Top Quark Production at the LHC. Masato Aoki (Nagoya University, Japan) For the ATLAS, CMS Collaborations

Transcription

1 Top Quark Production at the LHC Masato Aoki (Nagoya University, Japan) For the ATLAS, CMS Collaborations

2 Phys. Rev. D 83 (2011) , Phys. Rev. D 82 (2010) , Phys. Rev. D 81 (2010) , Comput. Phys. Commun. 182 (2011) 1034 LHC: top quark factory with pp collisions s 7 TeV 8 TeV Top pair Single top: t-ch Single top: s-ch ± ± 0. 2 Single top: Wt ± ± fb TeV + 20 fb TeV per experiment 5,600,000 top pairs, 2,700,000 single top events Top Quark Production at the LHC 2

3 Measurement of top quark Precise tests of perturbative QCD Precise understanding of background in new physics and Higgs searches New physics may be associated with top quark production Top Quark Production at the LHC 3 t H H t t c,g t c,g t t W W t t

4 Inclusive σ tt σ 7 TeV pp collisions ATLAS and CMS combination Total uncertainty : 5.8% ATLAS-CONF CMS PAS TOP First LHC combination First step in the discussion towards the harmonization of systematic treatment For the moment there were still important differences: e.g. treatment of generator systematics This could be a very good motivation for top modeling studies Top Quark Production at the LHC 4

5 New results on inclusive σ tt Improved analysis technique CMS: dilepton with 2.3 fb ± 2. 5 stat syst ± 3. 6 lumi pb More refined event selections and analysis techniques, better estimate of systematics Eur. Phys. J. C72 (2012) 2202 σ tt New tool ATLAS: l+jets with 2.8 fb ± 2 stat ± 17 syst ± 3 lumi pb Soft Muon b-tagger ATLAS-CONF BSM-sensitive channel ATLAS: t+jets with 1.7 fb -1 Use hadronic tau 194 ± 18 stat ± 46 syst pb Eur. Phys. J. C, 73 3 (2013) 2328 CMS: t+jets with 3.9 fb -1 Use hadronic tau 152 ± 12 stat ± 32 syst ± 3 lumi pb arxiv: Energy: 8 TeV ATLAS: l+jets with 5.8 fb ± 2 stat ± 31 syst ± 9 lumi pb CMS: l+jets with 2.8 fb ± 9 stat syst ± 10 lumi pb CMS: dilepton with 2.4 fb ± 3 stat ± 11 syst ± 10 lumi pb ATLAS-CONF , CMS PAS TOP , CMS PAS TOP Top Quark Production at the LHC 5

6 Eur. Phys. J. C (2013) 73: 2261 tt differential cross 7 TeV, 2.05 fb -1, l+jets, at least one b-tag tt reconstruction by likelihood-based kinematic fitter Robust unregularized unfolding of m tt, y tt, p T tt compared with MCFM, ALPGEN, MC@NLO (and approx. NNLO for m tt ) Mostly systematics dominated (Jet/E T miss reco.): 10~20% Full covariance matrix provided All the measurements are in agreement with the standard model Top Quark Production at the LHC 6

7 arxiv: , CMS PAS TOP , CMS PAS TOP tt differential cross 7 TeV 5 fb -1, and 8 TeV 12 fb -1 l+jets channel (at least 4 jets, at least 2 b-tagged jets) tt reconstruction: Constrained kinematic fitting algorithm Typical systematic uncertainty: 5.4% 3.9% from experimental uncertainty 3.8% from modeling uncertainty Dilepton channel (at least 2 jets, at least 1 b-tagged jets) tt reconstruction: Alternative kinematic reconstruction method Wider top-mass assumption (100GeV - 300GeV ) Typical systematics uncertainty: 3.9% 2.8% from experimental uncertainty 2.7% from modeling uncertainty Top Quark Production at the LHC 7

8 arxiv: , CMS PAS TOP , CMS PAS TOP tt differential cross 7 TeV data 8 TeV data Good agreement between data and theoretical predictions The approximate NNLO provides the best description of the data Top Quark Production at the LHC 8

9 ATLAS-CONF Jet multiplicity in tt event ATLAS: 7 TeV, 4.7fb -1, l+jets channel, at least one b-tagged jet Number of jets (n jets ) measurement varying jet p T threshold Unfolded n jets distributions compared with several MC predictions Systematics dominated by Jet/E T miss reco. Discrepancy at large n jets for MC@NLO+HERWIG Reasonable agreement with ALPGEN+PYTHIA(or HERWIG) and POWHEG+PYTHIA p T >25GeV p T >40GeV p T >60GeV Top Quark Production at the LHC 9

10 CMS PAS TOP Additional jets in l+jets CMS: 7 TeV, 5 fb -1, l+jets channel Additional jets in tt events extracted by fitting to likelihood discriminant Comparing with MadGraph, MC@NLO, POWHEG A slight discrepancy with MC@NLO Top Quark Production at the LHC 10

11 Eur.Phys.J. C72 (2012) 2043, CMS PAS TOP Additional jets in dilepton Look at tt (ll + 2 b-jets) + additional jets ATLAS: 2 fb 7TeV CMS: 5 fb TeV Gap fraction: Fraction of events produced in the absence of an additional jet above a p T (Q 0 ) threshold Full rapidity interval: All those generators give a reasonable description of the data Central: MC@NLO is too large Forward: None of the predictions agrees with data Central y 2.4 y 2.1 Forward Top Quark Production at the LHC 11

12 CMS PAS TOP CMS: bb associated with tt 7 TeV, 5 fb -1 Dilepton + 4 jets Measure σ(tt bb)/σ(tt jj) Large cancellation of uncertainties b ID by Combined Secondary Vertex tagger (CSV) Combining SV and Track-based lifetime info Signal extraction by fitting to b-jet multiplicity σ(tt bb)/σ tt jj = 3. 6 ± 1. 1 stat ± 0. 9(syst) MADGRAPH: 1.2% POWHEG: 1.3% Δ = 39% 31%: Data stat. 23%: mistag rate 6.7%: Signal modeling 6.0%: b-tag eff. Top Quark Production at the LHC 12

13 Single top at LHC Alternative top quark production via the weak interaction Sensitive to many models of new physics Allow for a measure of V tb without assumptions about the number of quark generations Can be used to measure the b-quark parton distribution function t-channel s-channel Wt-channel Top Quark Production at the LHC 13

14 Phys. Lett. B 716 (2012) , Phys. Rev. Lett. 110 (2013) Wt associated TeV Final state: two leptons + E miss T + one b-jet Simultaneous fit of BDT outputs in different jet-bin regions (1-jet bin: signal region, 2>=jet bin: background control region) First evidence from ATLAS using 2fb -1, and confirmation by CMS with more stats. Δσ/σ=34% 16%: JES 15%: PS 10%: Gen. 10% Pile-up Δσ/σ=31% 20%: Stat. 15%: JES 10%: PS 22 variables 4 variables L [fb -1 ] Wt cross section [pb] Significance V tb ATLAS ± 2. 9(stat.) ± 4. 9(syst.) 3.3σ CMS σ exp (th.) Top Quark Production at the LHC 14

15 CMS PAS TOP , ATLAS-CONF t-channel single TeV miss Final state: one lepton + E T + one b-jet + one recoil jet Signal extracted by a fitting with ATLAS: NN discriminant CMS: η distribution of recoil jet * 11 input variables L[fb -1 ] t-channel cross section [pb] V tb ATLAS ± 2. 4 stat. ± 18. 0(syst.) CMS 5.0 Δσ/σ=19% 9%: I/FSR 9%: b-tag 8%: JES 7%: Gen ± 5. 7 stat. ± syst. ± 4. 0(lumi.) Δσ/σ=16% 8%: JES 6%: Gen. 5%: Muon 5%: b-tag 5%: PDF ± exp. ± 0. 02(th.) Top Quark Production at the LHC 15

16 ATLAS-CONF , CMS PAS TOP R t : ratio of top and anti-top in t-channel R t is sensitive to PDF x [0.02,0.5] can be probed W-charge asymmetry [10-3,10-1 ] at LHC [0.005,0.3] at Tevatron ATLAS@7 TeV: 1.81±0.10 stat. ATLAS: 7 TeV 4.7 fb -1 Fit to NN outputs for l + and l - CMS: 8 TeV 12 fb -1 Fit to h of recoil jets for l + and l - Both results agree with SM predictions CMS@8 TeV: 0.20 (syst.) 1.76±0.14 stat ± (syst) Top Quark Production at the LHC 16

17 Summary Many top measurements from 7 TeV 5 fb -1 of data, and with further statistics of 8 TeV data First LHC σ tt combination Improved σ tt and σ t measurements Large statistics of the LHC sample allows to perform more detailed top measurements Differential cross section Jet multiplicity bb associated with tt R t measurement in t-channel single top Need to improve modeling of the top production in order to be able to probe kinematics regions where new physics may exist More detailed and interesting top results yet to come Top Quark Production at the LHC 17

18 BACKUP SLIDES Top Quark Production at the LHC 18

19 CMS PAS TOP CMS: Vector boson associated with tt 7TeV, 5fb -1 Trilepton approach : tt +Z lvbjjb+ll Same-sign dilepton approach : tt +Z and tt +W σ tt V = stat (syst) pb 4.7σ significance! Top Quark Production at the LHC 19

20 Top Quark Production at the LHC 20

21 Eur. Phys. J. C72 (2012) TeV: Further improvement CMS: σ tt in dilepton with 2.3 fb -1 More refined event selections and analysis techniques, better understanding of systematics Signal extraction by a profile likelihood ratio method to N jets N b jets ± 2. 5 stat (syst) ± 3. 6(lumi) pb Δσ/σ=4.2% Main systematics 2.2% Lumi. 1.9% JES 1.7% BR(W ln) * MADGRAPH used for tt MC Top Quark Production at the LHC 21

22 arxiv: tt with TeV Final state with taus sensitive to charged Higgs CMS: τ+jets in 3.9 fb -1 of data Hadronic τ candidate BDT to separate τ from e/m 4jets ( 1 b-tagged) Largest background from multijet Control sample from untagged data Signal extraction by fitting to Neural Network discriminant 152 ± 12 stat ± 32 syst ± 3 lumi pb Δσ/σ=23% 11% from JES 9% from τ ID Top Quark Production at the LHC 22

23 ATLAS-CONF TeV: tt with semileptonic b-tag ATLAS: 4.7 fb TeV High p T and central lepton(=1) and jets( 3) Soft Muon Tagger (SMT) Uncertainty on σ tt measurement: 1.4% 1.3% from muon identification 0.6% from c 2 matching efficiency Uncorrelated with other b-taggers Cut & count analysis: σ tt = 165 ± 2(stat) ± 17(syst) ± 3(lumi) pb Total uncertainty : 10.5% 6.6% from signal modeling 3.1% from BR(b μx) 5.5% from W+jets estimate 4.4% from multijets estimate SMT b-tagged Signal region Top Quark Production at the LHC 23

24 ATLAS-CONF , CMS PAS TOP TeV: tt in l+jets channel One high p T central lepton, and jets with at least one b-tagged jet Signal extracted by a fit to ATLAS: Likelihood discriminant CMS: M lb distribution 3 jets 4 jets NN-based b-tagger Jet prob. b-tagger Δσ/σ=13% Δσ/σ=13% 11%: signal modeling 8%: b-tag 6%: Jet/E miss T reco. 5%: Jet/E miss T reco. 3.7%: luminosity 4.4%: luminosity L [fb -1 ] σ tt ATLAS ± 2 stat ± 31 syst ± 9(lumi) CMS ± 9 stat syst ± 10(lumi) Top Quark Production at the LHC 24

25 CMS PAS TOP CMS result in dilepton TeV 2.4 fb -1 of data A simple and robust cut&count Analysis baseline is the same as 7 TeV analysis Channel ee mm em ll Cross section [pb] 231 ± 8 stat ± 15 syst ± 10(lumi) 220±6 stat ± 15 syst ± 10(lumi) 227 ± 4(stat) ± 11(syst) ± 10(lumi) 227 ± 3(stat) ± 11(syst) ± 10(lumi) Δσ/σ =6.7% 4.4% from luminosity 2.5% from JES Top Quark Production at the LHC 25

26 Jet multiplicity in 7 TeV, 5 fb -1, dilepton channels Unfolded jet multiplicities comparing with several QCD calculations MadGraph and POWHEG describe well the data MC@NLO generates lower multiplicities than observed Top Quark Production at the LHC 26

27 8 TeV: tt with b-tagging at ATLAS Use 5.8 fb -1 of data High p T and central lepton(=1) and jets( 3) At least one b-tagged jet Use neural network-based tagger Signal extraction by fitting to a likelihood discriminant (lepton rapidity, aplanarity) Δσ/σ=13% 1. 11% from signal modeling 2. 6% from Jet/E T miss reco % from luminosity ATLAS-CONF σ tt = 241 ± 2(stat. ) ± 31(syst.) ± 9(lumi.) pb Top Quark Production at the LHC 27

28 8 TeV: tt with b-tagging at CMS Up to 2.8 fb -1 of data High p T and central lepton(=1) and jets( 4) At least one b-tagged jet Signal extraction by fitting to M lb distribution Δσ/σ=13% 8% from b-tag 5% from Jet/E T miss reco. 4.4% from luminosity CMS PAS TOP σ tt = ± 9. 0 stat syst. ± lumi. pb Top Quark Production at the LHC 28

29 ATLAS-CONF R t : ratio of top and anti-top in t-channel R t is sensitive to PDF x [0.02,0.5] can be probed W-charge asymmetry [10-3,10-1 ] at LHC [0.005,0.3] at Tevatron ATLAS: 4.7 fb -1 of 7TeV data Signal extraction by fitting NN outputs top quark anti-top quark σ(t) σ(t ) 53.2±1.7 stat. ±10.6 syst. pb 29.5±1.5 stat. ±7.3 syst. pb R t 1.81±0.10 stat (syst.) Δσ(t)/σ(t)=20%, Δσ(t )/σ(t)=25% (JES is dominant: 16 20%) ΔR t /R t =13% (6% Stat., 4% for MC stat., Bkg, JES, ISR/FSR ) Top Quark Production at the LHC 29

30 CMS PAS TOP R t measurement at 8 TeV CMS: 8 TeV, 12 fb -1 Signal extraction by a fit to η distributions of recoil jet for l + and l -, simultaneously σ(t) σ(t ) R t 49.6±2. 0 stat ±8. 8 syst pb 28.2±2. 2 stat ±4. 8 syst pb 1.76±0.14 stat ± (syst) Δσ(t)/σ(t)=18%, Δσ(t )/σ(t )=19% Signal modeling is dominant: 11 15% ΔR t /R t =15% 9% from data stat. 8% from PDF 7% from W+jets, tt extraction top quark anti-top quark Top Quark Production at the LHC 30

31 Top Quark Production at the LHC 31

32 Top Quark Production at the LHC 32

33 Top Quark Production at the LHC 33

34 Top Quark Production at the LHC 34

35 Top Quark Production at the LHC 35

36 Top Quark Production at the LHC 36

37 Top Quark Production at the LHC 37

38 Top Quark Production at the LHC 38

39 Top event in the detector 33% 67% tt analysis modes e/m + jets 34.3% All hadronic 59.2% ee/mm/em 6.4% *t is considered as either hadronic or e/m Top Quark Production at the LHC 39