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Prospects of Top Quark Properties @ ATLAS

Prospects of Top Quark Properties @ ATLAS. A.Onofre (onofre@lipc.fis.uc.pt). Top Mass Top Charge Top Spin and Spin Correlations Top t  Wb decay tt Resonances Top FCNC decays Single Top FCNC Production. Outline. Top Properties (T7 CSC Note+ST). Conclusions. Studies done with tt Events.

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Prospects of Top Quark Properties @ ATLAS

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  1. Prospects of Top QuarkProperties @ ATLAS A.Onofre (onofre@lipc.fis.uc.pt)

  2. Top Mass • Top Charge • Top Spin and Spin Correlations • Top tWb decay • tt Resonances • Top FCNC decays • Single Top FCNC Production Outline • Top Properties (T7 CSC Note+ST) • Conclusions

  3. Studies done with tt Events • Top Mass, Top Charge, Top Spin and Spin Correlations, Top tWb decay and tt Resonances Dileptonic Topology Semileptonic Topology b W(had) e,m W ≥4 jets,DR=0.4 pT>40GeV 2 b-jets t(had) e,m W pT>20GeV b 2 leptons 2 b-jets t(lep) pT>20GeV • Top FCNC decays (tqX, X=g,Z,g) and Single-top

  4. Top Mass Many analyses performed in the past or being developed recently: • Cut based • Kinematic fit • Template method, • Matrix Element method, • Analyses with soft muon b-tagging, • high pT top, • Analysis in leptonic final states with J/y • Correlation between lepton pT and mt

  5. ATLFAST (reminder) L=10fb-1 (SN-ATLAS-2004-040) • FULLSIM (CSC) L=1fb-1 Tot(sys) = 1.3 GeV Tot(stat) = 0.1 GeV • Top Mass SACLAY Analysis: choice of light jet pair and in-situ re-calibration using a 2fit to the PDG W mass • Systematic uncertainties: • Jet energy scale • 1% on light jet  0.2 GeV/c2 on mt • 1% on b-jet  0.7GeV/c2 on mt • ongoing ISR/FSR , b-quark fragm.

  6. SM (Qtop=+2/3): • Exotics (Qtop= -4/3): b(-1/3) b(-1/3) t(-4/3) l-(-1) t(2/3) l+(+1) W- W+ nl Exotic nl SM • For top quark determination • I) Determination of b-jet charge • II) Correct (lepton, b-jet) pairing Critical moment (Atlfast, PHYS-2003-35) • Top Charge

  7. A) Weighting Technique: B) Semileptonic Decay: • Invariant mass criteria: Mtop=175 GeV m( l , b1) m( l ,b2) b2 l b1 • Top Charge I) Determination of b-jet Charge: II) Correct (l±, b) Pairing:

  8. L~0.5fb-1 l- l+ (B.Zilka,S.Tokar) • Top Charge A) Weighting Technique: -0.0842  0.0044 b 0.0868  0.0043 b ( Eff.=4.1% Purity: 89.3% ) B) Semileptonic Decay: (A. Tonoyan, E.Khramov)

  9. tt Spin Correlation Parameters: Although t and t not polarised in tt pairs, their spins are correlated Mtt<550 GeV A=0.42 AD =-0.29 Mtt<550 GeV • Top Spin and Spin Correlations (Zhu Chengguang) • Double Angular Distributions:

  10. ATLFAST (reminder) L=10fb-1 (Eur.Phys.J.C44S2 2005 13-33) • FULLSIM (CSC) L=1fb-1 Semileptonic • Top Spin and Spin Correlations • Semileptonic + Dileptonic • Syst (Eb-jet,mtop,FSR) • 4-6% precision Preliminary Selection efficiency 2.9%(2.7% for Rome)

  11. Isolated single electron trigger Single muon trigger • Top Spin and Spin Correlations • Trigger Studies: • Results (Preliminary): Level of Precision of A, AD ~40% L=1fb-1

  12. Level of Precision of Alj~40% (Low MC) Alj Alj~30% (High MC) L=1fb-1 • Top Spin and Spin Correlations • Spin Asymmetries can also be used: (spin analysing power al+=1.0, aj=-0.51) • Error versus Luminosity: SM (LO): Alj=-0.0396

  13. V-A SUPPRESSED • Top Decays: 1) the tWb decay • By measuring the fraction of longitudinal W´s in top quark decays we are: • Testing a Standard Model prediction: F0=0.7 FL=0.3 • Probing the structure of the Wtb vertex

  14. How to measure the W Helicity Fractions? Using lepton angular distribution (with respect to top direction) in W cm system: SM(LO): F0=0.703 , FL=0.297 , FR=3.6x10-4 cos(ql*) (NLO): F0=0.695 , FL=0.304 , FR=0.001 • Top tWb decay (SM) • Angular Distribution @ W c.m.

  15. ATLFAST (reminder) L=10fb-1 (Eur.Phys.J.C44S2 2005 13-33) • FULLSIM (CSC) L=1fb-1 (CDF) First Simultaneous fit: • Results (Preliminary) • dF0/F0~ 6%;dFR ~ 0.03 (Zhu Chengguang) • Top tWb decay (SM) • Syst ( Eb-jet,mtop,FSR ) • dF0/F0~ 2%;dFR ~ 0.01

  16. Top tWb decay (BSM) • Anomalous Couplings @ the Wtb Vertex VR,gL,gR Change F0,FL,FR Eur.Phys.J. C50 (2007) 519-533 • How to Probe Anomalous Couplings? • Extract Limits from F0,FL and FR (and ratios) • Fit angular distr. with VR, gL and gR (mb≠0) • Use Angular Asymmetries

  17. Top tWb decay (BSM) • Angular Asymmetries: (SM, LO): AFB=-0.2225 , A+=0.5482 , A-=-0.8397 (NLO): AFB=-0.2269 , A+=0.5429 , A-=-0.8402

  18. A- A+ L=10fb-1 L~1fb-1 • Top tWb decay (BSM) (N. Castro) • Asymmetries Error Versus Luminosity • Anomalous Couplings

  19. tt Resonances Resolution Current Limits: Semileptonic (E.Cogneras,D.Pallin) • Discovery Potential of a Narrow tt Resonance Discovery Potential: • Window in mass spec. • Compute the number of resonance events required for discovery: nX = 5s deviation on nSM

  20. tqg tqZ tqg • Expected 95% CL Limits: Br(tqg) <1.3x10-3 • 5s Results: Br(tqg) >9.4x10-5 Br(tqZ) >4.4x10-4 Br(tqg) >4.3x10-3 • Top FCNC decays • FCNC in tt Events • ATLFAST (reminder) L=10fb-1 (SN-ATLAS-2007-059)

  21. 5s Results: Br(tqg) ~ 10-3 Br(tqZ) ~ 10-2 - 10-3 Br(tqg) ~ 10-2 • Top FCNC decays (F. Veloso) • FULLSIM L=1fb-1 • Results Crucially Depend on Tagging Efficiencies (e, m, b, jets and g) • Likelihood Method works (need to have well defined shapes) • Gluon Channel more difficult

  22. FULLSIM L=1fb-1 • 5s Results: Br(tqg) ~ 10-3 • Top FCNC decays (w/o b-tag) (F. Veloso) • Minimize c2 by looping on jets (b,q=j1,j2) and scan on pnZ to reconstruct kinematics

  23. “Direct” • ATLFAST (reminder) L=10fb-1 kqg=anomalous coupling L =scale of new physics • Results: • Event Selection: 1 lep ( pT>20GeV, |h|<2.5 ) 1 b-jet ( pT>40GeV, |h|<2.5 ) pT > 20GeV ( W and t pT, mbl, mT(W), HT, mt ) • Systematics: • Dssignal (8%), btag (6%), ISR (3.5%), • PileUp (4%) • Total ~ 12% (hep-ex/0702005) Estimate: e(ug)=1.08%, e(cg)=1.81% Back: W+j(80%), single-t(9%) Br(tug)~O(10-3) Br(tcg)~O(10-2) • FCNC in Single-t Production (T.L. Cheng, P.Teixeira Dias)

  24. The X-section: The X-section: • FCNC in Single-t Production (R.Santos, P.Ferreira) • The Direct Production is not the full Story • The ggqt Processes: Phys.Rev. D74 (2006) 014006 • The gqgt Processes:

  25. 95% CL Limits: • 5s Discovery: Br(tqg) ~O(10-4) Br(tqg) ~ O(10-3-10-4) 5s Discovery 95% CL Limit: • FCNC in Single-t Production • Just To Have an Idea of the Results for : L=10fb-1 • 5s and 95% CL Limits obtained • New Contributions Give Same Order of Magnitude Results as Direct Production Mechanism • 1 Order of magnitude better than ttbar for the gluon channel

  26. Conclusions • Atlas will perform precision studies in the top sector • Several Methods Available to Extract Physical Observables • Already @ 1fb-1: • Top Mass ~ O(few GeV/c2) • Top Charge (2/3 versus -4/3) > 5s significance • Spin Correlation Parameters (A,AD) ~ 40% error • Spin Asymmetries ~ 40% error • W helicity fractions (F0, FL, FR )~ 6%, ~10% and ~0.03 error • Angular Asymmetries (A+,A-) ~ 3% and 1% error • Anomalous Wtb Couplings (VR, gL, gR ) ~ 0.1, 0.05 and 0.03 error • tt Resonances (1TeV) ~ (s×Br)≥ 8 pb • FCNC top Decays (Br[tqX], X=g,Z,g) ~ 10-2 - 10-3

  27. Next Top Workshop (every 2 years) 2008

  28. Spare Slides

  29. Top Mass @ TEVATRON

  30. stt @ TEVATRON

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