Higgs fiducial and differential cross section measurements at ATLAS - PowerPoint PPT Presentation

Higgs fiducial and differential cross section measurements at ATLAS Dag Gillberg 
 CERN 2014-12-07

Outline 1. Why measure cross sections? 2. Definition of fiducial volume: its acceptances and NP corrections 3. Overview of the measurement 4. Signal extraction 5. Correction for detector effects 6. Uncertainties 7. Physics results: 1. Fiducial cross sections 2. Differential cross sections Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 2

Why cross sections? Cross sections offer a direct measurement of Higgs production rates in the data with • minimal assumptions on the underlying model (‘model independent’). Test of the compatibility of the SM with the data. • Can compare data to a range of different theory models now and in the future. • The inclusive Higgs production cross section is a hot topic in the theory community • Lot of activity to calculate the ggF Higgs production cross section to N 3 LO. • ! ! ! ! ! ! Differential cross sections offer a model independent way of probing the properties of the • Higgs boson. ‘State-of-the-art’ MC generator predictions are now at NLO accuracy in QCD, with • some steps towards NNLO. Higgs differential cross section measurements Higgs differential xsec combination 02/12/2014 Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 3 4 michaela.queitsch-maitland@cern.ch

ggF inclusive cross section 60 [pb] ggF inclusive cross section, s = 13 TeV, = m /2 , = m µ µ H H 0 0 ggF Uncertainty from largest scale-var deviation from nominal σ 55 50 45 Run 1 HXSWG recommendation (dFG m = m ) 0 H m = 125 GeV s = 13 TeV 40 H No EW correction, infinite top-mass approximation MSTW2008nnlo68cl, = 0.1171 α s 35 3 3 3 2 2 NNLO NNLO NNLO+ NNLO+ part. N LO part. N LO part. N LO π π 3 F.O. F.O. F.O. F.O. NNLL NNLL' N LL' baseline dFG ABNY STWZ dFMMV BBFMR BBFMR Benchmark summary from ggF XS WG Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 4

A few initial remarks • Presenting ATLAS Higgs cross section measurements • Measurements performed by extracting signal in the reference peak: 
 all Higgs production modes included in this peak (not only ggF) • m H = 125.4 GeV (ATLAS measured Higgs mass), 8 TeV data only (20 fb -1 ) • Only presenting the measurements in the γγ and ZZ channels 
 (with focus on γγ ) • Measurements are designed to be as model independent as possible • I’m not including the recently published WW ( * ) fiducial cross section measurement as part of the WW paper: https://cds.cern.ch/record/1954714 � ggF +5 . 4 +4 . 3 = 27 . 5 +6 . 9 fid , 0 j = 27 . 5 − 6 . 5 fb − 5 . 3 − 3 . 7 � ggF +3 . 1 fid , 1 j = 8 . 4 − 3 . 0 ± 1 . 9 = 8 . 4 ± 3 . 6 fb . (stat.)(syst.) • See paper for details. The approach is a bit different from the γγ and ZZ results I will show. For example, the expected VBF contribution is subtracted. Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 5

Cross section measured For γγ and ZZ Jet definition Higgs kinematics: p T H, | y H | Jet activity: N jets, p jet1 jets: anti- k t R =0.4, | y |<4.4 Spin & CP: cos θ * p T > 30 GeV ZZ only: m 34 = dilepton-mass of offshell Z γγ only Fiducial regions: γγ only N jets 50 GeV threshold Higgs kinematics: p Tt VBF-enhanced: 
 Jet activity: | y jet1 |, p Tjet2, | y jet2 |, H T,jets m jj >400, ∆ y jj > 2.8, ∆ ϕ ( γγ ,jj) > 2.6 VBF: m jj, p T γγ jj, ∆ y jj, ∆ ϕ ( γγ ,jj) Higgs + 1 lepton: 
 beam thrust: τ jet, ∑ τ jet at least one e or µ with 
 2D: p T H vs N jets bins: {0,1, ≥ 2} jets, cos θ * vs p TH p T > 15 GeV, | η |<2.47 Spin & CP: ∆ ϕ jj Higgs + E Tmiss > 80 GeV • Binning determined by available statistics Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 6

Definition of fiducial volume • Fiducial volume defined at truth particle level Particles with a mean life time longer than: c 𝜐 > 10 mm • Z → • Idea: apply same selection criteria as applied in the data analysis same-flavour- 
 opposite-sign- 
 • Avoid model dependent extrapolation H → ZZ* pair (SFOS) • “Trivial” extrapolation kept in to simplify 
 definition (e.g. detector “crack”) • H → γγ : require the two photons from the Higgs 
 to be central: | η |<2.37 , and have 
 p T ≿ 44 GeV and 32 GeV (see exact def. below) • Reco-level: also avoid barrel-endcap transition 
 region: 1.37<| η |<1.52 (i.e. rely on MC for 
 fraction of MC events in this region) Acceptance ~63% ~50% Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 7

Fiducial acceptance • Fiducial acceptance as a function of Higgs p T for ggF only • Split into kinematic acceptance and photon isolation • Photon isolation requirement: 
 Acceptance factors ∑ E T < 14 GeV 
 ATLAS Simulation internal 1.4 of particles within DR<0.4, 
 Iso. Eff. Uncertainty H , s = 8 TeV → γ γ mimics ATLAS photon isolation ∫ c -1 L dt = 20.3 fb Iso 1.2 analysis selection Kin. Acc. Uncertainty c • Note: efficiency depend on A 1 amount of hadronic activity • Kinematic acceptance: 
 0.8 both photons central: | η |<2.37 
 p T γγ / m γγ > 0.35 and 0.25 0.6 • Quite stable (~61%) vs most variables 0.4 • Depends on the Higgs boost along z-axis (rapidty) 
 0 20 40 60 80 100 120 140 160 180 200 γ γ p [GeV] Fwd Higgs → fwd decay T H → ZZ does not apply any isolation requirements products Kinematic acceptance ~50% Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 8

Fiducial acceptance Acceptance factors ATLAS Simulation internal 1.4 Iso. Eff. Uncertainty H , s = 8 TeV → γ γ ∫ c -1 L dt = 20.3 fb Iso 1.2 Kin. Acc. Uncertainty c A 1 0.8 0.6 Acceptance factors ATLAS Simulation internal 1.4 0.4 Iso. Eff. Uncertainty H , s = 8 TeV → γ γ ∫ c -1 L dt = 20.3 fb Iso 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 1.2 Kin. Acc. Uncertainty | y | γ γ c A 1 0.8 0.6 0.4 0 1 2 ≥ 3 Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 9 N jets

Comparing analytical ggF predictions with data Note: in a differential distribution, each bin defines its own fiducial Fiducial volume. Hence equation below holds bin-by-bin. cross section that’s measured gluon fusion in data other production modes Fiducial XH = VBF+VH+ttH Acceptance ggF cross section Branching ratio Non-perturbative correction factor accounting for hadronization and 
 Kinematic acceptance for underlying event activity Higgs decay product to fulfil fiducial requirements Efficiency for photons to fulfil particle level isolation (part of γγ fiducial definition 
 not used for ZZ) Example for H → γγ inclusive fiducial cross section, m H = 125.4 GeV = 30.5 fb ~63% ~98% 1.00 ~4 fb LHC-XS: 19.15 pb SM prediction 0.228% 10

Comparing analytical ggF predictions with data Our estimates of the above factors are in HEP data … and the measurements of course http://hepdata.cedar.ac.uk/view/ins1306615

� � Non perturbative correction � � � Non-Perturbative Correction Factor Pythia8 AU2 CT10 UE Non-Perturbative Correction Factor Pythia8 AU2 CT10 UE 1.25 ATLAS Intenal ATLAS Intenal Herwig++ UE-EE-4-LO** Herwig++ UE-EE-4-LO** 1.25 Pythia6 P2011C Pythia6 P2011C Pythia6 P2012 Pythia6 P2012 1.2 1.2 Pythia6 AUET2B LO** Pythia6 AUET2B LO** Pythia6 AUET2B CTEQ6L1 Pythia6 AUET2B CTEQ6L1 1.15 1.15 Pythia6 AMBT2B LO** Pythia6 AMBT2B LO** Pythia6 AMBT CTEQ6L1 Pythia6 AMBT CTEQ6L1 Uncertainty 1.1 Uncertainty 1.1 1.05 1.05 1 1 0.95 0.9 0.95 0 20 40 60 80 100 120 140 0 1 2 3 4 5 6 7 8 9 10 � � p [GeV] N jets T,jet1 � � Non-Perturbative Correction Factor Pythia8 AU2 CT10 UE Bin-by-bin ratio: ATLAS Intenal Herwig++ UE-EE-4-LO** 1.2 Pythia6 P2011C “particle-level”/“parton-level” Pythia6 P2012 Pythia6 AUET2B LO** 1.15 Pythia6 AUET2B CTEQ6L1 Pythia6 AMBT2B LO** “parton-level”: ME+Parton-showering Pythia6 AMBT CTEQ6L1 Uncertainty 1.1 “particle-level”: adds hadronization+UE 1.05 (and beam-breakup) 1 0.95 0 0.5 1 1.5 2 Dag Gillberg (CERN) Higgs cross section measurements 2014-12-07 12 y � � � � � �

Differential cross section measurement overview 1. Signal extraction 2. Unfold to particle level 3. Plot and compare with 
 and divide by integrated 
 theory luminosity and bin-width correction factor 
 for detector effects 20.3 fb -1 
 (±2.8%) a) Spit dataset into bins of variable of a) correction for detector a) compare to particle level interest (here 4 N jets bins) effects with bin-by-bin prediction - i.e. no need for unfolding detector simulation b) For each bin, extract s from a s + b fit to the m γγ spectra b) convert to (“differential”) b) Can also compare with cross section by dividing by c) Large statistical uncertainty due to analytical calculations int. lumi (and bin-width) small s / b (parton level) but then need small parton → particle level 
 (NP) correction Dag Gillberg (CERN) 13