M easurement of Higgs boson proper tj es at ti e LHC - Secrets of the LHC !? - Reisaburo Tanaka (LAL, Orsay, ATLAS) February 11, 2015 HPNP2015, Toyama, Japan
Higgs Boson Property Measurements K. Cranmer 1. Higgs boson mass (M H ) & decay width ( Γ H ) 2. Higgs couplings to gauge bosons (g V ) and fermions (g F ) 3. Higgs boson quantum numbers J PC and tensor structure 4. Higgs potential - Higgs self-coupling ( λ ) The Standard Model Lagrangian - Higgs sector � 2 − y ij H ¯ L SM = D µ H † D µ H + µ 2 H † H − λ H † H � � � ψ i ψ j + h . c . 2 Couplings to Higgs Couplings to EW gauge bosons self-couplings fermions � � 1 + h � � 2 m f ¯ − µ 2 h 2 − λ 2 vh 3 − 1 8 λ h 4 ff µ + 1 1 + h � m 2 W W µ + W − 2 m 2 Z Z µ 0 Z 0 � � − · v µ v f 2 i m 2 − 3 i m 2 − 3 i m 2 − i m f v g µ ν V H H v 2 v v √ √ m H = 2 µ = λ v ( v = vacuum expectation value) The ultimate goal of particle physics of today is to fix the Standard Model (SM) Lagrangian and find the physics beyond the Standard Model (BSM). 2
1. Higgs Boson Mass in H →γγ λ = M 2 M H - the only parameter not fixed in the Standard Model ➭ Fixes . H v 2 Most precisely determined with H →γγ and 4 lepton channels. 200 weights / GeV -1 Ldt = 4.5 fb s = 7 TeV ∫ ATLAS 180 -1 Ldt = 20.3 fb s = 8 TeV ∫ Data s/b weighted sum 160 Combined fit: Mass measurement categories ∑ Signal+background 140 Background Signal 120 100 80 60 40 20 0 8 weights - fitted bkg 6 4 2 0 -2 -4 -6 ∑ -8 110 120 130 140 150 160 m [GeV] γ γ ATLAS: M H γγ = 125.98 ± 0.42 (stat.) ± 0.28 (syst.) = 125.98 ± 0.50 GeV CMS: M H γγ = 124.70 ± 0.31 (stat.) ± 0.15 (syst.) = 124.70 ± 0.34 GeV 3
Higgs Boson Mass in H → 4l Sophisticated 2D analysis with BDT (ATLAS) or Kin. Discrim. Variable (CMS). output ATLAS → → Data 0.1 H ZZ* 4 l ∫ Signal (m = 124.5 GeV = 1.66) -1 µ s = 7 TeV: Ldt = 4.5 fb H ZZ* ∫ Background ZZ*, Z+jets BDT -1 s = 8 TeV: Ldt = 20.3 fb 0.08 1 0.06 0.5 0.04 0 0.02 -0.5 0 -1 110 115 120 125 130 135 140 m [GeV] 4 4 l
Detector Calibration in e/ γ /µ Low p T leptons down to 5-7GeV/c are very important in H → 4l. ATLAS spent 1-year for detector calibration in ECAL(e/ γ ) and muon. Below few per mille calibration ! 0.02 Scale - + J/ e e ψ → Electrons, | |<0.60 η 0.015 - + Z e e → Δ Calibration uncertainty 0.01 p T of leptons 0.005 in H → ZZ* → 4l 0 -0.005 -0.01 -0.015 ∫ -1 ATLAS s =8 TeV, L d t =20.3 fb -0.02 10 20 30 40 50 60 70 80 90 100 E [GeV] T 1.005 MC µ µ ATLAS / m Z → µ µ 1.004 Data 2012, s =8 TeV Υ → µ µ Data 1.003 CB muons J/ µ ψ → µ µ µ m 1.002 1.001 1 0.999 0.998 0.997 ∫ -1 L dt = 20.3 fb 0.996 0.995 5 -2 -1 0 1 2 of the leading muon η
Higgs Boson Mass in H → 4l No significant mass difference between H →γγ and 4 lepton channels. ATLAS spent 1-year for detector calibration in ECAL(e/ γ ) and muon. Events / 2.5 GeV ATLAS 35 Data Signal (m = 124.5 GeV µ = 1.66) H ZZ* 4 l → → H 30 Background ZZ* ∫ -1 s = 7 TeV: Ldt = 4.5 fb Background Z+jets, t t ∫ -1 s = 8 TeV: Ldt = 20.3 fb 25 Systematic uncertainty 20 15 10 5 0 80 90 100 110 120 130 140 150 160 170 m [GeV] 4 l ATLAS: M H4l = 124.51 ± 0.52 (stat.) ± 0.06 (syst.) = 124.51 ± 0.52 GeV CMS: M H4l = 125.59 ± 0.42 (stat.) ± 0.17 (syst.) = 125.59 ± 0.45 GeV 6
Mass difference in H → 4l channels No significant mass difference among 4 lepton channels. Λ -2ln ATLAS 4e 14 4 µ → → H ZZ* 4 l 2e2 µ ∫ -1 2 2e 12 s = 7 TeV: Ldt = 4.5 fb µ Combined ∫ -1 s = 8 TeV: Ldt = 20.3 fb Dashed without systematics Dashed without systematics 10 8 6 σ 2 4 2 σ 1 0 121 123 125 127 129 m [GeV] H 7
Combined Higgs Boson Mass λ = M 2 M H - the only parameter not fixed in the Standard Model ➭ Fixes . H v 2 Most precisely determined with H →γγ and 4 lepton channels. δ M H precision below 0.3% level (PDG2014: δ M W ~190ppm, δ M Z ~23ppm, δ M top ~0.5%) . -1 -1 19.7 fb (8 TeV) + 5.1 fb (7 TeV) SM Combined CMS ) 4 =125.36 GeV) � 2.5 Combined +ZZ* ATLAS � � / H tagged � � � H + H ZZ � � � � � H � � � -1 s = 7 TeV Ldt = 4.5 fb � 3.5 H ZZ* 4 � � l H ZZ tagged � -1 s = 8 TeV Ldt = 20.3 fb � 2.0 Best fit 3 68% CL H (m 95% CL SM 2.5 1.5 � / � 2 Signal yield ( 1.0 1.5 1 0.5 0.5 0 0.0 123 123.5 124 124.5 125 125.5 126 126.5 127 127.5 123 124 125 126 127 m (GeV) m [GeV] H H ATLAS: M H = 125.36 ± 0.37 (stat.) ± 0.18 (syst.) = 125.02 ± 0.41 GeV CMS: M H = 125.02 ± 0.27 (stat.) ± 0.15 (syst.) = 125.02 ± 0.30 GeV 8
Higgs Boson Mass Difference No significant mass difference between H →γγ and 4 lepton channels. Opposite difference between ATLAS and CMS (with opposite color ...). Future: observation in mass difference in Δ M H ( γγ -4l), Δ M H (ggF-VBF) in γγ , -1 -1 19.7 fb (8 TeV) + 5.1 fb (7 TeV) 10 7 ln L Λ H tagged → γ γ -2ln CMS ATLAS Combined +4 l γ γ 9 H ZZ tagged → -1 s = 7 TeV Ldt = 4.5 fb ∫ H → γ γ H + H ZZ 6 → γ γ → Combined: Δ -1 s = 8 TeV Ldt = 20.3 fb ∫ - 2 H ZZ* 4 8 stat. + syst. → → l , (ggH,ttH), µ µ ZZ γ γ stat. only without systematics 5 (VBF,VH) µ 7 γ γ +0.26 +0.14 m = 125.02 (stat) (syst) H - 0.27 - 0.15 6 4 2 σ 5 3 4 2 3 2 1 1 σ 1 0 0 123 123.5 124 124.5 125 125.5 126 126.5 127 127.5 123 124 125 126 127 m (GeV) m [GeV] H H ATLAS: Δ M H ( γγ -4l) = +1.47 ± 0.67 (stat.) ± 0.28 (syst.) GeV (1.98 σ ) CMS: Δ M H ( γγ -4l) = -0.89 ± 0.57 GeV (1.6 σ ) 9
Future Improvements? Ultimate goal: Δ M H < 50 MeV Reductions of experimental systematic uncertainties. Source of systematics between ATLAS and CMS are different. ATLAS: iLq. Ar front-material, cell non-linearity, layer calibration, EM shower lateral shape, ID material, Z → ee calibration, etc. 10
2. Higgs Boson Width 1. Via direct measurements CMS-HIG-14-009 CMS H →γγ , 4l mass spectrum Γ H < 1.7 (2.3)GeV at 95% C.L. 2. Via Higgs coupling or invisible Higgs search BR(inv)<50% limit corresponds to Γ H < 2 Γ HSM (= 8MeV) assuming couplings to SM particles are as in the SM. 3. Via Higgs interferometry Destructive interference between Higgs signal and gg → VV continuum background. H →γγ (S. Martin, L. Dixon) - mass shift (depends on Higgs p T ) Δ M γγ = -70MeV for SM at NLO. H → WW * /ZZ * (N. Kauer, G. Passarino) - mass spectrum in high-mass end above M 4l > 2M top . Sensitivity on ΔΓ H ≲ O(100MeV) is feasible? 3 10 [GeV] LHC HIGGS XS WG 2010 2 10 H � 10 1 -1 10 Γ SM = 4 MeV H for M H = 125 GeV -2 10 200 300 500 100 1000 11 M [GeV] H
Higgs Interferometry in H →γγ Destructive interference between Higgs signal and continuum background. H →γγ (S. Martin, L. Dixon) Mass shift (depends on Higgs p T , maybe already interesting with 2-bin analysis.) Δ M γγ = -120MeV at LO and -70MeV at NLO for SM. g γ H W, t t, b · · · b, c, τ g γ ∗ b, c, . . . u, c, d, s, b · · · 20 Dixon, Li 2013 H →γγ 0 300 � 20 200 � M H � MeV � 40 100 � M H � MeV 0 � 60 3 � H � g � O � Α S Destructive Interf. � SM � � 100 Constructive Interf. 3 �� O � Α S 2 � H � g � q � O � Α S � 80 � 200 3 � H � g � q � O � Α S � 100 � 300 SM � 400 � 120 0 20 40 60 80 100 0 10 20 5 15 p T , H � GeV SM � H � � H 12
Higgs Interferometry in H →γγ Destructive interference between Higgs signal and continuum background. H →γγ (S. Martin, L. Dixon), Mass shift (depends on Higgs p T ) Δ M γγ = -120MeV at LO and Δ M γγ = -70MeV at NLO for SM. No experimental results yet. Takes time ... 13
Higgs Interferometry in H → 4l • Kauer-Passarino-Caola-Melnikov Effect • Off-shell signal is independent of Γ H ! • On-shell signal XS is proportional to 1/ Γ H • Take the ratio ! No interference effect for on-shell 30 gg → H → ZZ → ℓ ¯ gg2VV ℓν ℓ ¯ ν ℓ , M H =125GeV pp , √ s = 8TeV | H + cont | 2 25 H o ff shell d σ /dM ZZ [fb/GeV] H ZWA 20 15 10 5 0 124.99 124.995 125 125.005 125.01 M ZZ [GeV] 14
Higgs Interferometry or Higgs offshell coupling Events / 30 GeV 70 ATLAS Preliminary H → ZZ → 4 l 60 ∫ -1 s = 8 TeV: Ldt = 20.3 fb 50 Data gg+VBF → (H* → ) ZZ 40 Background q q → ZZ Background Z+jets, t t 30 All contributions ( =10) µ off-shell 20 10 0 300 400 500 600 700 800 900 1000 m [GeV] 4l Events / 30 GeV Data 25 ATLAS gg+VBF → (H* → ) ZZ Preliminary q q → ZZ H → ZZ → 2 e 2 ν WZ 20 Z( → ee/ µ µ )+jets ∫ -1 s = 8 TeV: Ldt = 20.3 fb WW/Top/Z → τ τ Other backgrounds All contributions ( µ =10) 15 off-shell Stat.+syst. uncertainties 10 5 15 400 500 600 700 m [GeV] T
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