DPF2013-156November 13, 2021

Exotic Higgs searches in CMS

A. Castaneda1a

aTexas A&M University at Qatar, Doha, Qatar

On behalf of the CMS Collaboration

We present some of the most recent results from the CMS Collabora-tion on searches for Higgs-like particles in models beyond the StandardModel. Several rare and exotic decay modes of the Higgs boson are ex-plored. The results of the searches are relevant for establishing whetherthe 125 GeV particle observed in Higgs boson searches at the LHC hasthe properties expected for a Standard Model Higgs boson.

PRESENTED AT

DPF 2013The Meeting of the American Physical Society

Division of Particles and FieldsSanta Cruz, California, August 13–17, 2013

1Corresponding author

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1 Introduction

In 2012 the ATLAS and CMS collaborations reported the observation of a new par-ticle with a mass of 125 GeV [1], the excess of events over the expected backgroundcorresponds to a local significance of more than five standard deviations, such excessis most significant in the two decay modes with the best mass resolution (γγ andZZ). The observed particle and its properties are consistent with the long-soughtHiggs boson [2]. Following the excitement after the discovery the collaboration isfacing a new challenge which is to reveal the true identity of this particle, whether itcorresponds to the predicted Standard Model Higgs boson or it is part of an extendedtheory in which there could be more than one Higgs-like particle, for instance, in thecontext of Supersymmetry. Most of these searches are undergoing and some of theresults from the 2011 and 2012 CMS data taking are reviewed in this paper.

2 The CMS experiment

The central feature of the CMS detector is a superconducting solenoid of 6m inter-nal diameter, providing a magnetic field of 3.8 T. Within the field volume, the innertracker is formed by a silicon pixel and strip tracker. It measures charged parti-cles within the pseudo-rapidity range |η| < 2.5. The pseudo-rapidity is defined asη = ln(tan(θ/2)) and θ is the polar angle, while φ is the azimuthal angle in radi-ans. The tracker provides an impact parameter resolution of approximately 15 mmand a resolution on transverse momentum (pT ) of about 1.5% for 100 GeV parti-cles. Also inside the field volume are a crystal electromagnetic calorimeter and abrass/scintillator hadron calorimeter. Muons are measured in gas-ionization detec-tors embedded in the iron flux return yoke, in the pseudo-rapidity range |η| < 2.4,with detector planes made using three technologies: drift tubes, cathode-strip cham-bers, and resistive-plate chambers. Matching muons to tracks measured in the silicontracker results in a transverse momentum resolution between 1% and 5%, for pT val-ues up to 1 TeV. Extensive forward calorimetry complements the coverage providedby the barrel and endcap detectors. A more detailed description of the CMS detectorcan be found in Ref. [3]

3 MSSM searches in CMS

The Standard Model has provided a remarkably successful description of presentlyknown phenomena, the experimental frontier has advanced into the TeV scale with

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no unambiguous hints of additional structure so far, it seems clear that the StandardModel has to be extended to describe the physics at higher energies, for instance,at the reduced Planck scale (MP = (8πGNewton)−1/2 = 2.4 × 1018 GeV) where thequantum gravitational effects become important. The enormous order of magnitudedifference between the electroweak and Planck scales (commonly known as the ”hi-erarchy problem”) does not represent a problem itself to the Standard Model butrather a disturbing sensitivity of the Higgs potential to new physics in almost anyimaginable extension of the Standard Model. The Standard Model demands a non-vanishing vacuum expectation value for the Higgs field, this requirement in addition tothe measured properties of the weak interactions lead to a squared value of the Higgsmass (m2

H) to be of the order of ∼(100 GeV)2, the problem comes from the enormousquantum corrections to this quantity from the virtual effects of every particle thatcouples to the Higgs field. If the scale of these corrections is of the order of Mp thesquared value of the Higgs mass is about thirty order of magnitudes larger than therequired by the Standard Model. By introducing a new symmetry relating fermionsand bosons those large corrections can be effectively cancelled, such symmetry iscommonly known as Supersymmetry (SUSY) and it is a transformation that turnsa bosonic state into a fermionic state and viceversa. The Minimal SupersymmetricStandard Model (MSSM) [4] extend the number of particles in the Standard Modelincluding the Higgs sector by adding an additional Higgs doublet giving rise to threeneutral Higgs bosons (h0, H0, A0) and two charged ones (H±). The phenomenologyof MSSM can be effectively described using only two parameters: the mass of theCP-odd Higgs boson (mA) and the ratio of the vacuum expectation values of the twoHiggs doublets (tan β).

The CMS collaboration has conducted several searches in the context of the MSSMscenario, one of the peculiarities of this model is that for large tan(β) the Higgs bosondecays to τ ’s and b-quarks play a more important role than in the Standard Modelwhich motivates the searches for some specific final states. The following is a list ofthe CMS searches reviewed in this paper.

• Search for a neutral Higgs boson decaying to a pair of b-quarks and producedin association with at least one additional b-quark (pp→ bH +X,H → bb)

• Search for a neutral Higgs boson decaying to a pair of τ leptons (pp → H +X,H → ττ)

• Search for a neutral Higgs boson decaying to a pair of opposite sign muons(pp→ H +X,H → µ+µ−)

Each of the three analysis mentioned above have their own sensitivity, backgroundcomposition and event selection, the fully description and results are reported in

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independent analysis notes and publications, in this paper only general details abouteach analysis are discussed. In the search for a neutral Higgs boson in a final statewith b-quarks [5] the most important background contribution comes from QCDmulti-jet events, the analysis was divided into two categories: the ”all-hadronic” andthe ”semi-leptonic”, in the latest one the presence of a non-isolated muon from ab-jet is required per event, both signatures use data-driven techniques to estimatethe background contribution and the analysis strategy is to search for an excess ofevents in the invariant mass distribution of the two leading b-jets. In the search witha final state with two τ leptons [6] three final states were considered: eτh,µτh andeµ, each lepton candidate was required to be isolated since τ ’s from Higgs bosonsare commonly isolated from the rest of the events activity, the events were divided intwo categories: the b-tag and the non-btag and the analysis strategy was to searchfor an excess of events in the di-tau invariant mass distribution. For the search ofa neutral Higgs boson decaying to a pair opposite sign muons the main backgroundis the Drell-Yan process, there are less important sources of background like tt andW±W±, more details about the background estimation methods for every search ispresented in table 1

Search Channel Main Back-ground

Estimation Method

pp→ bH,H → bball-hadronic QCD multi-jet Templates from a double-

btag-sample in datasemi-leptonic QCD multi-jet b-tagging probabilities

and nearest-neighbor-in-parameter-space technique

pp→ H → ττ eτh,µτheµ Z → ττ Using a sample of Z → µµevents where reconstructedmuons are replaced by sim-ulated taus (”embedding”)

pp→ H → µ+µ− µ+µ− Drell-Yan Background and signalshapes extracted from a fitto the di-µ invariant massin data

Table 1: Summary of the main background processes for MSSM searches and descrip-tion of the estimation method.

Neither of the three searches reported an excess of events over the expected StandardModel background and limits are set on tan(β) as a function of mA as shown inFigure 1.

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Figure 1: Left: Observed upper limits at 95% confidence level on tanβ as a functionof mA for the search of a neutral Higgs boson decaying to a pair of b-quarks forthe combined ”all-hadronic” and ”semi-leptonic” results, previous exclusion regionsfrom LEP and Tevatron in the multi-b jet channel are overlaid. Right: Region inthe parameter space of tan β versus mA excluded at 95% CL in the context of theMSSM for the search of a neutral Higgs boson decaying to a pair of tau leptons. Theexpected one and two standard deviations ranges and the observed 95% CL upperlimits are shown together with the observed exclusion region.

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4 NMSSM searches in CMS

The Next-to-Minimal Supersymmetric Model (NMSSM) [7] was introduced to re-move some of the fine-tuning used in MSSM, several reasons justify the study of thisextended theory and some of them are the following:

• Naturally solves in an elegant way the so-called µ problem, where µ is a di-mensional parameter, in MSSM this parameter has to be adjusted by hand toa value at the electroweak scale, it is desirable to have an extension in whichthis µ-term can be generated dynamically.

• In MSSM the Higgs sector is highly restricted (lightest Higgs is always theStandard Model like). An extended Higgs sector may relax this restriction andlower the experimental bounds (in NMSSM the lightest Higgs boson can be aslight as 1 GeV)

In the MSSM an additional gauge singlet is introduced which generates the µ-termdynamically, that is, an effective µ-term arises spontaneously and the adjustment byhand drops out. This is surely the main motivation for the NMSSM and may justifythe price to pay, which is the introduction of an additional gauge-singlet superfield.The particle content in the bosonic part of the singlet results in two additional Higgsbosons giving a total of seven compared with the five Higgs bosons in MSSM.

Searches for a light Higgs boson in the context of NMSSM have been explored inCMS, two of them are reviewed in this paper:

• Search for a light pseudo-scalar Higgs boson (a) decaying to a pair of muons ofopposite sign (a→ µ+µ−)

• Search for a non-Standard Model Higgs boson decaying to a pair of new lightbosons which further decay to a pair of opposite sign muons h→ 2a→ 4µ

The search for a light Higgs boson decaying to two opposite sign muons [8] is con-strained from previous measurement from Babar in the region ma < mΨ(1s) while forthe region ma > mΨ(3S) the Tevatron and the LHC have sensitivity. This channelis characterized by a large cross section but a small branching ratio to muons, theinvariant mass range was divided in two separate regions, the first one from 5.5 to8.8 GeV and the second one from 11.5 to 14 GeV, the region in between was excludeddue to the abundant contribution of bottonium resonances, no significance excess ofevents were found in either of these regions and limits were set on the production crosssection multiplied by the Branching ratio to muons as shown in Figure 2 The secondanalysis is a search for a pair of new light bosons in the context of NMSSM, each lightbosons decay to a pair of muons giving a final topology of a pair of di-muons withcompatible mass (mdi−µ1 ∼ mdi−µ2). The main backgrounds are the production of a

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pair of b-quarks (bb) and the direct production of double J/ψ, the bb background isestimated directly from data by selecting a bb enriched sample with events with onedi-muon plus additional ”orphan” muon, in this control region a background tem-plate is taken from the fit to the di-muon invariant mass, such template is validatedin events with two di-muons. The double-J/ψ background is estimated using MonteCarlo expectations and applying corrections from measurements in data. After allthe event selection only one event survived and it is compatible with Standard Modelbackground expectation, limits were set as a function of one of the non-StandardModel Higgs boson mass, considering different benchmark signal scenarios as shownin Figure 3.

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Figure 2: Upper limits at 95% C.L. on σ × B(pp → a → µ+µ−) in mass range1 (top) and mass range 2 (bottom) including systematic uncertainties. The dottedlines correspond to the expected limits, and the bands correspond to 1-and 2-σ leveluncertainties on the expected limits.

5 Summary and Outlook

The CMS collaboration has a broad program for Exotic Higgs searches, some of themhave already produced results analyzing the available data from CMS 2011 and 2012data campaigns. In this paper some of the searches in the context of MSSM and

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Figure 3: Left: mµµ1 vs mµµ2 for the isolated di-muon system showing the one eventin the data (shown as empty circle) which survived all selection requirements, theintensity of the shading indicates the background expectation which is a sum of thebb and the direct J/ψ pair production contribution. Right: The 95% CL upper limitsas functions of mh1 , for the NMSSM case, on σ(pp → h1,2 → 2a1) × B2(a1 → 2µ)with ma1 = 0.25GeV (dashed curve), ma1 = 2GeV (dash-dotted curve) and ma1 =3.55GeV (dotted curve). As an illustration, the limits are compared to the predictedrate (solid curve) obtained using a simplified scenario with σ(pp→ h1) = σSM(mh1),σ(pp→ h2)× B(h2 → 2a1) = 0, B(h1 → 2a1) = 0.8%, and B(a1 → 2µ) = 7.7%.

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NMSSM theories were reviewed, in neither of them was found a significant excess ofevents over Standard Model expectations, therefore limits were set as a function of theparameters of each extended theory, such limits improve the coverage from previousexperiments like Tevatron and LEP. The CMS collaboration is looking forward toaccumulate more data in the second phase of the experiment (beyond 2015) to confirmor reject the consistency of the new particle with the predicted Standard Model Higgsboson.

ACKNOWLEDGMENTS

The corresponding author is supported by the Qatar National Research Fund (QNRF)under project NPRP-5-464-1-080

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