Transverse Spin Physics at P HENIX

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

5. RHIC p+p accelerator complex ↑↑↓↓・・・ ↑↓↑↓・・・ 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

6. The PHENIX Detector • Philosophy • 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. s = 200 GeV P recorded L recorded LP4 data volume 2001-2002 transverse-spin run 15% 0.15 pb-1 20 TB first polarized proton collisions 2003 longitudinal-spin run 27% 0.35 pb-1 1.5 nb-1 35 TB spin rotators commissioned, AGS p-C CNI polarimeter 2004 commissioning run (longitudinal spin) 40% 0.12 pb-1 3.3 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% 3.8 pb-1 205 nb-1 262 TB AGS cold snake installed Statistics 2006: A long transverse spin run (radial polarization).We have accumulated 2.4 pb-1 with ~55% polarization so far.

9. ZDC Forward counter SMD 1 ZDC 3 modules: 150X0 5.1λI Very Forward Neutron ～1800cm 10cm blue beam yellow beam ±3 mrad Dx magnet SMD BBC position measurement with scintillators

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

11. Local Polarimeter – how to knowthe 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 yellow backward blue forward 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. favored Comparison with forward n Asymmetry in the forward BBC has the same sign while backward particle has opposite sign AN • Diffractive-like picture Y p AN(X) < 0, AN(Y) > 0 N*(D*)  n+X • kick-out/recoil picture X AN(X) > 0, AN(Y)?? p n

18. Eur.Phys.J.A7:109-119,2000 xF 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

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 pions AN 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 Run6L=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 neutronsMPC, central arm, ... • Single muons (K+), J/Psi, ... • Very forward protons • Test data at sqrt(s)=500 GeV

22. Boer and Vogelsang, PRD69:094025,2004 2 0 h j1 ST j2 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

23. =-3.1 =-3.65 Muon Piston Calorimeter • 3.1 < |h| < 3.65 • 192 2.2x2.2x18 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.