10-th Workshop on High Energy Spin Physics September 16-21, 2003, Dubna, Russia

1. 10-th Workshop on High Energy Spin Physics September 16-21, 2003, Dubna, Russia The STAR Spin Physics Program Sandibek B.Nurushev Institute for High Energy Physics, Protvino, Russia (On behalf of the STAR Collaboration)

2. Contents • Introduction • The polarized RHIC Complex • STAR detector • Lessons of the first polarized beam runs • Main goals of the STAR Spin Physics Program • Hyperon polarizations • Summary

3. Brazil: Universidade de Sao Paulo China: IHEP - Beijing IMP - Lanzhou IPP - Wuhan USTC INR - Shanghai Tsinghua University Grotia: University of Zagreb Czech Republic: NPI - AS CR Rez Great Britain: University of Birmingham France: IReS Strasbourg SUBATECH - Nantes Germany: MPI – Munich University of Frankfurt India: IOP - Bhubaneswar Panjab University University of Rajasthan Jammu University IIT - Bombay VECC - Kolcata Netherlands: NIKHEF Poland: Warsaw Univ. of Tech. Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino U.S. Laboratories: Argonne Berkeley Brookhaven U.S. Universities: Arkansas University UC Berkeley UC Davis UC Los Angeles Carnegie Mellon University Creighton University Indiana University Kent State University Michigan State University City College of New York Ohio State University Penn. State University Purdue University Rice University Texas A&M UT Austin Valparasio University Washington University Wayne State University Yale University The STAR Collaboration ~500 Collaborators12 Countries48 Institutions

4. Equipment to be installed after FY03 Polarized RHIC Complex

5. STAR – Solenoid Tracker At RHIC Spin Run0 Run1 Run2 and beyond Time Projection Chamber |h|<1.5 Magnet Coils Central Trigger Barrel |h| < 1 Silicon Vertex Tracker B=0.25T 0.5T Forward TPCs 2.4 <|h| < 4.0 2 m Endcap EMC 1< h <2 Df = 2p 4.2 m Barrel EMC 0< h< 1 Df =2p/5 |h| < 1 Df = 2p RICH: |h|<0.3, Df = p/6 Forward Pion Detector (FPD)3.1 < h < 4.4 + upgrade Beam-Beam Counters 2 .4<|h| < 5.0 18 papers in NIM A499 (2003)

6. STAR upgrades for Spin EMC (Half) Barrel STAR STAR adding lots of EM calori-metry to detect high-energy , e, 0 plus Beam-Beam Counters for relative luminosity and polarization monitoring. EMC’s and FPD’s partially implemented for 2003 run, will be completed before 2005. BBC East BBC West TPC Forward Pion Dets. (L,R,U,D on E; L,D on W) EndCap EMC (1/3) STAR uses observed asymmetry (AN~0.006) in inclusive forward charged particle production in Beam-Beam Counters: Top Interaction Vertex Left * Right Bottom BBC East 3.3<|h|< 5.0 BBC West BBC - luminosity monitoring detector at STAR • Fast, highly-segmented scintillation counter serves many purposes in STAR: • Minimum Bias Trigger • Absolute Luminosity • Relative Luminosity • Measurement of Transverse • Asymmetries See L.Bland talk

7. Lessons of the first polarized beam runsat  s=200 GeV 1. BBC detector.It revealed the asymmetry of charged particles on the level AN(1±0.2)10-3 for each run. This is comparable to AN(CNI) (3±0.3)10-3 . 2. TPC.The asymmetry of the Leading Charged Particles (LCP) is close to zero on the level AN(1±1)10-2 up to pT 4 GeV/c for charged particles of both signs. 3. FPD.It detected inclusive0asymmetry on the level AN(0.2±0.07) at xF0.5.

8. The Leading Charged Particle Asymmetry The asymptotic quark asymmetry Among the many complicated theoretical formulae the pQCD prediction for asymptotic quark asymmetry (polarization) is very simple, namely Here mq is the quark mass, mis the final hadronic mass, pT is the transverse momentum and where nf is the number of flavors.

9. The spin-orbital interaction • The soft scattering regime. It is well known from the dawn of the Spin Physics, that the spin orbital interaction (much smaller than the central potential) leads to the shift of the angular distribution of the scattered particles, so F.Halzen, Phys.Rev. 1962

10. The model of the quark polarization This above expression was modified by M.G. Ryskin(Sov. Jour. Nucl. Phys. 48 (1988) 1114). He assumed that two quarks in the colored string interact through the potential

11. The inclusive pion versus quark asymmetry The prediction can be verified at STAR

12. Global NLO QCD analysis of DIS data SLAC (E142, E143, E154, E155) CERN (EMC, SMC) DESY (HERMES) Spin-dependent PDFs 185 exp. points First moments at Q2 = 1 GeV2 DG not well constrained not extracted E. Leader, A. Sidorov, D. Stamenov Phys. Rev. D67 (2003) 074017

13. Spin Physics Program at STAR • Gluon Polarization Direct Photon + jet • Jet and DiJets • Heavy flavor production (?) • Quark / Anti-Quark Polarization & Flavor Decomposition • W production • Transversity & Transverse Spin Effects • Single transverse spin asymmetries • Transversity via Jet fragmentation • Transversity via Dijet or Drell-Yan pairs • New Physics ? • Parity violating asymmetries

14. Where is the spin of the proton? • At present, the gluon contribution to the proton spin (DG) is known only poorly from scaling violation in polarized deep inelastic scattering • STAR Spin goals: • determine the gluon contribution to the proton’s spin • determine the flavor decompositionof thequark (antiquark) polarization • probetransversity: the unknown, remaining leading-twist structure function

15. x z y Parton distributions in proton Quark chirality is conserved at all QCD and electroweak vertices, however quark chirality can flip in distribution function becausethey probe the soft regime where chiral symmetry is dynamically broken in QCD. Helicity probes quark-gluon mixingDq & DG Dq& DGProbability to find longitudinal (z direction) polarized quarks & gluons in longitudinal polarized nucleon moving in the z direction. Transversity probes dynamical chiral symmetry breaking dq Probability to find transversely (x direction) polarizedquarks in transversely polarized nucleon moving in the z direction. Helicityaverage probes quark-gluon mixingq & G q& GProbability density to find quarks in nucleon moving in the z direction helicity average helicity difference helicity flip

16. ALL(π0) Measurements at E704 A.Bazilevsky π0ALLfrom pp at s 1/2=20 GeV E704 The two-spin parameter ALL in inclusive π0 production by longitudinally-polarized protons and antiprotons on a longitudinally-polarized proton target has beenmeasured at 200 GeV Fermilab spin physics facility, for π0‘s at xF =0 with 1 ≤ pt ≤ 3 GeV/c. The results exclude, at 95% confidence level, values of ALL(pp)>0.1 and < − 0.1, for π0‘s produced by protons, and values of ALL(pp)>0.1 and < − 0.2 for incident antiprotons. The data are in good agreement with “conventional”, small or zero, gluon polarization.

17. ALL(nγ) Measurements at E704 The double-spin asymmetry, ALL, for inclusive multi-γ pair production was measured with a 200 GeV/c longitudinally-polarized proton beam and a longitudinally-polarized proton target. The ALL values were found to be consistent with zero. The ALL values have been compared with theoretical predictions of gluon polarization, ΔG/G. The results put restrictions on the size of ΔG/G in the region of 0.05<x<0.35.

18. STAR spin goals Measure of double-spin asymmetry ALL with longitudinally polarized protons Jet,di-jet production N – spin dep.yields of process L – yields of luminosity monitoring process R – relative luminosity P – beam polarization • Gluon spin-dependent distribution function • Gluon contribution to proton spin • Sign of DG N = spin dependent yields of process interest L = yield of luminosity monitoring process (high rate & spin independent) ( R = relative luminosity between different spin configuration) P = beam polarization(s) from polarimeter at RHIC “ ..A priori not even the sign of Гis known, and it may be negative.” R.L.Jaffe

19. STAR spin goals Measure of double-spin asymmetry ALL with longitudinally polarized protons N – spin dep.yields of process L – yields of luminosity monitoring process R – relative luminosity P – beam polarization Direct g production g +jet correlation • Gluon spin-dependent distribution function • Gluon contribution to proton spin • Sign of DG N = spin dependent yields of process interest L = yield of luminosity monitoring process (high rate & spin independent) ( R = relative luminosity between different spin configuration) P = beam polarization(s) from polarimeter at RHIC

20. Separate quark - Du, Dd , antiquark Du, Dd helicity distribution functions   STAR Spin Goals Measure of parity violating asymmetry AL with longitudinally polarized protons N – spin dep.yelds of process L – yields of luminosity monitoring process R – relative luminosity P – beam polarization ¯ ¯

21. STAR Spin Goals Transverse single pion asymmetry AN from E704 to STAR FNAL • ANincreases with xF and reaches 40% • AN ≈ 0 at xF≈ 0 • sign(AN) – charge(p) correlation • AN(pp) ≈ –AN(pp) • 0 - D.L. Adams, et al., Phys. Lett. B261(1991)201. • +/- - D.L. Adams, et al., Phys. Lett. B264(1991)462.

22. STAR Spin Goals Measure of double-spin longitudinal ALL and transverse ATT asymmetry for Drell-Yan pair production Longitudinally polarized density Dq Transverse polarized density dq Transversity distributions can not be measured in conventional DIS, semi-inclusive DIS is required. Transversity distributions are prime candidates for experiments at polarized proton collider.

23. STAR Spin Goals Measure of spin-transfer asymmetry Spin-dependent fragmentation function describes the transformation of a longitudinal polarized parton into a longitudinal polarized L Sensitivity to flavour polarization transfer. Negative s (1), (u+d) (2), (s+u+d)(3) transmission of polarization to L. Phenomena exist but are not understandable Measure longitudinal polarization transfer from proton beam to high-pT hyperons to probe hyperon spin structure • hadronisation • polarization transfer expected errors for STAR D.de Florian, M.Stratmann, W.Vogelsang PRL 81 (1998) 530; PR D57 (1998) 5811

24. STAR will be able after some upgrades to study a full set of the hyperon polarization parameters: I-diff. cross-section, P-polarization, AN-asymmetry, R, R’ -spin rotation parameters, A, A’ -longitudinal spin parameters, DNN -normal spin transfer parameters and Aij (i,j=n,s,l)-double spin parameters. Hyperon polarization as a probe of the QGP. Hyperon Polarization at STAR

25. STAR Spin Goals Measure of parity-violating spin asymmetry for one jet production Standard Model test Asymmetry is nonzero due to electroweak QCD interference (g & Z0) New parity-violating interactions could lead to large modifications of the SM predictions • quark compositeness • new short-range interaction Search for Measure parity-violating asymmetries for jet production at pT ~ 100 GeV/c to search for effects of new short-range interactions (over and above expected parity violation from interference of Z0 with gluon-exchange

26. G (x) determination via ALL in p + p   + jet + X   Compton annihilation Double spin asymmetry: BEMC N+(-) : Spin dependent event yield R: Relative luminosity P: Beam polarization BEMC+EEMC ALL is sensitive to DG G.Skoro, M.T., hep-ph/0009028; E2-2001-40,JINR

27. Comparison with other experiments Sensitivity to Gluon Polarization at RHIC DG reconstruction • Simulation based on Pythia including trigger and and jet reconstruction efficiencies • Coverage of EMC (barrel) + EEMC (endcap)  0 < Φ < 2π and -1 < η < 2 • Jet reconstruction: Cone algorithm (seed = 1.5 GeV, R = 0.7) • Luminosity: 320 pb-1 • Polarization: 0.7 • s = 200GeV xg , xq reconstruction STAR scans a wide range of xg=0.01-0.3

28. Sign of ? Double spin asymmetry ALL: Inclusive jet production G (x) determination via ALL in p + p  jet+ jet + X  • Simulation based on Pythia including jet reconstruction efficiencies • Coverage of EMC(barrel)+EMC(endcap)  0 < Φ < 2π and -1 < η < 2 • Jet reconstruction: Cone algorithm (seed = 1.5 GeV, R = 0.7) • Luminosity: 8.1031 cm-2 s-1 s = 200 GeV • Polarization: 0.7 ALL is sensitive to sign of DG G.Skoro, M.T., M.Zupan Nuovo Cim. A111(1998)353 Nuovo Cim. A112(1999)809

29. Flavor Decomposition of the proton’s spin – – u , d determination via ALPV in p + p  W ± + X @  s = 500 GeV   Spin parity-violated asymmetry W select spin and flavor Forward (backward) lepton measurement Blue beam toward endcap Yellow beam away from endcap Detect W± in STAR via isolated high-pT daughter lepton, without away-side jet

30. Summary • Single spin asymmetryAN is measured by BBC. Precision is <10-3 allowing to control the transversal components of the beam polarization. • Significant single spin asymmetry in the inclusive 0 production is revealed by FPD in the polarized proton beam large xF region at s1/2 =200 GeV. • Firstsingleanddouble spin measurements in inclusive LCP production are made at STAR with transversally polarized protons. Measurements were done in the level of precision <10-2. Asymmetries are compatible with zero. • New measurements were done in this year with longitudinally polarized protons. • STAR at RHIC started a new generation of proton spin structure studies • gluon contribution to the proton’s spin • spin/flavor decomposition of the sea • double-spin asymmetries • polarization transfer • transversity

31. STAR Spin Results: Forward Pion Asymmetry and Cross Section p + p  “p0”+ X , s = 200 GeV STAR PRELIMINARY • Measured cross sections consistent with pQCD calculations. • Large spin effects observed for s = 200 GeV pp collisions, qualitatively • consistent with models extrapolating from FNAL E704 data at s = 20 GeV. • Large normalization uncertainty on measured AN is reduced when Pbeam • calibration exp’t is done.