1. Transverse Spin Physics at PHENIX
DIS2006
Apr. 21, 2006
Kiyoshi Tanida (Kyoto/RIKEN)
for the PHENIX collaboration

2. Outline Transverse spin physics – What’s there? The PHENIX experiment
Single spin asymmetry measurements
Very forward neutron
Mid-rapidity hadrons
Future plans
Summary

3. Transverse Spin Physics – What’s There?
Transversity dq
Unexplored fundamental PDF
Seen as AN (via Collins effect) and ATT
However, there are more mechanisms to produce spin observables (mostly AN) in pp collisions
Sivers effect: Left/right asymmetry in intrinsic kT  Produces AN
Twist-3 effect?
Soft physics
Not well understood – attractive

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

5. RHIC p+p accelerator complex
↑↑↓↓・・・
↑↓↑↓・・・
RHIC pC “CNI” polarimeters
absolute pH
polarimeter
BRAHMS
& PP2PP
PHOBOS
Siberian
Snakes
RHIC
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

6. The PHENIX Detector Philosophy Central Arms Muon Arms
high resolution & high-rate at the cost of acceptance
trigger for rare events
Central Arms
|h| < 0.35, Df ~ p
g, p0, e, p+-, ... – Identified
Momentum, Energy
Muon Arms
1.2 < |h| < 2.4
Momentum (MuTr)

7. 13 Countries; 62 Institutions; 550 Participants*
*as of March 2005

8. Statistics
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 transverse run – 0.15 pb-1)
49.5/44.5% pb nb TB
AGS cold snake installed
2006: A long transverse spin run (radial polarization). We have accumulated 2.4 pb-1 with ~55% polarization so far.

9. Very Forward Neutron 10cm ±3 mrad blue beam yellow beam Dx magnet ZDC
SMD
SMD
1 ZDC
BBC
ZDC
3 modules: 150X0 5.1λI
Forward counter
position measurement
with scintillators

10. Calculation of AN Square-root formula Smearing effect -- simulation
P~48%
neutron
charged
particles
neutron
LARGE!!
Without Minbias
With Minbias

11. Local Polarimeter – how to know the polarization direction?
AL: Need parity violation (e.g., L decay)
 technically difficult, no good reference
AN: Becomes 0 if longitudinal

12. Asymmetry with transverse (vertical) beam (RUN3)
(Raw Asymmetry) / (beam pol.) ø ø
BLUE
YELLOW

13. Asymmetry with transverse (radial) beam (RUN3)
(Raw Asymmetry) / (beam pol.) ø ø
BLUE
YELLOW

14. Asymmetry with longitudinal beam (RUN3)
(Raw Asymmetry) / (beam pol.) ø ø
BLUE
YELLOW

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

16. Coincident particles Tag neutron (or gamma) at ZDC
Measure AN of coincident particles at BBC
at forward/backward
Forward neutron, forward BBC, left-right < 0
Forward neutron, backward BBC, left-right
> 0
No significant asymmetry for backward ZDC tagged data or in top-bottom asymmetry.
Systematic error doesn’t include ANCNI error.

17. Comparison with forward n
Asymmetry in the forward BBC has the same sign while backward particle has opposite sign AN
favored
Diffractive-like picture Y p
AN(X) < 0, AN(Y) > 0
N*(D*)  n+X
kick-out/recoil picture X p
AN(X) > 0, AN(Y)?? n

18. Why such large asymmetries?
AN is produced via interferance of spin non-flip and spin-flip amplitudes
In Regge theory
Pomeron gives no spin-flip amplitude
We need spin-flip amplitude
One pion exchange model may explain the result
Cross-section at ISR is OK
xF-scaling at different sqrt(s)
Need more data
e.g., pT dependence of AN
coincident particles
Eur.Phys.J.A7: ,2000 xF

19. p0 and charged hadrons for y~0
Run2 result with ~0.15pb-1, P~15%
gg and qg processes are dominant (with small xB)
– transversity effect is suppressed
May provide infomation on gluon-Sivers effect
|h| < 0.35
PRL 95 (2005)
202001

20. Update on charged pionsAN
pT (GeV/c)
Improved polarization：　P=15% in 2001/02, P=47% in 2005
while statistics is smaller.
AN is 0 within 1%  interesting contrast with forward p

21. Future plans
We have already accumulated (and still taking) significant transverse spin data in Run L=2.4 pb-1, <P>=54%  LP2=0.7 pb-1 (~x20 of Run5)
Much better precision
Higher pT  nearing the xB region looked by forward pions
Radial polarization  AN of jet kT
A new detector, Muon Piston Calorimeter is installed  Forward p0
Coincidence measurement with forward neutrons MPC, central arm, ...
Single muons (K+), J/Psi, ...
Very forward protons
Test data at sqrt(s)=500 GeV

22. AN of Jet kT A probe to access to Sivers functions.
left/right asymmetry in the kT of the partons in the nucleon
Feasible with Run6 data 0 2 h
Boer and Vogelsang, PRD69:094025,2004 ST j1 j2

23. Muon Piston Calorimeter
=-3.1
=-3.65
3.1 < |h| < 3.65
x2.2x18 cm3 PWO crystals, 220 cm from vertex
(behind Beam-Beam counter)
Energy Resolution: 13%/E?? from beam test

24. Summary There was large asymmetry in very forward neutrons
Local Polarimeter
Similar at sqrt(s) = 200 GeV & 410 GeV
Coincidence measurement
Still the mechanism is unknown
In contrast with forward pions, AN was 0 for mid-rapidity charged pions
In Run6, we have accumulated much larger data sample  More results will come
AN of jet kT
New detector, MPC, in forward/backward region.