SOME FACTS THAT YOU SHOULD KNOW ABOUT BRITAIN Agata Adamczyk II a.
W µ parity violating asymmetries from the 2013 running period in … · 2015. 12. 18. · 6) F....
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W→ μ parity violating asymmetries from the 2013 running period in the PHENIX experiment R. Seidl *1 for the PHENIX collaboration During the 2013 data taking period 277 pb -1 of lon- gitudinally polarized proton collision data at a cen- ter of mass energy of 510 GeV were accumulated with an average beam polarization of 53% per beam at the PHENIX 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 po- larization in the nucleon real W boson production is an elegant way. The parity violation of the weak in- teraction directly selects the helicity of the quarks and anti-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 and a 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 and the question whether the polarized light sea is symmet- ric or not has been predicted rather differently in var- ious nucleon models. The analysis of W decay muons in the forward and backward muon arm detectors of PHENIX is not as straightforward as at central rapidi- ties as there is no clean W decay signature such as a Jacobian peak at half the W mass. Also a large number of background sources exist such as heavy flavor decay muons and hadrons decaying within the tracking vol- ume mimicking a high momentum muon as previously reported. With the help of kinematically different vari- Fig. 1. Total pp → W ± X × BR(W → l) cross sections for forward muon and previously published W → e results by PHENIX 1) and STAR 2) as well as predictions by Pythia 3) , CHE 4) and RHICBOS 5) . ables for signal and backgrounds candidate events were pre-selected by a likelihood ratio where only high sig- nal likelihood events were kept. Then the relative sig- nal and background contributions were fit by a maxi- mum 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 RIKEN Nishina Center beam polarization and dilution by background the pre- liminary results 6) for the single spin asymmetries were obtained as seen in Fig. 2. The results are in good agreement with the parameterizations and will even- tually be used in future iterations of the global he- licity fits to all the existing deep inelastic scattering and proton-proton collision data. The 2013 PHENIX W results are currently being prepared for publication and it is expected to reduce the systematic uncertain- ties which are dominated by the uncertainties on the signal to background ratio still. Fig. 2. Single spin asymmetries of W+Z decay leptons as a function of lepton rapidity. The preliminary PHENIX electron and muon results from the 2013 data taking period (red) and the published STAR electron results from 2012 (green) 7) are shown as well as various helicity parameterizations. References 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) 238 4) D. de Florian and W. Vogelsang, Phys. Rev. D 81 (2010) 094020 5) 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 ) [pb] ± l → BR(W × ) ± W → (pp σ 50 100 150 200 250 300 Sampled range | < 2.5 η 1.1 < | < 0.35 η -0.35 < < 1.0 η -1.0 < RHICBOS PYTHIA CHE PRD85 (2012) 092010 e → STAR W PRL 106 (2011) 062001 e → PHENIX W → PHENIX W -1 Ldt = 277 pb ∫ 2013 : ) total cross section ± l → BR(W × ) ± W → (pp σ L A -1.0 -0.5 0.0 0.5 1.0 + ,e + → +Z + W >16 GeV T P = 510 GeV s Run 13: p+p at (2013) L A NNPDFpol1.1 GRSV STD DSSV DNS KKP DNS Kretzer > 30 GeV e T P (2009-2012) e L A (2013) e L A - l η -2 -1 0 1 2 L A -1.0 -0.5 0.0 0.5 1.0 - ,e - → +Z - W (PRL 113 (2014) 072301) e L STAR A >25 GeV T DSSV E per arm (2013) -1 Sampled Luminosity: 277 pb - 104 - RIKEN Accel. Prog. Rep. 48 (2015) Ⅱ-4. Hadron Physics
Transcript of W µ parity violating asymmetries from the 2013 running period in … · 2015. 12. 18. · 6) F....
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W→ µ parity violating asymmetries from the 2013 running period inthe PHENIX experiment
R. Seidl∗1 for the PHENIX collaboration
During the 2013 data taking period 277 pb−1 of lon-gitudinally polarized proton collision data at a cen-ter of mass energy of 510 GeV were accumulated withan average beam polarization of 53% per beam at thePHENIX experiment at RHIC. This data correspondsto the largest data sample available for the polarizedW data analysis. In order to access the sea quark po-larization in the nucleon real W boson production isan elegant way. The parity violation of the weak in-teraction directly selects the helicity of the quarks andanti-quarks and the charge of the produced W bosonselects the quark and anti-quark flavors. For examplethe W− gets produced by a left-handed d quark anda right-handed anti-u quark. While the u and d quarkhelicities are already reasonably well known the seaquark helicities are only very poorly determined andthe question whether the polarized light sea is symmet-ric or not has been predicted rather differently in var-ious nucleon models. The analysis of W decay muonsin the forward and backward muon arm detectors ofPHENIX is not as straightforward as at central rapidi-ties as there is no clean W decay signature such as aJacobian peak at half the Wmass. Also a large numberof background sources exist such as heavy flavor decaymuons and hadrons decaying within the tracking vol-ume mimicking a high momentum muon as previouslyreported. With the help of kinematically different vari-
) [pb]± l→ BR(W×)±W→(ppσ50 100 150 200 250 300
Sam
pled
rang
e
| < 2.5η1.1 < |
< 0.35η-0.35 <
< 1.0η-1.0 <
RHICBOS
PYTHIA
CHE
PRD85 (2012) 092010 e→STAR W
PRL 106 (2011) 062001 e→PHENIX W
µ →PHENIX W
-1 Ldt = 277 pb∫2013 :
) total cross section± l→ BR(W×)±W→(ppσ
Fig. 1. Total pp → W±X ×BR(W → l) cross sections for
forward muon and previously published W → e results
by PHENIX1) and STAR2) as well as predictions by
Pythia3), CHE4) and RHICBOS5).
ables for signal and backgrounds candidate events werepre-selected by a likelihood ratio where only high sig-nal likelihood events were kept. Then the relative sig-nal and background contributions were fit by a maxi-mum unbinned likelihood fit. From those preliminarypp → W±X cross sections were extracted which turnedout to be consistent with NLO predictions, see Fig. 1.After correcting the raw single spin asymmetries for
∗1 RIKEN Nishina Center
beam polarization and dilution by background the pre-liminary results6) for the single spin asymmetries wereobtained as seen in Fig. 2. The results are in goodagreement with the parameterizations and will even-tually be used in future iterations of the global he-licity fits to all the existing deep inelastic scatteringand proton-proton collision data. The 2013 PHENIXW results are currently being prepared for publicationand it is expected to reduce the systematic uncertain-ties which are dominated by the uncertainties on thesignal to background ratio still.
+lη
-2 -1 0 1 2
LA
-1.0
-0.5
0.0
0.5
1.0+,e+µ→+Z+W >16 GeVµ
TP = 510 GeVsRun 13: p+p at (2013)µ
LA
NNPDFpol1.1GRSV STDDSSVDNS KKPDNS Kretzer
> 30 GeVeTP
(2009-2012)eLA (2013)e
LA
-lη
-2 -1 0 1 2
LA
-1.0
-0.5
0.0
0.5
1.0-,e-µ→+Z-W (PRL 113 (2014) 072301)e
LSTAR A>25 GeVTDSSV E
per arm (2013)-1Sampled Luminosity: 277 pb
Fig. 2. Single spin asymmetries of W+Z decay leptons as a
function of lepton rapidity. The preliminary PHENIX
electron and muon results from the 2013 data taking
period (red) and the published STAR electron results
from 2012 (green)7) are shown as well as various helicity
parameterizations.
References1) A. Adare et al. [PHENIX Collaboration], Phys. Rev.
Lett. 106 (2011) 0620012) L. Adamczyk et al. [STAR Collaboration], Phys. Rev.
D 85 (2012) 0920103) T. Sjostrandet al. Comput. Phys. Commun. 135 (2001)
2384) D. de Florian andW. Vogelsang, Phys. Rev. D 81 (2010)
0940205) P. M. Nadolsky and C. P. Yuan, Nucl. Phys. B 666
(2003) 316) F. Giordano [PHENIX Collabortion], to appear in JPCS
(Spin 2014 proceedings).7) L. Adamczyk et al. [STAR Collaboration], Phys. Rev.
Lett. 113 (2014) 072301
Neutral pion double helicity asymmetry†
K. Boyle∗1
A major goal of the RHIC Spin program is to de-termine the gluon spin distribution in the proton. Thequark spin contribution to the proton spin (∆Σ) is onlyabout 25%1), and so the remaining spin must be car-ried by the gluon spin (∆G), or by the gluon and quarkorbital angular momentum (Lq and Lg, respectively):
Sp =1
2=
1
2∆Σ+∆G+ Lq + Lg (1)
written in units of h̄.At RHIC, ∆G can be probed directly through mea-
surements of the double helicity asymmetry in polar-ized p+ p collisions, in this case for neutral pions:
ALL =1
PBPY
N++ −RN+−
N++ +RN+−
(2)
where PB and PY are the polarizations of the two pro-ton rings at RHIC, N is the yield of neutral pions,π0, ++ and +− indicate same and opposite helicitycombinations of the two beam helicities, and R is therelative luminosity, defined as R = L++/L+−, whichis required to normalize differences in the luminosityL between RHIC proton bunches.In 2009, RHIC PHENIX recorded 14 pb−1 with an
average polarization of 56%. The π0 ALL was mea-sured, and found to be consistent with previous results.The combined results from 20052), 20063) and 20094)
are plotted in Fig. 1. The systematic uncertainty fromrelative luminosity in 2009 was larger than in previousyears, and for the lowest π0 transverse momentum, pT ,was larger than the statistical uncertainties.
The combined data set are shown in Fig. 1 and Fig. 2compared to several theoretical expectations based onfits to the world polarized scattering data. In the caseof1), the RHIC 2005 and 2006 π0 data are also in-cluded. In fits that do not use RHIC data, such asGRSV5), LSS6) and BB7), there is large uncertainty in∆G and therefore in the expected π0 ALL. Fits includ-ing some RHIC data, such as DSSV1) and NNPDF8)
find a smaller range of possible ∆G. These data there-fore offer significant constraint on ∆G. Recently, theRHIC 2009 data have been included in an updatedversion of DSSV9), and indicate that the gluon spincontribution to the proton spin is about the same sizeas that of the quarks.
References1) D. de Florian, R. Sassot, M. Stratmann and W. Vogel-
sang, Phys. Rev. D 80, 034030 (2009).2) A. Adare et al. [PHENIX Collaboration], Phys. Rev. D
76, 051106 (2007).
† Condensed from the article in Phys. Rev. D 90, no. 1,012007 (2014)
∗1 RIKEN BNL Research Center
[GeV/c]T
p2 3 4 5 6 7 8 9
0 π LLA
-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025DSSV08
0≈g(x) ∆GRSV
GRSV-std
Run5+6+9 Correlated Systematic Uncert.
Tp
Run5+6+9 Not Included:4.8% Global Scaling Uncert.
Global Shift Uncert.-44.2x10
Fig. 1. Results for π0ALL vs. pT from the combined 2005,
2006 and 2009 PHENIX data sets. The data are com-
pared with several theoretical expectations.
[GeV/c]T
p2 4 6 8 10 12
0 π LLA
-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025NNPDF
BB10
LSS10
Run5+6+9 Corr. Syst. Uncert.
Tp
Fig. 2. Results for π0ALL vs. pT from the combined 2005,
2006 and 2009 PHENIX data sets. The data are com-
pared with several theoretical expectations.
3) A. Adare et al. [PHENIX Collaboration], Phys. Rev.Lett. 103, 012003 (2009).
4) A. Adare et al. [PHENIX Collaboration], Phys. Rev. D90, no. 1, 012007 (2014).
5) M. Gluck, E. Reya, M. Stratmann and W. Vogelsang,Phys. Rev. D 63, 094005 (2001).
6) E. Leader, A. V. Sidorov and D. B. Stamenov, Phys.Rev. D 82, 114018 (2010).
7) J. Blumlein and H. Bottcher, Nucl. Phys. B 841, 205(2010).
8) R. D. Ball et al. [The NNPDF Collaboration], Nucl.Phys. B 874, 36 (2013).
9) D. de Florian, R. Sassot, M. Stratmann and W. Vogel-sang, Phys. Rev. Lett. 113, 012001 (2014).
) [pb]± l→ BR(W×)±W→(ppσ
50 100 150 200 250 300
Sam
pled
rang
e
| < 2.5η1.1 < |
< 0.35η-0.35 <
< 1.0η-1.0 <
RHICBOS
PYTHIA
CHE
PRD85 (2012) 092010 e→STAR W
PRL 106 (2011) 062001 e→PHENIX W
→PHENIX W
-1 Ldt = 277 pb∫2013 :
) total cross section± l→ BR(W×)±W→(ppσ
+lη
-2 -1 0 1 2
LA
-1.0
-0.5
0.0
0.5
1.0+,e+→+Z+W >16 GeVTP
= 510 GeVsRun 13: p+p at (2013)LA
NNPDFpol1.1GRSV STDDSSVDNS KKPDNS Kretzer
> 30 GeVeTP
(2009-2012)eLA (2013)e
LA
-lη
-2 -1 0 1 2
LA
-1.0
-0.5
0.0
0.5
1.0-,e-→+Z-W (PRL 113 (2014) 072301)e
LSTAR A>25 GeVTDSSV E
per arm (2013)-1Sampled Luminosity: 277 pb
- 104 - - 105 -
Ⅱ-4. Hadron Physics RIKEN Accel. Prog. Rep. 48 (2015)RIKEN Accel. Prog. Rep. 48 (2015) Ⅱ-4. Hadron Physics
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