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W Physics at RHIC

W Physics at RHIC. Werner Vogelsang BNL Nuclear Theory 2007 RHIC/AGS Users Meeting. Introduction Basics of W production at RHIC Theory aspects Future opportunities Conclusions. Material from talks by. C. Weiss. P. Nadolsky. S. Arnold. A. Mukherjee. H. Yokoya. Outline:.

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W Physics at RHIC

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  1. W Physics at RHIC Werner Vogelsang BNL Nuclear Theory 2007 RHIC/AGS Users Meeting

  2. Introduction Basics of W production at RHIC Theory aspects Future opportunities Conclusions Material from talks by C. Weiss P. Nadolsky S. Arnold A. Mukherjee H. Yokoya Outline:

  3. I. Introduction

  4. Current “spin budget” of the nucleon:

  5. • Nucleon models make predictions, for example: Pion cloud Sullivan; Thomas Dressler; Fries, Schäfer, Weiss •correct picture? (relies on symmetries, F,D ) •important role played by sea ? •would like to know more:

  6. _ _ _ _ Large-NC ,  Quark Soliton Diakonov et al.; Dressler et al.; …

  7. HERMES Little is known so far: “SIDIS” HERMES, COMPASS, JLab • inconclusive • large inherent uncertainties

  8. Avakian, Brodsky, Deur, Yuan •also specific interest in large-x region : pQCD, Lz=0 Lz0 Constituent Quark models

  9. II. Basics of W production at RHIC

  10. At RHIC: If parity conserved:

  11. universal partonic scatt. perturbative QCD

  12. u unpol. •large scale Q~MW: pQCD •complementary to SIDIS, cleaner •large asymmetries “guaranteed” (at large x)

  13. •typically probed values of x relatively large (smallest accessible x is ) •will get only small part of first moments of pdfs •to test model predictions, x-dependence actually more relevant •recall, also large-x region an area for model predictions (and the lattice) •ultimately, become part of “global analysis” of all RHIC data

  14. III. Theory aspects

  15. Main issues: •radiative corrections: higher-order QCD corrections •take into account W decay : instead of (RHIC acceptance !) Hadronic decays (2 jets) ?

  16. Best developed tool: RhicBos P. Nadolsky, C.P. Yuan •Monte-Carlo integrator with NLO and NNLL qresummation accuracy HO: LO: (NLO relatively important, resummation moderately so) •Leptonic decays fully included. Lepton distributions for realistic acceptance.

  17. Nadolsky, Yuan

  18. Recent work on higher-order QCD corrections: . . . • partonic cross section : • higher orders : ”Threshold resummation” Mukherjee, WV inv. mass Q = MW

  19. • enhanced by parton distributions : z = 1 emphasized, in particular as 1

  20. Mukherjee, WV W+ All-order resummation of Sterman; Catani, Trentadue

  21. (El.weak)2 “doubly resonant” Renewed interest in hadronic W decays: Arnold, Metz, WV; Nadolsky First thing that comes to mind:

  22. Also: Bourrely, Soffer However, AL also arises from (QCD  El.weak):

  23. + - •many partonic channels (even for resonant ones) •no W charge identification •separation of W, Z hard? •denominator is QCD 2 jet cr.sec.  AL small (however, S/B better than at Tevatron) •higher-order corrections? Moretti, Nolten, Ross; Arnold, Metz, WV •higher event rates (BR) •can choose events with both jets seen. get directly •perhaps tool to see first PV signal

  24. One example:

  25. Potential improvements -- need study: •better variables (e.g. dijet pair mass mjj) •perhaps techniques for subtraction of main QCD background ?

  26. IV. Future opportunities

  27. Access to strangeness at RHIC II ? • associated W+charm production ? Sudoh, Yokoya “D-tagged W’s” g W- c s’

  28. Sudoh, Yokoya Polarization : Luminosity : Detection efficiency : Requires high luminosity

  29. e W- d u  Anselmino et al.; … W physics at eRHIC • charged current DIS

  30. Stratmann, WV Contreras et al. Q2>225 GeV2 L=2/fb •electroweak parameters? sin2(W) ?

  31. Conclusions & Outlook: • good control of theory: higher-order corrections, resummations. Power corrections likely small. • hadronic decays useful ? Needs further work. • further opportunities at RHIC II and eRHIC

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