Search for production of a Higgs boson and a single top quark Ken Bloom for the CMS Collaboration 1 August 2017
At the bottom ‣ We all know the five favorite Higgs production mechanisms and tend to forget about another ‣ The SM cross section for single top plus Higgs production is ~500x smaller than that for gluon fusion ‣ σ (tHq) = 71 fb ‣ σ (tHW) = 16 fb ‣ Why even bother looking? CMS HIG-15-002, JHEP 08 (2016) 045 8/1/17 Search for tH production — K. Bloom 2
At the bottom Higgs production in pp collisions at 13 TeV ‣ We all know the five favorite 100000 Higgs production ggF mechanisms and tend to 10000 forget about another ‣ The SM cross section for Cross section (fb) VBF single top plus Higgs 1000 WH ZH ttH production is ~500x smaller than that for gluon fusion ‣ σ (tHq) = 71 fb 100 ‣ σ (tHW) = 16 fb tH ‣ Why even bother looking? 10 arXiv:1610.07922 8/1/17 Search for tH production — K. Bloom 2
Discovery through interference q 0 q 0 ‣ Small cross section due q q to destructive W interference between W H H two diagrams ‣ Similar for tHW W t production b b ‣ Most production modes depend on the t t square of the coupling, insensitive to sign F f κ ATLAS and CMS ‣ If the sign of the top 2 Yukawa coupling is LHC Run 1 inverted ( κ t = -1), interference is 68% CL 1 constructive, and cross section is x10 larger! 95% CL Best fit ‣ Bounds on κ t largely derived from decays SM expected 0 ‣ Constraints assume no new particles in 1 − loops ‣ Composite Higgs, FCNC processes could Combined H → γ γ 2 H → ZZ H → WW − enhance cross section further H → τ τ H → bb 0 0.5 1 1.5 2 f κ V 8/1/17 Search for tH production — K. Bloom 3
CMS results from Run 1 ‣ Search for tHq production in four final states ‣ H →γγ , bb, WW (multileptons), ττ ‣ Analyses only set limits for κ t = -1 case ‣ Set limit of < 2.8 x σ tHq ( κ t = -1) at 95% CL CMS HIG-14-027, JHEP 06 (2016) 177 8/1/17 Search for tH production — K. Bloom 4
Run 2 searches for tH at CMS ‣ Searches for tH production are even more promising in Run 2 ‣ tHq cross section ~x4 larger at 13 TeV than 8 TeV ‣ Run 2 dataset has already exceeded Run 1 dataset ‣ Searches now include tHW as signal ‣ Improved analysis techniques, greater exploration of κ t ≠ -1 ‣ CMS has released results for searches in two Higgs decay modes ‣ H → bb: Largest branching ratio but very large tt background ‣ H → WW multileptons: small branching ratio but better S/B, non- prompt lepton backgrounds ‣ Commonalities: ‣ Both take advantage of top-quark semi-leptonic decay ‣ Both have tt (including ttH) as their most significant background 8/1/17 Search for tH production — K. Bloom 5
H → bb: selection ‣ One isolated high-pT lepton ‣ Missing energy from ν q 0 ‣ Three or four b jets q b ‣ One additional jet ¯ b H W t ‣ Lots of tt background! b ` + b W ⌫ Sample S( κ t = -1)/B g ¯ b 3 b jets 17.9/4051 4 b jets 2.8/177 8/1/17 Search for tH production — K. Bloom 6
H → bb: multivariate approaches everywhere ‣ Need to assign each of the jets to parent quarks of final state ‣ Develop multivariate discriminator based event quantities such as invariant masses, Δ R’s, jet η and pT values, jet charges and tagging info ‣ Choose single best assignment of jets to quarks as reconstruction hypothesis ‣ Do this separately under two different assumptions of initial state: tHq signal and tt background ‣ With tHq and tt reconstructions done, form kinematic quantities specific to each of the reconstructions and develop another discriminator based on them that distinguishes the two processes ‣ Validated in two-tag event sample, enriched in tt ‣ Fit distribution of that discriminator to templates from signal and background 8/1/17 Search for tH production — K. Bloom 7
H → bb: results ‣ Expected upper limit: CMS -1 CMS -1 Preliminary 2.3 fb (13 TeV) Preliminary 2.3 fb (13 TeV) Events/Bin Events/Bin Data Data Muon + electron channel Muon + electron channel 1500 tH(b b ) tH(b b ) 3 tag region 4 tag region 6.4 +3.7-2.2 x σ tH ( κ t =-1) at t t +lf t t +lf 60 κ = -1.0, κ = +1.0 t t +c c κ = -1.0, κ = +1.0 t t +c c t V t V t t +b t t +b 1000 t t +b b t t +b b 95% CL t t +2b t t +2b 40 t/ t t/ t t t H t t H Misc Misc 500 ‣ Observed upper limit: 6.0 20 Stat.+syst. Stat.+syst. 100x tHq 100x tHq 100x tHW 100x tHW 0 0 x σ tH ( κ t =-1) at 95% CL Data-Pred. Data-Pred. 0.5 0.5 Pred. Pred. Stat.+syst. Stat.+syst. 0 0 0.5 0.5 − − ‣ Comparable to 8 TeV − 1 − 0.5 0 0.5 1 − 1 − 0.5 0 0.5 1 BDT output BDT output result with much less integrated luminosity ‣ Inclusion of tHW, increased cross section, looser b-tag requirement ‣ Largest systematic uncertainties from jet energy scale and shower modeling CMS HIG-16-019 8/1/17 Search for tH production — K. Bloom 8
H → WW → leptons: selection (H → WW) process ‣ Trilepton final state ‣ μμμ , μμ e, μ ee, eee ‣ Z veto • • ‣ Same-sign dilepton final state • ‣ μμ , μ e ‣ Both cases • ‣ At least one b-tagged jet ‣ At least one non-tagged jet • ‣ ~75% H → WW, ~20% H → ZZ, ~5% H →ττ • ‣ Significant fraction of selected data events also pass selections • for ttH analysis, counted as signal 8/1/17 Search for tH production — K. Bloom 9
H → WW → leptons: backgrounds ‣ Two dominant sources of background n ‣ tt+(W/Z/H/ γ ) with prompt leptons l)$ ν $ l + ‣ Modeled with simulations b-jet ‣ tt with non-prompt leptons W + t ‣ Modeled with data using loose-to- t ̅ tight extrapolation from control W - b-jet regions $ q-jet ‣ Separate multivariate discriminators ν ν for two main backgrounds, using info l + q-jet l - on jet and b-jet multiplicities, forward Prediction e μ μμ 3l jet activity and kinematic properties of leptons Signal ( κ t = -1) 39 26 15 ‣ Combine information from two ttH ( κ t2 = 1) 35 24 18 discriminators into one variable Background 443 211 106 8/1/17 Search for tH production — K. Bloom 10
H → WW → leptons: results e μ μμ 3l ‣ Simultaneous maximum likelihood fit for all three channels, separately for different values of κ t / κ V ‣ Uncertainties dominated by background estimates, lepton ID ‣ Assume κ tau = κ t and all other parameters at SM values, and then combined tH+ttH signal strength is uniquely defined by κ t / κ V 8/1/17 Search for tH production — K. Bloom 11
H → WW → leptons: results ‣ κ t / κ V = -1: set limit of 1.4 x expected tH+ttH cross section ‣ κ t / κ V = 1: set limit of 3.1 x expected tH+ttH cross section ‣ κ t / κ V constrained to about [-1.25, 1.60] CMS HIG-17-005 8/1/17 Search for tH production — K. Bloom 12
Conclusions/Outlook ‣ tH production rate is sensitive to the sign of the top Yukawa couplings and other new physics ‣ CMS has searched for tH production in Run 2 data with two final states ‣ Results are already superseding those of Run 1 thanks to larger cross section at 13 TeV and improved analysis techniques ‣ Still to do: ‣ Increase H → bb statistics x10 with 2016 dataset ‣ Complete H →γγ analysis, should be most sensitive final state ‣ Obtain limits in the ( κ t , κ V ) plane ‣ Use same process to search for admixture of CP-odd Higgs boson ‣ Search for Higgs-mediated FCNC process tHq with q = u, c ‣ Combine results from all channels, publish… ‣ Many interesting opportunities ahead! 8/1/17 Search for tH production — K. Bloom 13
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