Kensuke Okada (RBRC) for the PHENIX collaboration Spin2010
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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 10/1/2010 K.Okada (RBRC) 1
description
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. - PowerPoint PPT Presentation
Transcript of Kensuke Okada (RBRC) for the PHENIX collaboration Spin2010
K.Okada (RBRC) 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
10/1/2010
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W bosons at RHIC
• An unique probe to access the flavor dependence of polarized sea quarks.
• Parity violating single spin asymmetry (AL).
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Polarized p+p collider
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RHIC-PHENIX 2009 run
• The first 500GeV p+p run. (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
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PHENIX Central arm: We
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EMCal + DC/PC1 trackingAcceptance : 0.35 in rapidity 0.5*2arms in
EMCal Trigger Fully efficient at 12GeV
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e energy and charge
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α = bend angle
pT= E(in EMCal)* sin
[GeV/c]
at 40GeV/c
data
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Jacobian peak is confirmed
+
-
Red histogram: with minimum track requirements Blue histogram: with an isolation cut
pT distribution of electron candidates
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Main background : Photon conversion Charged hadron interaction
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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)
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Consistent with the expectation (numbers)
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W,Z decay electrons
positronelectron
StatisticalSystematic (Background assumptions)
Normalization (acceptance, efficiency, luminosity)
uncertainties:
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Convert to the total W productionPHENIX 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.
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LHC Preliminary
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7TeV
LHC(ATLAS, CMS)preliminary points
They are also consistent with expectations. (See ICHEP presentations)
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Parity violating single spin asymmetry
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RHIC has 120 bunches polarized (every 106ns) Reduces detector time dependence
Concept: 1-beam polarized
Raw asymmetry:
Physics asymmetry :
Actual calculation
From 4 spin patterns (= 2 beams * 2 helicity patterns)
N+ : yields in helicity +N- : helicity –R : Correction for L
D: Dilution correctionP: Beam Polarization
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Parity violating raw asymmetries (L)
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BG Signal42counts
BG Signal13 counts
+ -
L=0 for Background (as expected)
Large L for Signal(especially in e+)
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Physics asymmetries (AL)
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D: 1.040.03 (+ signal) 1.140.10 (- signal)P: 0.390.04 (2 beam average)
+-
Limited to the physical region [-1,1].
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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.
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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.
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