samples are generated using the leading-order CTEQ6.6 [63] set of parton distribution functions (PDF), and are interfaced with pythia using the Z2* tune [64] for the underlying event activity at the LHC and to simulate jet fragmentation.

The signal samples are processed through a detailed simulation of the CMS detector based on Geant4 [65] and are reconstructed

with the same algorithms used for data. Table 1 shows the event selection efficiencies esjm obtained using the simulated benchmark samples for a few representative choices of (mh1, ma1), and (mrD, ctyD). To provide a simple recipe for future reinterpretations of the results in the context of other models, the variable agen is separately defined as the geometric and kinematic acceptance of this analysis calculated using only generator-level information. It is defined by selecting events containing at least four muons with pT > 8 GeV and |nl < 2.4, with at least one of these muons having pT > 17 GeV and |n| < 0.9. The new light boson must also decay with transverse decay length Lxy < 4.4 cm and longitudinal decay length Lz < 34.5 cm (both defined in the detector reference frame), to satisfy the "fiducial" region of the analysis. Table 1 shows agen along with the ratio esim/agen.

5. Background estimation

The SM background for this search is dominated by bb production and has small contributions from the electroweak production of four muons and direct J/^ pair production. The leading part of the bb contribution is due to b quark decays that result in a pair of muons, via either the semileptonic decays of both the b quark and the resulting c quark, or via resonances, i.e. w, p, 0, J/^. A smaller contribution comes from events with one genuine dimuon candidate and a second dimuon candidate containing one muon from a semileptonic b quark decay and a charged hadron misidentified as another muon.

Using data control samples, the bb background is modeled as a two-dimensional (2D) template Bbb(m1n, m2n) in the plane of the invariant masses of the two dimuons. The template describing the 2D probability density function is constructed as a Cartesian product B 17(m1ii) B8(m2ii), where the B17 and B8 templates model the invariant mass distributions for dimuons with and without the requirement that the dimuon contains at least one muon satisfying pT > 17 GeV and |n| < 0.9 respectively. The B17 shape is measured using a data sample enriched with bb events containing exactly one dimuon and one additional muon, under the assumption that the decay of one of the b quarks results in a dimuon pair containing at least one muon with pT > 17 GeV and |n| < 0.9, while the other b quark decays semileptonically resulting in the additional muon with pT > 8 GeV. For the B8 shape, a similar sample and procedure is used but the dimuon is required to have both prongs with pT > 8 GeV, while the additional muon must have pT > 17 GeV and |n| < 0.9. The two templates are required as the shape of the dimuon invariant mass distribution depends on the pT thresholds used to select the muons and whether the muons are restricted to the central (|n| < 0.9) region or can be in the full acceptance range (|n| < 2.4), as a result of the differences

2 2.5 -iw[GeV]

Fig. 1. Distribution of the invariant masses m1vs. m2for the isolated dimuon events following the application of all constraints except the ~ m2re-quirement of compatibility within the detector resolution. The compatible diagonal signal region (outlined with dashed lines) contains one data event (triangle) at = 0.33 GeV and m2= 0.22 GeV. There are also nine data events (white circles) which fail the m1(^ ~ m2compatibility requirement. The color scale indicates the expected SM background in range 2m< m2¡¡¡, < 2mT.

in the momentum resolution of the barrel and endcap regions of the tracker. The B17 and B8 distributions are fitted with a parametric analytical function using a sum of Bernstein polynomials and Crystal Ball functions [66] describing resonances. These event samples do not overlap with the sample containing two dimuons that is used for the main analysis and they have negligible contributions from non-bb backgrounds. Once the Bm2¡¡) template is constructed, it is used to provide a description of the bb background shape in the signal region. This technique assumes that each b quark fragments independently and that if the shapes of these distributions are measured using data samples with kinematics very similar to that of the background events then the effects of residual kinematically-induced correlations are small (albeit weakly induced, the shape depends on the b jet pT and the pT of the two b jets in background bb events tend to be similar). The background template is validated in a region where both dimuons fail the Isum < 2 GeV requirement and good agreement with data is observed.

The data events that satisfy all analysis selections but fail the m1~ m2requirement are used to normalize the B

template. This selection yields nine events in the offdiagonal sideband region of the plane, leading in the diagonal signal region to an expected rate of bb background events of 2.0 ± 0.7. This is essentially (9 ± V9) x 0.18/0.82, where 0.18 and 0.82 correspond to the integral of the areas under the background template inside and outside the signal diagonal region, respectively. These nine events in the off-diagonal sidebands of the (m1^, m2/^) plane are shown as white circles in Fig. 1.

The contribution from direct J/^ pair production is estimated using another data control sample. Events are selected with a trigger that requires at least three muon candidates, two of which have a common vertex and an invariant mass consistent with that of the J/^ particle. Events are further required to contain at least four reconstructed muons with pT > 3.5 GeV, which form dimuon pairs. This control sample does not specifically require that the dimuons satisfy the requirement Isum < 2 GeV since Isum is used to separate the contribution of "prompt" and "nonprompt" (from b quark decays) J/^ in data. Finally, both dimuons are required to have an invariant mass between 2.8 and 3.3 GeV. Following these requirements the data sample consists of events containing prompt and nonprompt J/^. To subtract the nonprompt com-

ponent, two independent methods have been studied: the first one divides the control sample based on the values of the isolation variable Isum for each of the two dimuons in each event. The number of events in which both dimuons satisfy the requirement Isum < 2 GeV is extrapolated from the regions in which at least one of the dimuons fails this requirement. The second approach uses the lifetime of the J/^ candidate, calculated under the hypothesis of it being produced at the beam line, as a discriminating variable. The data distribution is fitted in the isolated region using prompt and nonprompt templates from simulation and nonisolated sideband in data, respectively. Both approaches give consistent results within the associated uncertainties and the results of the isolation-based method are used in the final analysis. There are two mechanisms for the production of prompt double J/^ events: single- and double-parton scattering (SPS and DPS, respectively), corresponding to whether the two J/^ mesons are produced from one or two independent parton interactions. The number of prompt events in the control region is further separated into SPS and DPS components using the J/^ rapidity difference as the discriminating variable. Finally, the data-to-simulation normalization factor and the fraction of SPS and DPS events are extrapolated from the control to the signal region, resulting in a final estimation for the contribution from prompt double J/^ events of 0.06 ± 0.03 events.

The contribution from other SM processes (low mass Drell-Yan production and pp ^ Z/y* ^ 4^) is estimated with the CalcHEP 3.6.18 generator [67] using the HEPMDB infrastructure [68], and is found to be 0.15 ± 0.03 events in the entire signal region. The combined expected background contribution to the diagonal signal region is 2.2 ± 0.7 events. This background is represented by the color scale in Fig. 1.

6. Systematic uncertainties

The selection efficiencies for the offline muon reconstruction, trigger, and dimuon isolation requirements are obtained from simulation, and are corrected with scale factors derived from comparison between data and simulation using Z ^ ¡i and J/^ ^ samples. The scale factor per event is found to be fdata/esim = 0.93 ± 0.07 and it accounts for the differences in the efficiency of the trigger, the efficiency of the muon reconstruction and identification for each of the four muon candidates, and the combined efficiency of the isolation requirement for the two dimuon candidates. The estimate accounts for correlations associated with the presence of multiple muons per event. The main systematic uncertainty is the offline muon reconstruction (4.1%), which includes an uncertainty (1% per muon) to cover variations of the scale factor as a function of the muon pT and n. Other systematic uncertainties include: the uncertainty in dimuon reconstruction effects related to overlaps of muon trajectories in the tracker and in the muon system (3.5%), the trigger efficiency (1.5%), the uncertainty in the efficiency caused by the modeling of the tails in the dimuon invariant mass distribution that arises from the requirement that the two dimuon masses are compatible (1.5%), and the dimuon isolation (negligible). The uncertainty in the integrated luminosity of the data sample (2.6%) [69] is also included. All uncertainties quoted above are related to variations in the signal efficiency due to experimental selection and sum up to 6.3%. The uncertainties related to variations in the signal acceptance due to the model include: the uncertainties related to the PDFs and the knowledge of the strong coupling constant as, which are estimated by comparing the PDFs in CTEQ6.6 [63] with those in NNPDF2.0 [70] and MSTW2008 [71], following the PDF4LHC recommendations [72,73]. Using the analysis benchmark samples, they are found to be 3% for the signal acceptance. The variation

of the renormalization and factorization scales has a negligible effect. In addition a re-weighting procedure is applied to the Higgs boson pT spectra in the benchmark signal samples to reproduce the NNLO+NNLL prediction [74] and account for possible changes to the analysis acceptance. Only a weak sensitivity to this is expected and the result of the re-weighting procedure is limited by the statistical uncertainty of the simulated samples (2%), which is therefore included as a conservative systematic uncertainty on this effect. Thus, the total systematic uncertainty in the signal acceptance and selection efficiency is 7.3%.

7. Results

After the full analysis selection is applied to the data sample, one event is observed in the diagonal signal region, as shown in Fig. 1. This is consistent with the expected background contribution of 2.2 ± 0.7 events.

For future reinterpretations of this analysis, the results can be presented as a 95% confidence level (CL) upper limit on a(pp ^ 2a + X) B2(a ^ 2i) agen = N(m¡¡)/(Lr), where agen is the generator-level kinematic and geometric acceptance defined earlier. The calculation uses the integrated luminosity L = 20.7 fb—1 and central value r of the ratio r = fdata/agen = 0.63 ± 0.07. The ratio includes a scale factor correcting for experimental effects not included in the simulation and its uncertainty covers the variation in the ratio over all the benchmark model points used. The limit is calculated as a function of the dimuon mass using the CLS approach [75,76]. The chosen test statistic is based on the profile likelihood ratio and is used to determine how signal- or background-like the data are. Systematic uncertainties are incorporated in the analysis via nuisance parameters with a log-normal probability density function and are treated according to the fre-quentist paradigm. The overall statistical methodology used in this analysis was developed by the ATLAS and CMS Collaborations in the context of the LHC Higgs Combination Group and is described in [3,77]. The obtained limit as a function of dimuon mass m^ can be conveniently approximated as a constant everywhere except the vicinity of the observed event, where it follows a Gaussian distribution:

N(mii) < 3.1 + 1.2 exp —

(mn — 0.32)2 2 x 0.032

resulting in

a (pp ^ 2a + X) B2 (a ^ 2i) agen (m

< 0.24 + 0.09 exp —

(m,i — 0.32)2

2 x 0.032

where m^ is measured in GeV and the cross-section limit is expressed in femtobarns. This limit is applicable to models with two pairs of muons coming from light bosons of the same type with a mass in the range 2m/x < ma < 2mT, where the new light bosons are typically isolated and spatially separated (so as to satisfy the isolation requirements).

The weak model dependence of the ratio r allows for a simple reinterpretation of the results in other models. This requires calculating agen, as defined earlier, and then the full efficiency fdata can be calculated by multiplying agen by the ratio r.

There are certain subtleties that must be taken into account when reinterpreting the model-independent results of this analysis in the context of other models, particularly with the isolation requirement. An event should be considered to satisfy the selection requirements if there are at least two well isolated yD decaying to muon pairs. Experimentally, isolation is based on charged tracks

but it may be insufficient to just require the absence of generatorlevel charged particles in the isolation cone. For example a neutral pion decaying to a pair of photons, that convert into electrons, may result in the reconstruction of one or more tracks. This would be particularly relevant for models with more than two dark photons produced in the same event, some of which may decay to hadrons or electrons. In this case the safest approach is to require that there are no particles with pT > 0.5 GeV within the yD isolation cone. This restriction would result in a more conservative limit but it would be robust against these effects.

The results from this analysis are also interpreted in the context of the NMSSM and the dark SUSY benchmark models, and 95% CL upper limits on the product of the cross section and branching fraction are derived. In these models both the Higgs boson production cross section and the branching fractions can vary significantly, depending on the choice of parameters. In the absence of broadly accepted benchmark scenarios, the production cross sections in these examples are normalized to that of the SM Higgs boson with a mass of 125 GeV [78].

In the case of the NMSSM benchmark scenario, the production cross sections and branching fractions for h1 and h2 can vary substantially depending on the chosen parameters. An exact interpretation of these results requires evaluating the experimental acceptance using the generator-level acceptance for each of the two h12 bosons, and then using the measured upper limit on the sum of two contributions to derive limits for any choice of NMSSM model parameters. To present results in a fashion allowing for straightforward interpretation, we note that if one of the two CP-even Higgs bosons is the 125 GeV state observed at the LHC, then the other one is either lighter or heavier. In the NMSSM it is typical that one of the two has approximately the SM production cross section and a small B(hi ^ 2a), whereas the other one has a suppressed production rate and large B(hi ^ 2a) due to its large singlet fraction. In Fig. 2 (left) the limit at each mass point is calculated taking the CP-even Higgs boson with the corresponding mass as the only source of signal events; the curve below 125 GeV applies to NMSSM models in which mh1 < mh2 = 125 GeV, with h1 decays dominating the rate of 4i events. The limit at mh = 125 GeV corresponds to the case where 125 GeV = m^ < m^2, with h1 decays still responsible for the vast majority of signal-like events. The points above 125 GeV correspond to model points for which only h2 (mh2 > mh1 = 125 GeV) is allowed to have a sizeable rate of observable 4i events. Finally, for models with mh2 > 150 GeV, the limit at 150 GeV can be used as a conservative estimate of the production rate limit. In each of these scenarios it is possible that the other Higgs boson also contributes some fraction of the 4i signal events, in which case the limit shown is more conservative than would be given by an exact evaluation.

In the case of the dark SUSY scenario, a 95% CL limit on the product of the Higgs boson production cross section and the branching fractions of the Higgs boson (cascade) decay to a pair of dark photons is determined. The limit set in the (mYD, s) plane from this analysis is shown in Fig. 2 (right), along with limits from other experimental searches, where the lifetime is directly related to the kinetic mixing parameter s and the mass of the dark photon m№ via t№ (s, m№) = s—2 f (m№), where f (m№) is a function that depends only on the mass of the dark photon [79]. The significant vertical structures in the limits visible in Fig. 2 (right) arise because the total width of the dark photon varies rapidly in those mass regions due to resonant decays to hadrons. This search constrains a large, previously unconstrained area of the parameter space. Unlike the other results in the figure, the CMS and ATLAS limits are model-dependent and only valid under the assumption that B(h ^ 2n1 ^ 4i + X) = 0. The recent ATLAS analysis [42]

s : Î-1.5

NMSSM 95% CL upper limits:

ma = 3.55 GeV _ - •- ma'= 2 GeV -*- mu = 0 ?5 GeV

Reference model: 1— o{pp->h,->a1a1) = 0.008xoM ->2p) = 7.7%

20.7 fb1 (8 TeV)

m. <m.= 125 GeV

h, = h2:

125 GeV = m. s m.

20.7 fb"1 (8 TeV)

90 100 110 120 130 140 150 mass of h. [GeV]

ATLAS (90% CL)

pp-^h-^n^YDYDnDnD B(h—>YoYd+X) = 0.1 - 40% 0.5 1.0 1.5

mass of Yd [GeV]

Fig. 2. Left for benchmark model 1: 95% CL upper limits from this search for the NMSSM scenarios with ma1 = 0.25 GeV (dashed curve), ma1 = 2 GeV (dash-dotted curve) and mai = 3.55 GeV (dotted curve) on a (pp — h1/2 — 2a1) B2(a1 — 2j) as a function of mh1 in the range 86 < mh1 < 125 GeV and of mh2 for mh2 > 125 GeV. As an illustration, the limits are compared to the predicted rate (solid curve) obtained using a simplified scenario with a (pp — hi — 2ai) = 0.008 aSM, which yields predictions for the rates of dimuon pair events comparable to the obtained experimental limits, and B(aj — 2j) = 7.7%. The chosen B(aj — 2j) is taken from [17] for ma1 = 2 GeV and tan p = 20. Right for benchmark model 2: 95% CL upper limits (black solid curves) from this search on a (pp -— h — 2yD + X) B(h — 2yD + X) (with mn1 = 10 GeV, mnD = 1 GeV) in the plane of two of the parameters (e and m№) for the dark SUSY scenarios, along with constraints from other experiments [42-56] showing the 90% CL exclusion contours. The colored contours represent different values of B(h — 2yD + X) in the range 0.1-40%.

focused on highly displaced objects and these searches therefore probe different regions of the available parameter space.

8. Summary

A search for pairs of new light bosons produced in the decay of a Higgs boson, that subsequently decay to pairs of oppositely charged muons, is presented. One event is observed in the signal region, with 2.2 ± 0.7 events expected from the SM backgrounds. A model independent upper limit at 95% CL on the product of the cross section, branching fraction, and acceptance is obtained. This limit is valid for light boson masses in the range 2m^ < ma < 2mT. The obtained results allow a straightforward interpretation within a broad range of physics models that predict the same type of signature. The results are compared with two benchmark models in the context of the NMSSM and dark SUSY, including scenarios predicting a nonnegligible light boson lifetime.

Acknowledgments

We would like to thank J. Ruderman for his guidance with the theoretically motivated benchmark samples of dark SUSY. We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC and thank the technical and administrative staffs at CERN and at other CMS institutes for their contributions to the success of the CMS effort. In addition, we gratefully acknowledge the computing centres and personnel of the Worldwide LHC Computing Grid for delivering so effectively the computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMWFW and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus); MoER, ERC IUT and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC

(Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS and RFBR (Russia); MESTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United Kingdom); DOE and National Science Foundation (USA).

Individuals have received support from the Marie-Curie programme and the European Research Council and EPLANET (European Union); the Leventis Foundation; the Alfred P. Sloan Foundation; the Alexander von Humboldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation a la Recherche dans l'Industrie et dans l'Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the Ministry of Education, Youth and Sports (MEYS) of the Czech Republic; the Council of Science and Industrial Research, India; the HOMING PLUS programme of the Foundation for Polish Science, cofinanced from European Union, Regional Development Fund; the Compagnia di San Paolo (Torino); the Consorzio per la Fisica (Trieste); MIUR project 20108T4XTM (Italy); the Thalis and Aristeia programmes cofinanced by EU-ESF and the Greek NSRF; and the National Priorities Research Program by Qatar National Research Fund.

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CMS Collaboration

V. Khachatryan, A.M. Sirunyan, A. Tumasyan

Yerevan Physics Institute, Yerevan, Armenia

W. Adam, E. Asilar, T. Bergauer, J. Brandstetter, E. Brondolin, M. Dragicevic, J. Erö, M. Flechl, M. Friedl, R. Frühwirth1, V.M. Ghete, C. Hartl, N. Hörmann, J. Hrubec, M. Jeitler1, V. Knünz, A. König, M. Krammer1, I. Krätschmer, D. Liko, T. Matsushita, I. Mikulec, D. Rabady2, B. Rahbaran, H. Rohringer, J. Schieck1, R. Schöfbeck, J. Strauss, W. Treberer-Treberspurg, W. Waltenberger, C.-E. Wulz1

Institut für Hochenergiephysik der OeAW, Wien, Austria

V. Mossolov, N. Shumeiko, J. Suarez Gonzalez

National Centre for Particle and High Energy Physics, Minsk, Belarus

S. Alderweireldt, T. Cornelis, E.A. De Wolf, X. Janssen, A. Knutsson, J. Lauwers, S. Luyckx, S. Ochesanu, R. Rougny, M. Van De Klundert, H. Van Haevermaet, P. Van Mechelen, N. Van Remortel, A. Van Spilbeeck

Universiteit Antwerpen, Antwerpen, Belgium

S. Abu Zeid, F. Blekman, J. D'Hondt, N. Daci, I. De Bruyn, K. Deroover, N. Heracleous, J. Keaveney, S. Lowette, L. Moreels, A. Olbrechts, Q. Python, D. Strom, S. Tavernier, W. Van Doninck, P. Van Mulders, G.P. Van Onsem, I. Van Parijs

Vrije Universiteit Brussel, Brussel, Belgium

P. Barria, C. Caillol, B. Clerbaux, G. De Lentdecker, H. Delannoy, D. Dobur, G. Fasanella, L. Favart, A.P.R. Gay, A. Grebenyuk, T. Lenzi, A. Léonard, T. Maerschalk, A. Mohammadi, L. Perniè, A. Randle-conde, T. Reis, T. Seva, L. Thomas, C. Vander Velde, P. Vanlaer, J. Wang, F. Zenoni, F. Zhang3

Université Libre de Bruxelles, Bruxelles, Belgium

K. Beernaert, L. Benucci, A. Cimmino, S. Crucy, A. Fagot, G. Garcia, M. Gui, J. Mccartin, A.A. Ocampo Rios,

D. Poyraz, D. Ryckbosch, S. Saiva Dibien, M. Sigamani, N. Strobbe, M. Tytgat, W. Van Driessche,

E. Yazgan, N. Zaganidis

Ghent University, Ghent, Belgium

S. Basegmez, C. Beluffi4, O. Bondu, G. Bruno, R. Casteiio, A. Caudron, L. Ceard, G.G. Da Siiveira, C. Deiaere,

D. Favart, L. Forthomme, A. Giammanco5, J. Hoiiar, A. Jafari, P. Jez, M. Komm, V. Lemaitre, A. Mertens, C. Nuttens, L. Perrini, A. Pin, K. Piotrzkowski, A. Popov6, L. Quertenmont, M. Seivaggi, M. Vidai Marono

Université Catholique de Louvain, Louvain-la-Neuve, Belgium

N. Beiiy, T. Caebergs, G.H. Hammad

Université de Mons, Mons, Belgium

W.L. Aidá Júnior, G.A. Aives, L. Brito, M. Correa Martins Junior, T. Dos Reis Martins, C. Hensei,

C. Mora Herrera, A. Moraes, M.E. Poi, P. Rebeiio Teies

Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil

E. Beichior Batista Das Chagas, W. Carvaiho, J. Chineiiato7, A. Custodio, E.M. Da Costa,

D. De Jesus Damiao, C. De Oiiveira Martins, S. Fonseca De Souza, L.M. Huertas Guativa, H. Maibouisson,

D. Matos Figueiredo, L. Mundim, H. Nogima, W.L. Prado Da Siiva, A. Santoro, A. Sznajder,

E.J. Toneiii Manganote7, A. Viieia Pereira

Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil

S. Ahuja, C.A. Bernardesb, A. De Souza Santos, S. Dograa, T.R. Fernandez Perez Tomeia, E.M. Gregoresb, P.G. Mercadanteb, C.S. Moon3'8, S.F. Novaesa, Sandra S. Paduia3, D. Romero Abad, J.C. Ruiz Vargas

a Universidade Estadual Paulista, Sao Paulo, Brazil b Universidade Federal do ABC, Sao Paulo, Brazil

A. Aieksandrov, V. Genchev2, R. Hadjiiska, P. Iaydjiev, A. Marinov, S. Piperov, M. Rodozov, S. Stoykova, G. Suitanov, M. Vutova

Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria

A. Dimitrov, I. Giushkov, L. Litov, B. Paviov, P. Petkov

University of Sofia, Sofia, Bulgaria

M. Ahmad, J.G. Bian, G.M. Chen, H.S. Chen, M. Chen, T. Cheng, R. Du, C.H. Jiang, R. Piestina9, F. Romeo, S.M. Shaheen, J. Tao, C. Wang, Z. Wang, H. Zhang

Institute of High Energy Physics, Beijing, China

C. Asawatangtrakuidee, Y. Ban, Q. Li, S. Liu, Y. Mao, S.J. Qian, D. Wang, Z. Xu, W. Zou

State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China

C. Aviia, A. Cabrera, L.F. Chaparro Sierra, C. Fiorez, J.P. Gomez, B. Gomez Moreno, J.C. Sanabria

Universidad de Los Andes, Bogota, Colombia

N. Godinovic, D. Leias, D. Poiic, I. Puijak

University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, Split, Croatia

Z. Antunovic, M. Kovac

University of Split, Faculty of Science, Split, Croatia

V. Brigijevic, K. Kadija, J. Luetic, L. Sudic

Institute Rudjer Boskovic, Zagreb, Croatia

A. Attikis, G. Mavromanolakis, J. Mousa, C. Nicolaou, F. Ptochos, P.A. Razis, H. Rykaczewski

University of Cyprus, Nicosia, Cyprus

M. Bodlak, M. Finger10, M. Finger Jr.10

Charles University, Prague, Czech Republic

A. Ali11, R. Aly, S. Aly, Y. Assran12, A. Ellithi Kamel13, A.M. Kuotb Awad14, A. Lotfy, R. Masod11,

A. Radi15'11

Academy of Scientific Research and Technology of the Arab Republic of Egypt, Egyptian Network of High Energy Physics, Cairo, Egypt

B. Calpas, M. Kadastik, M. Murumaa, M. Raidal, A. Tiko, C. Veelken

National Institute of Chemical Physics and Biophysics, Tallinn, Estonia

P. Eerola, M. Voutilainen

Department of Physics, University of Helsinki, Helsinki, Finland

J. Härkönen, V. Karimäki, R. Kinnunen, T. Lampén, K. Lassila-Perini, S. Lehti, T. Lindén, P. Luukka, T. Mäenpää, J. Pekkanen, T. Peltola, E. Tuominen, J. Tuominiemi, E. Tuovinen, L. Wendland

Helsinki Institute of Physics, Helsinki, Finland

J. Talvitie, T. Tuuva

Lappeenranta University of Technology, Lappeenranta, Finland

M. Besancon, F. Couderc, M. Dejardin, D. Denegri, B. Fabbro, J.L. Faure, C. Favaro, F. Ferri, S. Ganjour, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry, E. Locci, M. Machet, J. Malcles, J. Rander,

A. Rosowsky, M. Titov, A. Zghiche

DSM/IRFU, CEA/Saclay, Gif-sur-Yvette, France

S. Baffioni, F. Beaudette, P. Busson, L. Cadamuro, E. Chapon, C. Charlot, T. Dahms, O. Davignon, N. Filipovic, A. Florent, R. Granier de Cassagnac, S. Lisniak, L. Mastrolorenzo, P. Miné, I.N. Naranjo, M. Nguyen, C. Ochando, G. Ortona, P. Paganini, S. Regnard, R. Salerno, J.B. Sauvan, Y. Sirois, T. Strebler, Y. Yilmaz, A. Zabi

Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France

J.-L. Agram16, J. Andrea, A. Aubin, D. Bloch, J.-M. Brom, M. Buttignol, E.C. Chabert, N. Chanon, C. Collard, E. Conte16, J.-C. Fontaine16, D. Gelé, U. Goerlach, C. Goetzmann, A.-C. Le Bihan, J.A. Merlin2, K. Skovpen, P. Van Hove

Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Université de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France

S. Gadrat

Centre de Calcul de l'Institut National de Physique Nucleaire et de Physique des Particules, CNRS/IN2P3, Villeurbanne, France

S. Beauceron, C. Bernet9, G. Boudoul, E. Bouvier, S. Brochet, C.A. Carrillo Montoya, J. Chasserat, R. Chierici, D. Contardo, B. Courbon, P. Depasse, H. El Mamouni, J. Fan, J. Fay, S. Gascon, M. Gouzevitch,

B. Ille, I.B. Laktineh, M. Lethuillier, L. Mirabito, A.L. Pequegnot, S. Perries, J.D. Ruiz Alvarez, D. Sabes, L. Sgandurra, V. Sordini, M. Vander Donckt, P. Verdier, S. Viret, H. Xiao

Université de Lyon, Université Claude Bernard Lyon 1, CNRS-IN2P3, Institut de Physique Nucléaire de Lyon, Villeurbanne, France

Z. Tsamalaidze10

Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi, Georgia

C. Autermann, S. Beranek, M. Edelhoff, L. Feld, A. Heister, M.K. Kiesel, K. Klein, M. Lipinski, A. Ostapchuk, M. Preuten, F. Raupach, J. Sammet, S. Schael, J.F. Schulte, T. Verlage, H. Weber, B. Wittmer, V. Zhukov6

RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany

M. Ata, M. Brodski, E. Dietz-Laursonn, D. Duchardt, M. Endres, M. Erdmann, S. Erdweg, T. Esch, R. Fischer, A. Güth, T. Hebbeker, C. Heidemann, K. Hoepfner, D. Klingebiel, S. Knutzen, P. Kreuzer, M. Merschmeyer, A. Meyer, P. Millet, M. Olschewski, K. Padeken, P. Papacz, T. Pook, M. Radziej, H. Reithler, M. Rieger, F. Scheuch, L. Sonnenschein, D. Teyssier, S. Thüer

RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany

V. Cherepanov, Y. Erdogan, G. Flügge, H. Geenen, M. Geisler, W. Haj Ahmad, F. Hoehle, B. Kargoll, T. Kress, Y. Kuessel, A. Künsken, J. Lingemann2, A. Nehrkorn, A. Nowack, I.M. Nugent, C. Pistone,

0. Pooth, A. Stahl

RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany

M. Aldaya Martin, I. Asin, N. Bartosik, O. Behnke, U. Behrens, A.J. Bell, K. Borras, A. Burgmeier, A. Cakir, L. Calligaris, A. Campbell, S. Choudhury, F. Costanza, C. Diez Pardos, G. Dolinska, S. Dooling, T. Dorland,

G. Eckerlin, D. Eckstein, T. Eichhorn, G. Flucke, E. Gallo, J. Garay Garcia, A. Geiser, A. Gizhko,

P. Gunnellini, J. Hauk, M. Hempel17, H. Jung, A. Kalogeropoulos, O. Karacheban17, M. Kasemann, P. Katsas, J. Kieseler, C. Kleinwort, I. Korol, W. Lange, J. Leonard, K. Lipka, A. Lobanov, W. Lohmann17, R. Mankel, I. Marfin17, I.-A. Melzer-Pellmann, A.B. Meyer, G. Mittag, J. Mnich, A. Mussgiller, S. Naumann-Emme, A. Nayak, E. Ntomari, H. Perrey, D. Pitzl, R. Placakyte, A. Raspereza, P.M. Ribeiro Cipriano, B. Roland, M.Ö. Sahin, J. Salfeld-Nebgen, P. Saxena, T. Schoerner-Sadenius, M. Schröder, C. Seitz, S. Spannagel, K.D. Trippkewitz, C. Wissing

Deutsches Elektronen-Synchrotron, Hamburg, Germany

V. Blobel, M. Centis Vignali, A.R. Draeger, J. Erfle, E. Garutti, K. Goebel, D. Gonzalez, M. Görner, J. Haller, M. Hoffmann, R.S. Höing, A. Junkes, R. Klanner, R. Kogler, T. Lapsien, T. Lenz, I. Marchesini, D. Marconi,

D. Nowatschin, J. Ott, F. Pantaleo2, T. Peiffer, A. Perieanu, N. Pietsch, J. Poehlsen, D. Rathjens, C. Sander,

H. Schettler, P. Schleper, E. Schlieckau, A. Schmidt, J. Schwandt, M. Seidel, V. Sola, H. Stadie, G. Steinbrück, H. Tholen, D. Troendle, E. Usai, L. Vanelderen, A. Vanhoefer

University of Hamburg, Hamburg, Germany

M. Akbiyik, C. Barth, C. Baus, J. Berger, C. Böser, E. Butz, T. Chwalek, F. Colombo, W. De Boer, A. Descroix, A. Dierlamm, M. Feindt, F. Frensch, M. Giffels, A. Gilbert, F. Hartmann2, U. Husemann, F. Kassel2,

1. Katkov6, A. Kornmayer2, P. Lobelle Pardo, M.U. Mozer, T. Müller, Th. Müller, M. Plagge, G. Quast, K. Rabbertz, S. Röcker, F. Roscher, H.J. Simonis, F.M. Stober, R. Ulrich, J. Wagner-Kuhr, S. Wayand, T. Weiler, C. Wöhrmann, R. Wolf

Institut für Experimentelle Kernphysik, Karlsruhe, Germany

G. Anagnostou, G. Daskalakis, T. Geralis, V.A. Giakoumopoulou, A. Kyriakis, D. Loukas, A. Markou, A. Psallidas, I. Topsis-Giotis

Institute of Nuclear and Particle Physics (INPP), NCSR Demokritos, Aghia Paraskevi, Greece

A. Agapitos, S. Kesisoglou, A. Panagiotou, N. Saoulidou, E. Tziaferi

University of Athens, Athens, Greece

I. Evangelou, G. Flouris, C. Foudas, P. Kokkas, N. Loukas, N. Manthos, I. Papadopoulos, E. Paradas, J. Strologas

University of Ioannina, Ioannina, Greece

G. Bencze, C. Hajdu, A. Hazi, P. Hidas, D. Horvath18, F. Sikler, V. Veszpremi, G. Vesztergombi19, A.J. Zsigmond

Wigner Research Centre for Physics, Budapest, Hungary

N. Beni, S. Czellar, J. Karancsi 20, J. Molnar, Z. Szillasi

Institute of Nuclear Research ATOMKI, Debrecen, Hungary

M. Bartok21, A. Makovec, P. Raics, Z.L. Trocsanyi, B. Ujvari

University of Debrecen, Debrecen, Hungary

P. Mal, K. Mandal, N. Sahoo, S.K. Swain

National Institute of Science Education and Research, Bhubaneswar, India

S. Bansal, S.B. Beri, V. Bhatnagar, R. Chawla, R. Gupta, U. Bhawandeep, A.K. Kalsi, A. Kaur, M. Kaur, R. Kumar, A. Mehta, M. Mittal, N. Nishu, J.B. Singh, G. Walia

Panjab University, Chandigarh, India

Ashok Kumar, Arun Kumar, A. Bhardwaj, B.C. Choudhary, R.B. Garg, A. Kumar, S. Malhotra, M. Naimuddin, K. Ranjan, R. Sharma, V. Sharma

University of Delhi, Delhi, India

S. Banerjee, S. Bhattacharya, K. Chatterjee, S. Dey, S. Dutta, Sa. Jain, Sh. Jain, R. Khurana, N. Majumdar, A. Modak, K. Mondal, S. Mukherjee, S. Mukhopadhyay, A. Roy, D. Roy, S. Roy Chowdhury, S. Sarkar, M. Sharan

Saha Institute of Nuclear Physics, Kolkata, India

A. Abdulsalam, R. Chudasama, D. Dutta, V. Jha, V. Kumar, A.K. Mohanty2, L.M. Pant, P. Shukla, A. Topkar

Bhabha Atomic Research Centre, Mumbai, India

T. Aziz, S. Banerjee, S. Bhowmik22, R.M. Chatterjee, R.K. Dewanjee, S. Dugad, S. Ganguly, S. Ghosh, M. Guchait, A. Gurtu23, G. Kole, S. Kumar, B. Mahakud, M. Maity22, G. Majumder, K. Mazumdar, S. Mitra, G.B. Mohanty, B. Parida, T. Sarkar22, K. Sudhakar, N. Sur, B. Sutar, N. Wickramage24

Tata Institute of Fundamental Research, Mumbai, India

S. Sharma

Indian Institute of Science Education and Research (IISER), Pune, India

H. Bakhshiansohi, H. Behnamian, S.M. Etesami25, A. Fahim26, R. Goldouzian, M. Khakzad,

M. Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi, F. Rezaei Hosseinabadi, B. Safarzadeh27, M. Zeinali

Institute for Research in Fundamental Sciences (IPM), Tehran, Iran

M. Felcini, M. Grunewald

University College Dublin, Dublin, Ireland

M. Abbresciaa b, C. Calabriaa b, C. Caputoa b, S.S. Chhibraa b, A. Colaleoa, D. Creanzaa c, L. Cristellaa b, N. De Filippisa c, M. De Palma a'b, L. Fiorea, G. Iasellia c, G. Maggia'c, M. Maggia, G. Minielloa'b, S. Mya'c, S. Nuzzoa b, A. Pompilia b, G. Pugliesea c, R. Radognaa b, A. Ranieria, G. Selvaggia b, A. Sharmaa, L. Silvestrisa 2, R. Vendittia b, P. Verwilligena

a INFN Sezione di Bari, Bari, Italy b Université di Bari, Bari, Italy c Politecnico di Bari, Bari, Italy

G. Abbiendia, C. Battilana2, A.C. Benvenutia, D. Bonacorsia b, S. Braibant-Giacomellia b, L. Brigliadoria b, R. Campaniniab, P. Capiluppiab, A. Castroa b, F.R. Cavalloa, G. Codispotia b, M. Cuffianiab, G.M. Dallavallea, F. Fabbria, A. Fanfania b, D. Fasanellaa b, P. Giacomellia, C. Grandia, L. Guiduccia b, S. Marcellinia, G. Masettia, A. Montanaria, F.L. Navarriaa'b, A. Perrottaa, A.M. Rossi a'b, T. Rovellia'b, G.P. Siroli a'b, N. Tosi a'b, R. Travaglini a'b

a ¡NFN Sezione di Bologna, Bologna, Italy b Université di Bologna, Bologna, Italy

G. Cappelloa, M. Chiorbolia'b, S. Costa a'b, F. Giordanoa, R. Potenzaa'b, A. Tricomia'b, C. Tuvea'b

a ¡NFN Sezione di Catania, Catania, Italy b Université di Catania, Catania, Italy c CSFNSM, Catania, ¡taly

G. Barbaglia, V. Ciullia b, C. Civininia, R. D'Alessandroab, E. Focardia b, S. Gonzia b, V. Goria b, P. Lenzia'b, M. Meschinia, S. Paolettia, G. Sguazzonia, A. Tropianoa'b, L. Viliania b

a ¡NFN Sezione di Firenze, Firenze, ¡taly b Université di Firenze, Firenze, Italy

L. Benussi, S. Bianco, F. Fabbri, D. Piccolo

¡NFN Laboratori Nazionali di Frascati, Frascati, ¡taly

V. Calvellia b, F. Ferroa, M. Lo Veterea'b, E. Robuttia, S. Tosia'b

a ¡NFN Sezione di Genova, Genova, Italy b Université di Genova, Genova, Italy

M.E. Dinardo a'b, S. Fiorendia'b, S. Gennaia, R. Gerosaa'b, A. Ghezzia'b, P. Govonia'b, S. Malvezzia, R.A. Manzonia'b, B. Marzocchia'b'2, D. Menascea, L. Moronia, M. Paganonia'b, D. Pedrinia, S. Ragazzia'b, N. Redaellia, T. Tabarelli de Fatisa b

a ¡NFN Sezione di Milano-Bicocca, Milano, Italy b Université di Milano-Bicocca, Milano, Italy

S. Buontempoa, N. Cavalloa'c, S. Di Guida a'd'2, M. Espositoa'b, F. Fabozzia'c, A.O.M. Iorioa'b, G. Lanzaa, L. Listaa, S. Meolaa'd'2, M. Merolaa, P. Paoluccia'2, C. Sciaccaa'b, F. Thyssen

a ¡NFN Sezione di Napoli, Napoli, Italy b Université di Napoli 'Federico ¡¡', Napoli, Italy c Université della Basilicata, Potenza, ¡taly d Université G. Marconi, Roma, Italy

P. Azzia 2, N. Bacchettaa, D. Biselloa b, R. Carlina b, A. Carvalho Antunes De Oliveiraa b, P. Checchiaa, M. Dall'Ossoa b'2, T. Dorigoa, U. Dossellia, F. Gaspariniab, U. Gaspariniab, A. Gozzelinoa, S. Lacapraraa, M. Margonia'b, A.T. Meneguzzoa'b, J. Pazzinia'b, M. Pegoraroa, N. Pozzobona'b, P. Ronchesea'b,

F. Simonettoa,b, E. Torassaa, M. Tosia'b, S. Vaninia'b, M. Zanetti, P. Zottoa'b, A. Zucchettaa'b'2,

G. Zumerlea,b

a ¡NFN Sezione di Padova, Padova, ¡taly b Université di Padova, Padova, ¡taly c Université di Trento, Trento, Italy

A. Braghieria, M. Gabusia b, A. Magnania, S.P. Rattia b, V. Rea, C. Riccardia b, P. Salvinia, I. Vaia, P. Vitulo a'b

a ¡NFN Sezione di Pavia, Pavia, ¡taly b Université di Pavia, Pavia, ¡taly

L. Alunni Solestizia b, M. Biasinia b, G.M. Bileia, D. Ciangottinia'b'2, L. Fanoa'b, P. Laricciaa'b, G. Mantovani a'b, M. Menichellia, A. Sahaa, A. Santocchiaa'b, A. Spieziaa'b

a ¡NFN Sezione di Perugia, Perugia, Italy b Université di Perugia, Perugia, ¡taly

K. Androsov3'28, P. Azzurria, G. Bagliesia, J. Bernardini3, T. Boccali3, G. Broccoloa c, R. Castaldi3, M.A. Ciocci3'28, R. Dell'Orso3, S. Donato3'c'2, G. Fedi, L. Foà3'^, A. Giassi3, M.T. Grippo3'28, F. Ligabue3'c, T. Lomtadze3, L. Martini 3'b, A. Messineo3'b, F. Palla3, A. Rizzi3b, A. Savoy-Navarro3'29, A.T. Serban3, P. Spagnolo3, P. Squillaciotia'28, R. Tenchini3, G. Tonellia b, A. Venturi3, P.G. Verdini3

a INFN Sezione di Pisa, Pisa, Italy b Université di Pisa, Pisa, Italy c Scuola Normale Superiore di Pisa, Pisa, Italy

L. Barone 3'b, F. Cavallari3, G. D'imperio3'b'2, D. Del Re3'b, M. Diemoz3, S. Gelli3 b, C. Jorda3, E. Longo 3'b, F. Margaroli 3'b, P. Meridiani3, F. Micheli3'b, G. Organtini3'b, R. Paramatti3, F. Preiato3'b, S. Rahatlou3'b,

C. Rovelli3, F. Santanastasio3 b, L. Soffi3'b, P. Traczyk 3'b'2

a INFN Sezione di Roma, Roma, Italy b Université di Roma, Roma, Italy

N. Amapane3 b, R. Arcidiacono3 c, S. Argiro3 b, M. Arneodo3 c, R. Bellan3 b, C. Biino3, N. Cartiglia3, M. Costa3'b, R. Covarelli3'b, D. Dattola3, A. Degano3'b, N. Demaria3, L. Finco3'b'2, C. Mariotti3, S. Maselli3, E. Migliore3'b, V. Monaco3'b, E. Monteil3'b, M. Musich3, M.M. Obertino3 c, L. Pacher3'b, N. Pastrone3, M. Pelliccioni3, G.L. Pinna Angioni3 b, F. Ravera3 b, A. Romero3b, M. Ruspa3 c, R. Sacchi3 b, A. Solano3 b, A. Staiano3, U. Tamponi3

a INFN Sezione di Torino, Torino, Italy b Université di Torino, Torino, Italy c Université del Piemonte Orientale, Novara, Italy

S. Belforte3, V. Candelise3 b'2, M. Casarsa3, F. Cossutti3, G. Della Ricca3 b, B. Gobbo3, C. La Licata3 b, M. Marone 3'b, A. Schizzi3'b, T. Umer3'b, A. Zanetti3

a INFN Sezione di Trieste, Trieste, Italy b Université di Trieste, Trieste, Italy

S. Chang, A. Kropivnitskaya, S.K. Nam

Kangwon National University, Chunchon, Republic of Korea

D.H. Kim, G.N. Kim, M.S. Kim, D.J. Kong, S. Lee, Y.D. Oh, A. Sakharov, D.C. Son

Kyungpook National University, Daegu, Republic of Korea

H. Kim, T.J. Kim, M.S. Ryu

Chonbuk National University, Jeonju, Republic of Korea

S. Song

Chonnam National University, Institute for Universe and Elementary Particles, Kwangju, Republic of Korea

S. Choi, Y. Go, D. Gyun, B. Hong, M. Jo, H. Kim, Y. Kim, B. Lee, K. Lee, K.S. Lee, S. Lee, S.K. Park, Y. Roh

Korea University, Seoul, Republic of Korea

H.D. Yoo

Seoul National University, Seoul, Republic of Korea

M. Choi, J.H. Kim, J.S.H. Lee, I.C. Park, G. Ryu

University of Seoul, Seoul, Republic of Korea

Y. Choi, Y.K. Choi, J. Goh, D. Kim, E. Kwon, J. Lee, I. Yu

Sungkyunkwan University, Suwon, Republic of Korea

A. Juodagalvis, J. Vaitkus

Vilnius University, Vilnius, Lithuania

Z.A. Ibrahim, J.R. Komaragiri, M.A.B. Md Ali30, F. Mohamad Idris, W.A.T. Wan Abdullah

National Centre for Particle Physics, Universiti Malaya, Kuala Lumpur, Malaysia

E. Casimiro Linares, H. Castilla-Valdez, E. De La Cruz-Burelo, I. Heredia-de La Cruz31, A. Hernandez-Almada, R. Lopez-Fernandez, G. Ramirez Sanchez, A. Sanchez-Hernandez

Centro de Investigation y de Estudios Avanzados del ¡PN, Mexico City, Mexico

S. Carrillo Moreno, F. Vazquez Valencia

Universidad ¡beroamericana, Mexico City, Mexico

S. Carpinteyro, I. Pedraza, H.A. Salazar Ibarguen

Benemerita Universidad Autonoma de Puebla, Puebla, Mexico

A. Morelos Pineda

Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico

D. Krofcheck

University of Auckland, Auckland, New Zealand

P.H. Butler, S. Reucroft

University of Canterbury, Christchurch, New Zealand

A. Ahmad, M. Ahmad, Q. Hassan, H.R. Hoorani, W.A. Khan, T. Khurshid, M. Shoaib

National Centre for Physics, Quaid-¡-Azam University, Islamabad, Pakistan

H. Bialkowska, M. Bluj, B. Boimska, T. Frueboes, M. Górski, M. Kazana, K. Nawrocki, K. Romanowska-Rybinska, M. Szleper, P. Zalewski

National Centre for Nuclear Research, Swierk, Poland

G. Brona, K. Bunkowski, K. Doroba, A. Kalinowski, M. Konecki, J. Krolikowski, M. Misiura, M. Olszewski, M. Walczak

Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland

P. Bargassa, C. Beirao Da Cruz E Silva, A. Di Francesco, P. Faccioli, P.G. Ferreira Parracho, M. Gallinaro, L. Lloret Iglesias, F. Nguyen, J. Rodrigues Antunes, J. Seixas, O. Toldaiev, D. Vadruccio, J. Varela, P. Vischia

Laboratório de Instrumentado e Física Experimental de Partículas, Lisboa, Portugal

S. Afanasiev, P. Bunin, M. Gavrilenko, I. Golutvin, I. Gorbunov, A. Kamenev, V. Karjavin, V. Konoplyanikov, A. Lanev, A. Malakhov, V. Matveev32, P. Moisenz, V. Palichik, V. Perelygin, S. Shmatov, S. Shulha, N. Skatchkov, V. Smirnov, T. Toriashvili33, A. Zarubin

Joint Institute for Nuclear Research, Dubna, Russia

V. Golovtsov, Y. Ivanov, V. Kim34, E. Kuznetsova, P. Levchenko, V. Murzin, V. Oreshkin, I. Smirnov, V. Sulimov, L. Uvarov, S. Vavilov, A. Vorobyev

Petersburg Nuclear Physics Institute, Gatchina (St. Petersburg), Russia

Yu. Andreev, A. Dermenev, S. Gninenko, N. Golubev, A. Karneyeu, M. Kirsanov, N. Krasnikov, A. Pashenkov, D. Tlisov, A. Toropin

¡nstitute for Nuclear Research, Moscow, Russia

V. Epshteyn, V. Gavrilov, N. Lychkovskaya, V. Popov, I. Pozdnyakov, G. Safronov, A. Spiridonov, E. Vlasov, A. Zhokin

Institute for Theoretical and Experimental Physics, Moscow, Russia

A. Bylinkin

National Research Nuclear University 'Moscow Engineering Physics Institute' (MEPhI), Moscow, Russia

V. Andreev, M. Azarkin35, I. Dremin35, M. Kirakosyan, A. Leonidov35, G. Mesyats, S.V. Rusakov, A. Vinogradov

P.N. Lebedev Physical Institute, Moscow, Russia

A. Baskakov, A. Belyaev, E. Boos, M. Dubinin36, L. Dudko, A. Ershov, A. Gribushin, V. Klyukhin,

0. Kodolova, I. Lokhtin, I. Myagkov, S. Obraztsov, S. Petrushanko, V. Savrin, A. Snigirev

Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia

1. Azhgirey, I. Bayshev, S. Bitioukov, V. Kachanov, A. Kalinin, D. Konstantinov, V. Krychkine, V. Petrov, R. Ryutin, A. Sobol, L. Tourtchanovitch, S. Troshin, N. Tyurin, A. Uzunian, A. Volkov

State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, Russia

P. Adzic37, M. Ekmedzic, J. Milosevic, V. Rekovic

University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia

J. Alcaraz Maestre, E. Calvo, M. Cerrada, M. Chamizo Llatas, N. Colino, B. De La Cruz, A. Delgado Peris,

D. Domínguez Vázquez, A. Escalante Del Valle, C. Fernandez Bedoya, J.P. Fernández Ramos, J. Flix, M.C. Fouz, P. Garcia-Abia, O. Gonzalez Lopez, S. Goy Lopez, J.M. Hernandez, M.I. Josa,

E. Navarro De Martino, A. Pérez-Calero Yzquierdo, J. Puerta Pelayo, A. Quintario Olmeda, I. Redondo, L. Romero, M.S. Soares

Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain

C. Albajar, J.F. de Trocóniz, M. Missiroli, D. Moran

Universidad Autónoma de Madrid, Madrid, Spain

H. Brun, J. Cuevas, J. Fernandez Menendez, S. Folgueras, I. Gonzalez Caballero, E. Palencia Cortezon, J.M. Vizan Garcia

Universidad de Oviedo, Oviedo, Spain

J.A. Brochero Cifuentes, I.J. Cabrillo, A. Calderon, J.R. Castiñeiras De Saa, J. Duarte Campderros, M. Fernandez, G. Gomez, A. Graziano, A. Lopez Virto, J. Marco, R. Marco, C. Martinez Rivero, F. Matorras,

F.J. Munoz Sanchez, J. Piedra Gomez, T. Rodrigo, A.Y. Rodríguez-Marrero, A. Ruiz-Jimeno, L. Scodellaro,

I. Vila, R. Vilar Cortabitarte

Instituto de Física de Cantabria (IFCA), CSIC-Universidad de Cantabria, Santander, Spain

D. Abbaneo, E. Auffray, G. Auzinger, M. Bachtis, P. Baillon, A.H. Ball, D. Barney, A. Benaglia, J. Bendavid, L. Benhabib, J.F. Benitez, G.M. Berruti, G. Bianchi, P. Bloch, A. Bocci, A. Bonato, C. Botta, H. Breuker,

T. Camporesi, G. Cerminara, S. Colafranceschi38, M. D'Alfonso, D. d'Enterria, A. Dabrowski, V. Daponte, A. David, M. De Gruttola, F. De Guio, A. De Roeck, S. De Visscher, E. Di Marco, M. Dobson, M. Dordevic, T. du Pree, N. Dupont-Sagorin, A. Elliott-Peisert, J. Eugster, G. Franzoni, W. Funk, D. Gigi, K. Gill, D. Giordano, M. Girone, F. Glege, R. Guida, S. Gundacker, M. Guthoff, J. Hammer, M. Hansen, P. Harris, J. Hegeman, V. Innocente, P. Janot, H. Kirschenmann, M.J. Kortelainen, K. Kousouris, K. Krajczar, P. Lecoq, C. Lourengo, M.T. Lucchini, N. Magini, L. Malgeri, M. Mannelli, J. Marrouche, A. Martelli, L. Masetti, F. Meijers, S. Mersi, E. Meschi, F. Moortgat, S. Morovic, M. Mulders, M.V. Nemallapudi, H. Neugebauer, S. Orfanelli, L. Orsini, L. Pape, E. Perez, A. Petrilli, G. Petrucciani, A. Pfeiffer, D. Piparo, A. Racz,

G. Rolandi39, M. Rovere, M. Ruan, H. Sakulin, C. Schäfer, C. Schwick, A. Sharma, P. Silva, M. Simon, P. Sphicas40, D. Spiga, J. Steggemann, B. Stieger, M. Stoye, Y. Takahashi, D. Treille, A. Tsirou, G.I. Veres19, N. Wardle, H.K. Wöhri, A. Zagozdzinska41, W.D. Zeuner

CERN, European Organization for Nuclear Research, Geneva, Switzerland

W. Bertl, K. Deiters, W. Erdmann, R. Horisberger, Q. Ingram, H.C. Kaestli, D. Kotlinski, U. Langenegger, T. Rohe

Paul Scherrer Institut, Villigen, Switzerland

F. Bachmair, L. Bäni, L. Bianchini, M.A. Buchmann, B. Casal, G. Dissertori, M. Dittmar, M. Donegä, M. Dünser, P. Eller, C. Grab, C. Heidegger, D. Hits, J. Hoss, G. Kasieczka, W. Lustermann, B. Mangano, A.C. Marini, M. Marionneau, P. Martinez Ruiz del Arbol, M. Masciovecchio, D. Meister, N. Mohr, P. Musella, F. Nessi-Tedaldi, F. Pandolfi, J. Pata, F. Pauss, L. Perrozzi, M. Peruzzi, M. Quittnat, M. Rossini,

A. Starodumov42, M. Takahashi, V.R. Tavolaro, K. Theofilatos, R. Wallny, H.A. Weber

Institute for Particle Physics, ETH Zurich, Zurich, Switzerland

T.K. Aarrestad, C. Amsler43, M.F. Canelli, V. Chiochia, A. De Cosa, C. Galloni, A. Hinzmann, T. Hreus,

B. Kilminster, C. Lange, J. Ngadiuba, D. Pinna, P. Robmann, F.J. Ronga, D. Salerno, S. Taroni, Y. Yang

Universität Zürich, Zurich, Switzerland

M. Cardaci, K.H. Chen, T.H. Doan, C. Ferro, M. Konyushikhin, C.M. Kuo, W. Lin, Y.J. Lu, R. Volpe, S.S. Yu

National Central University, Chung-Li, Taiwan

P. Chang, Y.H. Chang, Y.W. Chang, Y. Chao, K.F. Chen, P.H. Chen, C. Dietz, F. Fiori, U. Grundler, W.-S. Hou, Y. Hsiung, Y.F. Liu, R.-S. Lu, M. Minano Moya, E. Petrakou, J.f. Tsai, Y.M. Tzeng, R. Wilken

National Taiwan University (NTU), Taipei, Taiwan

B. Asavapibhop, K. Kovitanggoon, G. Singh, N. Srimanobhas, N. Suwonjandee

Chulalongkorn University, Faculty of Science, Department of Physics, Bangkok, Thailand

A. Adiguzel, S. Cerci44, C. Dozen, S. Girgis, G. Gokbulut, Y. Guler, E. Gurpinar, I. Hos, E.E. Kangal45,

A. Kayis Topaksu, G. Onengut46, K. Özdemir47, S. Ozturk48, B. Tali44, H. Topakli48, M. Vergili,

C. Zorbilmez

Cukurova University, Adana, Turkey

I.V. Akin, B. Bilin, S. Bilmis, B. Isildak49, G. Karapinar50, U.E. Surat, M. Yalvac, M. Zeyrek

Middle East Technical University, Physics Department, Ankara, Turkey

E.A. Albayrak51, E. Gülmez, M. Kaya52, O. Kaya53, T. Yetkin54

Bogazici University, Istanbul, Turkey

K. Cankocak, Y.O. Günaydin55, F.I. Vardarli

Istanbul Technical University, Istanbul, Turkey

B. Grynyov

Institute for Scintillation Materials of National Academy of Science of Ukraine, Kharkov, Ukraine

L. Levchuk, P. Sorokin

National Scientific Center, Kharkov Institute of Physics and Technology, Kharkov, Ukraine

R. Aggleton, F. Ball, L. Beck, J.J. Brooke, E. Clement, D. Cussans, H. Flacher, J. Goldstein, M. Grimes, G.P. Heath, H.F. Heath, J. Jacob, L. Kreczko, C. Lucas, Z. Meng, D.M. Newbold56, S. Paramesvaran, A. Poll, T. Sakuma, S. Seif El Nasr-storey, S. Senkin, D. Smith, V.J. Smith

University of Bristol, Bristol, United Kingdom

K.W. Bell, A. Belyaev57, C. Brew, R.M. Brown, D.J.A. Cockerill, J.A. Coughlan, K. Harder, S. Harper,

E. Olaiya, D. Petyt, C.H. Shepherd-Themistocleous, A. Thea, I.R. Tomalin, T. Williams, W.J. Womersley, S.D. Worm

Rutherford Appleton Laboratory, Didcot, United Kingdom

M. Baber, R. Bainbridge, O. Buchmuller, A. Bundock, D. Burton, S. Casasso, M. Citron, D. Colling, L. Corpe, N. Cripps, P. Dauncey, G. Davies, A. De Wit, M. Della Negra, P. Dunne, A. Elwood, W. Ferguson, J. Fulcher, D. Futyan, G. Hall, G. Iles, G. Karapostoli, M. Kenzie, R. Lane, R. Lucas 56, L. Lyons, A.-M. Magnan, S. Malik, J. Nash, A. Nikitenko42, J. Pela, M. Pesaresi, K. Petridis, D.M. Raymond, A. Richards, A. Rose, C. Seez, P. Sharp t, A. Tapper, K. Uchida, M. Vazquez Acosta58, T. Virdee, S.C. Zenz

Imperial College, London, United Kingdom

J.E. Cole, P.R. Hobson, A. Khan, P. Kyberd, D. Leggat, D. Leslie, I.D. Reid, P. Symonds, L. Teodorescu, M. Turner

Brunel University, Uxbridge, United Kingdom

A. Borzou, J. Dittmann, K. Hatakeyama, A. Kasmi, H. Liu, N. Pastika, T. Scarborough

Baylor University, Waco, USA

O. Charaf, S.I. Cooper, C. Henderson, P. Rumerio

The University of Alabama, Tuscaloosa, USA

A. Avetisyan, T. Bose, C. Fantasia, D. Gastler, P. Lawson, D. Rankin, C. Richardson, J. Rohlf, J. St. John, L. Sulak, D. Zou

Boston University, Boston, USA

J. Alimena, E. Berry, S. Bhattacharya, D. Cutts, Z. Demiragli, N. Dhingra, A. Ferapontov, A. Garabedian, U. Heintz, E. Laird, G. Landsberg, Z. Mao, M. Narain, S. Sagir, T. Sinthuprasith

Brown University, Providence, USA

R. Breedon, G. Breto, M. Calderon De La Barca Sanchez, S. Chauhan, M. Chertok, J. Conway, R. Conway, P.T. Cox, R. Erbacher, M. Gardner, W. Ko, R. Lander, M. Mulhearn, D. Pellett, J. Pilot, F. Ricci-Tam, S. Shalhout, J. Smith, M. Squires, D. Stolp, M. Tripathi, S. Wilbur, R. Yohay

University of California, Davis, Davis, USA

R. Cousins, P. Everaerts, C. Farrell, J. Hauser, M. Ignatenko, G. Rakness, D. Saltzberg, E. Takasugi, V. Valuev, M. Weber

University of California, Los Angeles, USA

K. Burt, R. Clare, J. Ellison, J.W. Gary, G. Hanson, J. Heilman, M. Ivova Rikova, P. Jandir, E. Kennedy,

F. Lacroix, O.R. Long, A. Luthra, M. Malberti, M. Olmedo Negrete, A. Shrinivas, S. Sumowidagdo, H. Wei, S. Wimpenny

University of California, Riverside, Riverside, USA

J.G. Branson, G.B. Cerati, S. Cittolin, R.T. D'Agnolo, A. Holzner, R. Kelley, D. Klein, J. Letts, I. Macneill, D. Olivito, S. Padhi, M. Pieri, M. Sani, V. Sharma, S. Simon, M. Tadel, Y. Tu, A. Vartak, S. Wasserbaech59,

C. Welke, F. Würthwein, A. Yagil, G. Zevi Della Porta

University of California, San Diego, La Jolla, USA

D. Barge, J. Bradmiller-Feld, C. Campagnari, A. Dishaw, V. Dutta, K. Flowers, M. Franco Sevilla, P. Geffert,

C. George, F. Golf, L. Gouskos, J. Gran, J. Incandela, C. Justus, N. Mccoll, S.D. Mullin, J. Richman, D. Stuart, W. To, C. West, J. Yoo

University of California, Santa Barbara, Santa Barbara, USA

D. Anderson, A. Apresyan, A. Bornheim, J. Bunn, Y. Chen, J. Duarte, A. Mott, H.B. Newman, C. Pena, M. Pierini, M. Spiropulu, J.R. Vlimant, S. Xie, R.Y. Zhu

California Institute of Technology, Pasadena, USA

V. Azzolini, A. Calamba, B. Carlson, T. Ferguson, Y. Iiyama, M. Paulini, J. Russ, M. Sun, H. Vogel, I. Vorobiev

Carnegie Mellon University, Pittsburgh, USA

J.P. Cumalat, W.T. Ford, A. Gaz, F. Jensen, A. Johnson, M. Krohn, T. Mulholland, U. Nauenberg, J.G. Smith, K. Stenson, S.R. Wagner

University of Colorado at Boulder, Boulder, USA

J. Alexander, A. Chatterjee, J. Chaves, J. Chu, S. Dittmer, N. Eggert, N. Mirman, G. Nicolas Kaufman, J.R. Patterson, A. Rinkevicius, A. Ryd, L. Skinnari, W. Sun, S.M. Tan, W.D. Teo, J. Thom, J. Thompson, J. Tucker, Y. Weng, P. Wittich

Cornell University, Ithaca, USA

S. Abdullin, M. Albrow, J. Anderson, G. Apollinari, L.A.T. Bauerdick, A. Beretvas, J. Berryhill, P.C. Bhat,

G. Bolla, K. Burkett, J.N. Butler, H.W.K. Cheung, F. Chlebana, S. Cihangir, V.D. Elvira, I. Fisk, J. Freeman,

E. Gottschalk, L. Gray, D. Green, S. Grünendahl, O. Gutsche, J. Hanlon, D. Hare, R.M. Harris, J. Hirschauer,

B. Hooberman, Z. Hu, S. Jindariani, M. Johnson, U. Joshi, A.W. Jung, B. Klima, B. Kreis, S. Kwan^,

S. Lammel, J. Linacre, D. Lincoln, R. Lipton, T. Liu, R. Lopes De Sä, J. Lykken, K. Maeshima, J.M. Marraffino, V.I. Martinez Outschoorn, S. Maruyama, D. Mason, P. McBride, P. Merkel, K. Mishra, S. Mrenna, S. Nahn,

C. Newman-Holmes, V. O'Dell, O. Prokofyev, E. Sexton-Kennedy, A. Soha, W.J. Spalding, L. Spiegel, L. Taylor, S. Tkaczyk, N.V. Tran, L. Uplegger, E.W. Vaandering, C. Vernieri, M. Verzocchi, R. Vidal, A. Whitbeck, F. Yang, H. Yin

Fermi National Accelerator Laboratory, Batavia, USA

D. Acosta, P. Avery, P. Bortignon, D. Bourilkov, A. Carnes, M. Carver, D. Curry, S. Das, G.P. Di Giovanni, R.D. Field, M. Fisher, I.K. Furic, J. Hugon, J. Konigsberg, A. Korytov, T. Kypreos, J.F. Low, P. Ma, K. Matchev,

H. Mei, P. Milenovic60, G. Mitselmakher, L. Muniz, D. Rank, L. Shchutska, M. Snowball, D. Sperka, S.J. Wang, J. Yelton

University of Florida, Gainesville, USA

S. Hewamanage, S. Linn, P. Markowitz, G. Martinez, J.L. Rodriguez

Florida International University, Miami, USA

A. Ackert, J.R. Adams, T. Adams, A. Askew, J. Bochenek, B. Diamond, J. Haas, S. Hagopian, V. Hagopian, K.F. Johnson, A. Khatiwada, H. Prosper, V. Veeraraghavan, M. Weinberg

Florida State University, Tallahassee, USA

V. Bhopatkar, M. Hohlmann, H. Kalakhety, D. Mareskas-palcek, T. Roy, F. Yumiceva

Florida Institute of Technology, Melbourne, USA

M.R. Adams, L. Apanasevich, D. Berry, R.R. Betts, I. Bucinskaite, R. Cavanaugh, O. Evdokimov, L. Gauthier,

C.E. Gerber, D.J. Hofman, P. Kurt, C. O'Brien, I.D. Sandoval Gonzalez, C. Silkworth, P. Turner, N. Varelas, Z. Wu, M. Zakaria

University of Illinois at Chicago (UIC), Chicago, USA

B. Bilki61, W. Clarida, K. Dilsiz, S. Durgut, R.P. Gandrajula, M. Haytmyradov, V. Khristenko, J.-P. Merlo,

H. Mermerkaya62, A. Mestvirishvili, A. Moeller, J. Nachtman, H. Ogul, Y. Onel, F. Ozok51, A. Penzo, S. Sen63, C. Snyder, P. Tan, E. Tiras, J. Wetzel, K. Yi

The University of Iowa, Iowa City, USA

I. Anderson, B.A. Barnett, B. Blumenfeld, D. Fehling, L. Feng, A.V. Gritsan, P. Maksimovic, C. Martin, K. Nash, M. Osherson, M. Swartz, M. Xiao, Y. Xin

Johns Hopkins University, Baltimore, USA

P. Baringer, A. Bean, G. Benelli, C. Bruner, J. Gray, R.P. Kenny III, D. Majumder, M. Malek, M. Murray,

D. Noonan, S. Sanders, R. Stringer, Q. Wang, J.S. Wood

The University of Kansas, Lawrence, USA

I. Chakaberia, A. Ivanov, K. Kaadze, S. Khalil, M. Makouski, Y. Maravin, L.K. Saini, N. Skhirtladze, I. Svintradze, S. Toda

Kansas State University, Manhattan, USA

D. Lange, F. Rebassoo, D. Wright

Lawrence Livermore National Laboratory, Livermore, USA

C. Anelli, A. Baden, O. Baron, A. Belloni, B. Calvert, S.C. Eno, C. Ferraioli, J.A. Gomez, N.J. Hadley, S. Jabeen, R.G. Kellogg, T. Kolberg, J. Kunkle, Y. Lu, A.C. Mignerey, K. Pedro, Y.H. Shin, A. Skuja, M.B. Tonjes, S.C. Tonwar

University of Maryland, College Park, USA

A. Apyan, R. Barbieri, A. Baty, K. Bierwagen, S. Brandt, W. Busza, I.A. Cali, L. Di Matteo,

G. Gomez Ceballos, M. Goncharov, D. Gulhan, G.M. Innocenti, M. Klute, D. Kovalskyi, Y.S. Lai, Y.-J. Lee,

A. Levin, P.D. Luckey, C. Mcginn, X. Niu, C. Paus, D. Ralph, C. Roland, G. Roland, G.S.F. Stephans,

K. Sumorok, M. Varma, D. Velicanu, J. Veverka, J. Wang, T.W. Wang, B. Wyslouch, M. Yang, V. Zhukova

Massachusetts Institute of Technology, Cambridge, USA

B. Dahmes, A. Finkel, A. Gude, P. Hansen, S. Kalafut, S.C. Kao, K. Klapoetke, Y. Kubota, Z. Lesko, J. Mans, S. Nourbakhsh, N. Ruckstuhl, R. Rusack, N. Tambe, J. Turkewitz

University of Minnesota, Minneapolis, USA

J.G. Acosta, S. Oliveros

University of Mississippi, Oxford, USA

E. Avdeeva, K. Bloom, S. Bose, D.R. Claes, A. Dominguez, C. Fangmeier, R. Gonzalez Suarez,

R. Kamalieddin, J. Keller, D. Knowlton, I. Kravchenko, J. Lazo-Flores, F. Meier, J. Monroy, F. Ratnikov, J.E. Siado, G.R. Snow

University of Nebraska-Lincoln, Lincoln, USA

M. Alyari, J. Dolen, J. George, A. Godshalk, I. Iashvili, J. Kaisen, A. Kharchilava, A. Kumar, S. Rappoccio

State University of New York at Buffalo, Buffalo, USA

G. Alverson, E. Barberis, D. Baumgartel, M. Chasco, A. Hortiangtham, A. Massironi, D.M. Morse, D. Nash, T. Orimoto, R. Teixeira De Lima, D. Trocino, R.-J. Wang, D. Wood, J. Zhang

Northeastern University, Boston, USA

K.A. Hahn, A. Kubik, N. Mucia, N. Odell, B. Pollack, A. Pozdnyakov, M. Schmitt, S. Stoynev, K. Sung, M. Trovato, M. Velasco, S. Won

Northwestern University, Evanston, USA

A. Brinkerhoff, N. Dev, M. Hildreth, C. Jessop, D.J. Karmgard, N. Kellams, K. Lannon, S. Lynch,

N. Marinelli, F. Meng, C. Mueller, Y. Musienko32, T. Pearson, M. Planer, R. Ruchti, G. Smith, N. Valls, M. Wayne, M. Wolf, A. Woodard

University of Notre Dame, Notre Dame, USA

L. Antonelli, J. Brinson, B. Bylsma, L.S. Durkin, S. Flowers, A. Hart, C. Hill, R. Hughes, K. Kotov, T.Y. Ling,

B. Liu, W. Luo, D. Puigh, M. Rodenburg, B.L. Winer, H.W. Wulsin

The Ohio State University, Columbus, USA

O. Driga, P. Elmer, J. Hardenbrook, P. Hebda, S.A. Koay, P. Lujan, D. Marlow, T. Medvedeva, M. Mooney, J. Olsen, C. Palmer, P. Piroue, X. Quan, H. Saka, D. Stickland, C. Tully, J.S. Werner, A. Zuranski

Princeton University, Princeton, USA

V.E. Barnes, D. Benedetti, D. Bortoletto, L. Gutay, M.K. Jha, M. Jones, K. Jung, M. Kress, N. Leonardo, D.H. Miller, N. Neumeister, F. Primavera, B.C. Radburn-Smith, X. Shi, I. Shipsey, D. Silvers, J. Sun, A. Svyatkovskiy, F. Wang, W. Xie, L. Xu, J. Zablocki

Purdue University, West Lafayette, USA

N. Parashar, J. Stupak

Purdue University Calumet, Hammond, USA

A. Adair, B. Akgun, Z. Chen, K.M. Ecklund, F.J.M. Geurts, M. Guilbaud, W. Li, B. Michlin, M. Northup,

B.P. Padley, R. Redjimi, J. Roberts, J. Rorie, Z. Tu, J. Zabel

Rice University, Houston, USA

B. Betchart, A. Bodek, P. de Barbaro, R. Demina, Y. Eshaq, T. Ferbel, M. Galanti, A. Garcia-Bellido, P. Goldenzweig, J. Han, A. Harel, O. Hindrichs, A. Khukhunaishvili, G. Petrillo, M. Verzetti, D. Vishnevskiy

University of Rochester, Rochester, USA

L. Demortier

The Rockefeller University, New York, USA

S. Arora, A. Barker, J.P. Chou, C. Contreras-Campana, E. Contreras-Campana, D. Duggan, D. Ferencek, Y. Gershtein, R. Gray, E. Halkiadakis, D. Hidas, E. Hughes, S. Kaplan, R. Kunnawalkam Elayavalli, A. Lath, S. Panwalkar, M. Park, S. Salur, S. Schnetzer, D. Sheffield, S. Somalwar, R. Stone, S. Thomas, P. Thomassen, M. Walker

Rutgers, The State University of New Jersey, Piscataway, USA

M. Foerster, G. Riley, K. Rose, S. Spanier, A. York

University of Tennessee, Knoxville, USA

O. Bouhali64, A. Castaneda Hernandez, M. Dalchenko, M. De Mattia, A. Delgado, S. Dildick, R. Eusebi, W. Flanagan, J. Gilmore, T. Kamon65, V. Krutelyov, R. Montalvo, R. Mueller, I. Osipenkov, Y. Pakhotin, R. Patel, A. Perloff, J. Roe, A. Rose, A. Safonov, I. Suarez, A. Tatarinov, K.A. Ulmer2

Texas A&M University, College Station, USA

N. Akchurin, C. Cowden, J. Damgov, C. Dragoiu, P.R. Dudero, J. Faulkner, S. Kunori, K. Lamichhane, S.W. Lee, T. Libeiro, S. Undleeb, I. Volobouev

Texas Tech University, Lubbock, USA

E. Appelt, A.G. Delannoy, S. Greene, A. Gurrola, R. Janjam, W. Johns, C. Maguire, Y. Mao, A. Melo, P. Sheldon, B. Snook, S. Tuo, J. Velkovska, Q. Xu

Vanderbilt University, Nashville, USA

M.W. Arenton, S. Boutle, B. Cox, B. Francis, J. Goodell, R. Hirosky, A. Ledovskoy, H. Li, C. Lin, C. Neu, E. Wolfe, J. Wood, F. Xia

University of Virginia, Charlottesville, USA

C. Clarke, R. Harr, P.E. Karchin, C. Kottachchi Kankanamge Don, P. Lamichhane, J. Sturdy

Wayne State University, Detroit, USA

D.A. Belknap, D. Carlsmith, M. Cepeda, A. Christian, S. Dasu, L. Dodd, S. Duric, E. Friis, B. Gomber,

M. Grothe, R. Hall-Wilton, M. Herndon, A. Hervé, P. Klabbers, A. Lanaro, A. Levine, K. Long, R. Loveless, A. Mohapatra, I. Ojalvo, T. Perry, G.A. Pierro, G. Polese, I. Ross, T. Ruggles, T. Sarangi, A. Savin, N. Smith, W.H. Smith, D. Taylor, N. Woods

University of Wisconsin, Madison, USA

t Deceased.

1 Also at Vienna University of Technology, Vienna, Austria.

2 Also at CERN, European Organization for Nuclear Research, Geneva, Switzerland.

3 Also at State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China.

4 Also at Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Université de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France.

5 Also at National Institute of Chemical Physics and Biophysics, Tallinn, Estonia.

6 Also at Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia.

7 Also at Universidade Estadual de Campinas, Campinas, Brazil.

8 Also at Centre National de la Recherche Scientifique (CNRS) - IN2P3, Paris, France.

9 Also at Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France.

10 Also at Joint Institute for Nuclear Research, Dubna, Russia.

11 Also at Ain Shams University, Cairo, Egypt.

12 Also at Suez University, Suez, Egypt.

13 Also at Cairo University, Cairo, Egypt.

14 Also at Fayoum University, El-Fayoum, Egypt.

15 Also at British University in Egypt, Cairo, Egypt.

16 Also at Université de Haute Alsace, Mulhouse, France.

17 Also at Brandenburg University of Technology, Cottbus, Germany.

18 Also at Institute of Nuclear Research ATOMKI, Debrecen, Hungary.

19 Also at Eötvös Lorând University, Budapest, Hungary.

20 Also at University of Debrecen, Debrecen, Hungary.

21 Also at Wigner Research Centre for Physics, Budapest, Hungary.

22 Also at University of Visva-Bharati, Santiniketan, India.

23 Now at King Abdulaziz University, Jeddah, Saudi Arabia.

24 Also at University of Ruhuna, Matara, Sri Lanka.

25 Also at Isfahan University of Technology, Isfahan, Iran.

26 Also at University of Tehran, Department of Engineering Science, Tehran, Iran.

27 Also at Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran.

28 Also at Università degli Studi di Siena, Siena, Italy.

29 Also at Purdue University, West Lafayette, USA.

30 Also at International Islamic University of Malaysia, Kuala Lumpur, Malaysia.

31 Also at Consejo National de Ciencia y Tecnologia, Mexico, Mexico.

32 Also at Institute for Nuclear Research, Moscow, Russia.

33 Also at Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi, Georgia.

34 Also at St. Petersburg State Polytechnical University, St. Petersburg, Russia.

35 Also at National Research Nuclear University 'Moscow Engineering Physics Institute' (MEPhI), Moscow, Russia.

36 Also at California Institute of Technology, Pasadena, USA.

37 Also at Faculty of Physics, University of Belgrade, Belgrade, Serbia.

38 Also at Facoltä Ingegneria, Universitä di Roma, Roma, Italy.

39 Also at Scuola Normale e Sezione dell'INFN, Pisa, Italy.

40 Also at University of Athens, Athens, Greece.

41 Also at Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland.

42 Also at Institute for Theoretical and Experimental Physics, Moscow, Russia.

43 Also at Albert Einstein Center for Fundamental Physics, Bern, Switzerland.

44 Also at Adiyaman University, Adiyaman, Turkey.

45 Also at Mersin University, Mersin, Turkey.

46 Also at Cag University, Mersin, Turkey.

47 Also at Piri Reis University, Istanbul, Turkey.

48 Also at Gaziosmanpasa University, Tokat, Turkey.

49 Also at Ozyegin University, Istanbul, Turkey.

50 Also at Izmir Institute of Technology, Izmir, Turkey.

51 Also at Mimar Sinan University, Istanbul, Istanbul, Turkey.

52 Also at Marmara University, Istanbul, Turkey.

53 Also at Kafkas University, Kars, Turkey.

54 Also at Yildiz Technical University, Istanbul, Turkey.

55 Also at Kahramanmaras Sütcü Imam University, Kahramanmaras, Turkey.

56 Also at Rutherford Appleton Laboratory, Didcot, United Kingdom.

57 Also at School of Physics and Astronomy, University of Southampton, Southampton, United Kingdom.

58 Also at Instituto de Astrofísica de Canarias, La Laguna, Spain.

59 Also at Utah Valley University, Orem, USA.

60 Also at University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia.

61 Also at Argonne National Laboratory, Argonne, USA.

62 Also at Erzincan University, Erzincan, Turkey.

63 Also at Hacettepe University, Ankara, Turkey.

64 Also at Texas A&M University at Qatar, Doha, Qatar.

65 Also at Kyungpook National University, Daegu, Republic of Korea.