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Status of Top Quark Analyses at DØ. Marumi Kado. Measurement of the top production cross section Run II data Improved measurement of the top mass with Run I data. Lawrence Berkeley National Laboratory. On behalf of the DØ Collaboration. _.
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Status of Top Quark Analyses at DØ Marumi Kado Measurement of the top production cross section Run II data Improved measurement of the top mass with Run I data Lawrence Berkeley National Laboratory On behalf of the DØ Collaboration Marumi Kado - LBL
_ First Measurement of the tt Cross Section at s=1.96 TeV Lepton+jets (topological) Lepton+jets (soft muon tag) dileptons • Measurement based six analysis channels: • Cross section at Run II ~30% higher than at Run I • Predictions ranging from 6.7 to 7.5 pb • Data sample from mid-August until mid-January • with luminosities from 30 to 50 pb-1 • Triggers em and mm e+jets, m+jets e+jets/m, m+jets/m Br = 2.5 and 1.2% Br = 14.7% Br = 14.7% Efficient Not very pure Pure Not very efficient Pure and efficient Low branching Use calorimeter and muon system at all levels of the trigger (L1, L2 and L3) Marumi Kado - LBL
Improved legacy 0.5 cone algorithm with JES corrections (see talk by B. Kehoe) Object Identification Reconstruction of Jets and Jet energy scale: Reconstruction of electrons (only central): - Select EM particles (simple cone, shower shape, EM fraction) - Match with track (f, h, and E/p) Reconstruction of muons: Missing Transverse Energy: DØ Run II Preliminary DØ Run II Preliminary 2 EM No track required 2 EM 1 track required • Tracks in Muon system • Tracks in Central Tracker • Minimum Ionisation in the calorimeter ID Used for redundancy only to measure efficiencies From calorimeter with JES corrections (and muon correction) Marumi Kado - LBL
Dimuon Channel 42.6 pb-1 2 isolated muons, MET(Mmm), HT and more than 2 Jets Luminosity Selection criteria: Backgrounds: Instrumental Physical backgrounds Zmm DYmm QCD Heavy Flavor Ztt WWmm from MC Estimated from data DØ Run II Preliminary Zmm (MC) WW (MC) Data Signal (MC) * For s = 7pb Marumi Kado - LBL
em Channel 33.0 pb-1 1 electron, 1 isolated muons, MET, METCAL , HT (e) and more than 2 Jets Luminosity Selection criteria: Backgrounds: Physical backgrounds Instrumental QCD and W+jets Ztt WWmm from MC Estimated from data (Fakes) DØ Run II Preliminary Z tt Fakes Njets * For s = 7pb Njets HT(e) (GeV) Marumi Kado - LBL
em Candidate Event m - Muon Track in the Calorimeter (MTC) Jet 1 e+ Jet 2 Marumi Kado - LBL
Lepton-plus-Jets Analyses 49.5 pb-1 40.0 pb-1 - Preselect a sample enriched in W events - Evaluate QCD multi-jet (as a function of Njets) - Estimate W+4jets assuming Berends scaling - Apply topological selection • Luminosities: e+jets and m+jets • Backgrounds: QCD multi-jets and W multi-jets • Method: • Preselection: • QCD background evaluation (matrix method): 1 EM object or muon, MET, soft muon veto Separate W+tt and QCD with loose (L) and tight (T) lepton characteristics. Efficiencies (LT) for signal eW+tt and background eQCD are measured independently: e+jets: Track match to the EM object m+jets: Muon isolation “Matrix method” Marumi Kado - LBL
e W+tt vs Njets DØ Run II Preliminary … are obtained from benchmark signal samplesn of Z ee or mm Non trivial dependence of eW+tt w.r.t. Njets (especially in the m+jets case)… • Signal probabilities… • Background nature • Background Probabilities… Correction taken from MC m+jets e+jets QCD Background due to leading p0 or compton QCD events and Fake track or g conversion QCD Background essentially due to Heavy Flavor semi-leptonic decays … are obtained from benchmark QCD samples with low MET Dependence of the eQCD w.r.t. MET and Njet … DØ Run II Preliminary DØ Run II Preliminary DØ Run II Preliminary e+jets e+jets e+jets Marumi Kado - LBL
DØ Run II Preliminary DØ Run II Preliminary W W+tt • Estimation of the QCD background: QCD W+tt W+tt DØ Run II Preliminary DØ Run II Preliminary W W+tt DØ Run II Preliminary DØ Run II Preliminary QCD W+tt W+tt Marumi Kado - LBL
DØ Run II Preliminary DØ Run II Preliminary • Berends scaling: Estimation of the W background for Njets 4: Apply topological cuts: a = 0.1640.02 a = 0.1450.02 38 (m+jets) 24.2 11.9 11.9 12.5 22 (e+jets) Apalanarity and HT * For s = 7pb Marumi Kado - LBL
m+jets Candidate Event m - Jet 5 Jet 1 MTC Jet 4 Jet 2 Jet 3 Marumi Kado - LBL
Soft Muon Tag Analyses (Loose/Tight sample) - Use the same preselection as l+jets - Require at least 3 jets - Apply mild topological cuts 75/23 (m+jets) 459/27 (e+jets) DØ Run II Preliminary DØ Run II Preliminary Selection before Soft Muon Tag When SMT is applied: e+jets m+jets 1/0 (m+jets) 0.20.2 (m) 9/2 (e+jets) 0.20.1 (e) QCD background. from matrix method W bkg. from Tag rate functions: DØ Run II Preliminary 0.40.1 (m) 0.00.1 (e) * For s = 7pb Marumi Kado - LBL
Cross Section Measurement • Combining the observation of all channels an excess of 3s is observed, compatible with a signal expectation at the 35% CL • The combined cross section is: Marumi Kado - LBL
Status of the Top Mass Measurement in the Lepton+Jets Channels at Run I Likelihood method using most available information • Uses DØ Run I statistics (125 pb-1) & selection 91 events • Signal and background probability (simple realistic model): Additional cuts for this analysis: 4 Jets exclusively: 71 events Pb.: 22 events (pure sample) x reconstructed objects in the event (leptons, jets) a Parameter to estimate Folding object resolutions Transfer Functions Matrix element Acceptance PDF’s Background (VECBOS) Signal (No ISR or FSR) Pb Independent of a Marumi Kado - LBL
Likelihood definition: • Estimate the signal and background contributions and mtop: Signal c1=12 mtop W Bkg c2=10 (5.6 GeV from PRD 58 052001,1998) Large improvement on the statistical uncertainty (~2.4 stats) mW Expect a substantial improvement in the JES systematic Marumi Kado - LBL
Conclusions and Outlook • D0 measurement of the tt cross section at s=1.96 TeV carried out at Tevatron Run II: • Short term perspective:Dielectron channel and Lifetime tagging analyses • Medium term perspective:Complete analyses of mass and cross sections • Status of the new top Run I mass measurement: • Short term perspective:Improve JES systematic uncertainty,W helicity (Run I) • Medium term perspective:Top Properties (W helicity,spin correlations) and single top with Run II data • Long term perspective:top mass 2fb-1 2.7 GeV • 15fb-1 1.3GeV Marumi Kado - LBL
m+jets Candidate Event SV m - Jet 2 IP Jet 2 MTC Jet 1 Double tag event IP Jet 1 SV Marumi Kado - LBL