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Parity-Odd Asymmetry in W-Jet Events

Parity-Odd Asymmetry in W-Jet Events. Hiroshi Yokoya (Niigata U.). Ref. K.Hagiwara, K.Hikasa, N.Kai , Phys.Rev.Lett.52(1984)1076; K.Hagiwara, K.Hikasa, HY , hep-ph/0604208. RBRC workshop, June 18-23, 2006 “RHIC physics in the Context of the Standard Model”. Contents :.

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Parity-Odd Asymmetry in W-Jet Events

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  1. Parity-Odd Asymmetry in W-Jet Events Hiroshi Yokoya (Niigata U.) Ref. K.Hagiwara, K.Hikasa, N.Kai, Phys.Rev.Lett.52(1984)1076; K.Hagiwara, K.Hikasa, HY, hep-ph/0604208 RBRC workshop, June 18-23, 2006 “RHIC physics in the Context of the Standard Model”

  2. Contents : • Introduction : W-jet production • Parity-odd asymmetry in W-jet events • Phenomenology and Simulation • Summary

  3. Introduction • High-qT W-boson productions at Hadron Collider have been measured by UA1, UA2 Collaborations @ CERN CDF, D0 Collaborations @ FNAL Tevatron

  4. qT-distributions - Experiments - • Measurements in Tevatron Run-I CDF (’91) D0 (’98)

  5. qT-distributions - Theory - • High-qT (qT ~ MW) perturbation is good complete NLO calc. Arnold,Reno(’89);Gonsalves,Pawlowski,Wai(’89) (NNLO is modest ) Kidonakis,Vera (’04) K ~ 1.3, flat behavior c.f.) small-qT (qT ≪ MW) log corrections → qT-resummation Arnold,Kauffman(’91),Ellis,Ross,Veseli(’98),,,

  6. Lepton Angular Distributions • Rich information on the polarization of W-boson, i.e. • the details of production mechanism can be investigated P-even P-odd Fi : structure functions

  7. Collins-Soper Frame Collins-Soper frame (W-rest frame) W-jet c.m. frame (parton c.m. frame) Notice : Both frames are NOT constructible from observables, because of missing neutrino momentum.

  8. Lepton Angular Distributions • pQCD calculation : P-even parts : LO (tree-level) Chaichian,Hayashi,Yamagishi(’82) NLO (one-loop) Mirkes,Korner,Schuler(’91),Mirkes(’92) P-odd parts : LO (one-loop) Hagiwara,Hikasa,Kai(’84)

  9. Recent Results from CDF [hep-ex/504020] • Some of the P-even distributions are measured at Tevatron Run-I, • in good agreement with the pQCD prediction in NLO. • In Run-II, measurements of P-odd distributions may be possible. We study the simple and practical observables of the P-odd asymmetry, and perform a realistic Monte-Carlo simulation.

  10. Parity-odd asymmetry

  11. Parity-odd asymmetry The Nobel Prize in Physics 1957 T.D. Lee and C.N. Yang

  12. Parity-odd asymmetry • β-decay of polarized nucleus : P

  13. Parity-odd asymmetry • Parity transformation : • Parity-odd observables : • with spin : • without spin :

  14. ~ Parity-odd and Naïve-T ( T )-odd • P-odd observables without spins are interesting, • because these are at the same time T-odd. ~ ~ • T-transformation : • T-transformation : • (anti-unitary)

  15. ~ Unitarity and T-odd quantity • Unitarity of S-matrix absorptive part ~ • T-odd quantity Time-reversal violation → proportional to the absorptive parts of scattering amplitude

  16. One-loop calculation Hagiwara,Hikasa,Kai(’84) • one-loop calculation in pQCD • on the absorptive part of scattering amplitude

  17. One-loop calculation Hagiwara,Hikasa,Kai(’84) with CTEQ6M

  18. Phenomenology and Monte Carlo Simulation

  19. Collins-Soper Frame Collins-Soper frame (W-rest frame) W-jet c.m. frame (parton c.m. frame) Notice : Both frames are NOT constructible from observables, because of the missing neutrino momentum.

  20. Two-fold ambiguity • (longitudinal) neutrino momentum • is not observable Laboratory frame • → Two-fold ambiguity in determining • W-jet c.m. frame • Collins-Soper frame Advantage of CS frame : only the sign of cosθ can’t be determined. sinθ and φ can be determined.

  21. Realistic Observables • qT is observable, • from jet transverse momentum Laboratory frame • Pseudo-rapidity difference • of lepton and jet, instead of

  22. Monte-Carlo simulation • Tevatron Run-II : Luminosity : • “standard” CDF cuts : CDF hep-ex/504020 • W → lepton detection : • jet identification : W’s transverse mass : Jet cone size : • qT minimum cut :

  23. Effective Higher-Order enhancement LO Matrix Elements with “effective” H.O. enhancement setting absorb the H.O. enhancement into LO result, approximately • good as well, for P-even distributions Mirkes,Ohnemus (’94) • not confirmed for P-odd, • because NLO is not known. Kidonakis,Vera(’04)

  24. Results : Event yield • Total number of events for one lepton-flavor ~ 50,000. c.f.) for Run-I we get: # ~ 16,000. : 12,676. : 6,941. CDF

  25. ④ ① + - - + ② ③ Results : Observable P-odd asymmetries • Left-right asymmetry ～ 5% at large Δη more than 5σ deviation from zero-asymmetry is expected • sign(sin2φ) asymmetry (combining all Δy and qT)

  26. RHIC case : pp collision • looser cut for qT minimumto use more events → perturbation works well? Perhaps, we need qT-resummation for the azimuthal angular distributions D.Boer and W.Vogelsang, hep-ph/0604177

  27. RHIC case : • W+, one-lepton flavor # of events ~ 11,000. • Left-right asymmetry →

  28. Summary • High-qT W-boson production at Hadron colliders • well-described by (NLO) pQCD • lepton angular distributions are measured at Tevatron • P-odd asymmetries in decay-lepton angular distributions • naïve-T-odd as well • arise from the absorptive part of scattering amplitudes • new test of the pQCD prediction • Monte-Carlo simulation for Tevatron Run-II and RHIC • two-fold ambiguity → realistic observables • we proposed observable asymmetries

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