Scholarly article on topic 'Decoupling MSSM Higgs sector and heavy Higgs decay'

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

Abstract The decoupling limit in the MSSM Higgs sector is the most likely scenario in light of the Higgs discovery. This scenario is further constrained by MSSM Higgs search bounds and flavor observables. We perform a comprehensive scan of MSSM parameters and update the constraints on the decoupling MSSM Higgs sector in terms of 8 TeV LHC data. We highlight the effect of light SUSY spectrum in the heavy neutral Higgs decay in the decoupling limit. We find that the chargino and neutralino decay mode can reach at most 40% and 20% branching ratio, respectively. In particular, the invisible decay mode BR ( H 0 ( A 0 ) → χ ˜ 1 0 χ ˜ 1 0 ) increases with increasing Bino LSP mass and is between 12%–15% (13%–20%) for 30 < m χ ˜ 1 0 < 100 GeV . The leading branching fraction of heavy Higgses decay into sfermions can be as large as 80% for H 0 → t ˜ 1 t ˜ 1 ⁎ and H 0 / A 0 → τ ˜ 1 τ ˜ 2 ⁎ + τ ˜ 1 ⁎ τ ˜ 2 . The branching fractions are less than 10% for H 0 → h 0 h 0 and 1% for A 0 → h 0 Z for m A > 400 GeV . The charged Higgs decays to neutralino plus chargino and sfermions with branching ratio as large as 40% and 60%, respectively. Moreover, the exclusion limit of leading MSSM Higgs search channel, namely g g , b b ¯ → H 0 , A 0 → τ + τ − , is extrapolated to 14 TeV LHC with high luminosities. It turns out that the ττ mode can essentially exclude regime with tan β > 20 for L = 300 fb − 1 and tan β > 15 for L = 3000 fb − 1 .

Academic research paper on topic "Decoupling MSSM Higgs sector and heavy Higgs decay"

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Physics Letters B

www.elsevier.com/locate/physletb

Decoupling MSSM Higgs sector and heavy Higgs decay

CrossMark

Tong Li

AfiC Centre of Excellence for Particle Physics at the Terascale, School of Physics, Monash University, Melbourne, Victoria 3800, Australia

ARTICLE INFO

Article history:

Received 8 October 2013

Received in revised form 12 November 2013

Accepted 19 November 2013

Available online 26 November 2013

Editor: M. cvetic

ABSTRACT

The decoupling limit in the MSSM Higgs sector is the most likely scenario in light of the Higgs discovery. This scenario is further constrained by MSSM Higgs search bounds and flavor observables. We perform a comprehensive scan of MSSM parameters and update the constraints on the decoupling MSSM Higgs sector in terms of 8 TeV LHC data. We highlight the effect of light SUSY spectrum in the heavy neutral Higgs decay in the decoupling limit. We find that the chargino and neutralino decay mode can reach at most 40% and 20% branching ratio, respectively. In particular, the invisible decay mode BR(H0(A0) ^

XfXi) increases with increasing Bino LSP mass and is between 12%-15% (13%-20%) for 30 -100 GeV. The leading branching fraction of heavy Higgses decay into sfermions can be as large as 80% for H0 ^ tit} and H°/A0 ^ rir2* + The branching fractions are less than 10% for H0 ^ h0h0 and 1% for A0 ^ h0Z for mA > 400 GeV. The charged Higgs decays to neutralino plus chargino and sfermions with branching ratio as large as 40% and 60%, respectively. Moreover, the exclusion limit of leading MSSM Higgs search channel, namely gg, bb ^ H0, A0 ^ t +t-, is extrapolated to 14 TeV LHC with high luminosities. It turns out that the tt mode can essentially exclude regime with tan f > 20 for L = 300 fb-1 and tan f > 15 for L = 3000 fb-1.

© 2013 The Author. Published by Elsevier B.V. All rights reserved.

1. Introduction

The discovery of the Higgs boson at the LHC [1] raises two questions to theoretical particle physicists about the Higgs mechanism: Is the discovered Higgs boson a pure Standard Model (SM) Higgs or SM-like Higgs from new physics theory? Can the LHC prove or disprove new physics associated with Higgs sector? To answer these questions, it is important to investigate the implication of existing Higgs search data for extended Higgs sector in new physics framework and propose dedicated Higgs search signatures for experimentalists to test.

One of the best motivated theories beyond the SM is the weak scale supersymmetry (SUSY). In the framework of the Minimal Su-persymmetric Standard Model (MSSM), unlike SM, the Higgs sector is composed of two Higgs doublets [2,3]. After electroweak symmetry breaking, one has five physical Higgses, namely two CP-even Higgses h0, H0, one CP-odd one A0 and charged Higgses H±. Between the two CP-even Higgs bosons, the one which couples to gauge bosons more strongly is SM-like. Moreover, the tree level Higgs masses are only determined by CP-odd Higgs mass parameter mA and the ratio of two doublets' vacuum expectation

* This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funded by SCOaP3.

E-mail address: nklitong@hotmail.com.

values tan f. Requiring the SM-like production cross sections of a 126 GeV Higgs boson with decay to diphoton and gauge bosons splits the MSSM Higgs parameters into two distinct regions [4]:

(a) The "non-decoupling" region with mA < 130 GeV and tan f < 10 [5]. In this region, the heavy CP-even state H0 is SM-like, while the light CP-even Higgs h0 and the CP-odd one A0 are nearly degenerate in mass and close to mZ , and the charged state H± is slightly heavier [6].

(b) The "decoupling" region with mA > 300 GeV [5]. In this region, the light CP-even Higgs h0 is SM-like, while all the other Higgs bosons are nearly degenerate with mA [7].

The non-decoupling scenario leads to light non-SM-like Higgs states which could be searched immediately without SUSY parameter dependence [8]. However, this scenario is highly constrained by both MSSM Higgs search bounds and b-quark rare decays [9]. The decoupling limit could thus be the most likely MSSM Higgs scenario in light of MSSM Higgs search results and the measurements of low-energy observables.

The leading channels probing decoupling scenario are the production of heavy neutral Higgses H0, A0 from gluon fusion, bb annihilation and associated process with b quarks in final state, followed by decay into bb or t +t- [10]. In particular, with tau Yukawa coupling enhanced in large tanf regime, the tt decay mode puts the most stringent constraints on the heavy Higgs

0370-2693/$ - see front matter © 2013 The Author. Published by Elsevier B.V. AH rights reserved. http://dx.doi.Org/10.1016/j.physletb.2013.11.044

states as the bb production would be overwhelmed by a huge QCD background. However, the current bound and exclusion limit of tt channel are generally based on predictions from generic two Higgs doublet model or some particular SUSY benchmarks [11]. As well known, the fit to 126 GeV Higgs mass and signal excesses indicates light SUSY sparticles, for instance superpartners of top quark and tau lepton. Given light SUSY spectrum, the heavy neutral Higgses decay would change dramatically and result into altered exclusion limit of tt channel [12]. The SUSY products effect in the heavy Higgs decay would also open rich LHC phenomenology [13]. This Letter aims to examine the current status of decoupling scenario and future perspectives for heavy Higgses decay and production. We highlight the complex pattern of heavy Higgses decay, in particular for small tan fi region, taking into account the updated Higgs search bounds and latest flavor measurements. We perform the extrapolation of tt mode to the center-of-mass energy of 14 TeV with high luminosities at the LHC.

The rest of the Letter is organized as follows. In Section 2, we present the parameter choices relevant for Higgs observation in our scan. We also present the scanning results with subject to the constraints from the searches of Higgs and sparticles and flavor measurements. We also highlight the exotic patterns of heavy Higgs decay and extrapolate the tt decay mode in Section 3. We summarize our results in Section 4.

used to impose the exclusion constraints from LEP2 [21], the Teva-tron [22] and the LHC. We further require that the light CP-even Higgs boson is SM-like and satisfies the following properties

h0 in the mass range of 124-128 GeV, (6)

a x BR(gg ^ h0 ^ yy)MSSM > 80% (a x BR)sm, (7)

a x BR(gg ^ h0 ^ WW/ZZ)MSSM > 60%(a x BR)sm- (8)

The experimental flavor measurements considered here include b ^ sy [23] and the LHCb report on Bs ^ ¡— [24]. In our study, we use the following experimental limits

BR(Bs ^ Xsy)exp = (3.43 ± 0.21) x 10

BR(Bs ^ exp = (2.9

+i.i\ -1.0/

which are consistent with SM predictions [25-27]

BR(BS ^ Xsy)sM = (3.15 ± 0.23) x 10

BR(BS ^ mV-)sm = (3.23 ± 0.27) x 10-9.

We also take the observed excess of B ^ Dtvt [28] as an upper limit. In our numerical study, we use Superlso 3.3 [29] to evaluate the above flavor observables.

2. SUSY parameter region and experimental bounds

To figure out the impact of experimental data on SUSY, it is crucial to scan the parameters relevant for the current Higgs observation and flavor measurements and extract the surviving space. We follow the procedure in Ref. [4] to explore the consistent parameter space. To perform a comprehensive scan over the MSSM parameter space, besides the parameters adopted in Ref. [4], we take into account the stau sector in the scan

1 < tanß< 55, 50 GeV < MA < 1000 GeV, 100 GeV </a, < 2000 GeV,

100 GeV < M;

Mq3 < 2000 GeV,

-4000 GeV < At < 4000 GeV,

100 GeV < M T

iTR, Mhj < 2000 GeV, -4000 GeV < AT < 4000 GeV, 100 GeV < M2 < 2000 GeV.

(1) (2)

In addition, we focus on the reduced high MA range in order to study the decoupling region:

300 GeV < Ma < 1000 GeV.

The U(1) gaugino mass Mi, however, is unconstrained in the MSSM since Bino does not contribute much to either the Higgs sector, or the flavor observables. Moreover, as indicated by the measurement of dark matter relic density, the dark matter candidate in the MSSM is more likely to be a Bino-like neutralino with a mass heavier than 30 GeV [14,15]. We thus prefer the Bino neutralino as the lightest supersymmetric particle (LSP) and take

m ~ o ^ M1 = 90 GeV for illustration, unless stated otherwise. Other

SUSY soft masses, which are less relevant to our consideration, are all fixed to be 3 TeV.

21. Constraints from the Higgs searches and b rare decays

We perform our scan by using the FeynHiggs 2.9.5 package [16-19] to calculate the Higgs masses, SUSY spectrum, couplings and Higgs decay/production rates. HiggsBound 4.0.0 [20] is

2.2. Results for allowed region

We generate large random data samples and pass them through the above constraints. Taking into account both the Higgs search results and the flavor constraints, we first show the surviving points in Fig. 1(a) in the tanfi-mA plane. One can see that the measured Higgs mass window and current Higgs search data push the lower limit of mA to 400 GeV. Further b rare decay constraints allow the whole region of mA > 400 GeV and 5 < tan fi < 40. However, due to the enhancement of MSSM contributions to Bs ^ by tan6 fi and reduction by 1/m4A, the large tan fi and small mA regime is highly constrained by b rare decays. Note that although some points have tan fi > 45, more data probing for heavy Higgs regime in near future would immediately restrict mA > 800 GeV with large tanfi. In the following we examine the surviving region favored by Higgs observation and flavor constraints.

In the MSSM, as is well known, the loop correction of the lightest MSSM Higgs mass is dominated by the stop sector and can raise mh0 to the observed value of Higgs boson mass. The leading stop loop correction is given by [30]

2n 2 v2 sin2 ß

X2 , + 1 -

where Xt = At — ¡i cot fi and MS = ym^ m~t2. Thus, as the measured Higgs mass is relatively heavier than tree level MSSM Higgs, the stop masses and stop mixing parameter Xt are strongly related to the Higgs mass in the MSSM. To satisfy the Higgs mass constraint, the stop masses are approximately given by [31]

m? ~m2 + m2— , m? ~m? + m^(1 +

t1 q3 t ^ m2 ) t2 tR t \ m2 )

for |Xt l~miR » mQ3, (12)

with the switch of m^ ^ m~tR for |Xt| — m^ » m~tR, unless both stops are very heavy. The light stop is thus mostly left-handed (right-handed) and its mass is governed by mQ (m~tR) for m~tR » mQ (mQ » mtR ). As seen from the stop mixing effect in Fig. 1(b) in the plane of Xt/vs. m^, the ranges of Xt, m^, m~tR

Fig. 1. (a) tanf vs. mA for surviving points satisfying bounds from LEP2, Tevatron, LHC and m^ = 126 ± 2 GeV (red open square), and further including b rare decay constraints (blue filled circle). The following figures are all for points passing all constraints considered here. (b) Xt/^m^ m~t2 vs. m^. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this Letter.)

sit nearly maximal stop mixing for light stops. Note that the values of light sbottom and sneutrino mass are determined by mq3

and m~L , respectively, and thus mostly bL and vtl.

As well discussed before, there are two main mechanisms leading to a simultaneous enhancement of the diphoton production rate in the MSSM [32]. Firstly, the largest partial contribution to the total width of SM-like Higgs decay, namely r(h0 ^ bb), would decrease if the bottom Yukawa is enhanced. As a result, the total decay width of h0 will be reduced and thus the yy rate gets enhancement. Fig. 2 (a) shows the allowed parameter space relevant for the SM-like Higgs production in the plane of At versus m^. The current Higgs bounds strongly favor relatively large ¡ and positive At with |At| > 2 TeV. This is because large positive product iAt leads to a large positive radiative correction to bottom Yukawa which is needed to suppress r(h0 ^ bb) so as to enhance a(gg ^ h0 ^ yy) [4,32].

The second mechanism is due to the effect of SUSY particles in the direct enhancement of the r(h0 ^ gg/yy), for instance light stop and stau [33]. The stop loop contributions to the gg and yy amplitudes are approximately proportional to [31,34]

(m? + m22 - X?).

Hence, we show the stop effect in Higgs production described in

Eq. (13) in Fig. 2 (b) in the plane of (m2 + m2 - X2)/104 GeV ver-

sus mt1 . For light stop, as one can see, the enhanced contribution of stop in the r(h0 ^ yy) dominates over the reduction in the gluon fusion production such that for gg ^ h0 ^ yy rate being above 0.8 of the SM value. Moreover, an enhancement of r(h0 ^ yy)/r(h0 ^ yy)sM as large as a factor of 2 is possible as a result of light stau effect in the loop, as seen in Fig. 2 (c).

2.3. Discussion of SUSY sparticle searches

Additional constraints come from direct sparticle searches, for instance stop and sbottom. In principle, the stop and sbot-tom mass limit drops lower for small mass difference between the stop/sbottom and the Bino LSP. One can always tune the free Bino mass to be large enough to give soft decay products and thus evade the stop/sbottom search limits. Recently, ATLAS reported that light stops with m^ < 200 GeV and any kinematically allowed

neutralino LSP mass are essentially excluded if BR(t1 ^ cx0) = 100% [35]. However, this bound could be weakened if other decay mode with lighter sparticle, such as t1 ^ T1vTb, overwhelms t1 ^ cx1 as pointed out in Ref. [31]. Also, if Bino mass is not

that large and mt — mx0 > mW + mb(mt), the main decay mode

is given by t1 ^ bW+X0 (tx°). We then have freedom for Bino mass to survive light stop, given the gap between stop bound and kinematic limit.

ATLAS also released that any sbottom with mass less than

650 GeV is not allowed if mx0 < 100 GeV and BR(b1 ^ bx0) =

X1 1 100% [36]. For small values of mQ , we have light left-handed

sbottom in the spectrum as m^ ~ m^. Thus, this case tends to

be in conflict with the above limit if mb — mx0 > 20 GeV or

m~ 0 < 100 GeV. However, if Wino neutralino stays between sbot-tom and Bino LSP, the left-handed sbottom prefers to decay to it with BR(b1 ^ bx20) being typically around 80%-90% [9], even though relatively suppressed by the available phase space. With the further decay of x0 into h0(*)x'0 or Z(*)x1°, these longer decay chains give soft decay products and small missing energy undetected in the detector. As a result, the current sbottom search would not highly restrict the small m^ case.

In addition, CMS put the lower limit on the m~± ~0 to 330 GeV

X1 ,x2

under the assumption of m~0 — m~0 > mZ and BR(y° ^ Zx°) =

A7 /1 2 1

BR(x± ^ W±x10) = 100% [37]. This limit would not directly constrain the spectrum with small mass difference m 0 - m 0 as well as possible suppression of chargino/neutralino decays.

3. Heavy Higgs decay and search sensitivity

3.1. Heavy Higgs decay

In the decoupling limit, the heavy non-SM-like Higgses H0, A0 and H± have rich decay modes, especially in the small tan f regime. Fig. 3 shows the branching ratios of heavy neutral Higgs bosons decay into fermion pairs. In this limit, the H0/A0 coupling to the top quarks is suppressed by 1/ tan f, while the couplings to bottom quarks and tau leptons are enhanced by tan f. As seen in Fig. 3, a majority of points have BR(H0/A0 ^ bb) < 80% and BR(H0/A0 ^ t +t-) < 30%. However, for exceptional significant points in Fig. 3, the H0/A0 ^ tt mode could be dominant for tan f < 10 in particular.

Fig. 2. (a) At vs. m^3, (b) (mi + m? — Xt2)/104 GeV vs. mt1 and (c) r(h0 ^ yy)/r(h0 ^ yy)sm vs. mT1.

Fig.3. (a) BR(H0 ^ ff) vs. mH0 and (b) BR(A0 ^ ff) vs. mA0.

Small values of ¡ , M2 are allowed in the decoupling scenario. We thus expect kinematically occurred heavy Higgs decay into pairs of chargino and neutralino. The MSSM Higgs bosons mainly couple to mixtures of higgsino and gaugino components [3].

Therefore, for ¡i » Mi,2 or ¡i ^ Mi,2, the decays of the heavy Higgs bosons into pairs of pure gaugino or higgsino are strongly suppressed. The mixed decay H0/A0 ^ X^X^, Xti0 2 Xt30 4 will then have significant branching fractions. For ¡i ~ M2, on the

Fig.4. (a) BR(H0 ^ XfXj ) vs. mH0 and (b) BR(A0 ^ xrxp vs. mA0.

Fig. 5. BR(H0 ^ x±Xjf) 'n the plane of M2 vs. ¡, for (a) i = j = 1 and (b) i = 1, j = 2. The color scale gives the branching fraction of H0 ^ Xt^xJ decay. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this Letter.)

other hand, all the heavy Higgses have comparable decay rates into chargino/neutralino. We show the BR(H0/A0 ^ x±xj) and BR(H0/A0 ^ x°xin Figs. 4, 5 and 6. One can see that the branching ratio of chargino and neutralino decay mode can reach at most 40% and 20%, respectively. In particular, the invisible decay mode of heavy Higgses, namely H0/A0 ^ X10jt10, relies on the arbitrary Bino LSP mass and has important implication for the dark matter candidate search at the LHC. The BR(H0(A0) ^ XX10X;10) increases with increasing Bino LSP mass and the maximal value can reach between 12%-15% (13%-20%) for 30 < mx0 < 100 GeV. For the sample with maximal H0/A0 ^ X10jt10 decay rate, with increasing mx0, some other leading neutralino modes H0/A0 ^

XX0 Xti=1 have decreasing branching fractions by a few percent correspondingly. This invisible decay mode could be tested through mono-b-jet signature in gb ^ bH0/A0 production.

Indicated by the fit to Higgs mass and signals, light sfermions also play important role in the heavy Higgs decay. In the decoupling limit, the heavy neutral Higgses couplings to sfermion current eigenstates are given by [3]

CH0 7/

_ f (f — QfsW)mz sin2fi + f 1mf (Afr{+ ¡¡rf2) \

y \mf (Afr{ + ¡rf ) QfsWm2Z sin2fi + mfr{ J '

CA0 ff

i 0 — 2 mf (Af (tan fi)—2,3 + ¡¡)\

\i mf (Af (tan fi)—2,3 + ¡) 0 / ,

where rU = —cotfi, r'd = r[ = —tanfi, rU = —1 and r'd = rl2 = 1. For CP-even Higgs H0, these couplings contain term proportional to m2f and thus get enhanced for the third generation sfermions.

The CP-odd Higgs A0 only couples to f1 f2 mixtures with couplings a mf. The stop decay mode for A0 is then forbidden as at least one stop has to be very heavy to accommodate SM-like Higgs mass. Figs. 7 (a) and (b) show that the branching fraction of heavy Higgses decay into sfermions can be as large as 80% for H0 ^ f^j and H0/A0 ^ T1T2J + TjT2. Moreover, with increasing |At|, both

H0 and A0 have increasing branching ratio of TT + TfT2 decay mode [31]. In Fig. 8 we display the dependence of heavy Higgs decay into light sfermions on SUSY soft masses. The decay H0 ^ f1f} is dominant for either < 500 GeV, mtR > 0.9 TeV or m^ > 1 TeV, m~tR < 500 GeV with only one light stop. While H0 ^ T1 Tf + Tf t2 could be dominant for m^, mfR < 800 GeV with two light staus.

The decays H0 ^ h0h0 and A0 ^ h0 Z are known to complement heavy Higgs searches at low values of tan fi and intermediate MA masses [10,38]. In the decoupling limit with MA > 400 GeV constrained by current Higgs searches, the corresponding partial decay widths are suppressed by 1/mH0 and coupling cos2 (fi — a) ^ 1, respectively. Their branching fractions are thus decreasing quickly with at most 10% for H0 ^ h0h0 and 1% for A0 ^ h0 Z.

3.2. Future heavy Higgs search sensitivity

As one can see from previous subsection, SUSY effects could vary the tt mode of heavy Higgs decay significantly. One has to consider the variation of tt exclusion limit given various SUSY decay products, for the small values of tan fi in particular. We now improve measurement potential for the search of heavy

MSSM Higgs decay into т + т-. Assuming the signal and background events go up by the same factor when the energy enhanced, we simply scale the signal sensitivity with ^asignai x L based on the expected upper limit on the тт channel [11], where aSigncii = a(gg, bb ^ H0, A0 ^ т+тat 14 TeV LHC and L is the integrated luminosity. The extrapolation of excluded region for тт mode at 14 TeV LHC is shown in Fig. 9 with L = 300 fb-1 and 3000 fb-1. Note that as the expected limit of MA is 800 GeV in the CMS search, we only show the extrapolation for MA less than 800 GeV. One can see that, in the plane of tan в-Ma with MA < 800 GeV, the тт mode can only essentially exclude regime with tan в > 20 for L = 300 fb-1 and tan в > 15 for L = 3000 fb-1. The dominant SUSY decay modes of neutral Higgses give at most a few percent of uncertainty for the above exclusion.

4. Conclusions

The decoupling limit in the MSSM Higgs sector is the most likely scenario in light of the Higgs discovery. This scenario is further constrained by MSSM Higgs search bounds and flavor measurements. We performed a comprehensive scan of MSSM parameter space and updated the constraints on the decoupling MSSM Higgs sector in terms of 8 TeV data. The light SUSY spectrum in

Mg3 (GeV) Mu (GeV)

(a) (b)

Fig.8. (a) BR(H0 ^ t1tj) in the plane of MfR vs. and (b) BR(H0 ^ i;1it2* + T2T*) in the plane of MTR vs. Mf . The color scale gives the branching fraction of H0 ^ ff* decay. (For interpretation of the references to color in3 this figure legend, the reader is referred to the web version3 of this Letter.)

Fig. 9. Exclusion for H0/A0 ^ tt mode in the plane of tan fi vs. mA with L = 300 fb—1 (purple open circle) and 3000 fb—1 (green open triangle), based on surviving region in Fig. 1. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this Letter.)

charge of SM-like Higgs mass and signal excesses was discussed. We highlighted the effect of light SUSY spectrum in the heavy neutral Higgs decay in the decoupling limit. We found that the measured Higgs mass window and current Higgs search data push mA to at least 400 GeV. Further b rare decays do not put more stringent constraints on the surviving region. The chargino and neu-tralino decay mode can reach at most 40% and 20% branching ratio, respectively. In particular, the invisible decay mode BR(H0(A0) ^ X°X°) increases with increasing Bino LSP mass and is between 12%-15% (13%-20%) for 30 < mx0 < 100 GeV. The leading branching fraction of heavy Higgses decay into sfermions can be as large

as 80% for H0 ^ tit* and H0/A0 ^ fjT* + fif2. H

and A0 ^ h0 Z have the branching fraction less than 10% and 1%, respectively, for mA > 400 GeV. The branching ratio of charged Higgs decay to neutralino plus chargino and sfermions can be as large as 40% and 60%, respectively. Moreover, these dominant SUSY products alter the normal heavy Higgs decay modes dramatically, in particular for small tan fi region. We extrapolated the exclusion limit of leading MSSM Higgs search channel, namely gg, bb ^ H0, A0 ^ t +t—, to center-of-mass energy of 14 TeV with high luminosities at the LHC based on surviving region and exceptions of

dominant SUSY decay channels. It turns out that the tt mode can essentially exclude regime with tanß > 20 for L = 300 fb-1 and tanß > 15 for L = 3000 fb-1.

Acknowledgements

We would like to thank Marcela Carena and Ian Lewis for useful discussions. This work was supported in part by the Australian Research Council.

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