LHC Run1 Higgs Results. Quentin Buat - Simon Fraser University On behalf of the ATLAS and CMS collaborations

Transcription

1 LHC Run1 Higgs Results Quentin Buat - Simon Fraser University On behalf of the ATLAS and CMS collaborations Rencontres de Moriond, QCD session - March 24th, 216 1

2 Introduction During LHC Run1, ATLAS and CMS collected ~ 5 fb of pp collisions data The Higgs boson has been observed by both experiments This talk reviews the measurements of the Higgs boson couplings to the SM particles, mass, spin and CP properties 2

3 SM Higgs boson at the LHC Production Decays 86% 7%.5% 5% Higgs BR Total Uncert ττ cc bb γγ gg Zγ WW ZZ LHC HIGGS XS WG µµ M H [GeV] 3

4 Bosonic decays ATLAS H WW* Highly 8 sensitive, discovery channels Presence 6 of lepton/photon reduces Obs± statthe impact of the jet-induced backgrounds Bkg± syst γγ, ZZ have the best mass resolution Misid 4 Events / 1 GeV Events / 1 / 1 GeV GeV GeV ATLAS: 6.8σ, CMS: 4.8σ s =8TeV, 2.3fb s =7TeV, 4.5fb (a) n j 1, e µee/ µµ ATLAS Higgs WW VV Top DY H WW* (b) Background-subtracted s =8TeV, 2.3fb Obs- Bkg s =7TeV, 4.5fb Bkg± syst (a) n j 1, e Higgs µee/ µµ Obs± stat Bkg± syst Higgs WW Misid VV Top DY 5 1 (b) 15 Background-subtracted Phys. Rev. D 92, 126 (215) Obs m - [GeV] Bkg Bkg± T syst Events / GeV data - fitted bkg Events / 3 GeV Data CMS Phys. Rev. D. 9, (214) L dt = 4.5 fb, L dt = 2.3 fb, Central low-p Tt s = 7 TeV s = 8 TeV s = 7 TeV, L = 5.1 fb ; ATLAS Phys. Rev. D 89 (214) 927 Data s = 8 TeV, L = 19.7 fb ZX Signalbackground Background Signal ATLAS: 5.σ CMS: 5.6σ * Zγ, ZZ m H = 126 GeV (GeV) m 4l m γγ ATLAS: 6.6σ CMS: 7.σ [GeV]

5 Phys. Rev. Lett. 114, Mass measurement Measurement relies on the two high resolution channels: γγ, 4l In-situ calibration of calorimeters and muon spectrometers with highstat samples of Z ll and J/ψ ll Mass determined with a precision of 24 MeV. Measurement still statistically limited. Systematic uncertainties largely dominated by energy and momentum scale determination 5

6 Fermionic decays Vjets, ttbar and QCD are major backgrounds Poor mass resolution Developed MVA/Categorization approaches ATLAS: 1.7σ, CMS: 2.σ JHEP1(215)69 ATLAS: 4.4σ, CMS: 3.4σ CMS, 4.9 fb at 7 TeV, 19.7 fb JHEP 5 (214) 14 at 8 TeV [1/GeV] 25 µτ, eτ h, τ h τ h, eµ h 4 2 SM H(125 GeV) ττ Data - background Bkg. uncertainty H bb ττ S / (SB) Weighted dn/dm [GeV] SM H(125 GeV) ττ Observed Z ττ tt Electroweak QCD H ττ m ττ m ττ [GeV] 6

7 JHEP 9 (214) 87 CMS s = 7 TeV, fb ; s = 8 TeV, fb tth production mode γγ bb τ h τ h Search performed in several decay modes: bbbar, γγ, WW, ττ bbbar: larger rate but complicated final state γγ: clean but very low stat WW: leptonic final state best sensitivity 4l 3l Same-Sign 2l Combination Best fit σ/σ SM at m H = GeV New for Moriond EWK Events ± µ ± CMS tth, e channel s = 8 TeV, L = 19.5 fb 25 Data tth JHEP 9 (214) 87 ttw ttz/γ* 2 ttγ WZ Others 15 Non Pr Ch misid tth x Data/Pred BDT output

8 ATLAS/CMS couplings combination Ratio of cross-section and branching ratio Assuming the SM branching ratios VBF: observed with 5.4σ significance (exp 4.7) VH combined: Observed with 3.5σ significance (exp 4.7) tth: 2.4σ excess above SM. Observed significance 4.4σ (exp 2.) σ(gg H ZZ) σ VBF /σ { ggf σ WH /σ ggf σ ZH /σ ggf σ tth /σ ggf WW ZZ BR /BR γγ ZZ BR /BR most model-independant check (assuming narrow width) ATLAS and CMS Preliminary LHC Run 1 ATLAS CMS ATLASCMS ± 1σ ± 2σ Th. uncert. ττ: observed with 5.5σ significance (exp 5.) ττ ZZ BR /BR bb ZZ BR /BR Parameter value norm. to SM prediction 8

9 ATLAS/CMS couplings combination Production and decay strength Measure the ratio between observed rate and SM expectations µ i = i /( i ) SM µ f =BR f /(BR f ) SM µ ggf ATLAS and CMS Preliminary LHC Run 1 ATLAS CMS ATLASCMS ± 1σ ± 2σ γ γ µ ATLAS and CMS LHC Run 1 Preliminary ATLAS CMS ATLASCMS ± 1σ µ VBF µ WH µ ZZ µ ZH µ WW µ tth µ ττ µ µ bb Parameter value Parameter value Global signal strength for all prod. and decay modes measured with ~1% accuracy µ =1.9 ±.7 stat ±.4 exp syst. ±.3 th. bkg ±.7 th. signal 9

10 ATLAS/CMS couplings combination Couplings measurement: κ framework Parameterization of the Higgs sector with different hypothesis Use couplings modifiers σ i = κ i2 σi (SM); Γ f = κ f 2 Γf (SM) μ fi = κ i 2 κf 2 / (ΓH /Γ H (SM)) Each κ affects the coupling between the Higgs boson and another particle. Loops A. Resolved with SM content (no BSM) B. Write as effective κ g and κ γ Total width A. Αssume no BSM contribution B. Allow additional contributions SM coupling structure assumed -> only accounts for the relative rates 1

11 ATLAS/CMS couplings combination Couplings measurement: effective loop couplings Use couplings modifiers Need an additional assumption to remove the degeneracy between κ and Γ: assume κv 1 σ i = κ i2 σi (SM); Γ f = κ f 2 Γf (SM) ATLAS and CMS LHC Run 1 Preliminary 2 2 μ fi = κ i κf / (ΓH /Γ H (SM)) Loops A. Resolved with SM content (no BSM) B. Write as effective κ g and κ γ Total width A. Αssume no BSM contribution B. Allow additional contributions κ Z κ W κ t κ τ κ b κ g κ γ BR BSM κ V 1 BR BSM = ± 1σ ± 2σ SM coupling structure assumed -> only accounts for the relative rates Parameter value 11

12 ATLAS/CMS couplings combination Couplings measurement: SM particles Use couplings modifiers σ i = κ i2 σi (SM); Γ f = κ f 2 Γf (SM) μ fi = κ i 2 κf 2 / (ΓH /Γ H (SM)) Loops v V m κ V or v F m κ F ATLAS and CMS LHC Run 1 Preliminary Observed SM Higgs boson W Z t A. Resolved with SM content (no BSM) B. Write as effective κ g and κ γ Total width µ τ b A. Αssume no BSM contribution 4 1 B. Allow additional contributions SM coupling structure assumed -> only accounts for the relative rates Particle mass [GeV] 2 12

13 ATLAS/CMS couplings combination Couplings measurement: fermions and bosons Use couplings modifiers σ i = κ 2 i2 σi (SM); Γ f = κ f Γf (SM) 2 2 μ fi = κ i κf / (ΓH /Γ H (SM)) Loops A. Resolved with SM content (no BSM) B. Write as effective κ g and κ γ κ f F 2 ATLAS and CMS LHC Run Preliminary H γγ 1 H ZZ H WW.5 H bb H ττ Combined.5 Total width A. Αssume no BSM contribution B. Allow additional contributions SM 68% CL Best fit 95% CL SM coupling structure assumed -> only accounts for the relative rates κf V 13

14 Differential cross-sections Measure differential cross-sections for quantities like p T (H), y H, jet multiplicity unfolded at particle level γγ and 4l benefit from a rather inclusive selection and simple background subtraction Study the QCD effects in H kinematics and break the degeneracy between the SM particles and potential NP in the loops [pb/gev] H T dσ / dp Phys. Rev. Lett. 115, 9181 EPJC 76 (216) 13 HRES XH XH = VBF VH tth bbh data, tot. unc. s = 8 TeV, 2.3 fb ATLAS pp H γγ, 4l syst. unc. ) σ(n jets CMS Data σ SM (H γγ) from LHC Higgs XS WG AMC@NLO XH POWHEG HJ XH POWHEG XH -5 POWHEG XH, FW =5E POWHEG XH, FW =-5E XH = VBFVHttH γγ 19.7fb (8TeV) -4 GeV GeV Ratio to HRes ph T [GeV] Ratio to POWHEGXH N jets 14

15 Spin parity measurement Studies performed in the bosonic channels using distributions of angles between Higgs decay products Alternative J P scenarios tested agains the SM : SM is strongly favoured against pure alternate scenario Study of mixing scenario will benefit from larger datasets foreseen in Run2 ~ q EPJC 75 (215) 476 Phys. Rev. D 92 (215) 124 ATLAS P J = h Observed Expected SM ± 1 σ SM ± 2 σ SM ± 3 σ P J ± 1 σ P J ± 2 σ P J ± 3 σ P J = J P = 2 κ q =κ g J P κ q = = 2 p <3 GeV T H ZZ* 4l s = 7 TeV, 4.5 fb s = 8 TeV, 2.3 fb H WW* eνµν s = 8 TeV, 2.3 fb H γγ s = 7 TeV, 4.5 fb s = 8 TeV, 2.3 fb J P κ q = = 2 p <125 GeV T J P = 2 κ q =2κ g p <3 GeV T J P = 2 κ q =2κ g p <125 GeV T / L ) P ln(l -2 J CMS H ZZ 2 m 2 h2 2 h3 Observed Expected ± 1σ P J ± 1σ ± 2σ P J ± 2σ ± 3σ P J ± 3σ 2 h 2 b 2 h6 2 h7-2 h 2 h9-2 h1-2 m 2 h2 2 h3 2 h 2 b 2 h6 gg production qq production 2 h7-2 h 2 h9-2 h1-2 m 19.7 fb (8 TeV) 5.1 fb (7 TeV) 2 h2 2 h3 2 h 2 b 2 h6 2 h7-2 h - 2 h9 decay-only discriminants 2 h1-15

16 Width studies Lifetime in 4l mass distribution Γ(SM) ~ 4 MeV, Direct constraints: MeV < Γ < 1.7 GeV Indirect constraint through the on-shell/off-shell ratio of gg H VV: Γ < 22.7 MeV (ATLAS), Γ < 26 MeV (CMS) SM H / Γ 95% CL limit on Γ H EPJC (215) 75:335 ATLAS H ZZWW off-shellon-shell κ g/v,on-shell =κ g/v,off-shell s = 8 TeV: Ldt = 2.3 fb ± 1σ ± 2σ Expected limit (CLs) Observed limit (CLs) Events / 6 GeV 1 5 PLB 736 (214) 64 CMS 19.7 fb (8 TeV) 5.1 fb (7 TeV) Observed SM Γ H =1 Γ H SM Γ H =1 Γ H, f -3 f ΛQ =5 1, µ -4 f ΛQ =4.5 1 =2 1 ΛQ = VVH, φ =π ΛQ ggvv 4 total qq 4 l bkg. ZX l B RH* = K(gg VV) K(gg H* VV) m 4 l (GeV)

17 fb (8 TeV) -4.9 fb (7 TeV) Rare decays σ x B(H inv)/σ(sm) % CL limits Observed limit Expected limit Expected limit (1σ) Expected limit (2σ) CMS Preliminary CMS-PAS-HIG Still room for sizeable non SM decay mode Invisible decay: VBF production mode is the most sensitive Lepton Flavour Violation: H τμ (or τe or eμ) ATLAS and CMS report a small excess in the τμ channel Br(H τμ) < 1.51% (CMS) / 1.81% (ATLAS) S/(SB) Weighted Events / 2 GeV Combined VBF-tagged VH-tagged ggh-tagged Phys. Lett. B 749 (215) 337 CMS Data Bkgd. uncertainty SM H Z ττ Other tt, t, t 19.7 fb MisID'd τ, e, µ (8 TeV) LFV Higgs, (B=.84%) 2.4σ excess 17 Data-Bkgd (fit) Bkgd (fit) M(µτ) col [GeV]

18 First look at 13 TeV Dataset too small to reach Run1 sensitivity Fiducial cross-section measurement in 4l (and γγ for ATLAS) CMS-PAS-HIG5-4 ATLAS-CONF [fb] σ fid fb (7 TeV), 19.7 fb (8 TeV), 2.8 fb (13 TeV) CMS Preliminary Data (stat. sys. unc.) Systematic uncertainty Model dependence Standard model (m = 125 GeV) H [pb] σ pp H ATLAS Preliminary σ pp H m H = GeV H γ γ comb. data H ZZ * 4l syst. unc. QCD scale uncertainty Tot. uncert. (scale PDFα s ) 1 pp (H 4l) X s (TeV) s [TeV] s = 7 TeV, 4.5 fb s = 8 TeV, 2.3 fb s = 13 TeV, 3.2 fb 18

19 Conclusion Extensive study of the properties of the new boson with LHC Run1 data: H(125) is consistent with the SM predictions Most measurements are still statistically limited (precision of ~1%) Run2 is not sensitive to H(125) yet but soon: Stay tuned! 19

20 Additional material 2

21 ATLAS: LFV H τμ/h τe New results for Moriond EWK, Confnote in preparation ATLAS Preliminary s = 8 TeV L dt = 2.3 fb Expected ± 1σ Expected ± 2σ Observed Excluded ATLAS Preliminary s = 8 TeV L dt = 2.3 fb Expected ± 1σ Expected ± 2σ Observed Excluded eτ had, SR1 µτ, SR1 had eτ had, SR2 µτ, SR2 had eτ had, Comb µτ, Comb had eτ lep, SR nojets µτ, SR lep nojets eτ lep, SR withjets µτ, SR lep withjets eτ lep, Comb µτ, Comb lep eτ, Comb µτ, Comb % CL upper limit on Br(H eτ), % % CL upper limit on Br(H µτ), % 21

22 L. Dell Asta - Moriond EWK 22

23 CMS: LFV H τμ/h τe Phys. Lett. B 749 (215) 337 CMS-PAS-HIG

24 JHEP11(215)211 ATLAS LFV: H τμ Analysis performed in the τ h μ final state Background estimation similar to the H ττ analysis, dedicated tune of the mass estimator Slight excess corresponding to 1.3σ BR(H τμ) < 1.85% at 95% CL. Weaker than CMS limit but no combination (yet) with the τ e μ channel. 24

25 Couplings: ratios of κ 25

26 Couplings: bosonic vs fermionic production 26

27 PLB 738 (214) H μμ arxiv:

28 Phys. Rev. Lett. 114, Mass measurement 28

29 CMS H ττ JHEP 5 (214) 14 Analysis categories µ =.78 ±.23 29

30 ATLAS H γγ/zz 4l Phys. Rev. Lett. 115,

31 ATLAS H WW Systematic Uncert. 31

32 JHEP 4 (215) 117 ATLAS H ττ µ = (stat.) (syst.) ±.1 (theory syst.) - Observed (expected) significance: 4.5 (3.5)σ - Measured signal strength consistent with the SM in all channels/categories 32

33 JHEP1(216)172 ATLAS: VBF H invisible 33

34 CMS: H invisible (combo) 34

35 PLB 749 (215) ATLAS tth->ww 35