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Interpreting the LHC Higgs Search Results in the MSSM ∗ S Physics Letters B 710 (2012) 201–206 Contents lists available at SciVerse ScienceDirect Physics Letters B www.elsevier.com/locate/physletb Interpreting the LHC Higgs search results in the MSSM ∗ S. Heinemeyer a, O. Stål b, , G. Weiglein b a Instituto de Física de Cantabria (CSIC-UC), Santander, Spain b Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg, Germany article info abstract Article history: Recent results reported by the ATLAS and CMS experiments on the search for a SM-like Higgs boson ∗ Received 12 January 2012 both show an excess for a Higgs mass near 125 GeV, which is mainly driven by the γγ and ZZ Received in revised form 24 February 2012 decay channels, but also receives some support from channels with a lower mass resolution. We discuss Accepted 27 February 2012 the implications of this possible signal within the context of the minimal supersymmetric Standard Available online 2 March 2012 Model (MSSM), taking into account previous limits from Higgs searches at LEP, the Tevatron and the LHC. Editor: A. Ringwald The consequences for the remaining MSSM parameter space are investigated. Under the assumption of a Higgs signal we derive new lower bounds on the tree-level parameters of the MSSM Higgs sector. We also discuss briefly an alternative interpretation of the excess in terms of the heavy CP-even Higgs boson, a scenario which is found to be still viable. ©2012ElsevierB.V. Open access under CC BY license. 1. Introduction parameters (besides the SM parameters), commonly chosen as the mass of the CP-odd Higgs boson, M A , and tan β,theratio The Higgs boson [1] has for a long time been considered as the of the two vacuum expectations values. In the decoupling limit, only missing piece in the Standard Model (SM) of particle physics. M A 2M Z (where M Z denotes the mass of the Z boson), all Therefore, finding this particle has been one of the main tasks MSSM Higgs bosons except the lightest CP-even scalar h become of experimental high-energy physics. However, the main results heavy, whereas h has SM-like properties. In this limit it would be from the published searches so far have been exclusion limits (see difficult to separate hints for a SM Higgs boson from a potential e.g. the results from LEP [2],theTevatron[3], and the LHC [4,5]). MSSM counterpart. It is also in the decoupling limit where Mh Combining the experimental limits, the only allowed region (be- reaches its maximal value, Mh 135 GeV [9]. fore the latest results which will be discussed below) a relatively The LHC experiments recently extended their exclusion regions SM for a SM-like Higgs boson down to MSM 127 GeV, with the low- small window for the Higgs mass: 114 GeV < M H < 141 GeV. H SM This low mass region is also the one favoured by electroweak pre- est limit coming from CMS (M H < 131 GeV for ATLAS). In ad- SM cision tests, see e.g. [6]. dition, ATLAS reported exclusion of the range 114 GeV < M H < A low Higgs mass is predicted in supersymmetric extensions of 115.5 GeV, which is a region where sensitivity was not expected. the SM, where the quartic Higgs couplings are related to gauge Most interestingly, both experiments also reported about an excess SM = couplings. Exclusion of a heavy SM-like Higgs [3–5] can there- over the background expectation close to M H 125 GeV [10]. fore be considered as being in line with the predictions of su- Since this Higgs mass lies in the range compatible with supersym- persymmetry (SUSY). Besides predicting a light Higgs boson, SUSY metry, we report in this Letter on a first analysis and interpretation protects scalar masses from the large hierarchy of scales, it al- of these results in an MSSM context. lows for gauge coupling unification, and it can provide a dark matter candidate [7].Theminimal supersymmetric extension of 2. Experimental Higgs search results the SM (MSSM) [8] has two complex Higgs doublets. Following electroweak symmetry breaking, the physical spectrum therefore Both the LHC experiments (ATLAS and CMS) have reported [10] contains five Higgs bosons. Assuming CP conservation, these are on indications for an excess of Higgs-like events corresponding to ± denoted h, H (CP-even), A (CP-odd), and H (charged Higgs). At a Higgs boson mass the tree-level the MSSM Higgs sector can be described by two SM = M H 126 GeV (ATLAS), SM = M H 124 GeV (CMS). Corresponding author. * SM E-mail addresses: [email protected] (S. Heinemeyer), [email protected] Another excess at M H 119 GeV was reported by CMS, but not (O. Stål), [email protected] (G. Weiglein). confirmed by ATLAS. Consequently, we will not consider this value 0370-2693 ©2012ElsevierB.V. Open access under CC BY license. doi:10.1016/j.physletb.2012.02.084 202 S. Heinemeyer et al. / Physics Letters B 710 (2012) 201–206 ∗ in our analysis. The result is driven by an observed excess of events CP-even Higgs boson, H. Since the observed excess includes WW ∗ ∗ over SM background expectations in primarily the γγ and ZZ and ZZ final states, an interpretation in terms of the CP-odd channels, which provide relatively good resolution for the Higgs Higgs boson, A, appears to be highly disfavoured. boson mass. The local significance for the combined result is 3.6σ For our discussions of the possible interpretations of the as- for ATLAS and 2.6σ for CMS. However, when interpreted in a sumed signal, we use a phenomenological description of the (CP- global search containing many mass bins, the local significance is conserving) MSSM with all parameters given at the electroweak washed out by the look-elsewhere effect (LEE). This effect compen- scale. In order to determine the radiative corrections to the Higgs sates for the higher probability of random fluctuations generating masses it is necessary to specify, besides the tree-level parameters an excess anywhere when searching in more than one place. Tak- M A and tan β, also the relevant SUSY-breaking parameters enter- ing this into account, the significance of the reported result is ing at higher orders. In particular, the parameters in the stop and reduced to 2.5σ (1.9σ ) for ATLAS (CMS) when interpreted as a sbottom sector have a large impact in this context. Since for the SM Higgs search over the mass range from 110 GeV to 146 GeV. case where we interpret the assumed signal as the lighter CP- On the other hand, one could argue that when interpreting these even Higgs h we are interested in particular in determining lower results in a model where the allowed range for Mh is constrained bounds on the most relevant parameters, we fix those with smaller max to a smaller range by the theory (as in the MSSM), the LEE does impact on Mh to their values in the mh scenario [15], not apply to the same degree as for the SM interpretation. These new results are therefore even somewhat more interesting in an M1 = 100 GeV, M2 = 200 GeV MSSM context. m ˜ = 0.8MSUSY, μ = 200 GeV, (2) For the remainder of this Letter, encouraged by the excess re- g ported by ATLAS and CMS, we investigate a scenario where we so that conservative lower bounds are obtained for the other pa- assume the observation of a state compatible with a SM-like Higgs rameters. In Eq. (2) M1,2 and mg˜ are the soft SUSY-breaking gaug- bosonwithmassMh = (125 ± 1) GeV. We will discuss the implica- ino masses corresponding to the SM gauge group, and μ is the tions that such an assumed signal would have for the MSSM. While Higgs mixing parameter. This choice ensures that the correspond- the current statistical significance does not allow yet to draw firm ing contributions to Mh are such that one obtains (approximately) conclusions on the validity of the above assumption, our analysis is thehighestvalueforMh. In addition to varying the tree-level pa- in fact somewhat more general, as possible implications of observ- rameters, we allow for variation in the overall SUSY mass scale ing (or excluding) a state compatible with a SM-like Higgs else- MSUSY and the stop mixing parameter Xt ≡ At − μ cot β, where where in the allowed mass window 115.5GeV< Mh < 127 GeV At,b denotes the trilinear coupling of the Higgs to scalar tops or [10] can also be inferred. bottoms. We furthermore set Ab = At . The scalar top masses will be denoted as m˜ and m˜ below, with m˜ ≤ m˜ .Itshouldbe t1 t2 t1 t2 3. MSSM interpretation noted that when we discuss relatively low values of MSUSY this refers only to squarks of the third generation (which give rise to For calculating the Higgs masses in the MSSM we use the code the relevant Higgs mass corrections). The experimental bounds re- FeynHiggs [9,11,12] (v. 2.8.5). The status of higher-order cor- ported from squark searches at the LHC [16], on the other hand, rections to the masses (and mixing angles) in the neutral Higgs apply only to squarks of the first two generations, which are es- sector is quite advanced.1 The complete one-loop result within sentially irrelevant for Higgs phenomenology. We also do not apply the MSSM is available and has been supplemented by all pre- a lower bound on the gluino mass, which leads to more conserva- sumably dominant contributions at the two-loop level, see Ref. [9] tive lower limits on the parameters from the Higgs sector than for details.
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