Search for Higgs Bosons produced in associa3on with top quarks with the ATLAS detector

Transcription

1 Search for Higgs Bosons produced in associa3on with top quarks with the ATLAS detector Marine Kuna (INFN Roma) On behalf of The ATLAS Collabora3on Phenomenology 2015, PiOsburgh May 4, 2015 Marine Kuna - OH ATLAS - PHENO

2 Mo3va3ons Ø Discovery of a Higgs boson compa3ble with the Standard Model à proper3es measurement Coupling to other par3cles Propor3onal to the fermion s mass à strongest is coupling to top quark Ø Higgs produced in associa3on with a top quark pair (OH) allows direct access to Yukawa coupling of Higgs boson to top quark 4H (0.6%) Gluon fusion pp) top? v V m κ V or v F m κ F 1 10 ATLAS Preliminary s = 7 TeV, fb s = 8 TeV, 20.3 fb Observed SM Expected W Z t Ø OH analyses also sensi3ve to th: If κ f =- 1, κ v =1 (construc3ve interference) à ~13*σ th κ v µ τ b λ f = 2 m f ν Particle mass [GeV] 2 κ f Ø coupling strengths κ X 2 = Γ H X SM Γ H X à Any devia3on might be hint for new physics 2 Marine Kuna - OH ATLAS - PHENO 2015

3 Analysis Overview tth γγ Best mass peak resolu3on High signal purity But low branching frac3on: BR(Hà γγ)~0.2% Physics Le*ers B 740 (2015) L = 25 _ - 1 (7 & 8 TeV) g g _ t t H W _ b b W tth bb Highest branching frac3on But important Obar +heavy/light flavour background ATLAS- HIGG submi*ed to EPJC L = 20 _ - 1 (8 TeV) tth multileptons (WW/ττ/ZZ) Best theore3cal handle on background ATLAS- CONF L = 20 _ - 1 (8 TeV) Combina3on ATLAS- CONF L = 25 _ - 1 (7 & 8 TeV) Good signal purity and branching ra3o compromise But too low sta3s3cs Marine Kuna - OH ATLAS - PHENO

4 OHà γγ TeV tth γγ Ø Inclusive Hà γγ analysis (sideband fit for background) + addi3onal requirements for 2 categories depending on top pair decay: hadronic leptonic (semi or fully) H no lepton 6 jets 2 b- tag 1 lepton 1 b- tag E T miss > 20 GeV Ø Results on signal strength µ = µ OH =σ(oh)/σ(oh) SM Limit: µ OH (σ/σ SM ) < 6.7 obs (4.9 CL Measured µ: µ = (stat.) +0.8 (syst.) Ø Taking into account OH and th cross sec3ons dependence, also sets limits on coupling strength: κ t [ 1.3; CL Marine Kuna - OH ATLAS - PHENO

5 OHà bb 8 TeV tth bb Ø 2 Sub- Channels according to top pair decay modes: single lepton & dilepton Ø Both rely on (N jets, N b- tags ) categorisa3on to get signal enriched regions to enhance sensi3vity, and background- rich regions to beoer constrain backgrounds normalisa3on Ø Discriminants are: à For low signal rate regions: H T /H had t (di- lep/single- lep) Single- lep 4j 4b illustraeon à For high sensi3vity regions: Neural Network (NN) Dilep 3j 3b illustraeon Discriminants in each category: illustraeon for single- lep channel ATLAS Simulation Single lepton s = 8 TeV, 20.3 fb = 125 GeV m H N b- tag 4 S / B j, 2 b S/B < 0.1% B S / j, 3 b S/B = 0.2% B S / H had T H had T H had T j, 4 b S/B = 1.4% H T had : Σ p T (jets) 5 B S / j, 2 b S/B = 0.1% H T had B S / j, 3 b S/B = 0.4% NNHF B S / j, 4 b S/B = 2.5% NN H T : Σ p T (jets, leptons) 6 B S / N jets Marine Kuna - OH ATLAS - PHENO j, 2 b S/B = 0.2% H T had B S / j, 3 b S/B = 1.0% NN[ME] B S / j, 4 b S/B = 4.0% NN[ME]

6 Neural Network Discriminants 8 TeV tth bb Ø Neural Networks (NN) using kinema3c informa3on trained in each category 7 variables used to separate O+HF (heavy flavour) from O+light in 5j3b single- lep region Other NN regions use 10 or 12 variables to dis3nguish signal from background (mainly O+bb con3nuum) Matrix Element p T of fith leading jet IllustraEon for 6j, 4b single lepton category + 9 other variables 2 Matrix Elements variables added in single lep 6j3b & 6j4b (probability density funceon of integral over phase space of all inieal and final state parecles) Σp T /E for jets and leptons Marine Kuna - OH ATLAS - PHENO

7 Main Systema3cs and Results 8 TeV tth bb Ø Main background O+bb (Powheg+Pythia6 reweighted to Sherpa OpenLoops), 50% theory unc. constrained 15% (30% for O+cc) Ø Leading systema3cs: O+bb/cc normalisa3ons and modelling, Jet Energy Scale, mis- tag from O+light flavours µ = 1.5 ±1.1 µ OH (σ/σ SM ) < 3.4 obs (2.2 CL Dilepton Lepton+jets ATLAS tth (H bb) s=8 TeV, 20.3 fb Expected ± 1σ Expected ± 2σ Dilepton Lepton+jets ( tot ) ( stat ) 2.8 ± 2.0 ( 1.4 ) 1.2 ± 1.3 ( 0.8 ) Observed Combination Combination 1.5 ± 1.1 ( 0.7 ) Injected signal (µ=1) Best fit µ=σ/σ for m H =125 GeV SM 95% CL limit on σ/σ SM at m H =125 GeV Marine Kuna - OH ATLAS - PHENO 2015 tot. stat. ATLAS tth (H bb ) s=8 TeV, 20.3 fb 7

8 OHà mul3leptons 8 TeV tth multilep Ø 5 Channels orthogonal in light leptons and hadronic tau mul3plicity N hadronic taus (τ had ) l+2τ had SS: Same Sign 2lSS+1τ had 2lSS 6 categories: (==4, 5 jets) x (ee, eµ, µµ) 3l 4l 2 categories: Z depleted & Z enriched N light leptons (l) g KH(ττ) à 2l+τ had t 8 TeV Reject Obar background with: same sign di- leptons N lep 3 W + q b q Ø Sensi3vity to WW, ττ and ZZ Higgs decays H τ + τ + had ν τ Ordered by sensi3vity g t τ W l ν l ν τ b l ν l Marine Kuna - OH ATLAS - PHENO

9 2lSS+1τhad event display 8 TeV tth multilep In final state: 1 electron, 1 muon, 1 hadronic tau and 4 jets of which 2 b- tag 8 TeV Marine Kuna - OH ATLAS - PHENO

10 Main Backgrounds and Systema3cs 8 TeV tth multilep Ø Charge mis- iden3fica3on data driven, extrapola3on from Zà ee (only for 2l) Ø Non- Prompt (reducible, mainly Obar) from data, es3mated 8 TeV from extrapola3on from Control Regions with reversed lepton isola3on, ID variables and p T Ø OW, OZ (irreducible) from Monte Carlo (MC) + Data/MC agreement checks in Ø VV (diboson) from MC various Valida3on Regions Impact on signal strength uncertainty * * * *detector and reconstruceon systemaecs Events s = 8 TeV, 20.3 fb ATLAS Preliminary 2l0 Non-Prompt had category Charge misid tth(125) Data Number of jets Marine Kuna - OH ATLAS - PHENO Rare VV ttz ttw

11 Results 8 TeV tth multilep Ø Cut and count analysis: µ OH (σ/σ SM ) < 4.7 obs (2.4 CL Channel SM Higgs Backgrounds Data 2lSS+0τ had 6.6±1.4 77± l 11.4± ± lSS+1τ had 0.47±2 1.4± l 0.20±1 0.55± l+2τ had 0.68±7 16± TeV Slight excess in leptonic- only channels, deficit in hadronic tau channels 1l2τ had s = 8 TeV, L dt = 20.3 fb ATLAS Preliminary 4l µ = l1τ had 3l 2l0τ had Observed CL s limit Expected CL s Expected CL signal Injected s Expected ± 1 σ Expected ± 2 σ All % CL S limit on µ=σ/σ SM 11

12 and impact on combina3on Ø Clear OH signal produc3on but need stat to reduce uncertainty µ Higgs ATLAS =1.18 ± 0.10 (stat.) ± 7 (exp.sys.)±8(theo.sys.) ATLAS Preliminary m H = GeV H γγ H ZZ* H WW* H ττ VH Vbb H µµ H Zγ tth Overall: µ = ggf: µ = VBF: µ = WH: µ = ZH: µ = Overall: µ = ggf+tth: µ = VBF+VH: µ = Overall: µ = ggf: µ = VBF: µ = VH: µ = Overall: µ = ggf: µ = VBF+VH: µ = Overall: µ = WH: µ = ZH: µ = Overall: µ = Overall: µ = bb: µ = Multilepton: µ = γγ: µ = (GeV) m H Input measurements ± 1σ on µ μ ggf = μ VBF =1.23±0.32 μ VH =0.80±0.36 μ tth =1.81±0.80 ATLAS Preliminary s =7TeV, fb 1 68% CL: 95% CL: s =8TeV,20.3fb 1 m H =125.36GeV Parameter value Ø help to liy the sign ambiguity on κ t thanks to th Generic model allowing Beyond Standard Model in loops: no contraints on κ t from H γγ and H gg loops s = 7 TeV, fb s = 8 TeV, 20.3 fb Signal strength (µ) à Non SM rela3ve sign disfavoured at 1σ 12

13 Conclusions Ø With Run I Data, ATLAS has set limits and measurements on the Higgs boson produced in associa3on with a top quark pair through 3 channels: OHà γγ: µ < 6.7 obs (4.9 exp); µ = (stat.) +0.8 (syst.) OHà bb: µ < 3.4 obs (2.2 exp); µ = 1.5 ±1.1 OHà leptons: µ < 4.7 obs (2.4 exp); µ = All consistent with Standard Model Combined fioed result for OH produc3on is µ=1.81±0.80 σ(oh, 13 TeV)/σ(OH, 8 TeV) ~ 4 ATLAS combinaeon with CMS (µ=2.8±1.0) sell to come Ø The measures are all sta3s3cally limited Ø OH benefits most from space phase opening at 13 TeV à OH very promising for Run II!! Minimum bias W(ln) Z(ll) ZZ t (s-channel) t (t-channel) WH H (ggf) H (VBF) tt ttz tth A(0.5 TeV, ggf+bba) stop pair (0.7 TeV) gluino pair (1.5 TeV) Z' SSM (3 TeV) Q* (4 Tev) QBH (5 TeV) QBH (6 TeV) #TeV#/#8#TeV#inclusive#pp#cross3sec4on#ra4o# ggf VH VBF Marine Kuna - OH ATLAS - PHENO OH

14 GENERAL BACKUP Marine Kuna - OH ATLAS - PHENO

15 Limits Comparison with CMS CMS ATLAS Marine Kuna - OH ATLAS - PHENO

16 Measured Mu Comparison with CMS tth Channel µ = / SM (m H =125.7 GeV) bb l l Same-sign 2l Combined ATLAS (stat) ± ±0.80 (syst) + ATLAS only: 2l+1τ had channel! Marine Kuna - OH ATLAS - PHENO

17 BACKUP TTH GG Marine Kuna - OH ATLAS - PHENO

18 Feynman diagrams th processes OH W _ t _ b g H g t b W Marine Kuna - OH ATLAS - PHENO

19 Yukawa coupling measurement OHà γγ Ø Varia3ons of κ T influence produc3on of OH, th and BR(Hà γγ) Ø limits set on the total Higgs boson produc3on cross sec3on 3mes BR(Hà γγ) with respect to the SM cross sec3on value for different values of κ t Ø 95% CL exclusion below 1.3 and above mes the Yukawa coupling strength in the Standard Model Exclusion limits ProducEon cross seceons NegaEve log likelihood scan Data consistent with SM value κ T =+1 19

20 BACKUP TTH BB Marine Kuna - OH ATLAS - PHENO

21 Processes Marine Kuna - OH ATLAS - PHENO

22 tt+cc Single- lep analysis 4 j, 2 b 4 j, 3 b 4 j, 4 b ATLAS Simulation m H = 125 GeV s = 8 TeV 5 j, 2 b 5 j, 3 b 5 j, 4 b tt+light tt+cc tt+bb tt+v non-tt 6 j, 2 b 6 j, 3 b 6 j, 4 b Single lepton ATLAS Simulation Single lepton s = 8 TeV, 20.3 fb = 125 GeV B S / B S / B S / j, 2 b S/B < 0.1% HT 5 j, 2 b S/B = 0.1% HT 6 j, 2 b S/B = 0.2% HT B S / B S / B S / j, 3 b S/B = 0.2% NN 5 j, 3 b S/B = 0.4% NN (HF- LF) 6 j, 3 b S/B = 1.0% m H B S / B S / B S / NN[ME] 0.5 tt+light 4 j, 4 b S/B = 1.4% NN 5 j, 4 b S/B = 2.5% NN 6 j, 4 b S/B = 4.0% NN[ME] non-tt Marine Kuna - OH ATLAS - PHENO

23 Di- lep analysis 2 j, 2 b ATLAS Simulation m H = 125 GeV s = 8 TeV 3 j, 2 b 3 j, 3 b tt+light tt+cc tt+bb tt+v non-tt 4 j, 2 b 4 j, 3 b 4 j, 4 b Dilepton ATLAS Simulation Dilepton s = 8 TeV, 20.3 fb = 125 GeV S / B S / B j, 2 b S/B < 0.1% j, 2 b S/B = 0.1% HT HT S / B j, 3 b S/B = 0.6% NN m H B S / j, 2 b S/B = 0.3% HT B S / j, 3 b S/B = 1.5% NN S / B j, 4 b S/B = 5.9% NN Marine Kuna - OH ATLAS - PHENO 2015

24 Results Dilepton Lepton+jets Combination ATLAS tth (H bb) s=8 TeV, 20.3 fb Expected ± 1σ Expected ± 2σ Observed Injected signal (µ=1) % CL limit on σ/σ SM at m H =125 GeV Dilepton Lepton+jets Combination tot. stat. ATLAS tth (H bb ) Best fit µ=σ/σ SM s=8 TeV, 20.3 fb ( tot ) ( stat ) 2.8 ± 2.0 ( 1.4 ) 1.2 ± 1.3 ( 0.8 ) 1.5 ± 1.1 ( 0.7 ) for m H =125 GeV Marine Kuna - OH ATLAS - PHENO

25 Ranking Events / ATLAS 5 10 Data tth (µ =1.5) fit tth (µ =3.4) 95% excl. Bkgd tt+bb normalisation jet energy scale 1 tt+cc normalisation tt+bb renormalisation scale choice m bb µ ATLAS s = 8 TeV, 20.3 fb, m =125 GeV H Data / Bkgd tth (H bb) s=8 TeV, 20.3 fb Combined Single lepton and Dilepton tth (µ =1.5) + Bkgd. fit tth (µ =3.4) + Bkgd. 95% excl log (S/B) tt+v cross section tt+bb shower recoil scheme jet energy scale 2 light-jet tagging 1 tt+cc tt p reweighting T b-jet tagging 1 tt+cc top p reweighting T tt+bb renormalisation scale jet energy scale 3 light-jet tagging 2 tt+bb PDF (MSTW) (θ - θ 0 )/ θ Marine 10 Post-fit Impact on µ Kuna - OH ATLAS - PHENO Pull Pre-fit Impact on µ

26 NN entries lep+jets Second Fox- Wolfram moment of jets and leptons Marine Kuna - OH ATLAS - PHENO

27 NN entries lep- lep Marine Kuna - OH ATLAS - PHENO

28 BACKUP TTH LEPTONS Marine Kuna - OH ATLAS - PHENO

29 Processes g g b t H t W + Z 0 Z 0 W b l ν l b l + ν l l + l q q g g t H t W + W + W W b q ν l b l ν l q l + ν l l q g t W + q q b q b q H W + q g l t W + q τ had + g t W + q τ had + g t W W ν l b l g ν l H t τ + τ W ν τ τhad ν τ b l ν l g H t τ + τ W ν τ l ν l ν τ b l ν l Marine Kuna - OH ATLAS - PHENO

30 Signal and Backgrounds : 8 TeV b : reducible, data- driven es3mates, but abundant (~10 8 TeV) ν l l + ν l g g t t W + H τ + τ W l + l + ν l ν τ τ h ν τ q - : same signature thus irreducible, have to manage theory uncertain3es ν l l Z q q q b W q b ν l b W + l + Marine Kuna - OH ATLAS - PHENO ν l l +

31 CutFlow Marine Kuna - OH ATLAS - PHENO

32 Signal Regions Events s = 8 TeV, 20.3 fb ATLAS Preliminary 2l0 Non-Prompt had category Charge misid tth(125) Data 2012 Rare VV ttz ttw Events s = 8 TeV, 20.3 fb ATLAS Preliminary 3l category ttw Non-Prompt tth(125) Data 2012 Rare VV ttz Number of jets Number of jets Events 4 3 s = 8 TeV, 20.3 fb ATLAS Preliminary 2l1 ttw had category Non-Prompt tth(125) Data 2012 Rare VV ttz Events 4 3 s = 8 TeV, 20.3 fb ATLAS Preliminary 4l category ttw Non-Prompt tth(125) Data 2012 Rare VV ttz Events 16 s = 8 TeV, 20.3 fb ATLAS Preliminary Data l2 had category ttw tt Rare VV tth(125) ttz Number of jets Marine Kuna - OH ATLAS - PHENO Number 2015 of jets 32 Number of jets 2 0

33 Valida3on Regions Events 40 s = 8 TeV, 20.3 fb t t Z VR Data ATLAS Preliminary ttw Rare Non-Prompt VV 30 tth(125) ttz Events 35 s = 8 TeV, 20.3 fb t t W VR Data 2012 ATLAS Preliminary Non-Prompt Rare Charge misid tth(125) VV ttz ttw Data / Bkg Number of jets Data / Bkg Number of jets Marine Kuna - OH ATLAS - PHENO

34 Signal strength CMS µ = (ττ) Marine Kuna - OH ATLAS - PHENO

35 Limits 1l2τ had s = 8 TeV, L dt = 20.3 fb 4l ATLAS Preliminary 2l1τ had 3l 2l0τ had Observed CL s limit Expected CL s Expected CL signal Injected s Expected ± 1 σ Expected ± 2 σ All % CL S limit on µ=σ/σ SM Marine Kuna - OH ATLAS - PHENO

36 Event display 2l τ had Marine Kuna - OH ATLAS - PHENO

37 Event display 2l τ had Marine Kuna - OH ATLAS - PHENO

38 Event display 1l2τhad Marine Kuna - OH ATLAS - PHENO

39 BACKUP COMBINATION Marine Kuna - OH ATLAS - PHENO

40 ATLAS Preliminary m H = GeV H γγ H ZZ* H WW* H ττ VH Vbb H µµ H Zγ tth Overall: µ = 1.17 ggf: µ = 1.32 VBF: µ = 0.8 WH: µ = ZH: µ = 0.1 Overall: µ = 1.44 ggf+tth: µ = 1.7 VBF+VH: µ = 0.3 Overall: µ = 1.16 ggf: µ = 0.98 VBF: µ = 1.28 VH: µ = 3.0 Overall: µ = 1.43 ggf: µ = 2.0 VBF+VH: µ = 1.24 Overall: µ = WH: µ = 1.1 ZH: µ = 5 Overall: µ = -0.7 Overall: µ = bb: µ = Multilepton: µ = 2.1 γγ: µ = (GeV) m H Input measurements ± 1σ on µ Decays and produc3on μ ggf = μ VBF =1.23±0.32 μ VH =0.80±0.36 μ tth =1.81±0.80 ATLAS Preliminary s =7TeV, fb 1 68% CL: 95% CL: s =8TeV,20.3fb 1 m H =125.36GeV Parameter value s = 7 TeV, fb s = 8 TeV, 20.3 fb Signal strength Marine Kuna (µ) - OH ATLAS - PHENO

41 Summary of channels entering combina3on Marine Kuna - OH ATLAS - PHENO

42 κ T =- 1 tests If resolved Hà γγ loop or not Marine Kuna - OH ATLAS - PHENO

43 and impact on combina3on Ø Key for Higgs to top quark Yukawa coupling κ t highest produc3on mode signal strength Production process ggf VBF VH 0.93 ± 0.39 tth 1.62 ± 0.78 Signal strength µ at m H = GeV p p s = 8 TeV Combined s = 7 and 8 TeV i i h h i h i h i ± ± ± 0.80 h h i h i h i help to liy the sign ambiguity on κ t thanks to th Generic model allowing Beyond Standard Model in loops: no contraints on κ t from H γγ and H gg loops κ 2 X = Γ H X SM Γ H X but need stat to reduce uncertainty ATLAS Preliminary m H = GeV H γγ H ZZ* H WW* H ττ VH Vbb H µµ H Zγ tth (GeV) m H Overall: µ = ggf: µ = VBF: µ = WH: µ = ZH: µ = Overall: µ = ggf+tth: µ = VBF+VH: µ = Overall: µ = ggf: µ = VBF: µ = VH: µ = Overall: µ = ggf: µ = VBF+VH: µ = Overall: µ = WH: µ = ZH: µ = Overall: µ = Overall: µ = bb: µ = Multilepton: µ = γγ: µ = Input measurements ± 1σ on µ à Non SM excluded at 1σ s = 7 TeV, fb s = 8 TeV, 20.3 fb Signal strength (µ)

44 Summary of the talk Ø Title: Search for Higgs Bosons produced in associa3on with top quarks with the ATLAS detector Ayer the discovery of a Higgs boson, the direct observa3on of the coupling of this par3cle to top quarks is of par3cular importance. In this talk, a review of the latest ATLAS results on the search for the Higgs boson produced in associa3on with top quarks will be presented. Marine Kuna - OH ATLAS - PHENO