1. Spin Physics with STAR at RHIC Joanna Kiryluk (MIT) for the STAR Collaboration ICHEP 2004, Beijing, August 16-22, 2004 Outline: 1. 1.Goals of the spin program 2. 2.RHIC accelerator complex 3. 3.STAR detector 4. 4.First results (A N ) from pp at  s = 200 GeV 5. 5.Gluon polarization from inclusive jet  production 6. 6.Rare probes at RHIC 7. 7.Outlook

2. Relativistic Heavy Ion Collider (RHIC) - -the first polarized proton-proton collider The goals of STAR spin program at RHIC are to determine: Gluon polarization - poorly constrained from the NLO QCD analysis of g 1 (x,Q 2 ) structure function in DIS experiments Flavor separation of (anti-) quark polarization - limited sensitivity in semi-inclusive DIS measurements Transversity distributions - yet unmeasured RHIC - QCD lab to study the spin structure of the proton 2

3. Polarized proton-proton collisions with STAR (Solenoid Tracker At RHIC) Brookhaven National Laboratory, Upton NY, USA 542 collaborators from 51 institutions and 12 countries The STAR Collaboration PHENIX BRAHMS &PP2PPPHOBOS STAR 1.2 km RHIC 3

4. RHIC - First Polarized pp Collider YEAR 2004 YEAR 2005-6 pp Run200220032004 2005 Expected > 2006 LongTermGoals CM Energy 200 GeV 500 GeV and direction at STAR 0.15 T0.30 T/L0.40 L0.45 L/T0.7 L/T L max [ 10 30 s -1 cm -2 ]2 661680200 L int [pb -1 ] at STAR0.30.5 / 0.40.47 / 4320800 Stable polarization direction - transverse Longitudinal polarization at STAR/Phenix AGS Heclical Partial Snake Number of bunches: 55 - 112 2x10 11 protons/bunch (max)

5. Solenoidal Magnet B = 0.5 T Tracking Detectors Time Projection Chamber |  |<1.6 Forward TPC 2.5<|  |<4.0 Silicon Vertex Tracker |  |<1 Trigger Detectors Beam-Beam Counters 3.4<|  |<5 Zero-Degree Calorimeter |  |~6 Central Trigger Barrel |  |<1 + E-M Calorimeters - installation in stages to be completed before 2005 Barrel EMC |  |<1 Endcap EMC 1.0<  <2.0 Forward Pion Detector 3.3<|  <4.1 STAR is adding lots of EM calorimetry to detect high-energy , e ,  0 TPC+EMC for jet reconstruction BBC + scaler board system for relative luminosity and polarization monitoring STAR detector + STAR Upgrades Plans: Time of Flight, Forward Tracker, Micro-Vertex Detector CTB ZDC (BBC) Cutway side view of the detector where pseudorapidity  ln tan  Designed for Heavy Ion program to search for quark-gluon plasma 5

6. Longitudinal A LL Transverse A TT Transverse A N Longitudinal A L Single Spin Long term - Rare Probes 500 GeV Double Spin Short term - Run-2 STAR Spin Program Short term - Run-3-5 200 GeV STAR spin program requires charged particle tracking and identification of electrons, pions, photons and jets 6

7. Spin Asymmetry Measurements Require concurrent measurements: magnitude of beam polarization, P 1(2) RHIC polarimeter(s) direction of polarization vector at interaction point relative luminosity of bunch crossings with different spin directions: STAR spin dependent yields of process of interest: N i and N ij Statistical significance: Single Transverse Double Longitudinal 7

8. abort gaps (beam-gas background) beam-1 beam-2 bunch crossing# Time [Run Number] Relative Luminosity R=L ++ /L +- Luminosity vary with different spin orientation R = 1 and time dependent! 05/16/03 05/30/03 1.0 Relative Luminosity Measurement   Precision of relative luminosity monitoring critical: for A LL ~1%  A LL /A LL ~5% if  R/R~10 -3   RHIC stores up to 120 bunches per ring - different bunches injected with different spin orientation   Luminosity ~ BBC coincidence rate ( large cross section of ~27mb)   Scaler system used to count every pp collision fullfiling BBC East&West coincidence condition. Known up to  R stat ~10 -4 –10 -3 and  R syst <10 -3 8

9. Forward   Production pQCD calculations consistent with measured large-   0 cross sections Large transverse single-spin effects observed for  s = 200 GeV pp collisions Collins effect  transversity Sivers effect  orbital angular momentum k T kick in parton fragmentation initial partonic k T Additional measurements required to disentangle contributions Run-2 Results, PRL 92, 171801 (2004) 9

10. polarized beam unpolarized beam Z Y p( ,p T,  ) X Leading Charged Particle: - charged particle reconstructed in TPC for |  |< 1.0 and  with largest p T 0.4<p T < 5GeV; (momentum resolution  p/p ~ 0.02) x F < 0.05 STAR TPC A N consistent with 0 at x F ~ 0 - in agreement with pQCD models predictions. Leading Charged Particle Production at Midrapidity Run-2 Preliminary Results  10

11. Single spin asymmetries measured for p+p -> A + X, where A – hit(s) in the BBC L(R) – number of counts in Left (Right) or Top (Bottom) in the BBC East or BBC West (small annuli) counted every bunch crossing by the scaler system The BBC East and West data sets sorted by beam polarization states: 1. Polarized Yellow beam (sum over Blue beam polarization states) + heads towards the East 2. Polarized Blue beam (sum over Yellow beam polarization states) + heads towards the West BBC Transverse Single Spin Asymmetries BBC West BBC East LeftRight Top Bottom X Top Right Left Bottom 3.3<|  |< 5.0 (small tiles only) Interaction Vertex 11

12.   Unexpected A N of unknown origin measured with the BBC   Strong pseudorapidity dependence of A N for x F >0 and A N = 0 for x F <0   BBC - fast local polarimeter at STAR A N BBC = p1 A N CNI +p0 A N BBC ~0.7 A N CNI ~ 1% 3.9 <  < 5.0 A N BBC = 0 3.4 <  < 3.9 Transverse Single Spin Asymmetries BBC Preliminary (Run-3) Results CNI Asymmetry (x10 -3 ) BBC Asymmetry (x10 -3 ) 12

13. - Stable spin direction at RHIC is vertical - Spin Rotater brings to almost radial - D0/DX magnet causes spin precession - Longitudinal at IR - DX/D0/Spin Rotater put back to vertical How do we get longitudinal polarization? BBC - local polarimeter at STAR P vert P rad Rotators OFF Rotators ON CNI polarimeter BBC Longitudinal polarization at STAR (P vert and P rad < 3%) - first step to A LL measurement 13

14. Gluon polarization from inclusive jet production at  s = 200 GeV Sensitivity to the gluon polarization Jet  g=0  g=g max  g=- g max  g=g std A LL E T jet [ GeV] - - - - - - - - - - Jager, Stratmann, Vogelsang NLO pQCD calculations hep-ph/0404057 GRSV - std   <  < 1 STAR Run-5 projections P=0.4 and L int =7pb -1 GRSV pdf, Gluck et al PR D63 094005 (2001) Similar!.. 14

15. di-Jet Event Jet reconstruction at STAR - via TPC p T for charged hadrons and EMC E T for electro-magnetic showers 1) Full Barrel EMC completed for 2005 run with 120 modules covering 0 <  < 2π and |  < 1 4800 towers (sampling Pb-scintillator) + SMD + Preshower Energy resolution -  E/E ~ 0.16/√E 2) Triggers: High-Tower ( trigger bias at low jet E T ) E T > 2.4 GeV deposited in one tower (  x  = (0.05 x 0.05) Jet-Patch E T > 7 GeV over at least one “patch” (  = 1) x (  = 1) Jet E T 5-50 GeV 1 BEMC module  x  =1.0 x 0.1 3) Jets reconstruction - midpoint cone algorithm with splitting/merging Tevatron RunII, G.C. Blazey et.al. hep-ex/0005012 seed energy = 0.5 GeV, cone angle R = 0.7 in  and spliting/mering fraction f=0.5 cuts on (i) charged tracks  |  | 0.1 GeV/c (ii) jets: p T jet > 5 GeV/c   Run-3 data analysis well underway  A LL ~ 3x10 -2   Run-4 data production imminent  A LL ~ 7x10 -3 (expected)   Jet energy scale calibration in progress   Getting ready for a long Run-5 (10 weeks in 2005) :  A LL ~ 1.3x10 -3 ( planned ) Status: Present coverage  = 2π and  =1 15

16. Scale Q 2 ~ p T 2 of  Gluon polarization from Prompt Photon Production - Rare Probes at RHIC known from pDIS calculable in pQCD, The asymmetry A LL for at Leading Order:  The best determination of  G will result from a global analysis of the data from: RHIC (other channels, e.g. inclusive jet production), pDIS (HERMES, COMPASS), and possibly eRHIC through g 1 (x,Q 2 ) measurements over a wide range  Direct measurement of gluon polarization Simulated A LL HERMES: PRL 84, 2584 (2000) SMC:PRD70, 012002(2004)  G/G  Reconstructed x g Source: F.H. Heinsius, DIS 2004 16

17. Flavor Decomposition of the proton’s spin from single spin asymmetry A L PV in W boson production - Rare Probes at RHIC Semi-inclusive DIS - sensitivity reduced by fragmentation functions and e q 2 weighting W boson production in pp collisions 0.035 0.7 x x x =500GeV Produced through V-A interaction, helicity of the quark and anti-quark are fixed: A L PV (y W ) = = (W+) Ideal tool to study spin flavor structure of the proton Q 2 =M W 2 at Leading Order: Q 2 =2.5GeV 2 17

18. Summary and Outlook 1) 1)STAR spin program well under way. Essential equipment/procedures commissioned during 2002-2004: rotators, local polarimetry, accurate relative luminosity monitors; STAR detector upgrades: EMC’s, BBC’s, FPD. 2) 2)Run-2: 1 st pp collisions with transversly polarized beams  single transverse spin asymmetries: A N (  0, FPD), A N (leading h +/-,TPC) and A N (h +/- BBC) 3) Run-3 and -4: pp collisions with longitudinally polarized beams  BBC worked well as luminosity and polarization monitors   G sensitivity in jet production 4) 4)Run-5 goals and plans   G determination from A LL measurements in mid-rapidity jet production and  0 at  >1 (STAR unique!)  Sivers effects in back-to-back di-jet production (A N ) - sensitive to partonic k T Long term plan: (continuous effort for luminosity and beam polarization development needed ) Measurements with rare probes: A LL (  + jet), A L PV (W ± ) and transversity via mid- rapidity jet fragmentation