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Prospect for Top Properties Measurement in Atlas

Prospect for Top Properties Measurement in Atlas. A.Onofre (onofre@lipc.fis.uc.pt). Top Mass Top Charge Top Spin and Spin Correlations Top t  Wb decay Top FCNC decays FCNC in Single-t Production tt Resonances. Outline. Top Properties. Conclusions.

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Prospect for Top Properties Measurement in Atlas

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  1. Prospect for Top Properties Measurement in Atlas A.Onofre (onofre@lipc.fis.uc.pt)

  2. Top Mass • Top Charge • Top Spin and Spin Correlations • Top tWb decay • Top FCNC decays • FCNC in Single-t Production • tt Resonances Outline • Top Properties • Conclusions

  3. Most of the Studies done with tt Events • Top Mass, Top Charge, Top Spin and Spin Correlations, Top tWb decay and tt Resonances W(had) ≥4 jets,DR=0.4 pT>40GeV b t(had) e,m W 2 b-jets pT>20GeV e,m W b 2 b-jets 2 leptons t(lep) pT>20GeV Semileptonic Topology Dileptonic Topology • Top FCNC decays and FCNC in Single-t Production use different analyses

  4. 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

  5. A) Weighting Technique: B) Semileptonic Decay: • Invariant mass criteria: Mtop=175 GeV 1) Semileptonic Channel l and b1from the same top l and b2from different tops 2) Dileptonic Channel • Top Charge I) Determination of b-jet Charge: II) Correct (l±, b) Pairing: ( Cut optimized for mcr=145 GeV )

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

  7. 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:

  8. ATLFAST (reminder) L=10fb-1 (Eur.Phys.J.C44S2 2005 13-33) SM Error (±stat ±syst) A 0.42 0.014 0.023 AD -0.29 0.008 0.010 Semileptonic • Top Spin and Spin Correlations • Semileptonic + Dileptonic • Syst (Eb-jet,mtop,FSR) • 4-6% precision • FULLSIM (CSC) L=1fb-1 Preliminary Selection efficiency 2.9%(2.7% for rome)

  9. 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

  10. 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

  11. 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

  12. Top Decays: 1) the tWb decay • 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 (NLO): F0=0.695 , FL=0.304 , FR=0.001

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

  14. Top Decays: 1) the tWb decay • 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

  15. Top Decays: 1) the tWb decay • Angular Asymmetries: (SM, LO): AFB=-0.2225 , A+=0.5482 , A-=-0.8397 (NLO): AFB=-0.2269 , A+=0.5429 , A-=-0.8402

  16. (SM, LO) • FULLSIM (CSC) L=1fb-1 Likelihood Distributions: e+m e m • Top Decays: 1) the tWb decay (SN-ATLAS-2007-064) • ATLFAST (reminder) L=10fb-1 Three Different Samples: e, m, e+m

  17. Error Versus Luminosity A- A+ L~1fb-1 Flavour at the LHC Era Yellow Report (in prep.) • Top Decays: 1) the tWb decay (N. Castro) • Asymmetries • Anomalous Couplings

  18. tqg tqZ tqg • Top Decays: 2) Rare decays (FCNC) • Top FCNC Decays: Br(tqX) in Several Models: • Studied Decays: FCNC Decays in tt Events

  19. Current Limits: • 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 Decays: 2) Rare decays (FCNC) In the absence of signal: • ATLFAST (reminder) L=10fb-1 (SN-ATLAS-2007-059)

  20. 5s Results: Br(tqg) ~ 10-3 Br(tqZ) ~ 10-2 - 10-3 Br(tqg) ~ 10-2 • Top Decays: 2) Rare decays (FCNC) • 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 (F. Veloso)

  21. “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)

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

  23. L=10fb-1 • Event Selection: 1 lep ( pT>30GeV, |h|<2.5 ) 1 b-jet ( pT>50GeV, |h|<2.5 ) 1 non b-jet ( pT>25GeV, |h|<2.5 ) pT > 25GeV • Likelihood Analysis Cos(ql) PT(W) Very Preliminary e(qg)=1.4% Back:W+j(50%),t-chan(25%) tt(21%) Cos(qn*) mlb • FCNC in Single-t Production • Just To Have an Idea of the Results: • New Contributions Included in MC (TopReX 4.20)

  24. 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

  25. Conclusions • Atlas will allow to perform precision studies • Object Reconstruction (e, m, t, jets and g) Requires Care • Several Methods Available to Extract Physical Observables • Already @ 1fb-1: • 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 • FCNC top Decays (Br[tqX], X=g,Z,g) ~ 10-2 - 10-3

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