Fabrice Hubaut (CPPM) Top physics at LHC with tt events 1 Fabrice Hubaut CPPM/IN2P3Univ. de la Mditerrane (Marseille, FRANCE) On Behalf of the ATLAS and CMS Collaborations Rencontres de Moriond 2006, QCD session, March 18-25 Fabrice Hubaut (CPPM) Top physics at LHC with tt events 2 5 orders of magnitude Motivations for top quark physics Special role in the EW sector and in QCD Heaviest elementary particle known Yukawa coupling close to 1.0 Top and W masses constrain the Higgs mass Short lifetime ( 40 GeV 3 jets with highest p T NO b-TAG !! Full simulation Fabrice Hubaut (CPPM) Top physics at LHC with tt events 6 When performance improve, such as b-tagging ( b 60%, r uds 100, r c 10) non tt background (W+jets, bb,...) negligible sel ~ 3%, 80k evts/10 fb -1 S/B~12 (tt +X) Selection Precision studies (1-10 fb -1 ) 1 isolated lepton p T >20 GeV p T miss >20 GeV 4 jets (cone R=0.4) p T >40 GeV 2 b-tagged jets High statistics with a few fb -1, measurements limited by systematics Dileptonic channel also interesting 6 equations (p T =0, M lv = M W, M lvb = M t ) with 6 unknowns (p ) Full reconstruction Use W jj to calibrate light jet energy b with max. p T (jjb) for hadronic top p T miss for p T and M W constraint for p Z Other b for leptonic top: ~12 GeV Purity of reconstructed tt ~ 70% with rec ~ 30% combinatorial ~11 GeV L=10 fb -1 Apply this selection-recons. for -section, mass, polarization studies, Fabrice Hubaut (CPPM) Top physics at LHC with tt events 7 Top mass (1) Measurement method (semileptonic) Kinematic fit event by event using t and t sides M jj = M lv = M W and M jjb = M lvb = M t fit (M t fit, 2 ) by slices of 2 top mass estimator: m t =M t fit ( 2 =0) This selects well reconstructed b-jets (low effect due to final state radiation or leptonic b-decay) Results (semileptonic) m t linear with generated top mass Statistical error with 10 fb -1 : ~ 0.1 GeV hep-ex/ Fabrice Hubaut (CPPM) Top physics at LHC with tt events 8 Top mass (2) Source Error 10 fb -1 b-jet scale (1%)0.7 Final State Radiation0.5 Light jet scale (1%)0.2 b-quark fragmentation0.1 Initial State Radiation0.1 Combinatorial bkg0.1 TOTAL: Stat Syst 0.9 Other methods (invariant 3 jet jjb mass, large p T events,...) give higher systematics but will allow reliable cross-checks A ~1 GeV accuracy on M t seems achievable with 10 fb -1 at ATLAS/CMS Systematic errors on m t (GeV) in semileptonic channel Systematics from b-jet scale (full simulation): b-jet miscalibration factor Rec. Top mass (GeV) slope=0.7 GeV / % hep-ex/ Fabrice Hubaut (CPPM) Top physics at LHC with tt events 9 Top mass (3) Dileptonic (10 fb -1 ) Need to reconstruct full tt event to assess the 2 momenta 6 equations (p T =0, M lv = M W, M lvb = M t ) Assume m t and compute solution probability event by event using MC kinematic distributions Choose m t with highest mean probability on all events Systematic uncertainty: ~2 GeV (PDF + b-frag.) Final states with J/ (100 fb -1 ) Input top mass=175 GeV mean probability Mass hypthesis (GeV) Correlation between M lJ/ and m t Low statistics: ~1000 evts/100 fb -1 No systematics on b-jet scale ! Systematic uncertainty: ~1 GeV (b-frag.) Charge identification hep-ex/ hep-ph/ M lJ/ Fabrice Hubaut (CPPM) Top physics at LHC with tt events 10 Angle between: lepton in W rest frame and W in top rest frame Standard Model (M top =175 GeV) W polarization in top decay (1) Test the top decay (in fully reconstructed tt) with W polarization... Longitudinal W + (F 0 ) Left-handed W + (F L ) Right-handed W + (F R ) NLO ...measured through angular distribution of charged lepton in W rest frame Sensitive to EWSBTest of V-A structure 1/21 cos 1/N dN/dcos W+W+ b l+l+ t spin Fabrice Hubaut (CPPM) Top physics at LHC with tt events 11 W polarization in top decay (2) SM Error (stat syst) F0F FLFL FRFR Systematics dominated by b-jet scale, top mass and final state radiation (FSR) With 10 fb -1, can measure F 0 with a ~2% accuracy and F R with a precision ~1% Tevatron expectations (2 fb -1 ): F 0 stat /F 0 ~12% and F R stat /F R ~3% Combined results of semilep+dilep 2 parameter fit with F 0 +F L +F R =1 cos 1/N dN/dcos (M t =175 GeV) hep-ex/ fb -1 Semilep. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 12 W polarization in top decay (3) ) From W polarization, deduce sensitivity to tWb anomalous couplings model independent approach, i.e. effective Lagrangian and 4 couplings (in SM LO 1 2 limit (stat syst) on = 0.04 3 times better than indirect limits (B-factories, LEP) Less sensitive to and already severely constrained by B-factories F0F0 Anomalous coupling Fabrice Hubaut (CPPM) Top physics at LHC with tt events 13 tt spin correlation Test the top production t and t are not polarized in tt pairs, but their spins are correlated by measuring angular distribution of daughter particles in top rest frame A D =-0.29 M tt 20 GeV High statistics with a few fb -1, measurements limited by systematics Complementary to semileptonic channel Full reconstruction Assume top mass is known 6 equations (p T =0, M lv = M W, M lvb = M t ) with 6 unknowns (p ) If >= 1 solution (98%), solutions probability based on MC kinematic distributions Purity of reconstructed tt ~ 65% with rec ~ 80% Fabrice Hubaut (CPPM) Top physics at LHC with tt events 24 F 0 =0.699 F L =0.299 F R =0.002 F 0 =0.69 0.03 F L =0.30 0.02 F R =0.01 0.02 F 0 =0.70 0.03 F L =0.29 0.02 F R =0.01 0.02 W polarization: full simulation Good agreement Full sim / Fast sim on W and top kinematics compute a unique function (from Fast sim.) to correct for cuts and rec. effects apply it on Fast and Full sim. samples Very good agreement Full sim / Fast sim 1/N dN/dcos TopReX Fast sim.TopReX Full Full sim. 10 fb fb fb -1 cos Preliminary Fabrice Hubaut (CPPM) Top physics at LHC with tt events 25 tt spin correlation Measurement of tt spin correlation (NP B690 (2004) 81) angle btwn spin analyzers direction in the t(t) rest frame angle between daughter and top spin axis s Wbl +,d,sv,u,clej * (NLO) In top rest frame, polarisation (S) is measured with angular distributions of daughter: Degree to which its direction is correlated with top spin (spin analyzing power) * lej = least energetic jet in top rest frame Fabrice Hubaut (CPPM) Top physics at LHC with tt events 26 Top charge Q top =-4/3 (t W - b instead of t W + b) ? Method 1: Measurement of radiative top production and/or decay (pp tt ) is proportional to Q top 2 After selection+reconstruction (10 fb -1 ) (Q=-4/3) > (Q=2/3) Method 2: Measurement of daughter particle charge Associate b-lepton pair from the same top Compute the charge of b on a statistical basis: Separate the 2 Q top hypothesis needs less data than Method 1 (~1 fb -1 ) Tevatron (Method 2) : D0 (360 pb -1 ) excludes 94% CL (10/2005, not yet published) Q=2/3Q=-4/3 pp tt Background 70 Fabrice Hubaut (CPPM) Top physics at LHC with tt events 27 Yukawa coupling g t 2 Br(H bb, WW) Need separate measurements of Higgs decay branching ratios Statistical uncertainty on g t ~20% for M H 5.8 +catcher /E ~ 100%/ E 0.05 Fabrice Hubaut (CPPM) Top physics at LHC with tt events 29 LHC planning = = L= L= = L=