Evidence for Higgs Boson Decays to a Pair of τ-leptons

Transcription

1 Evidence for Higgs Boson Decays to a Pair of τ-leptons ET miss = 119 GeV μ (pt=6 GeV) τhad (pt=96 GeV) mττ =19 GeV Nils Ruthmann mjj =65 GeV Nils Ruthmann (Universität Freiburg) On Behalf of the ATLAS Collaboration Rencontres de Moriond EW 1 La Thuile - 1 March 1

2 Introduction BEH mechanism major ingredient of the SM Spontaneous breaking of the U(1)Y SU()L symmetry generating W,Z mass terms Lepton masses generated via independent Yukawa couplings V ( )=µ + ( ) L Yukawa = f v p ff f p ffh λf ~ mf Huge progress in the past years Discovery (γγ, ZZ*, WW*) Mass measurement ( mh ~ 15.5 ±.7 GeV ) Coupling measurements ( all SM like so far ) Spin determination ( strong preference for + ) Coupling to fermions assessed via loop contributions so far Direct confirmation of fermionic couplings important for identification as SM Higgs boson ATLAS m H = 15.5 GeV s = 7 TeV Ldt =.6-.8 fb s = 8 TeV Ldt =.7 fb 1 Signal strength (µ) Rencontres de Moriond EW - H ττ 1 March 1 H γγ µ = ±. ±.1 ± Low p µ = 1.6 Tt -. ±. +.7 High p µ = 1.7 Tt -.6 ±.5 jet high mass (VBF) µ = ±.6 VH categories µ = 1. ±.9 H ZZ* l VBF+VH-like categories Other categories µ = 1. µ = 1. µ = 1.5 H WW* lνlν µ = ±. ±.17 ± ±.5 ±.1 ±.1 ±.1 +1 jet µ =.8 ±. +.7 jet VBF µ = 1. ± Comb. H γ γ, ZZ*, WW* ± ±.15 µ = ±.11 σ(stat) σ(sys) σ(theo) Total uncertainty ± 1σ on µ Phys. Lett. B 76 (1) 88

3 Higgs Boson LHC p LHC (8 TeV) PDF t,b H Gluon-Fusion: Colored initial state & quark loop: important corrections Radiation leading to significant transverse momentum 19.7 pb p p q q Vector-Boson-Fusion: well separated Jets at Tree-Level! 1.58 pb PDF V V H p q q BR(H! )=6.% SM Higgs branching ratios (HDECAY) bb _ WW ττ gg ZZ cc _ γγ Zγ m (GeV/c ) H Three ττ decay channels: Leptonic ( light leptons + ν) Hadronic ( had. τ + ν) Semi-leptonic (1 light lepton + 1 had. τ + ν) Dominant background processes Z ττ top pair production Z ee / µµ Z ττ Multijets Z ττ W + Jets Multijets ll 1% lh 6% hh % Rencontres de Moriond EW - H ττ 1 March 1

4 Categorization Very loose preselection Categorization exploiting signal-sensitive phase-space: VBF category ( VBF signal fraction 55% -75% ) Identified by well separated jets High pt category ( Gluon-fusion signal fraction 7% - 75% ) Large transverse momentum of Higgs Boson candidate ATLAS-CONF-1-8 Rencontres de Moriond EW - H ττ 1 March 1

5 Discriminating Variables & Signal Extraction e/μ Δ R MET τhad Variety of background processes Real τ s & Misidentified τ s Jet(s) Resonant ττ-system e/μ MET Multiple variables needed to suppress them Z ττ: VBF tagging-jets topology Misidentified τ s: Use angular variables Δ R ATLAS-CONF-1-8 Jet faking τhad Non-Resonant ττ-system Combining up to 9 variables in Boosted Decision Trees Exploiting correlations across variables Extensively validated in control regions Rencontres de Moriond EW - H ττ 5 1 March 1

6 Results Combing all 6 BDT distributions ATLAS observes a significant excess of events Corresponding to.1 15 GeV (. σ expected ) Present in all three decay channels and categories The fitted signal strength corresponds to: μcomb = μggf x B/BSM = μvbf,vh x B/BSM = ATLAS-CONF-1-8 Rencontres de Moriond EW - H ττ 6 1 March 1

7 BACKUP Rencontres de Moriond EW - H ττ 7 1 March 1

8 κ F ) - lnλ(κ F 1 - ATLAS Preliminary s = 7 TeV Ldt =.6-.8 fb H ττ τ H lνlν ν H γγ γ s = 8 TeV Ldt =. fb H bb H l H γγ SM H l H ττ H lνlν Combined Best Fit H bb Not reviewed, for internal circulation only ATLAS Higgs combination March 19, 1 : 1 κ V γ γ,zz*,ww*,τ τ VBF+VH µ DRAFT γ γ,zz*,ww*,τ τ H ττ contributes (b) majorly to the overall ATLAS coupling fits particularly constraining Figure the signal : strength Likelihood in VBF contours production in the (µ f ggf+tth and the fermion coupling,µf VBF+VH ) plane for the cha ATLAS Preliminary H! ZZ [κ V,κ! F ] `, H! WW! ` `, H! and a Higgs boson mass m H = 15.5 GeV s = 7 TeV, Ldt =.6-.8 fb edge of the H! ZZ! ` contours is due to the small number of events in this chann Observed s = 8 TeV, Ldt =. fb ment of a positive pdf. The best-fit values to the data ( ) and the 68% (full) and SM expected Combined H γγ,zz*,ww*,ττ,bb contours are indicated, as well as the SM expectations (+) Coupling fits 15 Rencontres de Moriond EW - H ττ 8 1 March m H Standard Model Best fit 68% CL 95% CL = 15.5 GeV ATLAS-CONF-1-9 ATLAS s = 7 TeV s = 8 TeV Preliminary Ldt =.6-.8 fb Ldt =. fb H γ γ H ZZ* l H WW* lνlν H τ τ µ ggf+tth In the previous section signal strength scale factors µ f i for given Higgs boson producti

9 Event Selection e/μ νe/μ ντ E/ T ντ τhad E/ T τhad τhad ντ ντ E/ T e/μ e/μ νe/μ ντ ντ νe/μ Lep/Had Had/Had Lep/Lep Jet(s) Exactly 1 e/μ Exactly 1 hadronic tau Opposite charge Single lepton trigger or tau+lepton trigger Jet(s) Exactly hadronic taus At least one of them passing a tighter ID criteria (~% signal eff.) Opposite charge Di-tau trigger Jet(s) Exactly light leptons GeV < mll < 75 GeV (same flavour) GeV < mll < GeV (diff. flavour) No hadronic taus Opposite sign Single electron trigger Di-lepton trigger ATLAS-CONF-1-8 Rencontres de Moriond EW - H ττ 9 1 March 1

10 Mass Compatibility Weighting each event by ln(1+ S/B) of its corresponding BDT bin Visualizing the compatibility of the observed excess with a Higgs Boson of 15 GeV ATLAS-CONF-1-8 Alternative signal hypothesis are scaled to their fitted signal strength.. to focus on the shape difference Rencontres de Moriond EW - H ττ 1 March 1

11 Event Yields VBF& Boosted& Numbers&of&events&in&highest&& BDTcscore&bin&& LepTlep% LepThad% HadThad Signal& 5.7±1.7& 8.7±.5& 8.8±.& Bckg& 1.5±. 8.7±.& 11.8±.6 % 19% 18% 19% Signal&.6±.8& 8.±.5&.6±1.1& Bckg&.±1.8 ±& 11.±1.9 % % % 15% ATLAS-CONF-1-8 ATLAS observes a significant excess of events in all decay channels Corresponding to.1 15 GeV ( with. σ expected) Rencontres de Moriond EW - H ττ 11 1 March 1

12 Categorisation Category Selection τ lep τ lep τ lep τ had τ had τ had p T ( j 1 ) > (GeV) 5 5 p T ( j ) > (GeV) /5 VBF η( j 1, j ) >... b-jet veto for jet p T > (GeV) 5 - pt H > (GeV) - - p T ( j 1 ) > (GeV) - - Boosted pt H > (GeV) b-jet veto for jet p T > (GeV) 5 - Table : Selection criteria applied in each analysis category for each channel. Only event that fail VBF category selection are considered for the boosted category. Eventsintheτ lep τ had VBF category must also satisfy m ττ vis > GeV, and those that fail this requirement are not considered for the τ lepτ had boosted category. The τ had τ had p T ( j )thresholdis(5) GeVforjetswithin(outsideof) η <.. Rencontres de Moriond EW - H ττ 1 1 March 1

13 Major Uncertainties Impact of dominating uncertainties on the measured signal strength ATLAS-CONF-1-8 Source of Uncertainty Uncertainty on µ Signal region statistics (data). Z ll normalization (τ lep τ had boosted).1 ggf dσ/dpt H.1 JES η calibration.1 Top normalization (τ lep τ had VBF).1 Top normalization (τ lep τ had boosted).1 Z ll normalization (τ lep τ had VBF).1 QCD scale.7 di-τ had trigger efficiency.7 Fake backgrounds (τ lep τ lep ).7 τ had identification efficiency.6 Z τ + τ normalization (τ lep τ had ).6 τ had energy scale.6 Table 7: The important sources of uncertainty on the measured signal strength parameter µ, given as absolute uncertainties on µ. Rencontres de Moriond EW - H ττ 1 1 March 1

14 Input Variables VBF Boosted Variable τ lep τ lep τ lep τ had τ had τ had τ lep τ lep τ lep τ had τ had τ had m MMC ττ R(τ, τ) η( j 1, j ) m j1, j η j1 η j p Total T sum p T p T (τ 1 )/p T (τ ) ET miss φ centrality x τ1 and x τ m ττ, j1 m l1,l φ l1,l sphericity p l 1 T p j 1 T ET miss /p l T m T min( η l1 l,jets) j η centrality l 1 l η centrality lηcentrality τ 1, η centrality Table : Discriminating variables used for each channel and category. The filled circles identify which variables are used in each decay mode. Note that variables such as R(τ, τ) aredefinedeitherbetween the two leptons, between the lepton and τ had,orbetweenthetwoτ had candidates, depending on the decay mode. Rencontres de Moriond EW - H ττ 1 1 March 1

15 Mass Reconstruction (a) Fraction of Events / 5 GeV µτ had + eτ had Incl. 1 jet H(15) τ τ ATLAS Preliminary 5 15 m MMC τ τ [GeV] Fraction of Events / 5 GeV m(ττ)&reconstructed&by&missing&mass&calculator&(mmc)&& ee + eµ + µ µ Incl. 1 jet H(15) ττ ATLAS Preliminary...18 had had Incl. 1 jet ATLAS Preliminary Z H(15).1 m MMC τ τ [GeV] It&is&beÅer&in&VBF&and&Boosted&catego Estimating the neutrino four momenta.8 using known tau decay kinematics Majorly improving the mass resolution.6 Figure 19: Distributions for m MMC Z ττ%% ττ normalized t. data, and H τ + Lepclep& τ events in 1.%& the (a) τ lep τ lep,(b. preselection requirements Lepchad& and have 18.1%& at least 1 je 5 15 τ lep τ lep distributions are: GeV for H τ + τ Hadchad& 1.%& 11/6/1& τ lep CERN&seminar& τ had distributions are: 7 GeV for H τ & m + MMC [GeV] τ had τ had distributions are: 8 GeV for H τ + τ Fraction of Events / 5 GeV.18 H ττ%search:%m(ττ)%reconstruc@on% τ had τ had Incl. 1 jet H(15) τ τ ATLAS Preliminary Good%m(ττ)%resolu@on%is%single%most%effec@ve%tool%against%Z ττ% Fraction of Events / 5 GeV.1 m(ττ)&is&one&most&highly&ranked&bdt&input&variables& MMC&is&sophisYcated&technique&to&reconstruct&m(ττ)&in&presence&of&neutrino from&τcdecays&. MMC&resoluYon&in&events&with&at& least&one&jet&(table&below)& m MMC τ τ [GeV] MMC&resoluYon&depends&on&τcdecay type&and&event&topology& (c) ATLAS-CONF-1-8 Rencontres de Moriond EW - H ττ 15 1 March 1

16 Fake Estimate LepHad Statistically huge sample of misidentified τ s available in reversed ID region ( Anti-Taus ) Scaling it with a fake rate measurement: Shape & yield can be extrapolated into signal region ATLAS-CONF-1-8 N SR,ID = N CR,ID N CR,Fail ID N SR,Fail ID } Fake-Factor Prong L dt =.fb s = 8TeV ATLAS Preliminary VBF (stat. uncert.) VBF (stat. syst. uncert.) Boost (stat. uncert.) Boost (stat. syst. uncert.) FF = f W+Jets FF W +(1 f W+Jets )FF QCD p T ( τ had ) [GeV] Fake Factor measured separately in a W and a QCD control region combined into effective fake rate ( estimated fractional W/QCD contribution in SR ) Large (~%) uncertainties due to unknown q/g fractions in signal region Rencontres de Moriond EW - H ττ 16 1 March 1

17 Fake Estimate HadHad Preselection HH VBF BDT SR Boosted BDT SR Rest CR A Multijet template is built from not opposite sign events Charge (τ1) * Charge (τ) >= Enhanced in Multijet background due to little charge correlation Normalization extracted in combined Fit Δη (τ1,τ) included in the fit for its separation power between Z ττ and the Multijet background Rencontres de Moriond EW - H ττ 17 1 March 1

18 Events /.1 Text ee + Ebene eµ + µ µ VBF L dt =. fb Ebene s = 8 TeV Z ll CR Additional Control Region BDTs LepLep ATLAS Preliminary 5 x H(15) τ τ Z ee,µ µ ee + eµ + µ µ VBF ATLAS Preliminary ee + eµ + µ µ VBF ATLAS Preliminary 5 L dt =. fb s = 8 TeV CR L dt =. fb s = 8 TeV CR 5 x H(15) τ τ 5 x H(15) τ τ ee + eµ + µ µ VBF ATLAS Z τ Preliminary τ ee + eµ ee + µ + µ eµ VBF + µ µ Boosted Z ee,µ ATLAS ATLAS µ Z ee,µ µ Preliminary Preliminary L dt =. fb s = 8 TeV Z τ τ CR 15 L dt L dt =. fb. s fb= 8 TeV Z τ τ CR 5 5 x H(15) τ τ s = 8 TeV Z ll CR 5 x H(15) Zτ τ τ τ 5 x H(15) τ τ Z ee,µ µ Z ee,µ µ Z ee,µ µ BDT score BDT score ee + eµ + µ µ Boosted ATLAS Preliminary ee + eµ + µ µ Boosted ATLAS Preliminary ee + eµ + µ µ Boosted ATLAS Preliminary 7 ee + eµ + µ µ Boosted ATLAS Preliminary 6 ee + eµ + µ µ Boosted ATLAS Preliminary 6 L dt =. fb (a) (a) (a) (b) (b) (b) 6 L dt =. fb s = 8 TeV CR 6 L dt =. fb s = 8 TeV top-quark CR 5 x H(15) τ τ s = 8 TeV Z ll CR 6 L dt =. fb s = 8 TeV CR L dt =. fb s = 8 TeV top-quark CR x H(15) τ τ Z ee,µ µ x H(15) τ τ 5 x H(15) τ τ 5 x H(15) τ τ 5 µ τ had + eτ had VBF ATLAS Preliminary 7 ee 7 + eµ ee + µ + 5µ eµ Boosted µ + τ µ µ + Boosted eτ BoostedATLAS had had Z τ Preliminary τ Z ee,µ ATLAS Preliminary µ Preliminary ee + eµ ee + eµ µ µ + Boosted µ µ Boosted ATLAS ZATLAS τ Preliminary τ Z ee,µ µ 6 Z ee,µ µ 6 Z ee,µ µ L dt =. fb L dt =. L dt fb. s fb= 8 TeV L dt = Z τ τ CR 6. fb s = 8 TeV CR L dt =. fb s = 8 TeV top-quark CR 5 x H(15) τ τ 6 L dt =. fb s = 8 TeV top-quark CR s = 8 TeV CR 5 x H(15) τ τ s = 8 TeV Z τ τ CR 5 5 x H(15) 5 x H(15) Zτ τ τ τ τ τ 5 5 x 5 H(15) x H(15) τ τ τ τ Others 5 5 Others Fake τ Z ee,µ Z µ ee,µ Fake µ τ Z Z ee,µ ee,µ µ µ (b) (c) (d) Rencontres de Moriond EW - H ττ (c) 18 (d) 1 March 1 Events /.1 Events /.17 A. A. Additional Additional Control Control Region Region Figures Figures A. Additional Control Region Figures A. Additional Control Region Figures Events /.1 Events /.1 Events /.1 Events /.1 Events /.1 5 Events / Events /.1 Events /.1 Events /.1 (a) (a) Events /.1 Events /.1 Events /.1 Events /.1 ee + eµ + µ µ VBF ATLAS Preliminary ee + eµ + µ µ VBF ATLAS Preliminary L dt =. fb s = 8 TeV top-quark CR 18 L dt =. fb s = 8 TeV top-quark CR x H(15) τ τ 16 5 x H(15) τ τ 1 ee + eµ + µ µ VBF ATLAS Z τ Preliminary τ 1 Z ee,µ µ ee + eµ + µ µ VBF ZATLAS ee,µ µ Preliminary 1 1 L dt =. fb s = 8 TeV top-quark CR 18 L dt =. fb s = 8 TeV top-quark CR x H(15) τ τ x H(15) τ τ Z ee,µ µ 6 Z ee,µ µ (b) (b) Events /.1 Events /.1 Events /.1 Events /.1

19 Events /.1 Events / ee + eµ + µ µ Boosted L dt =. fb (a) s = 8 TeV Z ll CR ATLAS Preliminary 5 x H(15) τ τ Z ee,µ µ µ τ had + eτ had VBF ATLAS Preliminary L dt =. fb 5 x H(15) τ τ s = 8 TeV CR Others Fake τ (b) Additional Control Region BDTs LepHad Events /.17 Events /.17 Events /.17 Events / Events /.1 µ τ had µ τ had + eτ + had eτ had VBF VBF ATLAS ATLAS Preliminary L dt L = dt. =. fb fb (b) s = s8 = TeV 8 TeV top-quark CR CR 5 5 x H(15) x τ τ τ τ Z Z τ τ τ τ 5 µ τ + eτ Boosted µ τ + eτ VBF ATLAS µ τ had ATLAS Preliminary had had + eτ had had VBF ATLAS Preliminary Preliminary Others Others L dt = L. dt =. fb fb s = 8 TeV top-quark CR L dt =. fb s = 8 TeV Fake top-quark Fake τ τ CR 5 x H(15) τ τ s = 8 TeV CR 5 5 x x ZH(15) τ τ τ τ τ τ Z Z τ τ Others τ τ Fake τ Others Others Fake τ Fake τ BDT 1 (a) (a) Events /.17 Events /.17 Events /.17 Events / µ Others τ + eτ VBF ATLAS Others 1 µ τ Preliminary had had + eτ had had VBF ATLAS Preliminary Fake Fake τ τ L dt =. 6 6 fb s = 8 TeV W CR L dt =. fb s = 8 TeV W CR 5 5 x H(15) x H(15) τ τ τ τ 8 8 Others Others Fake Fake τ τ BDT µ τ had µ τ had + eτ + had eτ had VBF VBF ATLAS ATLAS Preliminary L dt L dt =. =. fb fb s = s 8 = TeV 8 TeV W WCRCR (b) (b) 5 5 x H(15) x τ τ τ τ Z Z τ τ τ τ Events /.1 Events / τ had τ had VBF L dt =. fb (c) s = 8 TeV CR s = 8 TeV µ τ had + eτ had Boosted ATLAS Preliminary L dt =. fb 5 x H(15) τ τ Others Fake τ ATLAS Preliminary 5 H(15) ττ Others Sideband CR Multijet (d) Events /.1 Events /.1 Events /.1 Events / µ τ had µ τ had + eτ + had eτ had Boosted ATLAS ATLAS Preliminary BDT BDT score score L dt =. fb s = 8 TeV CR L dt =. fb s = 8 TeV top-quark CR Events / (a) (a) (d) 5 5 x H(15) x τ τ τ τ Z Z τ τ τ τ µ τ had µ τ had + τ eτ + had eτ had τ had Boosted had Boosted ATLAS ATLAS Others Others ATLAS Preliminary Preliminary 5 L dt L = dt. = L. dt fb =. fb sfb= s8 = TeV 8 s TeVFake Fake = 8 TeV top-quark τ τ Sideband CR CR CR 5 5 x H(15) x τ τ τ τ 5 H(15) ττ Z Z τ τ τ τ Others Others Others Fake Fake τmultijet τ (c) (c) BDT BDT score Rencontres 1 de Moriond EW - H ττ 19 1 March 1 Events /.1 Events /.1 Events /.1 Events / µ τ had µ τ had + eτ + had eτ had Boosted ATLAS ATLAS Preliminary L dt L dt =. =. fb fb s = s 8 = TeV 8 TeV W WCRCR (b) (b) 5 5 x H(15) x τ τ τ τ Z Z τ τ τ τ 5 5 Others Others µ τ had µ τ had + eτ + had eτ had Boosted Boosted ATLAS Fake ATLAS Fake τpreliminary τ L L dt =. fb s = 8 TeV W CR 5 dt =. fb s = 8 TeV 5 W CR x H(15) x τ τ τ τ Z Z τ τ τ τ 5 5 Others Others 5 5 Fake Fake τ τ BDT (d) (d)

20 Rencontres de Moriond EW - H ττ 1 March 1 Additional Control Region BDTs HadHad Events /. τ had τ had VBF L dt =. fb s ATLAS Preliminary = 8 TeV Sideband CR 5 H(15) ττ Z ττ Others Events /. 5 τ had τ had Boosted L dt =. fb s ATLAS Preliminary = 8 TeV Sideband CR 5 H(15) ττ Z ττ Others Multijet Multijet