Tevatron measurements on Standad Model Higgs 49 th Rencontres de Moriond Electroweak Interactions and Unified Theories Federico Sforza on behalf of the CDF and D0 Collaborations Max Planck Institut für Physik 20 th March 2014 - La Thuile 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 1 / 19
The Tevatron The Tevatron Presented analyses use full Run II dataset: p collisions at √ s = 1 . 96 TeV per experiment ( ≃ 12 fb − 1 delivered) L ≃ 10 fb − 1 of p ¯ � Up to 30 -2 -1 Initial Luminosity ( × 10 cm s ) 450 01/03 01/04 01/05 01/06 01/07 01/08 01/09 01/10 01/11 400 350 300 p 250 200 1km 150 100 p 50 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 store number Store initial luminosity × 20 increase over years ⇒ driven by abundance of anti-protons Tevatron facts: Two instrumented collision points: CDF & D0 experiments First superconducting accelerator and largest anti-matter source in the world Run I and Run II cover almost 20 years of physics 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 2 / 19
The Tevatron A Very Brief History of Higgs Searches 40 95% CL Limit / SM Tevatron Run II Preliminary ∫ Tevatron role was unexpected several years ago: -1 35 Ldt=0.3-1.0 fb DØ Expected Excluded CDF Expected 30 Tevatron Expected LEP First Tevatron combination for SM Higgs 95% C.L.: Tevatron Observed 25 ⇒ 2006, 0 . 3 − 1 fb − 1 (CDF 8384 & D0 5227 Notes) 20 15 95% exclusion sensitivity O ( 10 ) × SM 10 100 fb − 1 needed to reach 2 σ sensitivity! 5 0 100 110 120 130 140 150 160 170 180 190 200 2 m (GeV/c ) H 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 3 / 19
The Tevatron A Very Brief History of Higgs Searches 40 95% CL Limit / SM Tevatron Run II Preliminary ∫ Tevatron role was unexpected several years ago: -1 35 Ldt=0.3-1.0 fb DØ Expected Excluded CDF Expected 30 Tevatron Expected LEP First Tevatron combination for SM Higgs 95% C.L.: Tevatron Observed 25 ⇒ 2006, 0 . 3 − 1 fb − 1 (CDF 8384 & D0 5227 Notes) 20 15 95% exclusion sensitivity O ( 10 ) × SM 10 100 fb − 1 needed to reach 2 σ sensitivity! 5 0 100 110 120 130 140 150 160 170 180 190 200 2 m (GeV/c ) H The July 2012 discovery of a new particle compatible with SM Higgs ( m H ≈ 125 GeV/c 2 ): ATLAS, CMS observation in 4 ℓ, γγ final states: Tevatron evidence in b ¯ b final state: 0 Local p Background p-value 2 ATLAS 2011 - 2012 10 -1 -1 Obs. Tevatron Run II, L Tevatron Run II, L ≤ ≤ 9.7 fb 9.7 fb 1-CL Observed b ∫ int int s = 7 TeV: Ldt = 4.6-4.8 fb -1 Exp. 1-CL Expected ∫ -1 ± σ 10 b s = 8 TeV: Ldt = 5.8-5.9 fb 1 1 s.d. ± 1 0 σ σ -1 1 10 ± 2 s.d. 1 σ 2 10 -2 -3 σ 10 3 1 σ -4 -1 10 10 σ 4 -5 10 -6 2 10 σ σ 5 -2 10 -7 10 -8 10 -9 σ 10 6 3 σ -3 10 10 -10 -11 10 110 115 120 125 130 135 140 145 150 100 105 110 115 120 125 130 135 140 145 150 m [GeV] 2 H m (GeV/c ) H Phys.Rev.Lett. 109, 071804 (2012) Phys. Lett. B 716 (2012) 1 and 30 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 3 / 19
The Tevatron Higgs Production Mode Differences at Tevatron and LHC Tevatron Higgs production modes (1.96 TeV): LHC Higgs production modes (8 TeV): 2 10 H+X) [pb] LHC HIGGS XS WG 2012 s = 8 TeV pp → H (NNLO+NNLL QCD + NLO EW) 10 → (pp p p → q q H ( N N L O σ Q C 1 pp D pp → + N → L O WH (NNLO QCD + NLO EW) E W ZH (NNLO QCD +NLO EW) ) pp → ttH (NLO QCD) -1 10 10 -2 80 100 200 300 400 1000 M [GeV] H Higgs production rate at LHC much higher than at Tevatron: LHC gluon fusion × 20, Vector Boson Fusion (VBF) × 30 ⇒ Abundant production modes for analysis of clean final states with small BR ( γγ , ZZ , WW , ττ ) LHC VH associate production × 4, also higher background: ⇒ Relevant and complementary studies from Tevatron! 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 4 / 19
SM Higgs Analyses: Cross Section and Couplings Analysis Classification SM Higgs decay branching fractions: High Mass: Low Mass: High BR final states for m H � 135 GeV/ c 2 High BR final states for m H � 135 GeV/ c 2 Main channel: gg → H → WW main channel: qq → VH → b ¯ b WW → ℓνℓν : low background V leptonic decay: online selection and background reduction High Higgs production rate Peculiarity of m H = 125 GeV/c 2 : BR ( H → b ¯ b ) ≃ 0 . 58, BR ( H → WW ) ≃ 0 . 21 ⇒ Both low and high mass analyses contribute to properties study 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 5 / 19
SM Higgs Analyses: Cross Section and Couplings Overview of H → WW Analysis Different di-lepton kinematic of H → WW decay and WW EWK production (background): Lepton plus ✁ E T selection (also hadronic τ ): ⇒ s / b event categorization to enhance sensitivity Low Higgs mass resolution because of 2 ν Lepton kinematic correlation for MVA discriminants: ⇒ Boosted Decision Trees (BDT), usually for D0 ⇒ Neural Networks (NN), usually for CDF Example of CDF H → WW NN output: Example of D0 H → WW BDT output: Events/0.30 Data 1800 -1 DØ, 9.7 fb , ll + E T Signal 20 × 1600 Z+jets Diboson 1400 W+jets Multijet 1200 t t 1000 Bkg. syst. 800 600 400 200 0 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 log (s/b) 10 Phys.Rev. D 88, 052012 (2013) Phys.Rev. D. 88, 052006 (2013) 2008: first post LEP analysis to exclude presence SM Higgs boson in mass range 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 6 / 19
SM Higgs Analyses: Cross Section and Couplings Overview of Low Mass Higgs Analyses VH → b ¯ b is the most sensitive channel at Tevatron: 3 analyses with similar topology: leptons (charged or neutral) + heavy flavor jets p → WH → ℓν + b ¯ p → ZH → ℓℓ + b ¯ p → VH → νν ( ν ✄ p ¯ p ¯ ℓ ) + b ¯ b b p ¯ b CDF: Phys.Rev.Lett. 109, 111804 (2012), CDF: Phys.Rev.Lett. 109, 111803 (2012), CDF: Phys.Rev.D 87, 052008 (2013), D0: Phys.Rev.Lett. 109, 121804 (2012), D0: Phys. Rev. Lett. 109, 121803 (2012), D0: Phys.Lett.B 716, 285 (2012) Phys.Rev.D. 88, 052008 (2013) Phys.Rev.D. 88, 052010 (2013) Similar background sources, different relative fractions between final states Aim to identify Higgs M b ¯ b resonance over falling background Background estimate with mixture of MC/data driven extraction from Control Regions (CR) Backgrounds Shape Normalization WW , WZ , ZZ , t ¯ t , single-top MC based NLO,NNLO (Theory) Multi-Jet (MJ) Data driven Fit to data W / Z + light flavor MC (ALPGEN), CR weighted data CR W / Z + heavy flavor MC based (ALPGEN) LO, fit to data Statistically limited dataset ⇒ Relax cuts ⇒ Keep background under control ⇒ Iterate 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 7 / 19
SM Higgs Analyses: Cross Section and Couplings Low Mass Searches Optimization Every aspect of analyses thoroughly optimized (often using MVA): Inclusive trigger strategy: single lepton, only ✚ ✚ E T , multiple objects ( E T + jets) Improved ℓ/ ✁ E T offline ID: relaxed cuts increases MJ ⇒ improve lepton ID/MJ-rejection b-tag: reduce background to 1 / 100 but limits jet selection efficiency ( ≃ 50%) Final Discriminant: large irreducible backgrounds ⇒ MVA sensitivity increase by 10-20% D0 NN b-tagger output composition: MVA b-tagging for both D0 and CDF Tunable efficiency/contamination working point Maximize significance from s / b categorization of signal region V. M. Abazov et al., Nucl.Instrum.Methods Phys.Res., Sect. A 620, 490 (2010) CDF b-tag working point comparison: D0 b-tag algorithm improvements and working points: J. Freeman et al., Nucl.Instrum.Methods Phys.Res., Sect. A 697, 64 (2013) 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 8 / 19
SM Higgs Analyses: Cross Section and Couplings Low Mass Searches Optimization Every aspect of analyses thoroughly optimized (often using MVA): Inclusive trigger strategy: single lepton, only ✚ ✚ E T , multiple objects ( E T + jets) Improved ℓ/ ✁ E T offline ID: relaxed cuts increases MJ ⇒ improve lepton ID/MJ-rejection b-tag: reduce background to 1 / 100 but limits jet selection efficiency ( ≃ 50%) Final Discriminant: large irreducible backgrounds ⇒ MVA sensitivity increase by 10-20% Single channel sensitivity improvements w.r.t. 1 fb − 1 analysis was also > 200 % (over luminosity)! 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 8 / 19
SM Higgs Analyses: Cross Section and Couplings Analysis Validation with VZ → HF Important analysis validation using known SM process as signal VZ associate production in s − channel with Z → b ¯ b mimics VH → b ¯ b signature σ VZ × BR ( Z → HF ) about 6 times VH ( M H = 125) Higher background due to W + jets M jj spectrum ⇒ very small s / b and challenging measurement! ) 2 -1 Tevatron Run II, L 10 fb Events / (20 GeV/c ≤ int WZ → HF evidence 1+2 b-Tagged Jets 800 Data — Bkgd 600 CDF and D0 low mass analyses WZ combined looking at VZ → HF signal ZZ 400 Higgs Signal Same data-set, analysis techniques, 2 m =125 GeV/c MVA discriminant strategy H 200 ⇒ σ VZ = 3 . 0 ± 0 . 6 ( stat ) ± 0 . 7 ( syst ) pb 0 ⇒ Strong signal evidence at 4 . 6 σ 0 50 100 150 200 250 300 350 400 ⇒ Consistent with σ SM , NLO 2 = 4 . 4 ± 0 . 3 pb Dijet Mass (GeV/c ) VZ Background subtracted di-jet invariant mass 20 th March 2014 F. Sforza (Max Planck Institut für Physik) 9 / 19
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