Transverse Spin Physics at PHENIX DIS 2006 Apr

Transverse Spin Physics at PHENIX DIS 2006 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 k. T Produces AN – Twist-3 effect? – Soft physics • Not well understood – attractive

The Relativistic Heavy Ion Collider accelerator complex at Brookhaven National Laboratory Brhams pp 2 pp PHENIX STAR

RHIC p+p accelerator complex RHIC p. C “CNI” polarimeters absolute p. H↑↑↓↓ ・・・ polarimeter↑↓↑↓・・・ BRAHMS & PP 2 PP PHOBOS Siberian Snakes PHENIX RHIC STAR Spin ・・・ Rotators ←←→→ ↓↓↑↑ ←→←→・・・ ↓↑↓↑・・・ LINAC Pol. Proton Source Siberian Snakes 5% Snake BOOSTER AGS 200 Me. V polarimeter 20% Snake Rf Dipoles ↓↓↑↑ ・・・ ↓↑↓↑・・・ AGS p. C “CNI” polarimeter Coulomb-Nuclear Interference

The PHENIX Detector • Philosophy – high resolution & high-rate at the cost of acceptance – trigger for rare events • Central Arms – | | < 0. 35, Df ~ – , 0, e, +-, . . . – Identified – Momentum, Energy • Muon Arms – 1. 2 < | | < 2. 4 – Momentum (Mu. Tr)

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

Statistics s = 200 Ge. V P recorded LP 4 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 ～ 1800 cm blue beam 10 cm ± 3 mrad yellow beam D magnet x SMD BBC ZDC 1 ZDC Forward counter position measurement with scintillators 3 modules: 150 X 0 5. 1λI

Calculation of AN • Square-root formula P~48% • Smearing effect -- simulation 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

ø BLUE (Raw Asymmetry) / (beam pol. ) Asymmetry with transverse (vertical) beam (RUN 3) ø YELLOW

ø BLUE (Raw Asymmetry) / (beam pol. ) Asymmetry with transverse (radial) beam (RUN 3) ø YELLOW

ø BLUE (Raw Asymmetry) / (beam pol. ) Asymmetry with longitudinal beam (RUN 3) ø YELLOW

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

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 • Diffractive-like picture Y p favored AN(X) < 0, AN(Y) > 0 N*(D*) n+X • kick-out/recoil picture X p n AN(X) > 0, AN(Y)? ?

Why such large asymmetries? • AN is produced via interferance of spin non-flip and spin-flip amplitudes Eur. Phys. J. A 7: 109 -119, 2000 • 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 – x. F-scaling at different sqrt(s) Need more data e. g. , p. T dependence of AN coincident particles x. F

0 and charged hadrons for y~0 • Run 2 result with ~0. 15 pb-1, P~15% • gg and qg processes are dominant (with small x. B) – transversity effect is suppressed • May provide infomation on gluon-Sivers effect | | < 0. 35 PRL 95 (2005) 202001

Update on charged pions AN p. T (Ge. V/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

Future plans • We have already accumulated (and still taking) significant transverse spin data in Run 6 L=2. 4 pb-1, <P>=54% LP 2=0. 7 pb-1 (~x 20 of Run 5) – – Much better precision Higher p. T nearing the x. B region looked by forward pions Radial polarization AN of jet k. T A new detector, Muon Piston Calorimeter is installed Forward 0 – Coincidence measurement with forward neutrons MPC, central arm, . . . – Single muons (K+), J/Psi, . . . – Very forward protons • Test data at sqrt(s)=500 Ge. V

AN of Jet k. T • A probe to access to Sivers functions. – left/right asymmetry in the k. T of the partons in the nucleon • Feasible with Run 6 data Boer and Vogelsang, PRD 69: 094025, 2004 2 0 j 1 ST h j 2

Muon Piston Calorimeter =-3. 1 =-3. 65 • 3. 1 < | | < 3. 65 • 192 2. 2 x 18 cm 3 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 Ge. V & 410 Ge. V Coincidence measurement Still the mechanism is unknown • In contrast with forward pions, AN was 0 for mid-rapidity charged pions • In Run 6, we have accumulated much larger data sample More results will come – AN of jet k. T – New detector, MPC, in forward/backward region.