Neutral Beyond-Standard-Model Higgs Searches in CMS

Transcription

1 Neutral Beyond-Standard-Model Higgs Searces in On bealf of te Collaboration I.N.F.N. Sezione di Bologna, Italy Searces for beyond te Standard Model neutral Higgs bosons at te experiment are presented. Te analyses are based on proton-proton collision data recorded by te experiment at 7, 8 and TeV centre-of-mass energies. Te exclusion limits determined by te null results of te searces are interpreted in te framework of models tat include extensions of te standard Higgs sector. PoS(CHARGED) Prospects for Carged Higgs Discovery at Colliders - October Uppsala, Sweden Speaker. c Copyrigt owned by te autor(s) under te terms of te Creative Commons Attribution-NonCommercial-NoDerivatives. International License (CC BY-NC-ND.). ttp://pos.sissa.it/

2 Neutral Beyond-Standard-Model Higgs Searces in. Introduction Te pysics program of te LHC run data-taking period during and as been most strikingly affected by te discovery of a new particle by bot te ATLAS and collaborations, tat as been identified as te Standard Model (SM) Higgs boson H. Te measured properties of tis particle are summarized in Ref. []. Te two experiments measure consistent values of te mass of te particle, corresponding to a combined value m H =.9 ±. (stat) ±. (sys) GeV. Te evidence in te τ + τ final state, togeter wit te non-observation in te µ + µ decay cannel demonstrates a non-universal coupling of te new particle to fermions. Finally a detailed analysis of te spin, CP and decay widt of te new particle, as well as a compreensive analysis of its coupling structure ave revealed consistency wit te expectations for te SM Higgs boson witin % precision. Teoretical models beyond te SM predict te existence of additional Higgs bosons, in wic te already discovered particle H is one of several scalar bosons, eiter neutral or carged, in a mass range accessible by te LHC experiments. In tis note te results of searces for additional eavy neutral Higgs bosons performed wit data recorded by te detector [] are summarized. Te analyzed data correspond to te full LHC run dataset collected during and at s = 7 8 TeV, and to te run- data at s = TeV collected up to july. Te run data correspond to integrated luminosities of. fb () and 9.7 fb (). Te run- data correspond to.-.7 fb () and.9 fb (). Te searces are generally performed in a model independent approac, and exclusion limits in terms of production cross section times te corresponding decay brancing ratio are presented. Te results are interpreted according to beyond-sm (BSM) Higgs scenarios, wic include te Two Higgs Doublet Model (HDM), te Minimal Supersymmetric SM (MSSM) and te Singlet Model. Te entire set of exclusion limits is used to constraint te parameters of suc models.. BSM Higgs scenarios From te most general HDM, two scenarios called type-i and type-ii can be derived. In HDM of type-i, te SU() L doublets couple to bot up- and down-type fermions equally; in HDM of type-ii, one doublet couples exclusively to up-type and te oter exclusively to downtype fermions. Te model predicts te existence of five Higgs pysical states: te tree neutral, H, and A, and te carged H ±. Te free parameters can be reduced to seven, and tey are cosen to be m, m A, m H, m H ±, te mixing angle of te CP-even Higgs states α, te ratio of te vacuum expectation values of te two doublets,, and te soft Z breaking mass parameter m. Te two angles α and β are substituted by cos(β α) and witout loss of generality. More details on te coice of te parameters can be found in [] Te MSSM is a specific example of a HDM of type-ii, in te framework of Supersymmetry. At tree level, te two free parameters m A and fully constrain te Higgs sector. Te Higgs sector of te MSSM as been studied extensively already before te advent of te LHC []. For te results presented in tis note te m mod+ and te MSSM scenario [][] ave been cosen. Te m mod+ scenario is a modification of te former m max scenario, developed after te discovery of te H, to make m compatible wit m H witin a teoretical uncertainty of ± GeV [7] in PoS(CHARGED)

3 Neutral Beyond-Standard-Model Higgs Searces in as muc of te parameter space as possible. Te MSSM scenario as recently been introduced as an effective MSSM model, trading te precise knowledge of mh. In tis way m =mh is a manifest requirement of te scenario. Tis scenario is strictly valid for ma > GeV and <. A detailed discussion of te MSSM scenario is given in Ref. [8].. Indirect constraints from te coupling of H. fb (7 TeV) fb (8 TeV) HDM Type II Observed 9% CL. q. fb (7 TeV) fb (8 TeV) q HDM Type I SM.. SM Best fit. -. cos(β-α) Expected 9% CL Best fit. -. Observed 9% CL Expected 9% CL. cos(β-α) Figure : General constraints on te HDM parameter space obtained from te compatibility wit te observed couplings of te H wen interpreted as te boson. Te lines sow te contours wic restrict te allowed parameter space at te 9% CL for a HDM of (left) type-i and (rigt) type-ii. Te observed constraints are sown in black. Te expected constraints assuming just te SM Higgs sector are indicated by te red continuous line. PoS(CHARGED) Wen interpreted as te boson, te predicted production and decay rates of te H are particularly sensitive to te angles α and β. In te HDM tese angles are free parameters. In te MSSM and MSSM tey can be expressed in terms of te free parameters ma and. Tus in bot cases te allowed parameter space is constrained by te production and decay of te H. Suc constraints ave been obtained using te inputs to te combined ATLAS and coupling analysis as presented in Ref. []. Te existing data ave been re-interpreted, witout introducing modifications in te selected analyses. Te production and decay rates of relative to te SM expectation ave been varied using te formalism of leading-order coupling modifiers, κi, as defined in Ref. [9]. Te 9% confidence level (CL) exclusion contours in te HDM of type-i and II, in te cos(β α)- plane, are sown in Figure as obtained from te observed couplings of te discovered H boson. Te observed exclusion contours are sown in black. Te expected exclusion contours, assuming only te SM Higgs sector, are indicated by te red continuous line. Also sown are te expectations by te SM (indicated by te red dased line) and te likeliood estimate (indicated by te black cross). Te results reflect te ig consistency of te H properties wit te expectation for te SM Higgs boson, and set severe constraints to te parameters of te model. Te details of tis analysis are described in [].

4 Neutral Beyond-Standard-Model Higgs Searces in. Direct searces A selected set of results on te searc of BSM neutral Higgs bosons obtained using run data ave been used to determine 9% CL exclusion limits witin te framework of HDM and MSSM models, as described in Ref. []. Suc limits are sown in te -m H (HDM) and -m A (MSSM) parameter space. Figure (left) sows te 9% CL exclusion contours in te HDM scenario (left) of type-i, as obtained by selected analyses tat ave been performed on te LHC run dataset. Te colored filled areas correspond to te excluded regions. As previously discussed, by definition te wole parameter space tat is displayed is mostly compatible wit te constraints imposed by te coupling of H. Te 9% CL exclusion contours of five direct searces in te MSSM m mod+ scenario are displayed in Figure (centre). Values up to are sown for masses up to m A = TeV. For larger values of te predictions become generally unstable. Te impact of te direct searces on te MSSM model are sown in Figure (rigt). Te regions were te MSSM is not strictly applicable are marked in gray. In te figure on te rigt, te constraint tat is obtained from te compatibility of te scenario wit te couplings of te H is also sown. Furter details on te interpretation of tese exclusion limits can be found in Ref. [] fb (7 TeV) fb Observed exclusion 9% CL Expected exclusion 9% CL H WW/ZZ (arxiv:.9) A/H/ ττ A ZH llττ (HIG-9) (arxiv:.99) A ZH llbb (arxiv:.99) Non-perturbative region (8 TeV) HDM Type I, cos(β-α)=., m = m H ± = m H + GeV A m H [GeV]. fb (7 TeV) fb (8 TeV) m = GeV m = GeV m = GeV m = GeV m = GeV Observed exclusion 9% CL Expected exclusion 9% CL τν (arxiv:8.777) H WW/ZZ (arxiv:.9) m A [GeV] ± H A/H bb (arxiv:.89) A/H/ µµ A/H/ ττ mod+ MSSM m (arxiv:8.7) (HIG-9). fb (7 TeV) fb (8 TeV) Model not strictly applicable Observed exclusion 9% CL Expected exclusion 9% CL Model not strictly applicable () (HIG-) A/H bb (arxiv:.89) A/H/ µµ MSSM (arxiv:8.7) A/H/ ττ (HIG-9) H (bbττ) / A Z (llττ) (arxiv:.8) H (bbγγ) (HIG-) H WW/ZZ (arxiv:.9) m A [GeV] Figure : Te 9% CL exclusion contours in HDM scenarios of type-i (left), in te MSSM m mod+ scenario (centre), and in te MSSM model (rigt), as obtained by selected analyses tat ave been performed on te LHC run dataset. Te searc for neutral Higgs bosons in te two-fermion final state pp /H/A f + f allows te test of te coupling of te extra bosons wit down-type fermions. Tis is particularly interesting for HDM type-ii and MSSM, wic predict an enancement of te coupling at large. For practical experimental reason te accessible final states are τ + τ, µ + µ and bb. Te production mecanism can occur eiter via gluon-gluon fusion and b-associated production. In tis latter case te analyses require te presence of b-tagged jets in te event, not associated to te Higgs candidate decay. Te τ + τ final state represents te golden cannel for tis type of searc, being te best compromise between a relatively large decay brancing ratio and a small background. Tese features make tis analysis te most sensitive searc to all tree neutral Higgs bosons in te MSSM. Te searc is performed in te µµ, eµ, µτ, eτ and τ τ final state decays of te τ into electrons, muons, and adrons. Te presence of neutrinos in te final state introduces complications in te in- PoS(CHARGED)

5 Neutral Beyond-Standard-Model Higgs Searces in variant mass reconstruction, te resolution of wic ranges between and % of te di-tau mass, depending on te final state. To enance te sensitivity of te analysis to te MSSM predictions, events are categorized according to te presence/absence of b-tagged jets. Te coarse mass resolution justifies te use of single mass templates obtained from te simulation wit PYTHIA [], produced for several values of m A. Te analysis as been performed using data taken at s = 7-8 TeV [], and it as been updated using data collected at TeV [] for an integrated luminosity of. fb. Model independent 9% CL exclusion limits are obtained in terms of σ B.R. for te production and subsequent decay to a tau pair of a generic boson φ as a function of m A, as sown in Figure for (left) te gluon-fusion production, and (centre) te b-associated production mecanism. No excess is found up to a test mass of TeV. Te results can also be interpreted in te contest of te m mod+ scenario of te MSSM, to set limits in te m A - plane as sown in Figure (rigt). 9% CL limit on σ(ggφ) B(φ ττ)(pb) - µτ +eτ +eµ+τ τ. fb ( TeV) Observed Expected ±σ Expected ±σ Expected (GeV) m φ 9% CL limit on σ(bbφ) B(φ ττ)(pb) - µτ +eτ +eµ+τ τ. fb ( TeV) Observed Expected ±σ Expected ±σ Expected (GeV) m φ mod+ m scenario 9% CL Excluded:. fb ( TeV) MSSM Observed ± σ Expected m ± GeV Expected ± σ Expected TeV(HIG-9) 8 m A (GeV) Figure : Expected and observed 9% CL exclusion limits on cross-section times brancing ratio for (left) te gluon fusion process and (centre) te b-associated production process of pp φ ττ. Te model dependent exclusion limits in te m A - for te m mod+ scenario of te MSSM is sown in (rigt). Te blue lines indicate te expected (dased) and observed (solid) exclusions obtained from te most recent run- searc for tis cannel [], and te red contour indicates te region wic does not yield a Higgs boson consistent wit a mass of GeV witin te teory uncertainties of ± GeV. Te searc for te bb final state benefits from te ig decay brancing ratio, but it suffers from te very ig b-jet background at LHC. Te analysis, performed using data collected at 8 TeV [], searces for eavy scalar bosons in b-associated production. For tis reason at least b- tagged jets are required in te event. Te mass of te Higgs candidate is reconstructed from te two leading b-jets in te event, wit a resolution of about %. Since in te MSSM te A and H bosons are degenerate in mass, a potential signal can be interpreted as te incoerent sum of tese two individual contributions. Te searc is performed in te mass range from to 9 GeV. Since no excess is observed, te 9% CL model independent exclusion limit can be translated into an exclusion limit in te m A - plane witin te MSSM model. A different analysis [] searcing for te same final state as been performed by te experiment using data collected at TeV. A generic neutral scalar decaying to bottom-quark pairs is excluded in te mass range from to GeV. Te excellent muon invariant mass resolution of te experiment as been exploited to searc for BSM neutral scalars decaying to µ + µ pairs at 7-8 TeV centre-of-mass energies []. Bot te gluon fusion and te b-associated production mecanisms are considered. Despite te PoS(CHARGED)

6 Neutral Beyond-Standard-Model Higgs Searces in very low decay brancing ratio, te analysis sensitivity is compatible wit te bb final state in te mass range were te available statistics is large enoug to perform a meaningful measurement. Model independent limits are determined for te σ B.R. of a generic neutral scalar decaying to a muon pair for masses up to GeV. Te results are also interpreted in te m mod+ scenario of te MSSM model as exclusion limits in te m A - plane, in te mass range m A < GeV. Searces for te decay of a eavy neutral scalar X decaying to a pair of ligt H bosons ave been performed. In te SM, at s = TeV te production cross section of a H pair is about fb. However te decay brancing ratio of te eavy X particle in two SM Higgs bosons can become significantly large in te singlet model, translating into a resonance wit mass m X. Te non resonant production mecanism, wic is not addressed in tis note, can also sow indications of new pysics via virtual loops or modified couplings, and it will acquire importance in te future, wit larger integrated luminosity. Te searc for a generic neutral resonance X of eiter spin or, decaying to a SM Higgs boson pair, were one H decays to a bb pair and te oter to a γγ pair as been performed by te experiment at s = TeV and it is described in Ref. []. A bencmark used for tis analysis is te Randall-Sundrum (RS) model of warped extra dimensions (WED) [7], tat predicts new spin- (radions) or spin- (excited gravitons) particles tat could decay to a SM Higgs pair if teir mass is eavier tan m H. Te analysis is restricted to te mass range < m X < 9 GeV, as for iger mass values te Higgs bosons become very boosted, tus reducing its detection efficiency. Te exclusion limits are sown in Figure. Te expectations for a spin- radion (left) and spin- graviton (excited graviton) based on te RS predictions are superimposed. σ(pp X HH bbγγ) [fb] L =.7 fb ( TeV) pp X HH bbγγ Spin- Resonance = TeV Bulk Radion, Λ R Observed 9% upper limit Expected 9% upper limit Expected limit ± σ Expected limit ± σ M X [GeV] σ(pp X HH bbγγ) [fb] L =.7 fb ( TeV) pp X HH bbγγ Spin- Resonance = Bulk Graviton, k/m Pl Observed 9% upper limit Expected 9% upper limit Expected limit ± σ Expected limit ± σ M X [GeV] Figure : Expected and observed 9% CL upper limits on te production of pp X H H bbγγ for te resonant analysis, assuming (left) spin- and (rigt) spin- for te resonance. Cross sections predicted by te RS model are sown (dased red lines). Te SM brancing ratio for H H bbγγ is assumed. PoS(CHARGED) Te searc for te process pp X H (bb)h (bb) performed by te experiment at s = TeV is described in Ref. [8]. Te analysis is performed over te mass range < m X < GeV. However, since te momenta and angles of te decay products of suc a resonance cange substantially over tis range and in order to maximize te sensitivity of tis searc, different event selection criteria are used for te two main kinematic regions: te low-mass region (LMR) for resonance mass ypoteses from GeV to GeV, and te medium-mass region (MMR) for masses from GeV to GeV. Te GeV transition tresold between te LMR and te MMR as been cosen to maximize te expected sensitivity. Te QCD multi-jet background

7 Neutral Beyond-Standard-Model Higgs Searces in is modeled in data by studying parametric fits in sideband regions. At least four b-tagged jets are required in te event, and te b-jets are suitably paired according to dedicated kinematic constraints to reconstruct te mass of te two H bosons, m H and m H. Signal and sidebands regions are defined according to te quantity ( ) ( ) χ mh GeV mh GeV = + (.) σ H σ H wic is sown in Figure (left) as a function of te two Higgs boson masses. Te 9% CL exclusion limits in terms of σ B.R. are sown in Figure (rigt) as a function of te m X mass ypotesis. Te expectations for a Kaluza Klein (KK) graviton are superimposed. (GeV) m H SR. fb ( TeV) SB m H (GeV) σ(pp X) BR(X H(bb) H(bb)) (fb). fb ( TeV) Expected Upper Limit Expected ± σ Expected ± σ Observed Upper Limit KK-Graviton, kl=, k/m =. Pl 8 m X (GeV) Figure : Illustration (left) of signal (SR) and side-band (SB) regions in te m H,m H plane. Te quantities m H and m H are te two reconstructed Higgs boson masses after b-tagging and kinematic selections for data. Te observed and expected upper limits (rigt) on te cross section for a spin- resonance X H(bb)H(bb) at a 9% CL. Teoretical cross sections for te RS KK-Graviton, wit k/m Pl =., kl =, decaying to four b-jets via Higgs bosons are overlaid.. Di-boson final state: X WW/ZZ Te searc for a generic neutral X resonance of unknown mass decaying to a di-boson pair W + W or ZZ allows te study of te low/intermediate region in te mass range from m W to m t, wen interpreted in te HDM and MSSM models. Above m t te decay cannel X tt would open up, tus significantly reducing te brancing ratio to boson pairs. Tis cannel is a good probe for singlet models, tat predict te existence of an additional eavy neutral Higgs boson. Te experiment as performed te searc for te process pp X Z(ll)Z(ll) using a fraction of te data collected at s = TeV in, as described in Ref. [9]. Te analysis is te extension of te four-lepton SM Higgs searc at iger mass values. Te invariant mass distribution of te four lepton final state (eeee, eeµµ, µµµµ) is reported in Figure (left). In addition to te peak corresponding to te SM Higgs boson wit m H = GeV, te distribution PoS(CHARGED)

8 Neutral Beyond-Standard-Model Higgs Searces in is populated by events wit masses iger tan m Z, were te searc for eavy additional Higgs bosons is performed. Te production mecanism of te additional Higgs boson can be eiter gluon fusion (gg) or vector-boson fusion (VBF), wic also includes te process V V H. Te fraction of gg produced events, f gg is ten related to te fraction of VBF-VH events, f V BF by te relation: f gg = f V BF. Te searc is performed for various Higgs widts assumptions. Figure (rigt) sows te expected and observed 9% CL exclusion limits of σ B.R. as a function of te Higgs mass ypotesis m X, wen te fraction f V BF is left to vary in te fit. No significant excess is observed in te mass range - GeV. Events / GeV.9 fb Data H() qq ZZ, Zγ* gg ZZ, Zγ* Z+X ( TeV) 8 8 m l (GeV) σ(pp X ZZ l) [fb].9 fb ( TeV) Expected Observed, 9% CL Γ = ± std. ± std. Γ = GeV Γ = GeV Γ = GeV [GeV] Figure : (left) Distribution of te four-lepton reconstructed invariant mass m l in te full mass range, including te SM-Higgs peak. (rigt) Observed and expected upper limit at te 9% CL on te X ZZ l cross section times te decay brancing ratio as a function of m X at several Γ X values, wit f V BF floated.. Conclusions Te discovery of te neutral resonance aving a mass of about GeV was a major acievement in LHC pysics. Tis resonance as been identified as te SM Higgs boson, as its properties and couplings wit fermions and bosons are very consistent wit te expectation for tis particle. However, according to BSM scenarios, it is possible tat te GeV particle is part of an extended Higgs sector wic would encompass te existence of additional neutral and carged particles of unknown mass. Te measurements performed by te and ATLAS experiments on te SM Higgs properties can be used to severely constrain suc new models, tat ave to be compatible wit te existence of te observed H. Moreover, direct searces of new neutral scalar particles ave been performed by te collaboration using data of te LHC collected during run and run-, to assess exclusion limits on te production and decay of suc ypotetical new particles. Te most stringent exclusion limits currently come from te ττ decay final state, but precise measurements on X H H and X WW/ZZ processes also contribute to set limits on te production and decay of suc particles. m X PoS(CHARGED) References [] Collaboration, Measurements of te Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and analysis of te LHC pp collision data at s = 7 and 8 TeV, Pysics Analysis Summary -PAS-HIG-,. 7

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