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William Christie, BNL Mini-symposium on Orbital Motion of Quarks in Hard Scattering I

Transverse Spin Results from 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. Outline Physics motivation

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William Christie, BNL Mini-symposium on Orbital Motion of Quarks in Hard Scattering I

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  1. Transverse Spin Results from 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. • Outline • Physics motivation • Brief introduction to the STAR Detector • STAR Transverse polarization Data sets • Cross section measurements • Forward 0 asymmetry • Future measurements • Summary

  2. The STAR Collaboration 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

  3. (DS)  G+ L Physics Motivation Proton Spin: Quark spinGluon SpinAngular momentum 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. DS ~ 0.2) 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 transversespinpreferences in a transversely polarized proton (p)  “transversity”  quark property decoupled from gluons b) quark and gluon transversemotionpreferences in p  spin-kT correlation related to quark/gluon orbital ang. mom.

  4. Barrel EM Calorimeter -1<η< 1 Triggering STAR Detector h - ln(tan(q/2) Lum. Monitor Local Polarim. Forward TPC 2.8 <  < 3.8 Beam-Beam Counters 2<|η|< 5 =0 Central Trigger Barrel = -1 =2 Silicon Vertex Tracker Triggering Endcap EM Calorimeter Forward Pion Detector 1<η< 2 -4.1<η< -3.3 Solenoidal Magnetic Field (5 kG) analyzes transverse momentum pT of charged particles Time Projection Chamber -1<η< 1  2003 2004 2005 Tracking

  5. East of STAR North South Top To STAR Bottom Transverse Polarization Data sets and FPD Configurations 2002 Run: <Pb> ~ 15%, Lint = 0.3 pb-1 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 2003 Run: <Pb> ~ 30%, Lint = 0.5 pb-1 • Upgraded Forward  Detector (FPD) • Pb-glass EM calorimeter • (from IHEP Protovino, used in E704) • Shower-Maximum Detector (SMD) • Preshower

  6. Polarization Pattern at STAR: Spin Up Spin Down Unpolarized Spin asymmetries in proton-proton collider 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 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 Single Spin Asymmetries (F.o.M = P2L) interactions (kHz)/crossing AN with left-right symmetric detectors Double Spin Asymmetries (F.o.M = P4L) bunch crossing number at STAR IR

  7. Top Interaction Vertex Left * Right Bottom BBC East 3.3<||< 5.0 (inner tiles) BBC West BBC gives triggering, (Rel.) Luminosity, and local polarimetry. 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 ANobs.~0.006. • Statistical uncertainty: dRstat ~10-4 -10-3 • Systematic uncertainty ( beam-gas background ) < 10-3 Example of R 2.1 <||< 5.0 R  1 and time dependent! 05/16/03 05/30/03 Time [Run Number] Positive xF Negative xF • = BBC L/R asym. •  = BBC T/B asym. BBC YCNI BCNI

  8. <z> <xq> <xg> Forward 0 production in a hadron collider Ep p0 p d EN qq qp p Au xgp xqp qg EN (collinear approx.) • Large rapidity p production (hp~4) probes asymmetric partonic collisions • Mostly high-x valence quark + low-x gluon • 0.3 < xq< 0.7 • 0.001< xg < 0.1 • <z> 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 NLO pQCD Jaeger,Stratmann,Vogelsang,Kretzer

  9. 2002 STAR Forward p0 Detector (aka pEEMC) p0 reconstruction at E=20~80GeV, 1 <pT < 4 GeV 3<h<4 Event Display SMD EMC M • Cluster separation in shower maximum detector and measured calorimeter energy serves as input to the 0 mass determination.

  10. Run 2 Results: Forwardp0Inclusive Cross Section • 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 = pT • Solid and dashed curves differ primarily in the g   fragmentation function 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)

  11. Run 2 Results: Large Analyzing Powers at RHIC STAR First measurement of AN for forward π0 production at s=200GeV Similar to FNAL E704 result at s = 20 GeV In agreement with several models including different dynamics: STAR collaboration, hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801 • 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 First shown at spin2002 • pT dependence? • xF<0? • AN with mid-rapidity correlation? • Spin dependence in jet?

  12. Run 3 Results: AN for forward & backward p0 production at s=200GeV Statistical error only for <h>=4.1 • Positive AN at large positive xF has been confirmed • Larger significance to be non-zero & positive than published data Thefirst measurement of negative xF AN has been done, and is consistent with zero •  Sensitive to twist-3 gluon-gluon correlation STAR Preliminary

  13. Run 3 Results: Add 0 cross sections at  = 4.0 xF and pT range of the data Different position for FPD relative to the beam, relative to already accumulated 2002 data, allows mapping of AN in xF and pT plane to begin

  14. Outlook Current FPD • Disentangling the dynamics of AN via • Higher precision AN measurement vs xF and pT • AN 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 kT balance  gluon Sivers function • Inside jet particle correlation  Collins function * Transversity h=4.2 h=3.2 ~2.4m square ~1500 cells h=2.5

  15. 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 p0 mesons at large positive xF was found to be large and positive • The first measurement of negative xF AN 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. Backup

  17. Coincidence Transverse Spin Measurements Should Unravel Transversity, Collins, Sivers Effects p spin AN pp  dijet + X s = 200 GeV 8  pT(1,2)  12 GeV |(1,2)|  1.0  p q + g  p D. Boer & W. Vogelsang predictions Jets with 2 hadrons detected  p q + … q p • 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 Lorbit ) 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, Pbeam=70% parton kT

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

  19. σf=0.23 ± 0.02± 0.03 0.05 STAR Partonic kT from Dijet Analysis Sivers Effect Prediction T. Henry 4.1 x 10 -4 D. Boer and W. Vogelsang, Phys.Rev. D 69 (2004) 094025 8 < pT1,2 < 12 GeV |η1,2 | < 1 AN kT = <kT>2 = ET sin (σf) ET = 13.0 ± 0.7sys → Trigger Jet STAR agrees well with World Data on Partonic kT df kT distribution • Curves are for various gluonic Sivers functions • Connection to partonic orbital angular momentum • Suppressed by Sudakov effect

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