Top Quark Physics in ATLAS Detector On behalf

Top Quark Physics in ATLAS Detector On behalf of the ATLAS Collaboration Regina Moles-Valls IFIC – Universitat de València

Top Physics Outline ATLAS Top Physics results presented in this talk: Top production: • Top quark pair cross section • Single top quark cross section Top Properties: • Top quark Mass • Top quark charge asymmetry • W polarization • Spin correlation New physics in top sector • Flavour Changing Neutral Current • ttbar resonances • Exotics heavy quark searches • … Studies on event and object reconstruction: b. JES , jet shapes, τ trigger, jet structure, … 20/10/2021 III Jornadas CPAN 2011 2

Top Physics Outline ATLAS Top Physics results presented in this talk: Top production: • Top quark pair cross section • Single top quark cross section Top Properties: • Top quark Mass M. Bosman, P. Casado, C. Conidi, L. Fiorini, D. Gerbaudo, C. Helsens, A. Juste, M. LL. Mir, J. Montejo, J. Nadal, I. Riu, F. Rubbo, A. Succurro, V. Vorwerk • Top quark charge asymmetry • W polarization • Spin correlation S. Cabrera, M. J. Costa(*), F. Fassi, J. Fuster, C. García, A. Irles, New physics in top sector S. Martí, R. Moles, M. Moreno-Llàcer, S. González, E. Oliver, • Flavour Changing Neutral Current S. Pedraza, T. Pérez, E. Ros, J. Salt, V. Sánchez, E. Valladolid, M. Villaplana, M. Vos, A. Wildauer (*) Top Group • ttbar resonances • Exotics heavy quark searches • … Convener Studies on event and object reconstruction: b. JES , jet shapes, τ trigger, jet structure, … J. A. Aguilar-Saavedra 20/10/2021 III Jornadas CPAN 2011 3

Top quark physics at LHC Single top production Top pair production Weak interaction Strong interaction Gluon fusion 85% t-channel ~65 pb Wt production ~16 pb Quark scattering 15% σtop (7 Te. V)= 165+11 -16 pb (theoretical NLO+NNLO) 20/10/2021 s-channel ~5 pb III Jornadas CPAN 2011 σtop (7 Te. V)≈ 84 pb (theoretical NLO+NNLO) 4

Top quark Physics in ATLAS Detector Top quark decays take place almost exclusively: t W+b ttbar Channel Products Full Hadronic (45%) Semi-leptonic (30%) Di-leptonic (11%) 6 jets l+MET+4 jets l=(e, μ) 2 l+MET+2 jet l=(e, μ, τ) Background Single top Channel Products t-channel Wt production s-channel 1, 2 l+MET+2, 3 jets Background 20/10/2021 III Jornadas CPAN 2011 5

ATLAS Performance for Top Physics ² Collecting useful data: ≈1 fb-1: σttμ+τ, resonances 0. 7 fb-1: mass, single top production, charge asymmetry, spin correlation, W polarization, … 200 pb-1: resonances 35 pb-1: FCNC 20/10/2021 III Jornadas CPAN 2011 6

ATLAS Performance for Top Physics ²Electron: Energy deposits in EM calorimeter with associated well reconstructed track in the ID ²Muon: Track segments in different layers of muon chambers are combined and matched with ID track ²Jets: Anti-kt 4 algorithm is used starting from energy cluster of adjacent calorimeters jets. Calibration is done using EM+HAD calorimeter information ²b-tagging: Based on impact parameter. It requires a good ID tracking performance ²Trigger: Trigger is based on signatures of e, μ and jets, as well as missing transverse energy B-jet Top quark in ATLAS needs: § Efficient e, μ, τ reconstruction § Good Jet reconstruction § b-jet tagging capability Top physics 20/10/2021 Full detector working!!! III Jornadas CPAN 2011 ETmiss Muon 7

Top production: • Top quark pair cross section • Single top quark cross section Top Properties: • Top quark Mass • Top quark charge asymmetry • W polarization • Spin correlation New physics in top sector • Flavour Changing Neutral Current • ttbar resonances • Exotics heavy quark searches • … 20/10/2021 III Jornadas CPAN 2011 8

Measurement of ttbar cross section ² Precise measurements of cross-section allow precision tests of perturvative QCD ² Validation of the SM at high energies: σtt. SM=165+11 -16 pb ² Some of these measurements open new windows to new physics ² ttbar sample important background in searches for physics BSM σ(tt) in lepton+jets final states ATLAS-CONF-2011 -121 ² Signature: lepton (e/μ), ETmiss, at least 3 jets ² Multivariate Analysis: ηl, p. Tleading jet, aplanarity and HT 3 σt(tt)=179 ± 3. 9(stat)± 9. 9(syst)± 6. 6(lumi) pb ² Uncertainty systematically dominated ² Challenging theoretical uncertainty: ²Δσ/σ = 6. 6% 20/10/2021 III Jornadas CPAN 2011 9

Measurement of ttbar cross section IFIC : ATLAS-CONF-2010 -119 ttbar cross-section in μ+τ final states jets(1 btag) ² Signature: μ and τ leptons, 2 or more ² Identification of τ-leptons uses a multivariate technique based on Boosted Decision Tree IFAE+IFIC: Analysis update in progress ATLAS-CONF-2010 -119 Etmiss, σt(μ+τ channel)=142 ± 21(stat)+20 -16(syst)± 5(lumi) pb The cross-section measurements has been performed in most of the ttbar final states: ² Single lepton+jets channel (w/wo b-tagging) ² Dilepton channel including all lepton flavour ² All hadronic channel Most of them are dominated by systematic errors 20/10/2021 III Jornadas CPAN 2011 IFAE: ATLAS-CONF-2011 -035 Analysis update in progress 10

Measurement of single top production ² Single top quark production via weak interaction provides a direct probe of W-t-b coupling and it is sensitive to new physics ² Measurement of the cross-section determines the quark mixing matrix element Vtbwithout assumption of quark generations ATLAS-CONF-2011 -101 t-channel σt. SM=64. 6+3. 3 -2. 6 pb ² Signature: lepton (e/μ), ETmiss, 2 -3 jets(btag) ² Cut-Based Analysis using discriminating variables: m(l, ν, btag), HT, Δη(b, j 1), |η(j 1)| σt(t-chan)=90+9 -9(stat)+32 -20(syst) =90+32 -22 pb ² Neural Network method has been used too Wt production σt. SM=15. 7+1. 3 -1. 4 pb s-channel ² Signature: 1/2 leptons(e/μ), ETmiss, 1/3 jets(btag) ² Cut-Based Analysis ² Signature: lepton (e/μ), ETmiss, 2 btag ² Cut-Based Analysis σt(Wt-channel)<39. 1 pb @95 CL 20/10/2021 σt. SM=4. 6± 0. 3 pb σt(s-channel)<26. 5 pb @95 CL III Jornadas CPAN 2011 11

Top production: • Top quark pair cross section • Single top quark cross section Top Properties: • Top quark Mass • Top quark charge asymmetry • W polarization • Spin correlation New physics in top sector • Flavour Changing Neutral Current • ttbar resonances • Exotics heavy quark searches • … 20/10/2021 III Jornadas CPAN 2011 12

Top Quark Mass ² Top quark mass is a fundamental parameter of the SM particle physics ² Several ATLAS top mass measurements has been performed: ² Signature: 1 lepton (e/μ), ETmiss, 4 jets(btag) ²Different methods: • 1 -dimensional Template (R 32= m. W/mtop) • 2 -dimensional template (mtop & JES) ² Combination: ATLAS-CONF-2011 -120 μ Channel mtop= (175. 9 ± 0. 9 stat ± 2. 7 syst) Ge. V IFIC: New methods to measure top quark mass in progress 20/10/2021 III Jornadas CPAN 2011 The uncertainty of the results is dominated by the systematic uncertainties: • JES Uncertainty for b-jets and light-jets • Initial and final state radiation • Some aspects of the MC modelling 13

Top Quark Charge Asymmetry ² SM expects ttbar production symmetric under charge conjugation at LO and small asymmetry due to the ISR and FSR at NLO: ² gg ² qq IFAE & UV. GRANADA: ar. Xiv: 1109. 3710 v 1 ttbar: symmetric IFAE: ATLAS-CONF-2011 -106 ttbar: top quarks emitted in the direction of the incoming quark anti-top quarks in the direction of the incoming anti-quark Tevatron (proton-antiproton): forward-backward asymmetry qq ttbar (90%) SM prediction AC≈ 0. 01 (G. Rodrigo) ² Signature: lepton (e/μ), ETmiss, >4 jets ² Unfolding: Rapidity distribution for ttbar are distorted by detector effects and acceptance ATLAS-CONF-2011 -106 ² Several processes BSM can alter this asymmetry LHC (proton-proton): top goes into forwards regions whereas anti-top keep more in the central region qq ttbar (15%) AC= -0. 024± 0. 016(stat)± 0. 023(syst) 20/10/2021 III Jornadas CPAN 2011 14

W Polarization ²Polarization of W bosons in top quark decays are sensitive to the structure Wtb-vertex (used to set limits on the anomalous contributions to the Wtb-vertex) W polarizatio n helicity fractions F 0 NNLO=0. 587± 0. 005 New physics can be parametrised in terms of an effective Lagrangian: FLNNLO=0. 311± 0. 005 FRNNLO=0. 0017± 0. 001 Anomalous coupling VR, g. L and g. R are absent in the SM at tree level ATLAS-CONF-2011 -122 Cosθ*: angle between charged lepton form the W decay and b quark form the top decay in the W boson rest frame ATLAS-CONF-2011 -122 UV. GRANADA: ATLAS-CONF-2011 - IFIC: W in single top analysis in progress 122 20/10/2021 III Jornadas CPAN 2011 15

Spin Correlations ² Top quark has short lifetime: ² Top decays before spin can flip ² Spin information is contained in the decay products (angular distributions) In the quark decay the V-A couplings fix the angular distribution of the decay products according to the polarization of the parent top quark via: ²Dilepton channel promise larger sensitivity: 2 leptons, Etmiss, ≥ 2 jets ² f. SM is the SM template strength: f. SM =NSM/(NSM+N 0) in SM f. SM=1 ²Results in agreement with ASMhelicity=0. 32 20/10/2021 III Jornadas CPAN 2011 ΔΦ = |Φ(l 1)-Φ(l 2)| 16

Top production: • Top quark pair cross section • Single top quark cross section Top Properties: • Top quark Mass • Top quark charge asymmetry • W polarization • Spin correlation New physics in top sector • Flavour Changing Neutral Current • ttbar resonances • Exotics heavy quark searches • … 20/10/2021 III Jornadas CPAN 2011 17

Flavour Changing Neutral Current searches ² According to the SM, FCNC are forbidden at tree level and much smaller at one loop. ² Several SM extensions predicts higher branching fractions for top quark FCNC decays. Top Pair ² One top decaying through SM and the other trough FCNC Single top No evidence of FCNC is found 20/10/2021 III Jornadas CPAN 2011 18

ttbar resonance searches Mass resonances in semi-leptonic channel ² Z’ resonance in the leptophobic scenario ² Special attention on top mass reconstruction (mtt): ²Comparison of top quark pair invariant mass with background only and signal+background hypoteses: ²If no excess in the comparison with SM predictions is found limit on the (σx. BR) vs mtt is set ² Narrow resonances predicted by leptophobic topcolour model can not be excluded ATLAS-CONF-2011 -087 ²Many models of physics BSM predict the existence of new resonances that decay predominantly into top quark pairs ² Kaluza-Klein gluon resonance in the Randall-Sundrum model ² K-K gluons with masses below 650 Ge. V are excluded @ 95 CL For resonance masses above 1 Te. V, the top quark decay products start to become strongly collimated, so reconstruction of these resonances is the subject of forthcoming studies: boosted topology IFIC: ATLAS-CONF-2011 -087 20/10/2021 III Jornadas CPAN 2011 19

Boosted tops ² For resonance masses higher than 1 Te. V the top quark candidates are Boosted tops ² Classical “resolved” algorithms, developed for tops at rest, are not adequate for highly boosted top decays: ²Jets from hadronic top decay not resolved ²Isolation of leptons ATLAS-CONF-2011 -073 ²In the “boosted” topology tops are reconstructed as “fat” jets IFIC: Imminent publication of ATLAS-CONF-2011 -073 20/10/2021 III Jornadas CPAN 2011 20

top partner searches ttbar events with large Missing transverse energy ² Model where new top quark partner are pair-produced and each top decay to an on-shell top (or anti-top) quark and long-lived undetected neutral particle ² TT->tt. A 0 A 0: ² ttbar signature ² Large Etmiss form undetected A 0 ² Many models present this signature ar. Xiv: 109. 4725 ² Data consistent with the SM predictions ² No evidence of an excess of ETmiss ² In absence of of signal an upper limit on the (σx. BR) is quoted: ² (σx. BR) of 1. 1 pb for m(T)=420 Ge. V and m(A 0)<1 o Ge. V excluded @ 95%CL ² In the exotic model of 4 th generation m(T)>420 Ge. V and m(A 0)>140 Ge. V are excluded IFAE: Top quark 4 th generation work in progress 20/10/2021 III Jornadas CPAN 2011 21

Studies on event and object reconstruction ²Top analysis require a hard work in reconstruction, performance detector, … Jet Shapes data/MC comparison Muon Scale Factor Tau trigger ATL-PHYS-INT-2011 -079 arxiv: 1110. 1530 v 1 B-jes uncertainty validation Fat Jet systematics ATL-COM-PHYS-2011 -123 QCD Background studies ATLAS-CONF-2011 -073 IFAE https: //svnweb. cern. ch/trac/atlasgrp/browser/Comb. Perf/ Jet. ETMiss/JESPaper 2010 Data. pdf IFIC 20/10/2021 III Jornadas CPAN 2011 22

Summary ² The top quark physics program in ATLAS is really huge! ² Many measurements has been done: ²Top Cross section: ²Top pair cross section has been performed in almost all the final states ²Single top cross section has been measured too ²Top quark properties: ² These ones have been extensively studied ²Searched for new physics: ² Studies are on-going and many results will arrive for next conferences ² At this moment many studies are on-going: ² Using more statistic (ATLAS has now 5. 2 fb-1) ² Increasing understanding of the detectors is continously improving ² New top precision measurements and observation are coming!!! The Spanish contribution to top quark physics in ATLAS is and will be really important 20/10/2021 III Jornadas CPAN 2011 23

Thank you very much 20/10/2021 III Jornadas CPAN 2011 24

Measurement of single top production o Single top quark production via weak interaction o Provides a direct probe of W-t-b coupling and is sensitive to new physics o Measurement of the cross-section determines the quark mixing matrix element Vtbwithout assumption of quark generations t-channel o Leptonic decay mode: e/μ, Etmiss, 2 -3 jets(btag) Cut-Based analysis • 4 discriminan variable: m(l, ν, btag), HT, Δη(b, j 1), |η(j 1)| Single top higher cross section σt. SM=64. 6+3. 3 -2. 6 pb ATLAS-CONF-2011 -101 σt(t-chan)=90+9 -9(stat)+32 -20(syst) =90+32 -22 pb • Consistent with SM t-channel expectation Neural network analysis • 13 variables used σt(t-chan)=105± 7(stat)+36 -30(syst) pb 20/10/2021 III Jornadas CPAN 2011 25

Measurement of single top production Single top higher cross section σt. SM=15. 7+1. 3 -1. 4 pb o Cut-Based method to select Wt contribution o After selection (15% purity) ATLAS-CONF-2011 -104 Wt production σt(Wt-channel)<39. 1 pb @95 CL s-channel o Leptonic decay mode: e/μ, Etmiss, 2 jets(btag) o Cut-based analysis method o Many variables as potential discriminators between signal and background o Signal purity in the signal region ~6% ATLAS-CONF-2011 -118 Single top higher cross section σt. SM=4. 6± 0. 3 pb σt(s-channel)<26. 5 pb @95 CL 20/10/2021 III Jornadas CPAN 2011 26

ttbar resonance searches ²Many models of physics BSM predict the existence of new resonances that decay ATLAS-CONF-2011 -087 predominantly into top quark pairs Mass resonances in semi-leptonic channel ² Z’ resonance in the leptophobic scenario ² Special attention on top mass reconstruction (mtt): ² Delta. Rmin algorithm to reduce IFS/FSR ² Comparison of top quark pair invariant mass with background only and signal-plus-background hypoteses: ² Comparison to SM predictions ² If no excess is found limit on the (σx. BR) vs mtt is set ² Narrow resonances predicted by leptophobic topcolour model can not be excluded. ² K-K gluon resonances in the Randall-Sundrum model ² Semileptonic channel ² K-K gluons with masses below 650 Ge. V are excluded @ 95 CL IFIC: ATLAS-CONF-2011 -087 20/10/2021 III Jornadas CPAN 2011 27

ttbar resonance searches Mass resonances in dileptonic resonances ATLAS-CONF-2011 -123 o K-K gluon resoances in the Randall-Sundrum model o Interesting variables: § HT + Etmiss : searches for an excess of this distribution (KK gluon resonances harder spectrum than SM quark production) g. KK for illustration o Resonance searches in the dilepton ttbar final state don’t show significant excess in HT + Etmiss spectrum. o Set limits on σB for KK gluon production o Mass of the KK-gluon in the Randall-Sundrum model higher than 0. 84 Te. V @95 CLMass For resonance masses above 1 Te. V, the top quark decay products start to become strongly collimated, so reconstruction of these resonances is the subject of forthcoming studies: boosted topology IFIC: ATLAS-CONF-2011 -123 20/10/2021 III Jornadas CPAN 2011 28

Measurement of ttbar cross section ² Precise measurements of cross-section allow precision tests of perturvative QCD ² Validation of the SM at high energies: σtt. SM=164+11 -16 pb ² Some of these measurements open new windows to new physics ² ttbar sample important background in searches for physics BSM ttbar cross-section in μ+τ final states IFAE+IFIC: Analysis update in progress ATLAS-CONF-2010 -119 ² Signature: μ and τ leptons, Etmiss, 2 or more jets(1 btag) ² Identification of τ-leptons uses a multivariate technique based on Boosted Decision Tree IFIC : ATLAS-CONF-2010 -119 σt(μ+τ channel)=142 ± 21(stat)+20 -16(syst)± 5(lumi) pb 20/10/2021 III Jornadas CPAN 2011 29

Measurement of ttbar cross section σ(tt) in lepton+jets final states ATLAS-CONF-2011 -121 ² Signature: lepton (e/μ), ETmiss, at least 3 jets ² Multivariate Analysis: ηl, p. Tleading jet, aplanarity and HT 3 σt(tt)=179 ± 3. 9(stat)± 9. 9(syst)± 6. 6(lumi) pb ² Uncertainty systematically dominated ² Challenging theoretical uncertainty: ²Δσ/σ = 6. 6% The cross-section measurements has been performed in most of the ttbar final states: ² Single lepton+jets channel (w/wo b-tagging) ² Dilepton channel including all lepton flavour ² All hadronic channel Most of them are dominated by systematic errors 20/10/2021 III Jornadas CPAN 2011 IFAE: ATLAS-CONF-2011 -035 Analysis update in progress 30