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

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

Overview of the RHIC spin project Main Physics  Study of spin structure of proton 1/2 = 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)

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

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

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

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 E704 @ FNAL AN for Carbon preliminary AN for proton

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

Statistics @PHENIX 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 transeverse run) 49.5/44.5% 3.8 pb-1 205 nb-1 262 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

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

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,...

p0 ALL -- PHENIX Theory model C.L. (%) GRSV-std 21.7-17.1 *GRSV-max (Dg=g) 0.0-0.0 *GRSV Dg=0 16.7-18.4 *GRSV Dg=−g 0.7-0.0 ¨ GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 53 (1996) 4775. * At input scale: Q2 = .4 Gev

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

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)

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

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

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)

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

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

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

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

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

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

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

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.)

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, ...

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

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

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

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

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.