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

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

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

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

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

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)

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

Statistics 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 2006: A long transverse spin run (radial polarization). We have accumulated 2.4 pb-1 with ~55% polarization so far.

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

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

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

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

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

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

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

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.

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

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.A7:109-119,2000 xF

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

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

Future plans We have already accumulated (and still taking) significant transverse spin data in Run6 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

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

Muon Piston Calorimeter =-3.1 =-3.65 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

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.