PaperlayerView exact revision on arXiv

Source-linked AI summary

Search for neutral MSSM Higgs bosons decaying to a pair of tau leptons in pp collisions

CMS Collaboration

arXiv:1408.3316v2hep-ex

TL;DR

The paper searches for neutral MSSM Higgs bosons decaying to tau pairs, a channel motivated by enhanced tau branching at large tan β. It analyzes CMS data with b-associated production included and finds no excess, setting limits in benchmark scenarios and on production rates.

  • Problem

    The search tests for neutral MSSM Higgs bosons in ττ, a channel of particular interest because its branching fraction is enhanced at large tan β.

    Source: §1 · p. 3

  • Method

    The CMS analysis uses 24.6 fb−1 at 7 and 8 TeV across five ττ signatures, including b-associated Higgs production, and applies a CLs profile-likelihood analysis.

    Source: §1 · p. 3, §3 · p. 8, §7 · p. 15

  • Results

    No excess is observed; the analysis reports 95% CL bounds, benchmark-scenario exclusions, and upper limits for gluon fusion and b-associated production.

    Source: §8 · pp. 16–18, §9 · p. 21

  • Takeaways & Limitations

    The results constrain MSSM parameter space, with much of the mmax scenario excluded by the Higgs-mass requirement and modified-scenario exclusions concentrated at low tan β.

    Source: §8 · p. 17

    The simpler event categorization reduces SM Higgs sensitivity because vector-boson-fusion and boosted-gluon-fusion production are not enhanced.

    Source: §3 · p. 8

Abstract

from arXiv · show

A search for neutral Higgs bosons in the minimal supersymmetric extension of the standard model (MSSM) decaying to tau-lepton pairs in pp collisions is performed, using events recorded by the CMS experiment at the LHC. The dataset corresponds to an integrated luminosity of 24.6 inverse femtobarns, with 4.9 inverse femtobarns at 7 TeV and 19.7 inverse femtobarns at 8 TeV. To enhance the sensitivity to neutral MSSM Higgs bosons, the search includes the case where the Higgs boson is produced in association with a b-quark jet. No excess is observed in the tau-lepton-pair invariant mass spectrum. Exclusion limits are presented in the MSSM parameter space for different benchmark scenarios, m[h,max}, m[h,mod+], m[h,mod-], light-stop, light-stau, tau-phobic, and low-m[H]. Upper limits on the cross section times branching fraction for gluon fusion and b-quark associated Higgs boson production are also given.

1 Introduction

The introduction motivates ττ searches as a probe of neutral MSSM Higgs bosons and describes the production mechanisms, data, and benchmark interpretations used. It also explains how benchmark scenarios accommodate the observed 125 GeV boson while varying MSSM parameters.

1 Introduction

  • The MSSM has two Higgs doublets yielding five physical bosons, with its tree-level Higgs sector parameterized by mA and tan β.The states are h, H, A, and H±; higher-order corrections introduce additional parameters.Source: §1 · p. 3, §1.1 · p. 4
  • At large tan β, b-associated production dominates and the ττ branching fraction is enhanced, motivating this search channel.Gluon fusion dominates for small and moderate tan β.Source: §1 · p. 3
  • The search uses 24.6 fb−1 of CMS data at 7 and 8 TeV across five ττ signatures, with benchmark and model-independent interpretations.The model-independent results give limits on σ · B(φ →ττ) for gluon fusion and b-associated production.Source: §1 · p. 3

1.1 MSSM Higgs boson benchmark scenarios

  • Traditional benchmark interpretations vary tan β and mA while fixing other radiative-correction parameters; this study also considers multiple alternative scenarios.For the cited benchmark setup, mA is fixed at 110 GeV while µ and tan β vary.Source: §1.1 · pp. 4–5
  • New benchmark scenarios accommodate h or H near 125 GeV within ±3 GeV, while changes to model parameters reopen regions excluded in the mmax scenario.The scenarios include light-stop, light-stau, τ-phobic, and low-mH variants; the light-stop scan stops at 600 GeV because the SUSY NLO correction calculation loses validity above that mass.Source: §1.1 · p. 4
  • Cross-section predictions combine higher-order calculations, including four- and five-flavor bbφ results matched with the Santander scheme.FEYNHIGGS supplies Higgs Yukawa couplings, while FEYNHIGGS and HDECAY provide branching fractions to tau leptons.Source: §1.1 · p. 5

2 Experimental setup, event reconstruction, and simulation

The CMS setup reconstructs particles and event objects, selects collision vertices, and mitigates pileup in jets and missing transverse energy. Simulated signal and background events are processed to model detector response and tau decays.

2 Experimental setup, event reconstruction, and simulation

  • Particle flow combines subdetector information to reconstruct particles used to form jets, hadronic tau candidates, and missing transverse energy.Missing transverse energy is the negative vector sum of reconstructed-particle transverse momenta.Source: §2 · p. 6
  • Jets use anti-kT with distance parameter 0.5, event-by-event pileup subtraction, and secondary-vertex and track-lifetime information for b tagging.Jets with |η| < 4.7 and b-tagged jets with |η| < 2.4 are used.Source: §2 · p. 6
  • Hadronic tau reconstruction identifies decay modes with one charged hadron and up to two neutral pions, or three charged hadrons, and rejects jets, electrons, and muons.Isolation uses charged hadrons, photons, and neutral hadrons in a cone around the lepton direction.Source: §2 · pp. 6–7
  • A multivariate correction separating primary-vertex and other components improves missing-transverse-energy resolution in Z →µµ events by roughly a factor of two with 25 additional pileup events.Pileup averages were 9 interactions per crossing in 2011 and 21 in 2012.Source: §2 · pp. 6–7
  • PYTHIA models MSSM signals, MADGRAPH and POWHEG model backgrounds, and simulated events pass through GEANT4 detector simulation and the data reconstruction algorithms.TAUOLA simulates tau decays, and additional interactions are reweighted to the observed pileup distribution.Source: §2 · p. 7

3 Event selection

Events are selected in five tau-pair signatures using dedicated triggers and channel-specific requirements, then split into categories sensitive to b-associated production and gluon fusion. The simpler categorization reduces model dependence but also reduces sensitivity to the Standard Model Higgs boson.

3 Event selection

  • Dedicated triggers combine electron, muon, and tau objects, with identification criteria and transverse-momentum thresholds tightened as instantaneous luminosity increased.Source: §3 · p. 7
  • In eτh and µτh, events require an electron above 20 (24) GeV or muon above 17 (20) GeV in 2011 (2012), plus an oppositely charged isolated τh above 20 GeV.Loose-isolation opposite-charge lepton pairs are vetoed to reduce Z → ee and Z → µµ contamination.Source: §3 · p. 7
  • The eµ and µµ channels require oppositely charged leptons above 20 and 10 GeV, while τhτh requires two oppositely charged τh above 45 GeV.The µµ selection uses a boosted decision tree to reduce Z → µµ background; the τh isolation requirement is below 1 GeV.Source: §3 · pp. 7–8
  • W+jets rejection uses a transverse-mass requirement below 30 GeV in eτh and µτh, and a ζ-axis discriminator in eµ.Source: §3 · p. 8
  • The b-tag category requires at least one b-tagged jet with pT > 20 GeV and at most one jet with pT > 30 GeV; the no b-tag category vetoes b-tagged jets above 20 GeV.The categories target b-quark-associated production and gluon fusion, respectively.Source: §3 · p. 8
  • The simpler categorization reduces model dependence but lowers SM Higgs sensitivity because vector-boson-fusion and boosted-gluon-fusion production are not enhanced.Source: §3 · p. 8

4 Background estimation

Background shapes and yields are estimated using data control samples and simulation, with methods tailored to each final state and process.

4 Background estimation

  • The largest Z → ττ background in eτh, µτh, and eµ is estimated by replacing data muons from Z → µµ events with simulated tau-decay particles and normalizing to the observed Z → µµ yield.Using collision data for jet energy and missing-energy modeling substantially reduces their systematic uncertainties.Source: §4 · p. 8
  • QCD multijet shapes and yields are estimated from same-sign or loose-isolation data samples, with opposite-sign-to-same-sign or tight-to-loose ratios used for normalization.The procedures differ by channel: eτh and µτh use same-sign ττ events, while τhτh uses opposite-sign events with loose τ isolation.Source: §4 · pp. 8–9
  • In eτh and µτh, W+jets shapes come from simulation and rates from a large-transverse-mass control region; in eµ, W+jets and multijet rates use relaxed-lepton data and measured efficiencies.Source: §4 · p. 9
  • Drell–Yan dimuon yield in µµ is fitted using muon-pair distance of closest approach, while simulated electron- and muon-pair yields in eτh and µτh are rescaled to Z → µµ data.The eτh Z → ee simulation also receives a data-measured e → τh fake-rate correction.Source: §4 · p. 9
  • The tt, diboson, and single-top backgrounds are estimated from simulation, with the tt yield checked in eµ events containing two b-tagged jets.Source: §4 · p. 9

5 Tau lepton-pair invariant mass

The analysis reconstructs the tau-pair invariant mass to distinguish Higgs signals from background, then examines mass distributions across channels and b-tag categories.

5 Tau lepton-pair invariant mass

  • The maximum-likelihood mττ reconstruction typically has 20% resolution for Z → ττ and improves separation of the main Z → ττ background from hypothetical MSSM A signals.Source: §5 · p. 11
  • Figure 2 compares normalized simulated visible-mass and reconstructed-mass distributions for Z → ττ and MSSM A signals at mA = 120, 200, and 300 GeV in µτh.Source: Figure 2 · p. 11
  • The five-channel no-b-tag mass distributions target gluon fusion, while the corresponding b-tag distributions enhance sensitivity to b-quark-associated production.The displayed channels are eτh, µτh, eµ, µµ, and τhτh.Source: §5 · p. 11, Figure 3 · p. 12, Figure 4 · p. 13

6 Systematic uncertainties

The analysis accounts for experimental uncertainties in yields and mass-spectrum shapes, as well as theoretical uncertainty in the MSSM signal cross sections.

6 Systematic uncertainties

  • Normalization uncertainties include luminosity (2.2% for 2011 and 2.6% for 2012), jet energy scale (1–10%), and tau identification and trigger efficiency (8%).Electron identification and trigger uncertainty is 2%, and the muon uncertainty is 2–3%.Source: §6 · p. 14
  • Shape uncertainties include electron, muon, and tau energy scales of 1%, 1%, and 3%, respectively; b-tagging efficiency uncertainty ranges from 2–7%.The b-tag mistag rate for light-flavor partons is accurate to 10–20%.Source: §6 · p. 14
  • Theoretical uncertainties on MSSM Higgs signal cross sections depend on tan β, mA, and benchmark scenario, and can reach approximately 25%.The calculations use MSTW2008 parton distribution functions and the recommended uncertainty prescription.Source: §6 · p. 14

7 Statistical analysis

The tau-pair mass spectra show no clear evidence for an MSSM Higgs signal, so the analysis sets exclusion limits using a modified frequentist CLs criterion. It combines likelihood fits across final states and event categories, with separate tests for a single narrow resonance and the three neutral MSSM Higgs bosons.

7 Statistical analysis

  • A binned maximum-likelihood fit uses tau-pair mass distributions across five final states and the b-tag and no-b-tag categories.For the µµ channel, the fit uses the two-dimensional distribution of mττ versus mvis.Source: §7 · p. 15
  • Systematic uncertainties enter as nuisance parameters, including continuous spectrum perturbations, single-bin background fluctuations, and fitted tail-shape parameters above 150 GeV.For major backgrounds in the mττ tail, the nominal distribution is replaced by a fit of the form f = exp[−mττ/(c0 + c1 · mττ)].Source: §7 · p. 15
  • The invariant-mass spectra show no clear evidence for an MSSM Higgs signal, so the analysis obtains exclusion limits using the modified frequentist CLs criterion.The test statistic is based on a profile likelihood ratio.Source: §7 · p. 15
  • For a single narrow resonance, the model-independent search sets 95% CL limits on σ · B(φ → ττ) for gluon fusion and b-quark-associated production.When extracting one production-mode limit, the rate of the other production mode is treated as a nuisance parameter.Source: §7 · pp. 15–16
  • The MSSM test compares the three-neutral-Higgs signal hypothesis with a Standard Model Higgs hypothesis, including backgrounds in both hypotheses.The model uses µ = 0 or 1; likelihoods are maximized with the corresponding nuisance parameters.Source: §7 · p. 16
  • At each mA and tan β point, the analysis determines masses, production cross sections, and ττ branching fractions for h, H, and A, then adds their contributions.Limits on tan β versus mA are obtained for the benchmark scenarios using the MSSM test statistic.Source: §7 · p. 16

8 Results

No clear MSSM Higgs signal is found, and 95% CL exclusion limits are set across benchmark scenarios. The exclusions differ by scenario, while the search also reports model-independent limits and a likelihood scan of the two production modes.

8 Results

  • Most mmax benchmark parameter space is excluded by the Higgs-mass requirement, while modified-scenario exclusions are mainly concentrated at low tan β.Figure 5 shows the mmax limits; Figure 6 covers the modified scenarios.Source: §8 · p. 17, Figure 5 · p. 17, Figure 6 · p. 18
  • The light-stop, light-stau, τ-phobic, and low-mH scenarios have 95% CL exclusion limits; in light-stop, most probed parameter space is excluded by this search or the Higgs-mass requirement.For low-mH, limits are on tan β versus µ with mA fixed at 110 GeV.Source: §8 · pp. 16, 18, Figure 6 · p. 18
  • Bottom- and top-loop interference in the MSSM ggφ cross section lets the direct search exclude some regions at low tan β.Source: §8 · p. 18
  • At 8 TeV, the search sets model-independent upper limits on σ·B(φ →ττ) versus mφ for gluon fusion and b-quark associated production, with observed limits in agreement with expectation.The limits assume a single narrow-width resonance; the expected dataset includes background and a 125 GeV SM Higgs boson.Source: §8 · p. 19, Figure 7 · p. 19
  • The two-dimensional likelihood scan of the gluon-fusion and b-quark-associated σ·B(φ →ττ) values is compatible with the 125 GeV SM Higgs expectation at mφ = 125 GeV.Source: §8 · p. 19, Figure 8 · p. 20

9 Summary

CMS searched for neutral MSSM Higgs bosons decaying to tau pairs, including production with a b-quark jet. No excess was observed, and the results include benchmark exclusion limits and production-mode cross-section limits.

9 Summary

  • The search used 24.6 fb−1 of CMS data at 7 and 8 TeV and included five ττ signatures and b-quark-associated Higgs production.The dataset comprised 4.9 fb−1 at 7 TeV and 19.7 fb−1 at 8 TeV.Source: §9 · p. 21
  • No excess was observed in the tau-lepton-pair invariant mass spectrum.Source: §9 · p. 21
  • Exclusion limits cover the listed MSSM benchmark scenarios, alongside cross-section-times-branching-fraction limits for gluon fusion and b-quark-associated production.The scenarios include mmax, mmod+, mmod−, light-stop, light-stau, τ-phobic, and low-mH.Source: §9 · p. 21

A Exclusion limits

The appendix presents 95% CL MSSM benchmark exclusion limits and model-independent upper limits for gluon-fusion and b-quark-associated production.

A Exclusion limits

Related papers

Loading 1408.3316v2…