The Top Quark at CDF Production & Decay Properties Tony Liss University of Illinois/CEA Saclay

Production at The production is dominantly qq at the Tevatron (opposite at LHC) State-of-the art theory calculations agree well with the latest measurements Most recent combined s is with only part of the data. Individual measurements use more: ~85% ~15%

Production Cross Section Measurement Event selection High Pt electron or muon (l+j) Second (OS) electron or muon or high-Pt track (ll) Missing ET>20 GeV Lepton+jets: ≥ 3 jets, |h|<2 w/at least 1 b-tag b-tag with secondary vertex, NN or m in jet Dileptons: ≥2 jets, |h|<2 These are the basic data selection of almost all of what follows…

Latest Measurements Dilepton channel: Require 2 jets for S/B Lepton+jets channel: b-tagging for S/B

Cross Section Systematics ID & b-tagging efficiencies Acceptance modeling (PDFs, JES) Backgrounds Non-W QCD Tag rate for non-b jets (“fake tags”) (lepton+jets) W+heavy flavor normalization Integrated luminosity uncertainty

Production Cross-Section Summary Dilepton measurements Lepton+jets measurements Sensitivity to tau decays All jets Combined ( 760pb-1 ) Band is theory for Mtop= 175 GeV/c2

Is it 85:15 qq:gg? cosθ* Production Mechanism Two CDF techniques: NN based on different FS kinematics Multiplicity of low-Pt tracks W+ ≥4 jets cosθ*

Production Mechanism/Low PT Multiplicity Multiplicity distributions taken from W+0 jet (qqbar) and high ET dijet (gluon-rich) data – corrected for gg or qq content. These are “extra” tracks: not part of a jet. Pt<3 GeV/c Fit to the data: Data-based templates: Ntrk: s(ggtt)/s(qq tt)= 0.07±0.14±0.07

Production Mechanism/FS Kinematics Spin correlations! Different for qq vs. gg: . Like Spin Unlike Spin Spin correlations lead to different decay kinematics. Use a NN with top velocity and production angle, 6 decay angles. fgg < 0.33 (0.61) at 68% (95%) C.L.

Production Mechanism Systematics Ntrk: Track multiplicity modeling <Ntrk> vs. Ng Removal of tracks from jets Choice of Jet Et threshold FS Kin: Reconstruction of final state JES, ISR/FSR, PDFs Both: Background modeling

What is the charge of the top quark? We assume this, but we have only recently measured it. Step 1: Pair a b-tagged jet with W+ or W- side l+j : Use the min c2 from the mass fitter (MT175 GeV/c2). ll: Use Mlb2 – reject pairing that gives highest value. Step 2: Measure the jet charge Measured with data to give 61% correct sign of Q.

Top Charge Results Measure the number of events with QW*Qb > or < 0 : Write likelihood fcn., using purity of jetQ assignment, number of signal events and number of QWQb>0 and <0. Minimize –lnL: Pseudo experiments with either SM or XM have distribution of max L like this: f+= frac. Of Q=+2/3 tops XM excluded at 87% C.L.

Top Charge Systematics Purity of the JetQ MC modeling Pairing ISR/FSR, PDF, JES Mtop Background modeling

What is the Lifetime of the Top Quark? Technique #1: Direct measurement Sensitivity to lifetime through d0 distribution of high-Pt lepton n SM: t & W decay happen almost at the primary interaction vertex. Long-lived top  broad impact parameter distribution. Data distribution: MC Templates: -lnL template fit to data: ct < 52.5 μm @ 95% C.L.

What is the Lifetime of the Top Quark? Technique #2: Indirect measure: Sensitivity through top width in Mtop reco. Templates: Fits to data:

Top Lifetime Systematics Direct: Modeling of the background d0 shapes Tagging efficiencies for backgrounds Modeling of QCD background Prompt resolution fcn. Modeling of the signal d0 shape Top decay kinematics ISR/FSR, PDFs, JES Indirect: Reconstructed mass distribution modeling MC modeling Background shapes Acceptance

Is the top decay V-A?  In the SM the V-A vertex gives Where W0,W-,W+ are longitudinal, left, and right-handed W bosons. For a massless b quark, G(W+)=0 . The different W boson polarizations give different angular distributions for the decay leptons: l + W+ b θ* W boson rest frame 

W Helicity Measurement The measurement uses l+j events. Full reconstruction of the event is performed using the top-mass kinematic fitter (Mtop175 GeV/c2) to find the W rest frame. Two types of fits are performed (both with f0+f++f-=1): 1D fits: Fix fraction, f+, of right-handed W bosons=0 Fit the longitudinal and left-handed fractions f0 & f-. 2D fits: Fit f0 & f+ simultaneously.

W Helicity Results 2D fit gives: F0= 0.61 ± 0.20 ± 0.03 F0 fit, F+0: F+ fit, F00.7: 2D fit gives: F0= 0.61 ± 0.20 ± 0.03 F+ = -0.02 ± 0.08 ± 0.03 .

W Helicity Systematics Shapes & Reconstructing the final state Background shapes ISR/FSR, PDFs, JES MC modeling Top mass

Charge Asymmetry in Top Production Charge asymmetry in top production, defined as Incoming parton rest-frame Arises as a result of interference at NLO But it’s a small effect… + A>0 + A<0

Measuring A Assuming CP conservation charge asymmetry  F/B asym: But a is not experimentally accessible. We use as the sensitive variable: The rapidity difference of the leptonically and hadronically decaying top quarks, signed by the charge of the lepton. (Related to cosa at L.O.) Requires full-reconstruction of top 4-vectors, done with modified c2 fitter.

Charge Asymmetry Results Check of background modeling with anti-b-tagged sample Fit to the data in the signal sample: ≥4 jets, ≥1 b-tag Afb=(28 ± 13 ± 5 ) % SM: 4-6% at NLO

Charge Asymmetry Systematics Background shapes MC generator JES, PDF, ISR/FSR Charge mis-ID Top mass

FCNC in top decays? BR ~ 10-14 in SM  Any observation is PBSM! Search in Zee,mm + 4 or more jets ≥ 1 b-tag No b-tags Event selection is optimized for best expected limit see nxt. pg.

FCNC Search Dominant backgrounds are Z+4 jets, WW, WZ. Background suppression is achieved via a mass c2 variable: Note: final state is neutrino-free.

FCNC in Top Decay - Results

MC modeling of b-tagging PDFs, JES, ISR/FSR BR(tZc) vs. BR(tZu) Mtop FCNC Systematics Z-boson helicity MC modeling of b-tagging PDFs, JES, ISR/FSR BR(tZc) vs. BR(tZu) Mtop

Summary Measurements of top production and decay are starting to get interesting… The understanding of the detector, built from >10 years of top physics is paying off. And we’ve only analyzed a fraction of the data Not yet analyzed & more coming Results in this talk We have a tremendous advantage of rate at LHC, but understanding the data will take time…