1. Current status of RHIC Spin Program
Workshop on Hadron Structure at J-PARC
Nov. 30, 2005
Kiyoshi Tanida (RIKEN/RBRC)

2. Outline Overview of the RHIC spin project Recent spin physics results
Cross section measurements
ALL measurements
AN measurements
Other measurements
Future prospects
Summary

3. Overview of the RHIC spin project
Main Physics  Study of spin structure of proton /2 = 1/2DS + DG + L (DS ~ 0.25)
How to study? ALL -- double spin asymmetry in pp collision ) ( +- + ++ - = s
= (parton pol.)2×
(aLL in parton reaction)

4. Examples of reaction channels
Direct photon: g + q  g + q - ~10% contribution from other processes (e.g.`qq  gg)  golden channel for gluon polarization - Need high luminosity (> 100 pb-1).
Jet, high-pT hadron production - mix of various processes, q+q, g+g, g+q, feasible at relatively small luminosity (~pb-1)
Heavy flavor
W -- spin-flavor structure

5. The Relativistic Heavy Ion Collider accelerator complex
at Brookhaven National Laboratory
PHENIX
STAR
Brhams
pp2pp

6. RHIC p+p accelerator complex
The polarimeters are experimental devices
RHIC pC “CNI” polarimeters
absolute pH
polarimeter
BRAHMS
& PP2PP
PHOBOS
RHIC
Siberian
Snakes
PHENIX
STAR
Siberian Snakes
Spin Rotators
5% Snake
LINAC
BOOSTER
AGS pC “CNI” polarimeter
Pol. Proton Source
AGS
Coulomb-Nuclear
Interference
200 MeV polarimeter
Rf Dipoles
20% Snake

8. polarimeters @RHIC preliminary “Analyzing power” or transverse
scattered
proton
(polarized)
proton beam
“Analyzing power”
or transverse
single-spin
asymmetry
polarized
proton target
or Carbon target
recoil proton
or Carbon
this exp
FNAL
AN for Carbon
preliminary
AN for proton

9. RHIC pp performance Lpeak Lstore Lweek Projection Bunch intensity
X1011
# of
Bunches
Lpeak
X1030
cm-2s-1
Lstore
Lweek
pb-1
Machine uptime
Pol at Store
Blue/Yellow
FY04
0.7 56
5.4
4.0 --
40%
FY05 min
0.9
FY05 max
1.0 79 16
8.2
3.0
50%
45%
FY05 operation 84
9.0
4.9
1.2
52%
48.5/43.5
1.12
(61 bunches)
110
(0.95x1011 protons/bunch) 13
1.8
61.9/58.4
Projection
June 23, 2005
RHIC/AGS User meeting 2005
BNL, Upton, NY 11973

10.
s = 200 GeV P recorded L recorded LP4 data volume
transverse-spin run
15% pb TB
first polarized proton collisions
2003 longitudinal-spin run
27% pb nb TB
spin rotators commissioned, AGS p-C CNI polarimeter
2004 commissioning run (longitudinal spin)
40% pb nb-1
AGS warm snake commissioned, gas-jet absolute polarimeter
2005 longitudinal-spin run (w/ short transeverse run)
49.5/44.5% pb nb TB
AGS cold snake installed
2005 – First long longitudinal-spin polarized-proton run
Figure of merit (LP4) more than 40 times larger than
that of previous runs

11. Recent spin physics results
Cross sections (not exactly spin, but important cross-check for data/theory reliability)
PHENIX p0 and direct photon
STAR inclusive jet production, forward p0
Brahms, p±
All agree well with NLO pQCD calculation

12. ALL measurements Currently available results: PHENIX STAR
midrapidity: p0, "jet" (multi-particle)
forward rapidity: J/Y
STAR
midrapidity: jet
In (near) future
charged hadrons, h, direct photon, heavy quarks,...

13. p0 ALL -- PHENIX Theory model C.L. (%) GRSV-std 21.7-17.1 *GRSV-max
(Dg=g)
*GRSV Dg=0
*GRSV Dg=−g
GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 53 (1996) 4775.
* At input scale: Q2 = .4 Gev

14. Inclusive jet -- STAR RUN3+4 data
Results limited by statistical precision
Total systematic uncertainty ~0.01 (STAR) + beam pol. (RHIC)

15. ALL for “jet” -- PHENIX
Jet detection -- Tag one photon, sum observed energy/momentum nearby (R < 0.3)
Jet pT estimated by simulations (modified PYTHIA)
Run3 data only
(Run5 data is
under analysis)

16. J/y ALL J/y: produced via almost pure gluon fusion
Will be sensitive to gluon polarization, now statistically limited.

17. AN measurements Brahms pp2pp STAR PHENIX
forward/backward charged pion, proton
pp2pp
AN in pp elastic scattering
STAR
forward p0
inclusive forward particles
midrapidity charged particles
PHENIX
midrapidity: charged particles, p0
very forward neutrons

18. forward p± -- Brahms 2 < h < 5.2 AN for negative xF
BRAHMS preliminary
2 < h < 5.2
AN for negative xF
are consistent with 0
protons: AN ~0
Signs are consistent with lower energy results
Twist-3 model can explain the result (flat xF distribution, lower AN for higher pT)

19. Forward p0 -- STAR Preliminary pT dependence was obtained
xF>0.4, h ~ 4
C/pT fit gives C = 0.07±0.01
@1 GeV/c
Comparison with theoretical calculation may constrain Sivers function

20. AN in pp2pp pp elastic scattering
~1s deviation from CNI curve -- interference of hadronic “non-flip” + electromagnetic “spin-flip”
Other contributions, e.g. Reggeon or Pomeron exchange exist? AN
s1/2=200 GeV
-t (GeV/c)2

21. AN of very forward neutron -- PHENIX LocalPol
PHENIX Collision Point
～1800cm
10cm
blue beam
yellow beam
Dx magnet
±2mrad
<AN>=-0.1100.015
@ s1/2=200 GeV
very forward:
pT ~ 0.1 GeV/c
almost no xF
dependence
Mechanism unknown

22. AN persists at sqrt(s) = 410 GeV
blue
forward
yellow
backward
raw asymmetry
yellow
forward
blue
backward

23. Other spin results I can't show all of them (e.g., Λ spin transfer)
Spin dependence of transverse momentum of jets
Back-to-back nature of jets is broken by initial/final state transverse momentum kT （e.g., intrinsic kT, soft gluon radiation）
Orbital angular momentum: kT× r introduces intrinsic kT in the initial state
 measurement of jet kT gives an access to parton orbital angular momentum

24. possible helicity effect
larger kT
smaller kT
Same
helicity
Opposite
helicity
We may observe net effect
(after averaging over impact factor)

25. kT Measurement in PHENIX
o - h correlation functions in f distribution
3.0<pT<4.0
Fit = const + Gauss(0)+Gauss()
1.5<pT<2.0
p+p s = 200 GeV 
d+Au
Intra-jet pairs angular width : N  jT fragmentation
Inter-jet pairs angular width : F  jT  kT ... fragmentation + kT

26. Helicity Dependence Hint of Helicity dependence?  not yet sure
Stat. only
Hint of Helicity dependence?
 not yet sure
Run05 data should yield a definite answer.
BS variance
(stat. + syst.)

27. Future prospects Budget situation for Run6 is very hard, but ...
We are going to accumulate > 100 pb-1 with P > 70% at s1/2=200 GeV by 2009.
Then switch to s1/2=500 GeV
 Determination of Dg(x) with many channels including direct photon
Other physics (no time to discuss...)
Detector upgrades are ongoing
STAR: Forward meson detector, trigger/DAQ, ...
PHENIX: Si-VTX detector, W trigger upgrade, ...

28. Jet ALL from STAR Run 5
Will be able to distinguish Dg=0 and g inputs

29. ALL from PHENIX Run 5
Direct photon
Jet ALL
h, electron, m, L, ...

30. ALL of direct photon “Golden Channel” for Dg, high luminosity required
s = 200 GeV until 2009
s = 500 GeV from 2009
GRSV-max (Dg=g)
GRSV-std

31. AN of Jet kT (Run 6 and beyond)
A probe to access to Sivers functions. 0 2 h
Boer and Vogelsang, PRD69:094025,2004
STAR projection

32. Summary
RHIC-spin has taken first long longitudinal-spin polarized-proton collision data in Run5
Preliminary results from Run 5 are available
ALL data from PHENIX and STAR have significant impact on the gluon spin contribution in the proton
Dg=g scenario is excluded
Many data on AN in various channels and other measurables -- interesting physics case
More data will come -- promising.