Top quark property measurements W. Verkerke (on behalf of the ATLAS and CMS collaborations) 1 PLHC Vancouver

Top quark production at the LHC LHC is an abundant source of top quarks, allows for a detailed investigation of many properties of the top quark Wouter Verkerke, NIKHEF, 2 t t b W q q b W l v top quark mass top quark charge spin correlations charge asymmetry NP decaying into tt tt with additional jets V-A structure CKM matrix elements FCNC couplings 3) Production properties 1) Intrinsic properties 2) Coupling properties 2

Production and reconstruction Top pair production provides the cleanest and most abundant source of top quarks for property studies –σ(tt) at 7 TeV = 160 pb, 5 fb-1 collected in 2011 at 7 TeV –results in ~50k reconstructed tt in e/μ+jets final state and ~10k in dilepton final state (with e,μ) Wouter Verkerke, NIKHEF, 3 t t b W q q b W l v Lepton+jets selection 1 electron or muon ≥4 jets of which 1 or 2 flavor tagged Missing E T from neutrino (typical purity ~70-85% purity) Dilepton selection 2 leptons (electron or muon) ≥2 jets (optional flavor tag) Missing E T from neutrinos (typical purity >90%) For many studies, do also Kinematic reconstruction Reconstruct full ttbar decay tree from reconstructed jets and lepton(s) 1) For each possible assignment Calculate compatibility with decay tree hypothesis (χ 2 or L) 2) Pick permutation with highest probability above certain threshold 3 - -

Top quark mass measurement Measure mass of hadronically decaying top quark ATLAS 1D method: measure R 32 ≡ m(qqb)/m(qq) Wouter Verkerke, NIKHEF t t b W q q b W l v Measure invariant mass of 3-jet system Main issue: Jet Energy Scale Exploit in various ways that m inv (qq) should be m(W) to experimentally constrain light jet energy scale… Reconstructed R32 distribution Simulation templates of R32 for various true m(top) Extract m(top) with template fit m(qq) m(qqb) 1 fb -1 4

Top quark mass measurement 2D method: measure m(qq) and m(qqb) simultaneously –ATLAS: Template fit on ‘best’ assignment –CMS: Ideogram method. like template fit, but use all jet/parton pairings in likelihood instead of ‘best one’, (weighted by simulation expectation of pairing being correct) t t b W q q b W l v m(qq) m(qqb) ATLAS: arXiv: submitted to EPJC CMS: CMS-PAS-TOP m(qqb)m(qq) 1 fb fb -1 5

Top quark mass measurements Summary of recent LHC mass measurements CMS also measured m(t)-m(t) –Uncertainty smaller than on m(t) because of cancellation of systematic uncertainties –Test of CPT invariance, most precise measurement so far Wouter Verkerke, NIKHEF As shown on prev page 2 fb fb -1 6 ATLAS ATLAS-CONF CMS JHEP 07 (2011) 049, arXiv:1204:2807, submitted JHEP - * *) Does not include UE and CR uncertainties

Top quark charge Measure top quark charge from its decay products Wouter Verkerke, NIKHEF t t b W q q b W l v W charge trivially determined from lepton charge 1) Determine b charge lepton charge from semi-leptonic decay b  c 2) Determine b charge from (p T ) weighted average charge of tracks in jets Correct W/b pairing important… 1)Modeling of soft leptons from b-jets 2) Modeling of weighted jet charge b ATLAS:ATLAS-CONF CMS: CMS-PAS-TOP fb fb -1 7

Top quark charge Discrimination power between Q= 2 / 3 and Q= 4 / 3 of a single event is weak, but strong for Q of an ensemble of O(1000) events: exotic charge Q= 4 / 3 excluded at >5σ Wouter Verkerke, NIKHEF Q comb per event per expt ATLAS jet charge CMS soft lepton fb fb -1

V-A structure of Wtb vertex Investigate V-A structure of Wtb vertex by examining polarization of W from top decay –NNLO calculation of SM: Polarization of W: (68.5±0.5)% longitudinal, (31.1±0.5)% LH, (0.17±0.01)% RH Wouter Verkerke, NIKHEF t t b W q q b W l v Measure opening angle cos(θ*) between l and b in rest frame of W Fold in effect of reconstruction Lepton+jets channel templates ATLAS: arXiv: , submitted JHEP CMS: CMS-PAS-TOP

V-A structure of Wtb vertex Measure fractions with template fit to data Wouter Verkerke, NIKHEF Combine l+jets and dilepton Good agreement with SM prediction 1 fb fb CMS: l+jets ATLAS: l+jets and dilepton (shown)

V-A structure of Wtb vertex Constraints on possible new physics –New physics can be parameterized in terms of an effective Lagrangian Wouter Verkerke, NIKHEF Zero in Standard Model Allowed region in g R vs g L (assuming V L =1 and V R =0) SM prediction 11

Measurement of R b ≡ Br(W  tb)/Br(W  tq) Standard model (CKM) predicts nearly all tops decay to Wb as V tb ≈ –Can also measure this by measuring rate of tagged b jets in tt events: Measure rate of 2,3 jet events with 0,1,2,3 tagged b-jets -Express rate prediction in terms of R b ≡ Br(W  tb)/Br(W  tq) -Fit model with R b as free parameter to data -Understanding of b-tagging efficiency leading source of systematic uncertainty Wouter Verkerke, NIKHEF t t b W b W l v l v R b =0.98 ± 0.04  R b >85% at 95% C.L. CMS: CMS-PAS-TOP fb -1 12

FCNC top production t  (c/u)g Standard model prohibits flavor changing neutral currents. –Test this by looking for processes with tug and tcg couplings  look for single top production qg  t  Wb –Very challenging experimental signature, looks very much like W+(h.f.) jets, no single good discriminating variable  Use 10 variable Neural Network discriminant NN Bayesian Analysis Convert to B(t  qg) t W b l v ATLAS: PLB 712 (2012) fb B(t  ug)< B(t  cg)<

FCNC top decay t  Zq Can also look for FCNC coupling tqZ in ttbar decays –Look for tt with 1x t  Wb and 1x t  Zq –Three lepton final state with small background (mainly diboson) Wouter Verkerke, NIKHEF t t q W b Z l v l l CMS: CMS-PAS-TOP ATLAS: arXiv: , submitted JHEP fb fb -1 Br(t  qZ) < 0.34% at 95% C.L. Br(t  qZ) < 0.73% at 95% C.L. NEW!

tt spin correlations Wouter Verkerke, NIKHEF Spins of t and t are predicted to be correlated in SM –Top decay before hadronization allows to measure top spin from its decay products  Can look for exp. evidence of spin correlations –At LHC at low m(tt) ttbar production dominated by like-helicity gluon pairs  like-helicity ttbar pairs. –In dilepton final states this results in correlations between the leptons in the azimuthal angle Δφ in the lab frame (Mahlon & Parke) t t b W b W l v l v No Spin corr. SM-like Spin corr. Measured value consistent with SM-like spin corr. No spin corr. scenario excluded at 5.1σ Fit to Fit result recast as asymmetry ATLAS: arXiv: , accepted by PRL 2.1 fb

Top quark rapidity and the ‘charge asymmetry’ New physics that modifies forward-backward asymmetry A FB distribution of top quark pairs at the Tevatron may modify the ‘charge asymmetry’ A C at the LHC Reconstruct tt system and measure top/anti-top (pseudo) rapidity difference in l+jets and dilepton channels t t b W q q b W l v Measure difference in (pseudo)-rapidity of top and anti-top quark ATLAS: arXiv: , submitted JHEP CMS: PLB 709, 28 1 fb fb CMS: l+jets ATLAS: l+jets and dilepton (shown) NEW! 4.7 fb -1

tt charge asymmetry Measured Δ|y| distribution may have reconstruction biases  Apply unfolding procedure to obtain truth-level distribution Wouter Verkerke, NIKHEF Reconstructed Δ|y| Unfolded Δ|y| (SM MC truth) Unfolding matrix 17 - ATLAS A C (l+jets) = ± ± A C (dilept.) = ± ± A C (comb.) = ± ± ± CMS A C (l+jets) = ± ± ±

tt charge asymmetry CMS measured various differential distributions –Obtained from 2D unfolding Wouter Verkerke, NIKHEF - 18

tt charge asymmetry No hint of discrepancy in A C at high m(tt) in either expt... Comparison of LHC A C with Tevatron A FB Wouter Verkerke, NIKHEF m(tt)>450 GeV… 19 -

Resonances decaying into tt Look for narrow/wide resonances in m(tt) spectrum that might originate from NP, e.g. Z’  tt, g KK  tt –Generally, limits set Z’/g KK masses around 1 TeV Wouter Verkerke, NIKHEF - l+jets dilepton boosted top CMS ATLAS ATLAS: ATLAS-CONF , arXiv:1205,5371, submitted EPJC (boosted paper to follow shortly) CMS: PAS-TOP-11-10, PAS-EXO , PAS-EXO NEW! 2.05 fb -1 Z’ g KK

Towards precision measurements Imperfect MC modeling of tt becoming large(st) systematic uncertainty in many LHC top measurements –Perform dedicated measurements to help improve this –Compare to Sherpa, Alpgen, PowHeg, Madgraph Example 1: CMS differential cross-section measurement Example 2: ATLAS measured fraction f gap of ttbar events with no extra jet in a central rapidity interval –Probes rate of production of additional jets in ttbar events, sensitive as many systematic uncertainties cancel in fraction definition. Wouter Verkerke, NIKHEF t t b W q q b W l v Jet p T threshold for gap definition 1.5<|y|<2.1: all generators have more jets than data ATLAS: arXiv: , submitted EPCJ CMS: TOP-PAS

Summary LHC is doing well as a top factory! –Both expts recorded about reconstructed tt pairs in 2011 LHC Top mass measurement program well underway, but not quite at Tevatron precision yet (except for mass diff) –Limited by understanding of detector and top modeling, will improve over time Rich program of top properties measurements now underway. Already several LHC measurement now worlds best –Observation of spin correlations, W polarization… All measurements consistent with SM (so far)  No signs of new physics Systematic uncertainties dominate most measurements now –Will improve with better understanding of detector –Will improve with better understanding of tt modeling, assisted by dedicated measurements Wouter Verkerke, NIKHEF