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Kensuke Okada (RBRC) for the PHENIX collaboration Spin2010

Measurement of Longitudinal Spin Asymmetries From W  Boson Decay in Polarized pp Collisions at s=500 GeV at RHIC-PHENIX. Kensuke Okada (RBRC) for the PHENIX collaboration Spin2010. W bosons at RHIC. An unique probe to access the flavor dependence of polarized sea quarks.

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Kensuke Okada (RBRC) for the PHENIX collaboration Spin2010

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  1. Measurement of Longitudinal Spin Asymmetries From WBoson Decay in Polarized pp Collisions at s=500 GeV at RHIC-PHENIX Kensuke Okada (RBRC) for the PHENIX collaboration Spin2010 K.Okada (RBRC)

  2. W bosons at RHIC • An unique probe to access the flavor dependence of polarized sea quarks. • Parity violating single spin asymmetry (AL). Polarizedp+p collider K.Okada (RBRC)

  3. RHIC-PHENIX 2009 run • The first 500GeV p+prun. (March to April, 2009) • Beam Polarization : <P>=0.39±0.04 • Integrated luminosity (with vertex cut) : Ldt=8.6/pb Today’s talk High pT electrons : Welectron decay channel K.Okada (RBRC)

  4. PHENIX Central arm: We EMCal + DC/PC1 tracking Acceptance : 0.35 in rapidity 0.5*2arms in  EMCal Trigger Fully efficient at 12GeV K.Okada (RBRC)

  5. e energy and charge α = bend angle data at 40GeV/c [GeV/c] pT= E(in EMCal)* sin  K.Okada (RBRC)

  6. Jacobian peak is confirmed + pT distribution of electron candidates Red histogram: with minimum track requirements Blue histogram: with an isolation cut - Main background : Photon conversion Charged hadron interaction K.Okada (RBRC)

  7. Consistent with the expectation + Signal shape after background subtraction electrons from W, Z bosons. With minimum track requirements The red curve shows the expectation (NLO) - K.Okada (RBRC)

  8. Consistent with the expectation (numbers) W,Z decay electrons positron electron uncertainties: Statistical Systematic (Background assumptions) Normalization (acceptance, efficiency, luminosity) K.Okada (RBRC)

  9. Convert to the total W production PHENIX acceptance （pT>30GeV, |y|<0.35） Total Z boson contribution + : ~7%, -: ~30% Fraction of the PHENIX + : ~22%, -: ~15% The first measurement (with an arXiv number) in p+p collisions. K.Okada (RBRC)

  10. LHC Preliminary They are also consistent with expectations. (See ICHEP presentations) LHC(ATLAS, CMS) preliminary points 7TeV K.Okada (RBRC)

  11. Parity violating single spin asymmetry RHIC has120 bunchespolarized (every 106ns)  Reduces detector time dependence Concept: 1-beam polarized N+ : yields in helicity + N- : helicity – R : Correction for L Raw asymmetry: D: Dilution correction P: Beam Polarization Physics asymmetry : Actual calculation From 4 spin patterns (= 2 beams * 2 helicity patterns) K.Okada (RBRC)

  12. Parity violating raw asymmetries (L) + - BG BG Signal 13 counts Signal 42counts L=0 for Background (as expected) Large L for Signal (especially in e+) K.Okada (RBRC)

  13. Physics asymmetries (AL) D: 1.040.03 (+ signal) 1.140.10 (- signal) P: 0.390.04 (2 beam average) + - Limited to the physical region [-1,1]. K.Okada (RBRC)

  14. AL (68%CL) and predictions + - They are consistent with all models for now. A non-zero asymmetry (98.4%CL) is observed in the positive candidates. K.Okada (RBRC)

  15. Summary • PHENIX central arm detects electrons from W boson decay. • The production cross section is as expected. The first measurement in p+p. • Measured the parity violating single spin asymmetry (non zero AL). • Submitted to a journal. (arXiv:1009.0505) • This is a start of RHIC W boson program. • Forward/backward muon channel. Today at 17:30 (Location C) by Y. Fukao. K.Okada (RBRC)

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