RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-4. Hadron Physics

W→ µ parity violating asymmetries from the 2013 running period inthe PHENIX experiment
R. Seidl∗1 for the PHENIX collaboration

Sampled rangeσ(pp(pp→→WW±±))×× BR(W
BR(W→→ ll±±)) totalσtotal cross
cross section
section2013 :∫∫ Ldt = 277 pb

PYTHIA
CHE
STAR W→→e
PRD85 (2012) 092010
PHENIX W →→e
PRL 106 (2011) 062001-1.0 <<ηη<< 1.01.0-1.0-0.35 <<η
η<< 0.350.35-0.35

PHENIX W →→µAALLW+++Z+Z→µ++,e,e++
WµPeTeT >> 30
30 GeVGeV
PTT>16>16 GeV
GeV PP
AeLeL (2009-2012)(2009-2012)
A
AµLL (2013)(2013)A
AeLeL (2013)(2013)A
NNPDFpol1.1
NNPDFpol1.1
GRSV STD
STD
GRSV
DSSV
DSSV
DNS KKP
KKPDNS
DNS Kretzer
Kretzer
DNS= 510
510 GeV
GeV
Run 13:13: p+pp+p at
at ss =
Run

0.5
0.5
0.0
0.0
-0.5
-0.5
-1.0
-1.0
1.0
1.0-2 W
-1-2
W--+Z
+Z→µ--,e,e-- -1 00

0.50.5111322STAR A
AeLeL(PRL(PRL1113 (2014)(2014) 072301)
072301)
STARη ++DSSV E
ETT>25>25 GeVGeVDSSV
ll0.00.0-0.5-0.5-1
Sampled Luminosity:
Luminosity: 277
277 pbpb-1
per armarm (2013)(2013)
Sampledper-1.0-1.0-2-2-1-1001122ηll-- 



1.1 << ||ηη|| <
< 2.5
2.5
1.1
50
50

100
100

150
150

200
200

250
250

300
300±±σσ(pp(pp→→WW±))×× BR(WBR(W→→ ll±)) [pb][pb]References±Fig. 1. Total pp → W X × BR(W → l) cross sections forforward muon and previously published W → e resultsby PHENIX1) and STAR2) as well as predictions byPythia3) , CHE4) and RHICBOS5) .

ables for signal and backgrounds candidate events werepre-selected by a likelihood ratio where only high signal likelihood events were kept. Then the relative signal and background contributions were fit by a maximum unbinned likelihood fit. From those preliminary
pp → W ± X cross sections were extracted which turned
out to be consistent with NLO predictions, see Fig. 1.
After correcting the raw single spin asymmetries for
∗1

1.0
1.0

Fig. 2. Single spin asymmetries of W+Z decay leptons as afunction of lepton rapidity. The preliminary PHENIX
electron and muon results from the 2013 data taking
period (red) and the published STAR electron resultsfrom 2012 (green)7) are shown as well as various helicity
parameterizations.

RHICBOS-1

beam polarization and dilution by background the preliminary results6) for the single spin asymmetries wereobtained as seen in Fig. 2. The results are in good
agreement with the parameterizations and will eventually be used in future iterations of the global helicity fits to all the existing deep inelastic scatteringand proton-proton collision data. The 2013 PHENIX
W results are currently being prepared for publicationand it is expected to reduce the systematic uncertainties which are dominated by the uncertainties on thesignal to background ratio still.

AALL

During the 2013 data taking period 277 pb−1 of longitudinally polarized proton collision data at a center of mass energy of 510 GeV were accumulated withan average beam polarization of 53% per beam at thePHENIX experiment at RHIC. This data corresponds
to the largest data sample available for the polarized
W data analysis. In order to access the sea quark polarization in the nucleon real W boson production isan elegant way. The parity violation of the weak interaction directly selects the helicity of the quarks andanti-quarks and the charge of the produced W boson
selects the quark and anti-quark flavors. For example
the W − gets produced by a left-handed d quark anda right-handed anti-u quark. While the u and d quark
helicities are already reasonably well known the sea
quark helicities are only very poorly determined andthe question whether the polarized light sea is symmetric or not has been predicted rather differently in various nucleon models. The analysis of W decay muonsin the forward and backward muon arm detectors ofPHENIX is not as straightforward as at central rapidities as there is no clean W decay signature such as a
Jacobian peak at half the W mass. Also a large numberof background sources exist such as heavy flavor decaymuons and hadrons decaying within the tracking volume mimicking a high momentum muon as previously
reported. With the help of kinematically different vari-1) A. Adare et al. [PHENIX Collaboration], Phys. Rev.
Lett. 106 (2011) 062001
2) L. Adamczyk et al. [STAR Collaboration], Phys. Rev.
D 85 (2012) 092010
3) T. Sjostrandet al. Comput. Phys. Commun. 135 (2001)
2384) D. de Florian and W. Vogelsang, Phys. Rev. D 81 (2010)
0940205) P. M. Nadolsky and C. P. Yuan, Nucl. Phys. B 666(2003) 31
6) F. Giordano [PHENIX Collabortion], to appear in JPCS
(Spin 2014 proceedings).
7) L. Adamczyk et al. [STAR Collaboration], Phys. Rev.
Lett. 113 (2014) 072301

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