Experimental aspects of top quark physics Lecture #3 Regina Demina University of Rochester Topical Seminar on Frontier of Particle Physics Beijing, China 08/15/05

Regina Demina, Lecture #32Outline Top charge W-helicity in top decays ttbar resonances Single top Control questions

08/15/05Regina Demina, Lecture #33 Top charge Electric charge is as fundamental quantum number as mass SM leaves little options for the predicted value of top-quark charge (+2/3e) Some beyond SM models suggest that the discovered “top quark” has actually a charge of -4/3e, while true top quark resides at ~270GeV and thus have eluded discovery –Chang,Chang,Ma PhysRevD59,091503(1999) From the experimental point of view this measurement is rather challenging, so we could not resist

08/15/05Regina Demina, Lecture #34 Top charge (the method) Rely on charge conservation –Q t =Q W +Q b –Q(top)= - Q(antitop) –Q (leptonic W)=Q (lepton) –Q (hadronic W)= - Q (leptonic W) Use double-tagged sample –Very good S/B –2 b-jets/event –fewer permutations B-jet to W is assigned using kinematic fitting procedure (HITFIT), which utilizes constraints due to –top mass, W-mass –total energy-momentum conservation (zero p T of ttbar system) Use only the best solution from HITFIT Main question: is how to determine the charge of the b-quark Or rather how to distinguish b- quark from anti-b Jet-charge algorithm

08/15/05Regina Demina, Lecture #35 Jet charge algorithm Total charge of the tracks within jet cone DR is correlated with the charge of the initial quark (b) Track with p T >0.5 GeV/c and |z trk -z PV |<0.1cm, charge q i Jet charge is defined as

08/15/05Regina Demina, Lecture #36 Jet charge algorithm Optimize discriminating power: a b mean, V b - variance Optimal values of a=0.6 and DR=0.5 were found using ttbar MC

08/15/05Regina Demina, Lecture #37 Jet charge calibration on data Use double-tagged muon+jet data – very clean bbar Reconstruct jet charge on probe jet Use correlations with muon’s charge for calibration

08/15/05Regina Demina, Lecture #38 Jet charge Performance on data must be corrected for –B-mixing (does not depend on p T Rel ) –Sequential decays of b-hadrons (depends on p T Rel ) –Contamination of ccbar (depends on p T Rel ) No public result yet…

08/15/05Regina Demina, Lecture #39 W helicity in top decays In SM F - =0.30, F 0 =0.70, F + =0 CDF RunI result: F+<0.18(95%CL)

08/15/05Regina Demina, Lecture #310 W helicity F+ <0.24 (90% CL) with tag F+ <0.24 (90% CL) F0= (stat) _-0.17 (syst) F0>0.25 (95%CL) LepPt: lep+jets + dileptons F0= F0 < 0.88 (95%cl)

08/15/05Regina Demina, Lecture #311 ttbar resonances in l+jets with b-tag Check ttbar invariant mass for possible resonance production DØ RunII Preliminary, 363pb -1 Events are kinematically constrained –m T =175GeV/c 2 –Leptonic and hadronic W masses  NNLO  tt)=6.77±0.42

08/15/05Regina Demina, Lecture #312 ttbar resonances in l+jets with b-tag Limit M(Z’)>680 GeV/c 2 with  =1.2%M Z’ at 95%CL *R. Harris, C. Hill, S. Parke hep-ph/ DØ RunII Preliminary, 363pb -1 * Run I limit 560 GeV/c 2 Run II limit 680 GeV/c 2

08/15/05Regina Demina, Lecture #313 Kinematics in l+jets sample DØ RunII Preliminary, 363pb -1

08/15/05Regina Demina, Lecture #314 Single (weak) top production t-channel pb s-channel pb (NLO, mt=175GeV,sqrt(s)=1.96TeV) high pt lepton high missEt two bjets (+1 light q) s-channel is sensitive to extra particles and dimensions t-channel sensitive to new top couplings (FCNC…) production decay Vtb

08/15/05Regina Demina, Lecture #315 Singletop search s-channel t-channel Just submitted PLB paper with most stringent limits to date Preliminary results for this summer, even better:  s < 5.0pb  t < 4.4pb hep-ex/ The signal is kinematically between W+jets and ttbar

08/15/05Regina Demina, Lecture #316 CMS is looking for new physics in particular the Higgs boson, supersymmetry and … One of the promising reactions: Httbar New Physics, New Particles? We watch for interesting events: ~1 / 400,000 or ~ 100 per second Higgs boson: h 0 H 0 A 0 H ± Example of ttbar collision