1. Spin Physics at RHIC Towards Precision QCD Physics, KEK, March 10, 2007
Naohito SAITO
(KEK)

2. Why Spin? Fundamental Concept in Physics
Appears in Many Different Levels
Galaxy to Space-Time Structure
Fundamental Quantum Number for Elementary Particles
Important in Symmetry Test
Parity
Time Reversal

3. Proton Spin Crisis Anomaly SLAC：Pol’ electron scattering
Consistent with QM
CERN：Pol’ muon
Discovery of Anomaly
Q-Spin Cont: DS ~ 0
DESY：Pure Proton
Confirm Anomaly
SLAC＆CERN：Hi Precision
Establish Anomaly
DS ~
>> ~

4. First Crisis? Proton has gone through many crisis Spin
Mass : mu~5 MeV/c2, md~10 MeV/c2
Saved by constituent quark model
Momentum :
Saved by gluon momentum
Spin
Helicity SR:
Theory guideline for separation (nf=3)
(Ji, Tang, and Hoodboy)

5. Probing the Proton Structure
EM interaction
Photon
Sensitive to electric charge2
Insensitive to color charge
Strong interaction
Gluon
Sensitive to color charge
Insensitive to flavor
Weak interaction
Weak Boson
Sensitive to weak charge ~ flavor
Insensitive to color

6. Spin Structure Studies: Exp’mt
COMPASS
Pol.m
HERMES
Pol.e±
JLab Exp’s
Pol.e-
RHIC Spin
Pol. pp
BELLE
e+e-
Pol.m Beam:
RICH-1
Pol.Target
SM1
SM2
2-stage spectrometer
LAS (Large angle) Kp
SAS(Small angle) 
SAS
LAS
Ecal1 &
Hcal1
m filter 1
m filter 2
Ecal2 &
Hcal2
RICH-2

7. RHIC at BNL Two independent rings: 3.83 km Max Energy Luminosity
NY City
Two independent rings: 3.83 km
120 bunches/ring
106 ns bunch intvl
Max Energy
p-p GeV
Au-Au 100/N + 100/N GeV
Luminosity
p - p 2x1032 cm-2s-1 (Polarized)
Au-Au 2x1026 cm-2s-1
RHIC

8. RHIC:First Polarized pp Collider

9. Gluon Polarization

10. Gluon is expected to be Polarized
To compensate the Spin SR: (not necessarily)
To recover QM expectation thru axial anomaly
Through Q2 evolution: DS and Dg mix
Dg~0.3 would be
enough
Dg~2 required
Q2 evolution of
the 1st Moment

11. History of Dg Hunting Hunting for Dg Direct Probe Indirect Probe
FNAL E704
High-pT p0
High-mass Multi-g pair
DESY HERMES
High-pT hadron pair
Indirect Probe
NLO Analysis by SMC
PRL 84(00)2584
PLB261(1991)197
PRD58(1998)112002
PLB336(1994)269

12. Status of Dg/g(x) from Lepton Scat. Or w/o RHIC Spin
Photon-Gluon Fusion Process for
2-”jet”
Open Charm
New COMPASS results!
Gluon Pol. Can be +, 0, -
Courtesy Vogelsang and Stratmann

13. Constraints on Dg(x) w/ p0 Prod.
pp  p0 X is sensitive to gggg and gqgq

14. “Standard” value of DG from pre-RHIC DIS data
Constraints on DG
“Standard” value of DG from pre-RHIC DIS data
Assuming DG = 0

15. AAC updates (S.Kumano, M. Hirai, NS, PRD (2006)
Include J-Lab, HERMES, COMPASS new data
Trial inclusion of PHENIX p0 ALL data
K-factor method a la CTEQ
Gluon Uncertainty significantly reduced!

16. Gluon Polarization Dg>0 preferred at large-x Dg=0.3±0.3
HERMES and COMPASS A1d data
Higher-twist effects?
Dg=0.3±0.3
Additional scale error of ~20%
previously 0.5±1.3
If no p0 data 0.5±1.1
Additional scale error ~20%

17. Improved Constraints Newly obtained 1st moments (Q2=1 GeV2)
Dg = 0.3±0.3
With additional scale error of ~20%
DS = 0.27±0.07
Still need to improve precision Dg
Lq and Lg, too!
GPD
Compare with Ji, Tang,Hoodboy Expectation

18. Extend x Range
ALL(p0) from Run 6/7 (65 pb-1) will extend x range to larger x
STAR jet measurement also provides precision data
500 GeV run will cover smaller x-range
FWD rapidity coverage also useful for smaller-x region
W. Vogelsang

19. Prompt Photon Production
Gluon Compton Dominates
10% Contamination from Annihilation
No fragmentation contribution in LO k2 P1 P2 k1 i ) ( 2 1 g q gq a x e A LL Ä D = å 1
0.001

20. Direct photon in Run-2006/7
W. Vogelsang k2 P1 P2 k1

21. Uncertain Unpolarized Glue
Valence-Q well determined
Sea is uncertain at large-x
Gluon is unknown at large and small-x
Need direct measurement
Not only for Dg but also for LHC

22. Sea Polarization

23. Sea Constraints: SDIS and QCD fit
QCD fit often assumes SU(3) symmetric sea
Need to include SIDIS data
Flavor separation by HERMES (talk by L. de Nardo)  important progress!
Still compatible with QCD fit
Significant constraints observed by de Florian et. al.
Small-x issue remains

24. W Production in pp Collisions
W is produced through pure V-A
Chirality is fixed  ideal for spin structure studies
W couples to weak charge ~ flavor
Flavor is (almost) fixed  ideal for flavor structure studies
Parity Violating Asymmetry AL :
J. Soffer et al.

25. Sea Constraints: RHIC W Prospects
Clear flavor separation
Weak charge ~ flavor
Clear spin information
Left handed current only
Start in 2009!
The 1st Commission starts tomorrow!
Projected statistical precision

26. Transverse Spin Physics

27. Single Transverse Spin Asymmetries
Fermilab E-704 reported Large Asymmetries AN
Could be explained as
Transversity x Spin-dep fragmentation (Collins effect),
Intrinsic-kT imbalance (Sivers effect) , or
Twist-3 (Qiu-Sterman, Koike)
Or combination of above
Left
Right

28. BRAHMS Results on AN
BRAHMS observed Large AN in charged pion production
Similar Trend to E704, but deviation from ZERO starts earlier?
Need to explore further!

29. More from BRAHMS p+ K+ K- p p- Pion Kaon Proton “+”>0 “-” <0
“-” >0 !!
Proton
“+” = 0
“-” > 0

30. RHIC Spin Roadmap submitted to DOE, Feb. 11, 2005 http://spin. riken
Year
P(%)
Weeks
(Com/Ph)
Lumi
CM Energy
Goals
2002 15
8 (5/3)
0.5 pb-1
200 GeV
Transverse Spin
2003 30
0.35 pb-1
Longitudinal Spin
Gluon Polarization?
2004 40
5(5/0)
0.15 pb-1
RHIC Commissioning
Pol. Gas Jet Target
2005 50 10
3.8 pb-1
410 GeV
Gluon Pol/Transv.
Commissioning
2006/7 70
13+10
~120 pb-1
0.1 pb-1
62.4 GeV
500 GeV
2008/9
10+10
~150 pb-1
~180 pb-1
W-Physics/Transv.

31. Past and Future of RHIC Spin Luminosity
Lost
Future

32. Asymmetries calculated for RHIC
RHIC Luminosity should be improved to realize these measurements…

33. Summary
No final answer yet… but qualitatively new picture of spin structure is emerging!
RHIC is still catching up Kodaira-san’s prediction
We would like to contribute to precision QCD physics by providing experimetal results from RHIC, and J-PARC.