Higgs to Fermions @ Jacobo Konigsberg, U. of Florida, June/2/14 - PowerPoint PPT Presentation

Higgs to Fermions @ Jacobo Konigsberg, U. of Florida, June/2/14

Outline Intro Higgs and Fermions Processes studied at CMS Analysis overview Results Conclusions and perspective 2

Higgs & Fermions We know a lot about the new H boson To generate particle masses in an SU(2) × U(1) gauge invariant way: introduce a doublet of scalar fields Φ =( Φ + Φ 0 ) with � 0 | Φ 0 | 0 � ̸ = 0 From its decays into ữ ’s, Z’s & W’s L S = D µ Φ † D µ Φ − µ 2 Φ † Φ − λ ( Φ † Φ ) 2 v = ( − µ 2 / λ ) 1 / 2 = 246 GeV ⇒ three d.o.f. for M W ± and M Z Couples to mass as expected from For fermion masses, use same Φ : SM Higgs L Yuk = − f e ( ¯ e , ¯ ν ) L Φ e R + ... The residual degree corresponds to the spin–zero Higgs particle, H. Spin/parity checks consistent with • The Higgs boson: J PC = 0 ++ quantum numbers. J P = 0 + M 2 • Masses and self–couplings from V : M 2 H = 2 λ v 2 , g H 3 = 3 v , ... H M 2 • Higgs couplings ∝ particle masses: g H ff = m f v , g HVV = 2 V v Since v is known, the only free parameter in the SM is M H (or λ ) . Same particle mass in decays to Padova 4/05/2011 The Higgs: status and perspectives – A. Djouadi – p.2/27 ữ ’s and Z’s > An important open question is whether the [same] new particle also couples to fermions, and in particular to down-type fermions, since the current measurements mainly constrain the couplings to the up-type top quark. > The determination of the couplings to down-type fermions requires direct measurement of the corresponding Higgs boson decays. 3

H production and decay Production t Gluon fusion LHC t H 87% t q Vector Boson V H Fusion (VBF) V 7% q q H Associated VH 6% _ q , Z W _ q t ttH H _ 0.6% q t Decay BR(h--> mu mu) =2.2 × 10 − 4 4

H production and decay Production t Gluon fusion LHC t H 87% t q Vector Boson V H Fusion (VBF) V 7% Boson q q H Associated VH couplings 6% _ q , Z W _ q t ttH H _ 0.6% q t Fermion couplings Decay BR(h--> mu mu) =2.2 × 10 − 4 4

ττ H production and decay Production t Gluon fusion LHC t H 87% t q Vector Boson V H Fusion (VBF) V 7% Boson q q H Associated VH couplings 6% _ q , Z W _ q t ttH H _ 0.6% q t Fermion couplings Substantial Decay BR to bb & BR(h--> mu mu) =2.2 × 10 − 4 4

γγ Indirect H-fermions evidence The observation of H=> at SM rate is already strong evidence for Higgs playing the right role vis-a-vis [some] fermions Higgs-top couplings in production and decay loops 5

ττ μμ Direct Higgs-fermion processes studied � � i.e. with public results at: https:/ /twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIG untagged decay VH ttH VBF BSM / ggH bb ✔ ︎ ✔ ︎ ✔ ︎ ✔ ︎ � ✔ ︎ ✔ ︎ ✔ ︎ ✔ ︎ ✔ ︎ ✔ ︎ ✔ ︎ ✔ ︎ � testing t-H coupling 6

Many sub-channels +VBF-tag Example Summer 2013 - more added over time 7

Challenges for Fermion Channels Object reconstruction b-jets and hadronic tau ID Signal vs. background small S => no channel left behind large backgrounds to understand well derived from data if possible use of standard candles Analysis toolbox to optimize sensitivity different tags, sub-channels, split phase-space, MVA’s M ff reconstruction precise calibrations, MVA 8

μμ γγ Challenges for Fermion Channels Object reconstruction SM Higgs Analyses b-jets and hadronic tau ID ττ Signal vs. background �� ! Thr WW Detector Resolution 20% small S => no channel left behind bb large backgrounds to understand well 10% derived from data if possible use of standard candles �� ! 1% Analysis toolbox to optimize sensitivity �� ! Sensitivity different tags, sub-channels, split J. Olsen+ phase-space, MVA’s Mass resolution vs sensitivity M ff reconstruction precise calibrations, MVA 8

μ μ H => bb BR ~ 58% b b 9

μ μ H => bb BR ~ 58% b b BUT QCD bb production is >10 7 bigger than Higgs production so ggH(bb) is out ! 9

VH(bb) PRD 89 (2014) 012033 Most sensitive signature ZH/WH with Z(ll, νν )/W(l ν ) Advantages Largest Higgs BR Direct coupling to down quark sector Challenge Poor S/B Key in analysis Sensitivity through boosted H/V B-tagging Improve bb mass resolution ( ~ 10%) Measure VZ(bb) ! Multi-variate analysis Backgrounds top, V+jets, V+HF, dibosons, QCD 10

VH(bb) PRD 89 (2014) 012033 Most sensitive signature ZH/WH with Z(ll, νν )/W(l ν ) Advantages Largest Higgs BR Direct coupling to down quark sector Challenge Poor S/B Key in analysis Sensitivity through boosted H/V B-tagging Improve bb mass resolution ( ~ 10%) Measure VZ(bb) ! Multi-variate analysis Backgrounds VZ(bb) cross-section top, V+jets, V+HF, dibosons, QCD measured as SM w/ 6-sigma significance 10

VH(bb) MVA Most sensitive signature ZH/WH with Z(ll, νν )/W(l ν ) Advantages Largest Higgs BR Direct coupling to down quark sector Challenge μ = 1.0 +- 0.5 Poor S/B Key in analysis Sensitivity through boosted H/V B-tagging Improve bb mass resolution ( ~ 10%) Measure VZ(bb) ! Multi-variate analysis Backgrounds top, V+jets, V+HF, dibosons, QCD expected and obs. significance = 2.1 σ 11

Less sensitive Hbb search VBF$H$ � $bb$ HIG-13-011 Fully$hadronic$final$stat$(b$jets),$dominated$ by$QCD$background.$ $ Increase$signal$sensiBvity$spliEng$the$ sample$in$4$categories$(NN).$ $ Use$ m bb $distribuBon$to$discriminate$signal$ from$background.$ Observed$limit$3.6$SM$ (expected$3$SM)$at$125$GeV$ Pablo ¡García-­‑Abia, ¡LHCP ¡2013 ¡ 33" 12

H => ττ BR ~ 6% arXiv:1401.5041, accepted by JHEP jet τ μ jet τ h NEW: Evidence for the 125 GeV Higgs boson decaying to a pair of tau leptons: arXiv:1401.5041 VBF candidate with H=> τ (h) τ ( μ ) 13

H => ττ Channels H=> ττ (with τ h and leptonic decays) µ τ , e τ , e µ , µµ , ee, ττ All tags: ggF, VBF, VH, ttH Advantages Test down-type f couplings w/ H=>bb A direct H=>leptons probe Challenge Small S Control τ h ID Reconstruct ττ mass (use MVA) Key in analysis Can calibrate with Z=> ττ Split by Nj, p T (j) and VBF Backgrounds Z=> ττ , QCD 14

H => ττ Channels H=> ττ (with τ h and leptonic decays) µ τ , e τ , e µ , µµ , ee, ττ All tags: ggF, VBF, VH, ttH Advantages Test down-type f couplings w/ H=>bb m ττ A direct H=>leptons probe Challenge Small S Control τ h ID Reconstruct ττ mass (use MVA) Key in analysis Can calibrate with Z=> ττ Split by Nj, p T (j) and VBF Backgrounds m ττ Z=> ττ , QCD 14

H => ττ Channels H=> ττ (with τ h and leptonic decays) µ τ , e τ , e µ , µµ , ee, ττ μ = 0.78 +- 0.27 All tags: ggF, VBF, VH, ttH Advantages Test down-type f couplings w/ H=>bb A direct H=>leptons probe Challenge Small S Control τ h ID Reconstruct ττ mass (use MVA) Key in analysis Can calibrate with Z=> ττ Split by Nj, p T (j) and VBF Backgrounds Z=> ττ , QCD observed (expected) signif. = 3.2 (3.7) σ 15

Evidence for H=>fermions [ ττ & bb] CMS-HIG-13-033, accepted by Nature “Evidence for the direct decay of the 125-GeV Higgs boson to fermions” In this paper we report the combination of these two channels which results, for the first time, in strong evidence for the direct coupling of the 125-GeV Higgs boson to down-type fermions, with an observed significance of 3.8 standard deviations, when 4.4 are expected. μ = 0.83 +- 0.24 16

ttH production: including bb & ττ W, Z Advantages _ q t Test Higgs couplings to real top quarks H _ Challenge q t coupling Small prod x-sect Small S Very busy events Higgs Key in analysis Include many H decay modes Semileptonic & dilepton ttbar decays Split in Njets and Nb-jets Sort out association of objects to processes MVA discriminants nnels Backgrounds ) ttbar, ttbar+X 17

ttH Results CMS-HIG-13-015 CMS-HIG-13-019 CMS-HIG-13-020 slight hint of direct H-top coupling Observed limit: 4.3 Expected limit: 2.9 18

H => ee, μμ ? BR( μμ ) ~ 2x10 -4 CMS-HIG-13-007 Main signatures lepton pairs with opposite sign #jets => GF/VBF Advantages Test second generation H-f couplngs Test new physics as SM is smaaaaall BR(H=>ee) ~ 2x10 -5 xBR(H=>mm) Challenge S/B impossibly small Good lepton ID H → ee H → µµ Key in analysis Good mass reconstruction H? Split by tags (#jets), mass res., eta(l) Backgrounds ... just limits =>H flavor non-universality vs taus DY, QCD fakes 19

H => ee, μμ ? BR( μμ ) ~ 2x10 -4 CMS-HIG-13-007 Main signatures lepton pairs with opposite sign #jets => GF/VBF Advantages Test second generation H-f couplngs Test new physics as SM is smaaaaall BR(H=>ee) ~ 2x10 -5 xBR(H=>mm) Challenge S/B impossibly small Good lepton ID H → ee H → µµ Key in analysis Good mass reconstruction H? Split by tags (#jets), mass res., eta(l) Backgrounds ... just limits =>H flavor non-universality vs taus DY, QCD fakes 19