The Top Quark Mass in the Muon+Jets Final State at s = 13 TeV in 2015 Data

Transcription

1 The Top Quark Mass in the Muon+Jets Final State at s = 13 TeV in 2015 Data CMS PAS TOP th Course of the ISSP, Erice Christoph Garbers, Nataliia Kovalchuk,Johannes Lange, Peter Schleper, Markus Seidel, Hartmut Stadie, Fred Stober June 20, 2017 June 20, 2017 Christoph Garbers 1

2 The CMS experiment slides from Highlights from CMS by I.Melzer-Pellmann LHC is a top factory CMS-TOP6-023 ~2 million ttbar pairs per week in Run2 (>2 fb/week) Hi S M mc ro ts f igh ghl ann ellm r-p lze Me ndra ssa -Ali urg b bell Isa Y Ham S DE New precise measurement of CMS at 5 TeV: Reference for future Heavy Ion studies with tops at same s/nucleon Improving the knowledge of gluon PDFs at high x Isabell Melzer-Pellmann The CMS Experiment ISSP 2017, Erice 36 Top mass measurement TOP6-022 Dominant measurement at 8 TeV, but precision improved by 13 TeV data Isabell Melzer-Pellmann June 20, 2017 Christoph Garbers The CMS Experiment ISSP 2017, Erice 37 2

3 The Top Quark Standard Model particle heaviest measured particle τ decay (top) s < τ hadronisation spin correlation conserved decays in 68.5 % hadronic, else in b quark + lepton + neutrino precision measurement for global fits 30 % of t t decays into e,µ+jets optimal channel branching ratio easy to trigger only one ν June 20, 2017 Christoph Garbers 3

4 Analysis Steps selection kinematic fit construct estimator for top mass using maximum likelihood parameterize templates in mt and jet energy scale factor JSF calibrate on MC systematic uncertainties evaluate on data Run I Result: 2015 CMS-TOP4-022 m t = ± 0.16 ± 0.48 GeV awaiting improvement due to higher crosssection, higher luminosity, NLO MC,... June 20, 2017 Christoph Garbers 4

5 MC and Data data: 2.2 fb 1 Run signal MC: powheg + pythia8 (tuned) default top quark mass GeV additional top-quark mass GeV, GeV,175.5 GeV, and GeV used for template fit background MC: W+Jets Single (anti)top Z+Jets Diboson QCD multijet plus additional samples for systematic uncertainties June 20, 2017 Christoph Garbers 5

6 Selection 1 muon + 4 jets High-Level-Trigger: isolated muon with p T > 20 GeV muon selection: p T > 25 GeV and η < 2.1 relative isolation veto on events with additional leptons jet selection: anti-k t, R = 0.4 at least 4 jets with each pt > 30 GeV, η < 2.4 R(muon,jet) > 0.3 b-tagging: CSVv2M 1% mis-tag, 70% efficiency at least two b-tags in selected jets event yield before b-tagging with b-tagging data estimated signal frac. 61.4% 90.9% June 20, 2017 Christoph Garbers 6

7 Kinematic Fit fitting the kinematics to a t t hypothesis four leading jets, containing two b-tagged jets mt fit hadr = mt fit lept, mw fit = 80.4 GeV, p T balance try different jet-parton assignments {bhad, W had } t hadr (t t correct) wrong jets, e.g. {blept, W had } t hadr (t t wrong) matching to other jets / matching did not work (t t unmatched) use goodness-of-fit P gof = exp( 1 2 χ2 ) private work fraction Permutations tt correct tt wrong tt unmatched Data Single t W+jets Z+jets QCD multijet Diboson P gof baseline final P gof > 0.2 t t correct 14.8 % 43.8 % t t wrong 8.9 % 22.3 % t t unmatched 76.4 % 33.9 % June 20, 2017 Christoph Garbers 7

8 Top-Quark / W-Boson Mass permutations of event candidates estimated f sig = 95.9% Permutations / 5 GeV Data/MC CMS Preliminary 2400 tt correct 2200 tt wrong 2000 tt unmatched 1800 Data fb (13 TeV) Single t W+jets Z+jets QCD multijet fit m t [GeV] CMS PAS TOP6-022 Permutations / 5 GeV Data/MC CMS Preliminary 5000 tt correct tt wrong tt unmatched 4000 Data fb (13 TeV) Single t W+jets Z+jets QCD multijet reco m W [GeV] CMS PAS TOP6-022 June 20, 2017 Christoph Garbers 8

9 Ideogram Method Likelihood fit of the (mt fit, mw reco) data to 2D (m t JSF) templates derived from simulation Illustration by M. Seidel June 20, 2017 Christoph Garbers 9

10 Approaches 2D approach: in-situ m t and JSF measurement 1D approach: JSF fixed to unity (with jet energy correction from γ/z + jet) hybrid/final approach: combination of 2D and 1D with the same weight June 20, 2017 Christoph Garbers 10

11 Result: 2D and 1D approach with σ stat : private work JSF log(l) = log(l) = 6.17 log(l) = [GeV] m t m 1D t = ± 0.27 (stat) ± 1.02 (syst) GeV mt 2D = ± 0.44 (stat+jsf) ± 1.10 (syst) GeV JSF = ± (stat) ± (syst) June 20, 2017 Christoph Garbers 11

12 Result hybrid approach JSF log(l) = CMS Preliminary 2.2 fb -2-2 (13 TeV) log(l) = 4 log(l) = [GeV] m t CMS PAS TOP6-022 Pseudo-experiments / 2 MeV 1400 This measurement CMS Preliminary 2.2 fb (13 TeV) σ stat+jsf (m ) [GeV] t m hyb t mt pole within O(1 GeV) (arxiv: Moch et al. 2014), or few 100 MeV (arxiv: Butenschoen et al. 2016) = ± 0.38 (stat+jsf) ± 0.70 (syst) GeV JSF hyb = ± (stat) ± (syst) CMS PAS TOP6-022 June 20, 2017 Christoph Garbers 12

13 Biggest Systematic Uncertainties δm hyb t [GeV] δjsf hyb JEC: Uncorrelated non-pileup 0.26 JEC: Flavor bottom 0.32 <0.001 PS Q 2 scale Underlying event Color reconnection modeling Underlying event and color reconnection modeling uncertainties still preliminary, currently reestimated for 2016 data June 20, 2017 Christoph Garbers 13

14 Summary CDF, lepton+jets GeV PRL 109 (2012) , 8.7 fb lepton+jets channel D0 matrix element, lepton+jets PRD 91 (2015) , 9.7 fb ATLAS 2011, lepton+jets EPJC 75 (2015) 330, 4.6 fb CMS 2011, lepton+jets JHEP 12 (2012) 105, 5.0 fb CMS 2012, lepton+jets PRD 93 (2016) , 19.7 fb CMS 2015 prel., lepton+jets TOP6-22 (2017), 2.2 fb CMS Run 1 combination PRD 93 (2016) World combination ATLAS, CDF, CMS, D0 arxiv: (2014) GeV m t [GeV] GeV GeV GeV GeV GeV GeV CMS PAS TOP6-022 first Run2 top quark mass result confirms s = 8 TeV CMS analyses good reference for Run 2 analyses to come June 20, 2017 Christoph Garbers 14

15 Thank you for your attention! private work June 20, 2017 Christoph Garbers 15