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Testing V-A

Ben Kilminster University of Rochester May 22, 2003 CIPANP. Testing V-A. in the Top Quark at CDF. Using top quark to study V-A A Method for searching for V+A Results from Run I and Run II expectations. Top Yukawa Coupling to the Higgs field ~ 1.

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Testing V-A

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  1. Ben Kilminster University of Rochester May 22, 2003 CIPANP Testing V-A in the Top Quark at CDF • Using top quark to study V-A • A Method for searching for V+A • Results from Run I andRun II expectations

  2. Top Yukawa Coupling to the Higgs field ~ 1 • In terms of the electroweak force, top is the only natural quark • Special Role in electroweak symmetry breaking ?

  3. Chicago  Booster CDF DØ Tevatron p source Main Injector (new) Fermilab Tevatron Upgrade Wrigley Field • New Main Injector: • Improve p-bar production • Recycler ring: • Reuse p-bars

  4. The CDF detector for Run II • CDF II: • 8 layers of silicon • New drift chamber (COT) • Extended lepton-ID:|h|>1

  5. ttbar production at the Tevatron • Mttbar= 350 GeV, ETev = 1960 GeV • Momentum fraction needed: x ~ 0.2 500 ttbars produced Run I 90% 10%

  6. b Top decays exclusively via weak interaction (100%) t-> W + b (Vtb~1) l- n l+ b n b q q b n l- q b q q q b Top Decay channels Top lifetime 1/(Vtb2*M3) ~ 10-24 Time for QCD confinement ~ λQCD~10-23s • Top most likely decays before hadronizing • All-Hadronic W’s decay hadronically 2 b jets 4 other jets • Lepton + Jets One hadronic W decay 1 High Pt lepton (e or μ) 2 b jets 2 other jets Missing Et • Dilepton W’s decay leptonically 2 High Pt leptons (e,μ) 2 b jets Missing Et 30% 45% 5%

  7. Physics of W helicity from top decay This analysis studies this 30%

  8. Using cosΨ*l M2lb = ½ (M2T – M2W)(1 + cosΨ*l) V-A : 30% left-handed 70% longitudinal V+A : 30% right-handed 70% longitudinal

  9. Event samples Chosen to minimize M2lb combinatorics and backgrounds • 3 ttbar sub-samples used from Run I (109 pb-1) • Dilepton e/mu 7 events (bkg 0.76) • b-jets are chosen as highest two Et jets in event • SVX double tagged l+j 5 events (bkg 0.2) • SVX single tagged l+j 15 events (bkg 2.4) • Standard top cuts applied (CDF top mass selection for all samples) • Sub-samples fit in combined likelihood to MC templates of V+A top, V-A top, and backgrounds

  10. DileptonComparing M2l+b [GeV2] distribution shapesV-A, V+A, backgrounds CDF Run I Preliminary Background contribution Z->tau+tau- 51 % WW 27 % W+jets fake 22 % Black line denotes Physical region for Correct pairings

  11. Top mass and jet energy scale systematics • If jet energy scale high, real top mass is low • Without correlation: • Top mass systematic: 0.21 • Jet energy scale systematic: 0.14 • With correlation: • Top mass systematic: 0.19 • Jet energy scale systematic: 0.04 World top mass: 174.3 ± 5.1GeV CDF l+j top mass: 175.9 ± 4.8 (stat) ± 5.3 (sys) GeV of sys: 4.4 GeV is due to jet energy scale

  12. CDF I preliminary

  13. CDF I preliminary

  14. Approaches for assigning confidence levels tofV+A = -0.21 +0.42-0.25(stat) ±0.21 (sys) • Neyman construction for confidence level • Simulate multiple “pseudo-experiments” to obtain spread of measurements for a range of values of ftrue • Fold in systematic uncertainty into each pseudo-result • Ignore whether each pseudo-result is physical or not • For each ftrue , calculate lower limit such that 95% of measurements would be greater than limit • Find fV+A such that the limit corresponds to the measurement

  15. Neyman Confidence Level of measurement CDF Run I Preliminary fV+A < 0.80 @ 95% CL

  16. Run 2 Expectations • Statistical uncertainties using event yields from CDF run 2 A TDR • Backgrounds contribution considered same as Run I • Systematic uncertainties estimated from Tev2000 report • Correlation between top mass and jet energy scale uncertainties calculated assuming CDF top mass measurement in 2 fb-1

  17. Run 2 Expected errors in measurement of fV+A

  18. The “Gamma 5 Brothers” Result: How much does V+A weigh in ? fV+A=-0.21 +0.42-0.25 (stat) ±0.21 (syst) fV+A < 0.80 @ 95% C.L. CDF I preliminary

  19. Conclusions • Searching for non-Standard weak interactions of top as a hint that top is important to the weak interaction itself. • Result is consistent with Standard Model and in fact excludes (to greater than 95% CL) the possibility of a right-handed tWb coupling • In Run II, this technique will be used to make a precise measurement

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