Differential Top Cross-section Measurements

Transcription

1 Differential op Cross-section Measurements ALPS207 Obergurgl Michael Fenton on behalf of the ALAS Collaboration University of Glasgow April 8, 207 Michael Fenton Differential op Cross-section Measurements April 8, 207 / 6

2 Outline Motivation 2 Analysis Strategy 3 Uncertainties 4 Results 5 Summary Michael Fenton Differential op Cross-section Measurements April 8, / 6

3 op production & Why do differential measurements of t t processes? [/2] he top quark is unique in the SM due to it s large mass: production dominated m t = by y t v/ QCD 2 decay before hadronisation only quark that can be studied in isolation precision QCD test same order as V.E.V in SM m t 73 GeV, v = 246 GeV direct sensitivity to new physics duction provides direct access mh t m2 Λ v 2 4π 2 Michael Fenton Differential op Cross-section Measurements April 8, / 6

4 Why do differential measurements of t t processes? [2/2] Major background to many interesting searches like t t H or SUSY Not always well described in current MC generators Differential measurements crucial input to MC tuning efforts! OPQ Differential data very useful to theorists: constraining EF operators: opfier gluon PDF at large x: Czakon et al highly sensitive to NNLO effects Czakon et al Michael Fenton Differential op Cross-section Measurements April 8, / 6

5 Outline Motivation 2 Analysis Strategy 3 Uncertainties 4 Results 5 Summary Michael Fenton Differential op Cross-section Measurements April 8, / 6

6 Analysis Strategy Select events Lepton+jets channel Utilize both resolved and boosted topologies 2 Estimate backgrounds 3 Reconstruct tops and t t system 4 Unfold data ICHEP Conference Note Michael Fenton Differential op Cross-section Measurements April 8, / 6

7 Analysis Strategy Select events 2 Estimate backgrounds -driven QCD estimate and W+jets MC based signal and other backgrounds 3 Reconstruct tops and t t system 4 Unfold data Events / GeV /Pred ALAS Preliminary - s = 3 ev, 3.2 fb Single top 3000 Resolved W+jets Z+jets Diboson 2500 V Multijets 2000 Stat.+Syst. Unc miss E [GeV] ICHEP Conference Note Michael Fenton Differential op Cross-section Measurements April 8, / 6

8 Analysis Strategy Select events 2 Estimate backgrounds 3 Reconstruct tops and t t system Measure p, y p t t, m t t, y t t (resolved only) 4 Unfold data ICHEP Conference Note Michael Fenton Differential op Cross-section Measurements April 8, / 6

9 Analysis Strategy Select events 2 Estimate backgrounds 3 Reconstruct tops and t t system 4 Unfold data Iterative Bayesian Unfolding (4 iterations) Unfold to particle level [GeV] (particle level) p ALAS Simulation Preliminary Resolved p [GeV] (detector level) Migration [%] ICHEP Conference Note Michael Fenton Differential op Cross-section Measurements April 8, / 6

10 Resolved Selection p > 25 GeV η < 2.5 b b p > 25 GeV η < 2.5 p > 25 GeV η < 2.5 l W t t W q p > 25 GeV η < 2.5 ν No explicit requirement = lepton 4 R=0.4 jet, 2 b-jet q p > 25 GeV η < 2.5 Events 3 40 ALAS Preliminary - s = 3 ev, 3.2 fb 20 Resolved 0 80 Single top W+jets Z+jets Diboson V Multijets Stat.+Syst. Unc. Events / GeV 3500 ALAS Preliminary - s = 3 ev, 3.2 fb Single top 3000 Resolved W+jets Z+jets Diboson 2500 V Multijets 2000 Stat.+Syst. Unc. Events / GeV 800 ALAS Preliminary - s = 3 ev, 3.2 fb Single top 600 Resolved W+jets Z+jets 400 Diboson V 200 Multijets Stat.+Syst. Unc /Pred Jet multiplicity /Pred miss E [GeV] /Pred p [GeV] Michael Fenton Differential op Cross-section Measurements April 8, / 6

11 Boosted Selection p > 25 GeV η < 2.5 b R >.5 b E miss + m W p > 25 GeV η < 2.5 E miss l > 60 GeV ν > 20 GeV R < 2.0 W t t φ(l, t had ) >.0 = lepton R=.0 jet, top tag, R=0.4 jet, b-jet W q q p > 300 GeV η < 2.0 Events / GeV ALAS Preliminary - s = 3 ev, 3.2 fb Boosted Single top W+jets Z+jets Diboson V Multijets Stat.+Syst. Unc. Events / GeV ALAS Preliminary - s = 3 ev, 3.2 fb Boosted Single top W+jets Z+jets Diboson V Multijets Stat.+Syst. Unc. Events / GeV 3 ALAS Preliminary - s = 3 ev, 3.2 fb Single top 2 Boosted W+jets Z+jets Diboson V Multijets Stat.+Syst. Unc. 2 /Pred Lepton p [GeV] /Pred ljet_m 300 Large-R jet mass [GeV] /Pred hadtop_pt_varbin_logscale p [GeV] Michael Fenton Differential op Cross-section Measurements April 8, / 6

12 Outline Motivation 2 Analysis Strategy 3 Uncertainties 4 Results 5 Summary Michael Fenton Differential op Cross-section Measurements April 8, / 6

13 Uncertainties Fractional Uncertainty [%] 60 ALAS Preliminary Fiducial phase-space 40 - s = 3 ev, 3.2 fb Relative cross-section Resolved Fractional Uncertainty [%] 80 ALAS Preliminary Fiducial phase-space 60 - s = 3 ev, 3.2 fb Relative cross-section Boosted Stat.+Syst. Unc. Stat. Unc. Flavor agging JES/JER Backgrounds IFSR, PDF, MC Stat. Hadronisation Hard Scaering p [GeV] Stat.+Syst. Unc. Large-R jet Backgrounds Hadronisation Stat. Unc. miss Lepton, E, Small-R jet IFSR, PDF, MC Stat. Hard Scaering [GeV] p Jet energy scale and b-tagging uncertainties largest in resolved Large-R jets systematics are dominant in boosted analysis Generator systematics important in both analyses Michael Fenton Differential op Cross-section Measurements April 8, 207 / 6

14 Outline Motivation 2 Analysis Strategy 3 Uncertainties 4 Results 5 Summary Michael Fenton Differential op Cross-section Measurements April 8, 207 / 6

15 op p d σ / d p / GeV /σ 2 3 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo d σ / d p / GeV /σ 2 3 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Boosted PWG+PY6 h damp =2m t radhi radlo p [GeV] 5 2 MC predicts harder spectrum than observed in data p [GeV] Similar slope seen in both regions, as has been observed previously Michael Fenton Differential op Cross-section Measurements April 8, / 6

16 op Rapidity t / Unit y t / d y d σ /σ.2 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo t / Unit y t / d y d σ /σ.6 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb.4 Boosted PWG+PY6 h radhi.2 damp =2m t radlo y Good agreement with all generators Statistics is dominant uncertainty y Michael Fenton Differential op Cross-section Measurements April 8, / 6

17 t t kinematics / GeV / d m d σ /σ ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi 2 PWG+PY6 h radlo damp =m t 3 / GeV / d p d σ /σ 2 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo / Unit y / d y d σ /σ ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo m [GeV] Powheg gives best description of p t t p and mt t [GeV] Expected high dependence of p t t on h damp parameter and radiation seings Powheg+Herwig++ much beer at high y t t y Michael Fenton Differential op Cross-section Measurements April 8, / 6

18 Outline Motivation 2 Analysis Strategy 3 Uncertainties 4 Results 5 Summary Michael Fenton Differential op Cross-section Measurements April 8, / 6

19 Summary Differential cross sections of t t production important in SM and BSM physics, experiment and theory, both as a signal and a background / GeV / d p d σ /σ ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo p [GeV] Modelling of t t process is generally good But top p slope from Run still remains NNLO corrections may account for this Biggest systematic is often the MC related ones Can use these results to improve the MC going forward Michael Fenton Differential op Cross-section Measurements April 8, / 6

20 BACKUP Michael Fenton Differential op Cross-section Measurements April 8, / 6

21 Run NNLO Comparison Michael Fenton Differential op Cross-section Measurements April 8, / 6

22 Resolved 8eV vs 3eV / GeV d σ / d p /σ ALAS - s = 8 ev, 20.3 fb Fiducial phase-space MC@NLO+HW AUE2 MadGraph+PY6 P20C PWG+HW6 AUE2 d σ / d p / GeV /σ ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo [GeV] p p [GeV] Michael Fenton Differential op Cross-section Measurements April 8, / 6

23 Boosted 8eV vs 3eV d σ / d p / GeV /σ 2 3 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Boosted PWG+PY6 h damp =2m t radhi radlo p [GeV] Michael Fenton Differential op Cross-section Measurements April 8, / 6

24 Common Object Definitions Electrons; gradient isolation, tight, η < 2.47 excluding crack, p > 25GeV, d0 BL sig < 5, zbl 0 sin θ < 0.5mm Muons; gradient isolation, medium, η < 2.5, p > 25GeV, d0 BL sig < 3, z0 BL sin θ < 0.5mm Small Jets; anti-k R=0.4, η < 2.5, p > 25GeV, with JV cut and calibration Large Jets; anti-k R=.0, η < 2.0, p > 300GeV, trimmed (R sub = 0.2 & f cut = 0.05), m > 50 GeV, p < 500 GeV b-tags; MV2c20 > ( 77% working point ) op-tags; p dependent large jet mass and τ 32 cuts, with 80% efficiency working point AL-PHYS-PUB At particle level flat m > 0 GeV, τ 32 < 0.75 is used to define fiducial volume Overlap removal: Jets within R < 0.2 of electron; Electrons within R < 0.4 of surviving jets; Jets with R < 0.4 of a muon removed if < 3 tracks; otherwise muon removed Michael Fenton Differential op Cross-section Measurements April 8, / 6

25 he factorisation and hadronisation scales are varied up by a factor of 2.0 while the h damp param- Michael Fenton Differential op Cross-section Measurements April 8, / 6 Samples Physics process Generator Cross-section PDF set for Parton shower une normalisation hard process t t Signal Powheg-Box v2 NNLO+NNLL C Pythia Perugia202 t t PS syst. Powheg-Box v2 NNLO+NNLL CEQ6L Herwig UE-EE-5 t t ME syst. MadGraph5_ NLO C Herwig UE-EE-5 amc@nlo t t rad. syst. Powheg-Box v2 NNLO+NNLL C Pythia radhi/lo s top t-channel Powheg-Box v NLO Cf4 Pythia Perugia202 s top s-channel Powheg-Box v2 NLO C Pythia Perugia202 s top Wt-channel Powheg-Box v2 NLO+NNLL C Pythia Perugia202 t t+w/z/ww MadGraph5_ NLO NNPDF2.3LO Pythia 8.86 A4 amc@nlo W( lν)+ jets Sherpa 2.. NNLO C Sherpa Sherpa Z( l l)+ jets Sherpa 2.. NNLO C Sherpa Sherpa WW, WZ, ZZ Sherpa 2.. NLO C Sherpa Sherpa able : Summary of MC samples, showing the hard process generator, cross-section normalisation precision, PDF choice as well as the parton shower and the corresponding tune used in the analysis. he Pythia and Herwig++ models use the CEQ6L PDFs for their respective parton shower PDFs. he factorisation and hadronisation scales are varied down by a factor of 0.5, simultaneously the h damp parameter is increased to 2m top. Furthermore the radhi tune variation from the P202 tune set is used.

26 Unfolding procedure Using the Iterative Bayesian method in RooUnfold with 4 iterations Master formula: dσ fid dx i L X i f i eff j M ij ( ) facc j Nreco j N j bkg () ( ) i feff i Npart,facc j N reco&part ( ) j Nreco&part N reco Michael Fenton Differential op Cross-section Measurements April 8, / 6

27 Uncertainties for Absolute Spectra Fractional Uncertainty [%] 60 ALAS Preliminary Fiducial phase-space 40 - s = 3 ev, 3.2 fb Absolute cross-section Resolved Fractional Uncertainty [%] 80 ALAS Preliminary Fiducial phase-space 60 - s = 3 ev, 3.2 fb Absolute cross-section Boosted Stat.+Syst. Unc. Stat. Unc. Flavor agging JES/JER Backgrounds IFSR, PDF, MC Stat. Hadronisation Hard Scaering p [GeV] Stat.+Syst. Unc. Large-R jet Backgrounds Hadronisation Stat. Unc. miss Lepton, E, Small-R jet IFSR, PDF, MC Stat. Hard Scaering [GeV] p Michael Fenton Differential op Cross-section Measurements April 8, / 6

28 op p (Absolute) / d p / GeV [pb] d σ 2 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo PWG+PY8 h damp =m t / d p / GeV [pb] d σ 2 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Boosted PWG+PY6 h damp =2m t radhi radlo p [GeV] p [GeV] Michael Fenton Differential op Cross-section Measurements April 8, / 6

29 op Rapidity (Absolute) [pb] t / Unit y t / d y d σ ALAS Preliminary Fiducial phase-space 20 - s = 3 ev, 3.2 fb Resolved 0 PWG+PY6 h damp =2m t radhi radlo [pb] t / Unit y t / d y d σ ALAS Preliminary Fiducial phase-space 5 - s = 3 ev, 3.2 fb Boosted PWG+PY6 h radhi 4 damp =2m t radlo y y Michael Fenton Differential op Cross-section Measurements April 8, / 6

30 t t kinematics (Absolute) / GeV [pb] / d m d σ ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi PWG+PY6 h radlo damp =m t / GeV [pb] / d p d σ 2 ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo [pb] / Unit y / d y d σ ALAS Preliminary Fiducial phase-space - s = 3 ev, 3.2 fb Resolved PWG+PY6 h damp =2m t radhi radlo m [GeV] p [GeV] y Michael Fenton Differential op Cross-section Measurements April 8, / 6