Spin Physics Progress with the STAR Detector at RHIC Spin related hardware improvements to STAR Important constraints on  G along the way – jets and  0 s Sivers Functions from jets at mid-rapidity J. Sowinski for the STAR Collaboration

Detector  =0 Forward Pion Detector Endcap EM Calorimeter Beam-Beam Counters Time Projection Chamber -1.6<η< 1.6 Barrel EM Calorimeter -1<η< 1 1<η< <η< <|η|< 5 Solenoidal Magnetic Field 5kG  =2  = -1 Tracking Lum. Monitor Local Polarim Triggering  = - ln(tan(  /2) STAR See talk by J. Kiryluk

Pb Scintillator sampling calorimeter – 21 rad. lengths 720 Towers give EM energy Shower Max. Detector for  0 /  discrimination Pre- and post-shower det’s for e/h discrimination 9,792 channels read out High Tower and Jet Patch triggers Endcap ElectroMagnetic Calorimeter /3 Towers 2004 All Towers. 1/3 SMD 2005 Fully Instr.

SMD profiles for a 9 GeV  0 candidate Charged tracks matched to fired EEMC towers for a 62 GeV Au+Au event Data MIPs ~ 0.3GeV  Online tower-only  0 reconstruction, 200 GeV Au+Au All events Mixed events Difference [200 GeV p+p (2003)] U V 8 cm 7 cm Inv. Mass

Scinti. + Pb sandwich sampling EMC 4800 projective towers (2  in , -1<  <1) Shower Max Detector-gas detector-18K strips Pre Shower Detector (first 2 layers) High tower trigger & 1x1 (η, φ) jet trigger Barrel ElectroMagnetic Calorimeter p T >3GeV 24 modules FY02 60 modules FY03 90 modules FY04 All modules (plan all elect.)FY05 One module = 40 towers #120 – the last one! August 2004

S z = ½ = ½  +  G + L z q + L z g First Moments at Q 0 2 =1 GeV 2 :  (MS) = 0.19 ± 0.05 ± 0.04  (AB) = 0.38  G (AB) = 0.99 (just one example of many)  0.03  0.02   0.31  0.22  0.45 — SMC Analysis, PRD 58, (1998) The Proton Spin Structure -  G Quark pol. well known from DIS But only a small fraction of p helicity Gluon polarization poorly determined Orb. Ang. Mom. unknown  G is accessible and a high priority at RHIC and STAR! STAR

A ~ P  P  a LL g part LL ^ pQCD Measure Know from DIS “  G”  G via partonic scattering from a gluon Dominant reaction mechanism Experimentally clean reaction mechanism Large a But jet and  0 rates are sufficient to give significant  G const. in 2005 data Prefer LL ^   -jet coinc. rare STAR Heavy flavor rare Jets and  0 s

STAR Sees and reconstructs jets Large solid angle is crucial But signal is mixture of multiple partonic subprocesses ggqq qg Inclusive Jets :LO W. Vogelsang p T (GeV) Fraction Leads to small but significant A LL in 2005 (~1/10 of these stats from 2004 currently being processed)

Polarized Proton Operation at RHIC Year 2002 ~2007  s = 200 GeV Improving L and Pol L (s -1 cm -2 ) 0.5x x x x x x10 30 Int. L (pb -1) (T/L) 0.3/ / /0.4 4/ Pol Spin flipper Transverse/Longitudinal Spin running T/L Division To be decided

Jager, Stratmann, Vogelsang NLO pQCD calculations hep-ph/ ~1/3 of the jet energy is EM Use EM cals for triggering jets  0 s carry ~same physics -1<  <1 EEMC 1<  <2 Significant const. on  G expected in 2005 data (~1/10 stats. from ’04 being analyzed) (error bar estimates too small pT<6 GeV) -1<  <1 BEMC Only STAR can track vs.  – EMCs+FPD –Different partonic contributions –Large  small x d  ab d  Simulation E EM /E jet

pTpT fraction STAR Quark – Gluon Compton Scattering p  p Direct   Jet Compton scattering dominates competing qq g  mechanism Coinc.  – jet relatively clean exp. signature E ,   and  jet determine x q, x g,  Allows extraction of  g(x) ^ Simulated full data set Source: F.H. Heinsius, DIS 2004 SMC:PRD70, (2004) HERMES: PRL 84, 2584 (2000) xgxg Eventually gives best determ. of  g(x) for existing experiments. Will get started in 2005 & 2006 but need L of and 500 GeV for g(x)

D. Boer and W. Vogelsang, Phys.Rev. D 69 (2004) Analyzing Powers at Mid-Rapidity Do processes invoked in forward scattering show up at large angles? For given parton at some x k T L =k T R Jet Measure STAR STAR Collab. Phys. Rev. Lett. 92 (2004) See A. Ogawa talk on fwd  0 s Sivers Function – Initial state correlation between k T and spin

4.1 x Partonic k T from Dijet Analysis k T =  2 = E T sin (   ) E T = 13.0  0.7 sys GeV Trigger Jet   = 0.23  0.02   ANAN 8 < p T1,2 < 12 GeV |η 1,2 | < 1 Sivers Effect Prediction STAR agrees well with World Data on Partonic k T D. Boer and W. Vogelsang, Phys.Rev. D 69 (2004) Curves are for various gluonic Sivers functions Connection to partonic orbital angular momentum Suppressed by Sudakov effect k T distribution STAR T. Henry, Quark Matter 2004, J. Phys. G kTkT SS 

Conclusions (Beginnings;-) RHIC will provide increasing L and P STAR EM calorimeters complete –Triggering –Large solid angle EM coverage –See poster on future upgrades Important constraints on  G expected in ‘05 –  0 s – Jets – Direct  s – longer term Investigations of transverse spin effects STAR

STAR Spin Physics Program – Near and Long Term Proton Spin Structure –Gluon contributions to the proton’s spin ♦ from jets and  0 s ♦ q + g  + jet,  G(x) ♦ Heavy flavors –Spin/momentum correlations ♦ Sivers Functions – dijets ♦ Collins Functions – Leading particle correl. in jets –Transversity –Flavor separated q, q – Origin of the sea Standard Model tests –Parity violation in jet production See A. Ogawa talk on fwd  0 s _ STAR

Future Upgrades – Inner and Forward Tracking  u(x)   d(x) _ _ Parity violating long. asymmetry in W production allows extraction of A L W - ~ u(x 1 )  d(x 2 )+d(x 1 )  u(x 2 ) __ Polarized q Flavor Asymmetry related to the nature of the sea _ Large  d-  u _ _ Nadolsky and Yuan, Nucl. Phys. B666 (2003) layer Si strip barrel and pixel detector Si planes and GEM for forward tracking Sensitivity in forward region Requires tracking for up to p T ~40 GeV e + /e - sign determination Tracking upgrade STAR ALAL