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![Page 1: Proton spin structure from longitudinally polarized pp collisions from PHENIXat RHIC Alexander Bazilevsky BNL The 6 th Circum-Pan-Pacific Symposium on.](https://reader036.fdocuments.us/reader036/viewer/2022062417/55151bcf550346a80c8b604c/html5/thumbnails/1.jpg)
Proton spin structure from longitudinally polarized pp
collisions from PHENIXat RHIC
Alexander BazilevskyBNL
The 6th Circum-Pan-Pacific Symposium on High Energy Spin Physics
July 30 – August 2, 2007Vancouver BC, Canada
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Nucleon Spin Structure
Naïve parton model:
1989 EMC (CERN):=0.120.090.14
Spin Crisis sdusdu
vv du 2
1
2
1
Determination of G and q-bar is the main goal of longitudinal spin program at RHIC
Gluons are polarized (G) Sea quarks are polarized:
Gqq 2
1
2
1
For complete descriptioninclude parton orbital angular momentum LZ:
ZLGqq 2
1
2
1
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Parton Distribution Functions (PDF)• Quark Distribution
q(x,Q2)=
q(x,Q2)=
q(x,Q2)=
=
unpolarised distributionunpolarised distribution
helicity distributionhelicity distribution
g(x,Q2)=
g(x,Q2)=
No Transverse Gluon Distribution in 1/2
• Gluon Distributionstransversity distributiontransversity distribution
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Polarized PDF from DISAsymmetry Analysis Collaboration
M. Hirai, S. Kumano and N. Saito, PRD (2004)
• Valence distributions well determined
• Sea Distribution poorly constrained
• Gluon can be either positive, 0, negative!
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… To polarized pp colliderUtilizes strongly interacting probes
Probes gluon directly Higher s clean pQCD interpretation Elegant way to explore guark and anti-
quark polarizations through W production
Polarized Gluon Distribution Measurements (G(x)):
Use a variety of probesAccess to different gluon momentum fraction xDifferent probes – different systematics
Use different energies s Access to different gluon momentum fraction x
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RHIC as polarized proton collider
BRAHMS & PP2PP (p)
STAR (p)
PHENIX (p)
AGS
LINACBOOSTER
Pol. Proton Source500 A, 300 s
GeVs
L
50050
onPolarizati%70
cms102 2132max
Spin Rotators
Partial Siberian Snake
Siberian Snakes
200 MeV Polarimeter AGS Internal PolarimeterRf Dipoles
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
2 1011 Pol. Protons / Bunch = 20 mm mrad
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PHENIX for Spin
Electromagnetic Calorimeter
Drift ChamberRing Imaging Cherenkov Counter
JMuon Id/Muon Tracker
Relative LuminosityBeam Beam Counter (BBC) Zero Degree Calorimeter (ZDC)
Local Polarimetry - ZDC
Philosophy (initial
design): High rate capability & granularityHigh rate capability & granularity Good mass resolution & particle IDGood mass resolution & particle ID Sacrifice acceptanceSacrifice acceptance
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PHENIX Long. Spin runs
Year s [GeV] Recorded L Pol [%]FOM (P4L)
2003 (Run 3) 200 .35 pb-1 32 3.7 nb-1
2004 (Run 4) 200 .12 pb-1 45 4.9 nb-1
2005 (Run 5) 200 3.4 pb-1 50 200 nb-1
2006 (Run 6) 200 7.5 pb-1 60 1000 nb-1
2006 (Run 6) 62.4 .08 pb-1 ** 48 4.2 nb-1 **
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Unpol. Cross Section in pppp0 X : hep-ex-0704.3599 pp X: PRL 98, 012002
Good agreement between NLO pQCD calculations and data confirmation that pQCD can be used to extract spin dependent pdf’s from RHIC data.
• Same comparison fails at lower energies
||<0.35
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Probing G in pol. pp collisions pp hX
hf
fXff
baba
hf
fXffLL
fXff
baba
LL Ddff
Dadff
dd
ddA
ba
baba
ˆ
ˆˆ
,
,
Double longitudinal spin asymmetry ALL is sensitive to G
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Measuring ALL
L
LR
RNN
RNN
PPdd
ddALL ;
||
1
21
(N) Yield (R) Relative Luminosity
BBC vs ZDC
(P) Polarization RHIC Polarimeter (at 12 o’clock)Local Polarimeters (SMD&ZDC)
Bunch spin configuration alternates every 106 ns Data for all bunch spin configurations are collected at the same time
Possibility for false asymmetries are greatly reduced
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ALL: 0
pT(GeV)
Run3,4,5: PRL 93, 202002; PRD 73, 091102; hep-ex-0704.3599
5 10
GRSV model:“G = 0”: G(Q2=1GeV2)=0.1“G = std”: G(Q2=1GeV2)=0.4
Stat. uncertainties are on level to distinguish “std” and “0” scenarios? …
PHENIX Preliminary Run6 (s=200 GeV)
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From soft to hard
exponential fit
Exponent (e-pT) describes our pion cross section data perfectly well at pT<1 GeV/c (dominated by soft physics):
=5.560.02 (GeV/c)-1
2/NDF=6.2/3
Assume that exponent describes soft physics contribution also at higher pTs soft physics contribution at pT>2 GeV/c is <10%
For G constrain use pi0 ALL data at pT>2 GeV/c
hep-ex-0704.3599
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From pT to xgluon
Log10(xgluon)NLO pQCD: 0 pT=29 GeV/c xgluon=0.020.3
GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 )
Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins
These data is not much sensitive to variation of G(xgluon) within our x range
Any quantitative analysis should assume some G(xgluon) shape
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From ALL to G (with GRSV)Calc. by W.Vogelsang and M.Stratmann
“std” scenario, G(Q2=1GeV2)=0.4, is excluded by data on >3 sigma level: 2(std)2
min>9Only exp. stat. uncertainties are included
(the effect of syst. uncertainties is expected to be small in the final results)
Theoretical uncertainties are not included
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Extending x range is crucial!Gehrmann-Stirling models
GSC: G(xgluon= 01) = 1 G(xgluon= 0.020.3) ~ 0
GRSV-0: G(xgluon= 01) = 0 G(xgluon= 0.020.3) ~ 0
GRSV-std: G(xgluon= 01) = 0.4 G(xgluon= 0.020.3) ~ 0.25
GSC: G(xgluon= 01) = 1
GRSV-0: G(xgluon= 01) = 0
GRSV-std: G(xgluon= 01) = 0.4
Current data is sensitive to G for xgluon= 0.020.3
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G: what’s next
Improve exp. (stat.) uncertainties and move to higher pT More precise G constrain in probed x range Probe higher x and constrain G vs x
Different s Different x
Different channels Different systematics Different x gqg sensitive to G sign
G
G
G
G
gq g
G
G
q
q
QQgg
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Improve exp. uncertaintiesNeed more FOM=P4 L (stat. uncertainty ~ FOM)
0: expectations from Run-8
Higher pT measurements probe higher x constrain G vs x
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Different channelsNeed more FOM=P4 L (stat. uncertainty ~ FOM)
Different sensitivities of charged pions to u and d provide more sensitivity to sign of G through qg scattering
Predictions are sensitive to fragmentation functions
Xpp Xpp
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Different channelsNeed more FOM=P4 L (stat. uncertainty ~ FOM)
XJpp /Xpp
Complementary to 0 measurements Need fragmentation functions
Probe G with heavy quarksOpen charm will come soonNeed more theoretical input
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pp + jet
Theoretically clean (no fragmentation at LO) Gluon Compton dominates sensitive to sign of G Requires substantial FOM=P4 L
PHENIX Projection
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Different ss=62 GeV 0 cross section described by NLO pQCD within theoretical uncertainties
Sensitivity of Run6 s=62 GeV data collected in one week is comparable to Run5 s=200 GeV data collected in two months, for the same xT=2pT/s
s=500 GeV will give access to lower x; starts in 2009
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Flavor decomposition
Measured through longitudinal single spin asymmetry AL in W production at s=500 GeV
First data expected in 2009-2010
Wdu
Wud
Wdu
Wud
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Other measurements
Helicity correlated kT from PHENIX
May be sensitive to orbital angular momentum
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PHENIX Upgrades
Silicon TrackingVTX (barrel) by 2009FVTX (forward) by 2011
Electromagnetic CalorimetryNCC by 2011MPC, already installed!
Muon trigger upgradeBy 2009Momentum selectivity in the LVL-1 trigger
G from heavy flavor, photon-tagged jetsExpanded reach in x
Flavor separation of spin asymmetriesW physics at 500GeV
Transverse Spin Physics (see talk by M.Liu)
rapidity
See talk by I.Nakagawa
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Summary RHIC is the world’s first and the only facility which provides collisions of
high energy polarized protons Allows to directly use strongly interacting probes (parton collisions) High s NLO pQCD is applicable
Inclusive 0 accumulated data for ALL has reached high statistical significance to constrain G in the limited x range (~0.020.3) G is consistent with zero Theoretical uncertainties might be significant
Extending x coverage is crucial Other channels from high luminosity and polarization Different s
PHENIX upgrades strengthen its capability in nucleon spin structure study Larger x-range and new channels (e.g. heavy flavor)W measurements for flavor decomposition
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PolarimetryUtilizes small angle elastic scattering in the coulomb-nuclear interference (CNI) region
Pbeam N
ANpC
N NL NR
NL NR
Fast relative polarization measurements with proton-Carbon polarimeter
Single measurement for a few seconds
(Relatively) slow absolute polarization measurements with polarized atomic hydrogen jet target polarimeter
Used to normalize pC measurementstargetNtarget
beamNbeam
PA
PA
targettarget
beambeam PP
Beam polarization in Run6: P ~ 60-65%
Polarization measurements in Run5:
P/P~6% and (PBPY)/(PBPY)~9%
pp or C12
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Backup: Rel. Lum. In PHENIX
Year [GeV] R ALL
2005 * 200 1.0e-4 2.3e-4
2006 * 200 3.9e-4 5.4e-4
2006 * 62.4 1.3e-3 2.8e-3
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Backup: s=62 vs 200 GeV
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Partonic Orbital Angular Momentum
Peripheral Collisions
Larger
Integrate over b, leftwith some residual kT
2Tk
Net pT kick
Central Collisions
Smaller 2TkJet 2
Jet 1
Jet 2 w/<kT>=0
Peripheral Collisions
Larger Jet 1
Jet 2 w/<kT>=0
Jet 2
Like helicities: Beam momenta
• Partonic orbital angular momentum leads to rotation of partons correlated with the proton spin vector
• This leads to different pT imbalances (pT-kicks) of jet pairs in semiclassical models
• Can be measured by measuring helicity dependence of <kT
2>
• Partonic orbital angular momentum leads to rotation of partons correlated with the proton spin vector
• This leads to different pT imbalances (pT-kicks) of jet pairs in semiclassical models
• Can be measured by measuring helicity dependence of <kT
2>
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Partonic Orbital Angular Momentum
• Partonic orbital angular momentum leads to rotation of partons correlated with the proton spin vector
• This leads to different pT imbalances (pT-kicks) of jet pairs in semiclassical models
• Can be measured by measuring helicity dependence of <kT
2>
• Partonic orbital angular momentum leads to rotation of partons correlated with the proton spin vector
• This leads to different pT imbalances (pT-kicks) of jet pairs in semiclassical models
• Can be measured by measuring helicity dependence of <kT
2>
Integrate over b, leftwith different residual kT
Net pT kick
Central Collisions
Larger 2TkJet 2
Jet 1
Jet 2 w/<kT>=0
2Tk
Peripheral Collisions
Smaller Jet 1
Jet 2 w/<kT>=0
Jet 2
Unlike helicities: Beam momenta
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Backup: W
W production» Produced in parity violating V-A process
— Chirality / helicity of quarks defined» Couples to weak charge
— Flavor almost fixed
W a b a bL
a b a b
u(x )d(x ) d(x )u(x )A
u(x )d(x ) d(x )u(x )
xa>>xb: AL(W+) → u/u(x) - -xb>>xa: AL(W+) → d/d(x)
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Backup: SIDIS for G
HERMES preliminaryHERMES preliminary
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Backup: GFrom M. Stratmann
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Backup: from G to ALL
GRSV: G(Q2=1GeV2)= 1.76 +1.89
By Marco&Werner