1. STAR William Christie, BNL Mini-symposium on Orbital Motion of Quarks in Hard Scattering I 2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and the Physical Society of Japan September 21, 2005. Transverse Spin Results from STAR Outline Physics motivation Brief introduction to the STAR Detector STAR Transverse polarization Data sets Cross section measurements Forward  0 asymmetry Future measurements Summary

2. STAR 500+ collaborators 52 institutions 14 countries Austria: Bern Brazil: Sao Paolo China: IHEP-Beijing, IMP-Lanzhou, Shanghai INR, Tsinghua, USTC, IPP-Wuhan Croatia: Zagreb Czech Republic: Nuclear Physics Institute-AS-CR England: Birmingham France: IReS - Strasbourg, SUBATECH-Nantes Germany: Frankfurt, MPI-Munich India: Bhubaneswar, Jammu, IIT, Panjab, Rajasthan, VECC-Kolkata Netherlands: NIKHEF Poland: Warsaw U. of Technology Russia: JINR - Dubna, IHEP – Protvino, MEPHI - Moscow S. Korea: Pusan U.S.: Argonne, Berkeley, Brookhaven National Laboratories UC Berkeley, UC Davis, UCLA, CalTech, Creighton, Carnegie-Mellon, Indiana, Kent State, Michigan State, CCNY, Ohio State, Penn State, Purdue, Rice, Texas, Texas A&M, Valparaiso, Washington, Wayne State, Yale Universities The STAR Collaboration

3. STAR Physics Motivation It has been determined, through polarized deep inelastic scattering experiments, that the quarks alone can not account for the spin of the proton (i.e.  To account for the spin of the proton, either the gluons are polarized and/or there are significant contributions to the protons spin from the orbital motion of its constituents. Would like to unravel the contributions to transverse spin asymmetries (an area of intense recent theoretical development) from: a) quark transverse spin preferences in a transversely polarized proton (p  )  “transversity”  quark property decoupled from gluons b) quark and gluon transverse motion preferences in p   spin-k T correlation related to quark/gluon orbital ang. mom.  G + L Quark spin Gluon Spin Angular momentum Proton Spin:

4. STAR Barrel EM Calorimeter -1<η< 1 STAR Detector  =0 Forward Pion Detector Endcap EM Calorimeter Beam-Beam Counters Time Projection Chamber -1<η< 1 1<η< 2 -4.1<η< -3.3 2<|η|< 5 Solenoidal Magnetic Field (5 kG) analyzes transverse momentum p T of charged particles  =2  = -1 Tracking 200320042005 Triggering h  - ln(tan(q/2) Lum. Monitor Local Polarim.  Forward TPC 2.8 <  < 3.8 Central Trigger Barrel Silicon Vertex Tracker

5. STAR Transverse Polarization Data sets and FPD Configurations 2002 Run: ~ 15%, L int = 0.3 pb -1 2003 Run: ~ 30%, L int = 0.5 pb -1 Upgraded Forward   Detector (FPD) Pb-glass EM calorimeter (from IHEP Protovino, used in E704) Shower-Maximum Detector (SMD) Preshower Forward   Detector (FPD, aka pEEMC) - 24 layer Pb-scintillator sampling calorimeter - 2 orthogonal planes of finely segmented triangular scintillator strips (Shower-Maximum Detector, or SMD) - 2 Preshower layers East of STAR Top Bottom NorthSouth

6. STAR Polarization Pattern at STAR: Spin Up Spin Down Unpolarized Spin asymmetries in proton-proton collider Double Spin Asymmetries (F.o.M = P 4 L) Single Spin Asymmetries (F.o.M = P 2 L) N = spin dependent yields of process interest L = yield of luminosity monitoring process R = relative luminosity between different spin configuration P = beam polarization(s) from polarimeter at RHIC Also need direction of polarization vector at IR A N with left-right symmetric detectors Requires 3 different process/measurements “Bunch/Spin sorting” Up to 120 bunches in RHIC Bunch Spacing 107nsec (9MHz) Alternating spin pattern Bunch/Spin sorted scaler system bunch crossing number at STAR IR interactions (kHz)/crossing

7. STAR Left Right Top Bottom * BBC West BBC East Interaction Vertex 3.3<|  |< 5.0 (inner tiles) BBC’s register hits for ~50% of  tot (pp); E  W coinc. discriminates against beam-gas bkgd. for good L monitoring; segmentation  local polarimeter with A N obs. ~0.006. Example of R Statistical uncertainty: dR stat ~10 -4 -10 -3 Systematic uncertainty ( beam-gas background ) < 10 -3 BBC gives triggering, (Rel.) Luminosity, and local polarimetry. Negative x F Positive x F = BBC L/R asym.  = BBC T/B asym. Time [Run Number] 2.1 <|  |< 5.0 R  1 and time dependent! 05/16/03 05/30/03  BBC  Y CNI  B CNI

8. STAR NLO pQCD Jaeger,Stratmann,Vogelsang,Kretzer Forward  0 production in a hadron collider Large rapidity  production   ~4  probes asymmetric partonic collisions Mostly high-x valence quark + low-x gluon 0.3 < x q < 0.7 0.001< x g < 0.1 nearly constant and high 0.7 ~ 0.8 Large-x quark polarization is known to be large from DIS Directly couple to gluons = A probe of low x gluons pdpd p Au  qq gg ENEN xqpxqp xgpxgp   ENEN (collinear approx.)

9. STAR 2002 STAR Forward   Detector (aka pEEMC) M    reconstruction at E=20~80GeV, 1 <p T < 4 GeV 3<  <4 Event Display SMD EMC o Cluster separation in shower maximum detector and measured calorimeter energy serves as input to the  0 mass determination.

10. STAR Run 2 Results: Forward   Inclusive Cross Section STAR data consistent with Next-to-Leading Order pQCD calculations in contrast to data at lower  s (Bourrely and Soffer, Eur.Phys.J. C36 (2004) 371-374 ) STAR data at  = 3.8 (hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801 )  = 3.3 (hep-ex/0403012, Preliminary) NLO pQCD calculations at fixed  with equal factorization and renormalization scales = p T Solid and dashed curves differ primarily in the g   fragmentation function

11. STAR Run 2 Results: Large Analyzing Powers at RHIC First measurement of A N for forward π 0 production at  s=200GeV Similar to FNAL E704 result at  s = 20 GeV In agreement with several models including different dynamics:  Sivers: spin and k  correlation in initial state (related to orbital angular momentum?)  Collins: Transversity distribution function & spin-dependent fragmentation function  suppressed? ( hep-ph/0408356 )  Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations STAR collaboration, hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801 STAR First shown at spin2002 p T dependence? x F <0? A N with mid-rapidity correlation? Spin dependence in jet?

12. STAR Run 3 Results: A N for forward & backward  0 production at  s=200GeV Positive A N at large positive x F has been confirmed  Larger significance to be non-zero & positive than published data The first measurement of negative x F A N has been done, and is consistent with zero  Sensitive to twist-3 gluon-gluon correlation STAR Preliminary Statistical error only for =4.1

13. STAR Different position for FPD relative to the beam, relative to already accumulated 2002 data, allows mapping of A N in x F and p T plane to begin x F and p T range of the data Run 3 Results: Add  0 cross sections at  = 4.0

14. STAR Outlook Disentangling the dynamics of A N via Higher precision A N measurement vs x F and p T A N with mid rapidity correlation Forward jet Proposal for forward calorimeter upgrade Heavy mesons and direct photons Low x gluons in nuclei Mid rapidity jets Di-jet k T balance  gluon Sivers function Inside jet particle correlation  Collins function * Transversity ~2.4m square ~1500 cells  =4.2  =3.2  =2.5 Current FPD

15. STAR Summary Forward hadron production at hadron-hadron collider selects high-x (thus high polarization) quark + low-x gluon scatterings Inclusive cross section is consistent with NLO pQCD calculations and PYTHIA(LO pQCD + parton showers) Analyzing power for forward  0 mesons at large positive x F was found to be large and positive The first measurement of negative x F A N has been done, and is consistent with zero Accumulation of significant (O 10 pb -1, P  50%) transverse polarization data set expected in upcoming FY06 RHIC run. Expect to start extracting information on dynamics responsible for transverse spin asymmetries.

16. STAR Backup

17. STAR Coincidence Transverse Spin Measurements Should Unravel Transversity, Collins, Sivers Effects p  p q g Jets with  2 hadrons detected + + … p p  q q  Study transversity by exploiting chiral-odd fragment’n “analyzing powers” (Collins or interference frag. fcns.) calibrated at BELLE  Search for spin-dependent transverse motion preferences inside proton (related to parton L orbit ) via predicted leading-twist spin- dependent deviation from back-to-back alignment of di-jet axes  study unique to RHIC spin STAR projections for 30 pb  1, P beam =70% parton k T ANAN pp  dijet + X  s = 200 GeV 8  p T (1,2)  12 GeV |  (1,2)|  1.0 D. Boer & W. Vogelsang predictions  p spin

18. STAR D. Boer and W. Vogelsang, Phys.Rev. D 69 (2004) 094025 Analyzing Powers at Mid-Rapidity Do processes invoked in forward scattering show up at large angles? Sivers Function – correlation between k T and spin For given parton at some x k T L =k T R Jet Measure STAR STAR Collab. Phys. Rev. Lett. 92 (2004) 171801

19. STAR 4.1 x 10 -4 Partonic k T from Dijet Analysis k T =  2 = E T sin (σ f ) E T = 13.0 ± 0.7 sys → Trigger Jet 0.03 0.05 σ f =  0.23 ± 0.02  ± df 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) 094025 Curves are for various gluonic Sivers functions Connection to partonic orbital angular momentum Suppressed by Sudakov effect k T distribution STAR T. Henry