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Determining Top Couplings

Determining Top Couplings. António Onofre (onofre@lipc.fis.uc.pt). ATLAS Collaboration. 1) Studies with tt events. Outline. Probing the Wtb vertex FCNC top decays. 2) Couplings in single top events. Cross section and V tb Beyond SM at production. 3) Conclusions.

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Determining Top Couplings

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  1. Determining Top Couplings António Onofre(onofre@lipc.fis.uc.pt) ATLAS Collaboration

  2. 1) Studies with tt events Outline • Probing the Wtb vertex • FCNC top decays 2) Couplings in single top events • Cross section and Vtb • Beyond SM at production 3) Conclusions

  3. “t-quarks are produced and decay as free particles” thad = LQCD-1 >> tdecay NO top hadrons What do we know about the top quark? • The top quark completes the three family structure of the SM • It´s massive • Spin=1/2 • Charge=+2/3 • Isospin=+1/2 • tbW • Large G=1.42GeV (mb,MW,as,EW corr.) Short lifetime dm/m ~1% Not directly -4/3 excluded @ 94%C.L.(D0) Not directly ~100% ct<52.5mm @95%C.L.(CDF) The TEVATRON is probing better than ever the top sector… The LHC will allow precision measurements of Top Quark Physics

  4. Production X-section: s ~ 833pb @ 14TeV 1) Studies with tt events W(had) ≥4 jets,DR=0.4 pT>40 GeV Clean Topology: tt back to back t(had) pT>20 GeV 2 b-jets t(lep) pT>20 GeV dominated by gg fusion (90% of total X-section) Semileptonic Topology: Golden Channel Used for several studies

  5. 1) Studies with tt events 100pb-1 3-jet invariant mass Combinatorial W+jets News from Commissioning Analysis Ivo van Vulpen (Top meeting Sep.27th) Wouter Verkerke No b-tag and MW cut • Relax cut on 4th jet (pT>20GeV) (increases signal significance) With only L=100pb-1 (few days of nominal low-lumi LHC operation) (ATLAS note available soon)

  6. 1) Studies with tt events Right-Handed fractionFR Longitudinal fraction F0 Left-Handed fractionFL 0 +1 +1/2 +1/2 W W -1/2 t t +1/2 b b b t -1/2 +1/2 W +1 • Probing the Wtb vertex • W boson has three helicity states: • “Left-handed”, “Longitudinal”, “Right-handed” • Top quark decay is the most significant • source of Longitudinal Ws. V-A SUPPRESSED

  7. 1) Studies with tt events (1/N)dN/dcos(y) Cos(y) • Probing the Wtb vertex Measure W polarization (F0, FL, FR) through: 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

  8. Semileptonic channel 1) Studies with tt events Corr.function + b Dileptonic channel Correct for Detector Effects e,m W W e,m b TOPREX (Assuming SM) ATLFAST • Probing the Wtb vertex (Eur.Phys.J.C44S2 2005 13-33) • Most Important Systematic Errors: • mt,Eb-jet, FSR, Hadronization and btag L=10fb-1 • dFR ~ 0.01 • dF0/F0~ 0.02

  9. 1) Studies with tt events MC@NLO ATLFAST MC@NLO MC@NLO FULL SIM • Probing the Wtb vertex • Full Simulation Studies with “Rome” sample (TopRex,MC@NLO,ALPGEN): ATL-PHYS-PUB-2006-022 • Comparison Fast and Full Simulation: • SM results (with MC@NLO) Statistical Errors Only • (SEMILEPTONIC ONLY) • Good agreement observed

  10. 1) Studies with tt events • Probing the Wtb vertex • Anomalous Couplings in the tbW decay: (PRD67 (2003) 014009, mb≠0) • How to test these new couplings ? • (They affect the F0,FL and FR and the angular distribution used before) • Several methods were used to test the sensitivity @ ATLAS: • Extract limits from previously obtained F0,FL and FR ; • Fit the angular distr. with new observables rR=FR/F0andrL=FL/F0; • Fit with the known dependence with VR, gL and gR(mb≠0); • Use new Asymmetries and study their dependence with VR, gL and gR.

  11. AFB [t=0] A± [t= (22/3-1)] ± 1) Studies with tt events • Use tbW decay in Semileptonic tt Events • New observables rR=FR/F0andrL=FL/F0 rL = 0.423 rR = 0.0005 (mb≠0) SM(LO): (NLO): rL=0.438 rR=0.002 A- AFB A+ SM(LO): • Probing the Wtb vertex Anomalous Couplings in the tbW decay • New Angular Asymmetries: AFB, A+ and A- (NLO): AFB=-0.2269 , A+=0.5429 , A-=-0.8402

  12. 1) Studies with tt events • Preselection: 1 lepton ( pT>25GeV, |h|<2.5 ) • ≥4 jets ( pT>20GeV, |h|<2.5 ) • 2 b-jets and pT>20GeV mW(had) Signal Back. mt(lep) • Statistics (10fb-1): • Signal: e=9% (220k) • Back: 36k events • Probing the Wtb vertex New Discriminant Analysis for Semileptonic Channel: • Discriminant Variables: mW,mt(had),mt(lep),pT-jets • Likelihood Ratio: ATLFAST

  13. 1) Studies with tt events sAFB/AFB ~ 6.6% sA+/A+ ~ 1.9% sA-/A- ~ 0.4% 1s Results: ATLFAST • Probing the Wtb vertex Anomalous Couplings in the tbW decay L=10fb-1

  14. 1) Studies with tt events 1s Limits: (only 1 at a time ≠ 0 ) gL=-0.016 ± 0.067 Two Dimension Regions: (ex. gR versus gL) • Probing the Wtb vertex Anomalous Couplings in the tbW decay A+,A-,rRandrL • Correlations Taken into Account: (2s) lim: gR >3 times better then current ind. limits • Studies with Full simulation under way (CSC):

  15. The top quark almost always decays to a b quark, B(tWb)~1 B(tWs)<0.18%, B(tWd)<0.02% (other decays are really rare) 1) Studies with tt events q, q, • FCNC top decays FCNC decays are highly suppressed in the SM: hep-ph/0409342 APPB35(2004)2695 At LHC Look for:

  16. 1) Studies with tt events ATLFAST • FCNC top decays Seq. and Disc. Type of analysis (p.d.f.) ATL-COM-PHYS-2006-049

  17. 1) Studies with tt events ATLFAST • FCNC top decays Br @ 95%CL (absence of signal) A) 5s Sensitivity: Dominant Systematic Errors: mt and eb-tag < 20% B) In the absence of signal: ATLAS: Br(tqg@95%CL)<0.14% Tevatron (L=2fb-1): level of few %  With 10 fb-1 already two orders of magnitude better than LEP/HERA/TEVATRON

  18. Vtb Vtb Vtb Vtb Wt-channel t-channel s ~ 250 pb s ~70pb W* (s-channel) s ~ 10 pb 2) Couplings in single top events • Cross section and Vtb Three different Processes (never observed yet) Powerfull Probe of Vtb ( dVtb/Vtb~few% @ LHC ) [ PRD 70 (2004) 114012, PL B524 2002 283-288 ] Theoretical uncertainties: • Quark-gluon luminosity inside b-quark (PDF) • Renormalization scale (m) • top mass (Dmtop=4.3GeV  s(W*) changed by 3%) Probe New PhysicsDifferently:ex. FCNC affects more t-channel ex. W´ affects more s-channel [ PRD63 (2001) 014018 ]

  19. Pre-Sel.: 1200(840)events for tb (tb),S/B=0.11( 0.09) HT,mT : 385(275)S/B=0.14(0.12) Syst: Eb-jet, btag, ISR+FSR, Lum. Error, back X-section s-channel: Nj=2(3),Nb=2 (L=30fb-1) ( ds/s ~ 18%) Pre-Sel+ HT,mT: 2710 events (S/B=3.) Syst: (as above) Back: tt and W+jets t-channel: ( ds/s ~ 12%) (L=10fb-1) Nj=2,Nb=1 Stat: e=4.6%(S/B=0.09) Syst: (as above) Wt-channel: (L=30fb-1) ( ds/s ~ 12%) Nj=3,Nb=1 2) Couplings in single top events • Cross section and Vtb 1 lepton, pT>25GeV/c High Missing ET (>25GeV) 2 jets, pT>25GeV, (at least 1 b) Common feature: (ATL-COM-PHYS-2006-057) Separate Channels by (Nj,Nb) in final state: L=30fb-1 Errors Dominated by Systematics

  20. t-channel: Ds/s ~12%(tot) • s-channel: Ds/s ~18%(tot) 2) Couplings in single top events • Cross section and Vtb Illustration of the Physics Potential: Tait,Yuan PRD63 (2001) 014018 L=30fb-1 (ATL-COM-PHYS-2006-057)

  21. Analysis: 1 lep ( pT>20GeV, |h|<2.5 ) 1 b-jet ( pT>30GeV, |h|<2.5 ) pT > 20GeV ( W and t pT, mbl, HT, mt ) 2) Couplings in single top events Preliminary • Beyond SM at production • Effective Lagrangian: kqg = anomalous coupling L = scale of new physics • Systematics: Dssignal (16%) btag (13%) ISR,FSR (6%) PileUp (8%) Tot ~20-25% • Results (10fb-1): In progress…

  22. 3) Conclusions • Several analysis using ATLFAST have already tested the ATLAS potential to probe top couplings. News are encouraging. • New full simulation tests under way (CSC Notes in preparation) • Other couplings are challenging (ttH, ttZ, ttg, ttg …); many studies under way • There is a lot of free room for improvements from the experimental point of view: several orders of magnitude can be gained with respect to present experimental limits on some couplings

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