1. STAR 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. STAR 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 Contents

3. STAR 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 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 The STAR Collaboration ~ 500 Collaborators 12 Countries 48 Institutions

4. STAR Equipment to be installed after FY03 Polarized RHIC Complex

5. STAR STAR – Solenoid Tracker At RHIC Run0Run1Run2 and beyondSpin Magnet Coils B=0.25T0.5T Endcap EMC 1<  <2  = 2  Barrel EMC 0<  < 1  =2  |  | < 1  = 2  Forward Pion Detector (FPD) 3.1 <  < 4.4 + upgrade Time Projection Chamber |  <1.5 Silicon Vertex Tracker Forward TPCs 2.4 < |  | < 4.0 Beam-Beam Counters 2.4< |  | < 5.0 RICH: |  |<0.3,  =  Central Trigger Barrel |h| < 1 2 m 4.2 m 18 papers in NIM A499 (2003)

6. STAR Left Right Top Bottom * BBC West BBC East Interaction Vertex 3.3<|  |< 5.0 STAR uses observed asymmetry (A N ~0.006) in inclusive forward charged particle production in Beam-Beam Counters: 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 STAR upgrades for Spin STAR EndCap EMC (1/3) EMC (Half) Barrel Forward Pion Dets. (L,R,U,D on E; L,D on W) 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 West BBC East TPC See L. Bland talk

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

8. STAR The Leading Charged Particle Asymmetry Among the many complicated theoretical formulae the pQCD prediction for asymptotic quark asymmetry (polarization) is very simple, namely Here m q is the quark mass, m is the final hadronic mass, p T is the transverse momentum and where n f is the number of flavors. The asymptotic quark asymmetry

9. STAR 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. STAR 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 The model of the quark polarization

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

12. STAR Global NLO QCD analysis of DIS data SLAC (E142, E143, E154, E155) CERN (EMC, SMC) DESY (HERMES) 185 exp. points E. Leader, A. Sidorov, D. Stamenov Phys. Rev. D67 (2003) 074017  G not well constrained not extracted Spin-dependent PDFs First moments at Q 2 = 1 GeV 2

13. STAR 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. STAR Where is the spin of the proton? At present, the gluon contribution to the proton spin (  G) 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 decomposition of the quark (antiquark) polarization probe transversity : the unknown, remaining leading-twist structure function

15. STAR Parton distributions in proton Helicity probes quark-gluon mixing  q  G  q &  G Probability to find longitudinal (z direction) polarized quarks & gluons in longitudinal polarized nucleon moving in the z direction. Transversity probes dynamical chiral symmetry breaking  q Probability to find transversely (x direction) polarized quarks in transversely polarized nucleon moving in the z direction. x y z Helicity average probes quark-gluon mixing q & G q & G Probability density to find quarks in nucleon moving in the z direction helicity difference helicity flip Quark chirality is conserved at all QCD and electroweak vertices, however quark chirality can flip in distribution function because they probe the soft regime where chiral symmetry is dynamically broken in QCD. helicity average

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

17. STAR A LL (n γ ) Measurements at E704 The double-spin asymmetry, A LL, for inclusive multi-γ pair production was measured with a 200 GeV/c longitudinally-polarized proton beam and a longitudinally-polarized proton target. The A LL values were found to be consistent with zero. The A LL 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 STAR spin goals Gluon spin-dependent distribution function Gluon contribution to proton spin Sign of  G Jet, di-jet production Measure of double-spin asymmetry A LL with longitudinally polarized protons “.. A priori not even the sign of Г is known, and it may be negative.” R.L.Jaffe N – spin dep.yields of process L – yields of luminosity monitoring process R – relative luminosity P – beam polarization N = spin dependent yields of process interest L = yield of luminosity monitoring process (high rate & spin independent) ( R = relative luminosity between different spin configuration) ( R = relative luminosity between different spin configuration) P = beam polarization(s) from polarimeter at RHIC

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

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

21. STAR STAR Spin Goals ●  0 - D.L. Adams, et al., Phys. Lett. B261(1991)201. ●  +/- - D.L. Adams, et al., Phys. Lett. B264(1991)462. Transverse single pion asymmetry A N from E704 to STAR FNAL A N increases with x F and reaches 40% A N ≈ 0 at x F ≈ 0 sign( A N ) – charge(   correlation A N ( pp ) ≈ – A N ( pp )

22. STAR STAR Spin Goals Measure of double-spin longitudinal A LL and transverse A TT asymmetry for Drell-Yan pair production Longitudinally polarized density  q Transverse polarized density  q 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 STAR Spin Goals Measure of spin-transfer asymmetry Spin-dependent fragmentation function describes the transformation of a longitudinal polarized parton into a longitudinal polarized  Measure longitudinal polarization transfer from proton beam to high-pT hyperons to probe hyperon spin structure hadronisation polarization transfer D. de Florian, M.Stratmann, W.Vogelsang PRL 81 (1998) 530; PR D57 (1998) 5811 Sensitivity to flavour polarization transfer. Negative s (1), (u+d) (2), (s+u+d)(3) transmission of polarization to . Phenomena exist but are not understandable expected errors for STAR

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

25. STAR STAR Spin Goals Measure of parity-violating spin asymmetry for one jet production Standard Model test New parity-violating interactions could lead to large modifications of the SM predictions Asymmetry is nonzero due to electroweak QCD interference (g & Z 0 ) 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 quark compositeness new short-range interaction Search for

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

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

28. STAR Double spin asymmetry A LL : Inclusive jet production l Simulation based on Pythia including jet reconstruction efficiencies l Coverage of EMC(barrel)+EMC(endcap)  0 < Φ < 2π and -1 < η < 2 l Jet reconstruction: Cone algorithm (seed = 1.5 GeV, R = 0.7) l Luminosity: 8.10 31 cm -2 s -1  s = 200 GeV l Polarization: 0.7 Sign of ? G.Skoro, M.T., M.Zupan Nuovo Cim. A111(1998)353 Nuovo Cim. A112(1999)809  G (x) determination via A LL in p + p  jet+ jet + X  A LL is sensitive to sign of  G

29. STAR Flavor Decomposition of the proton’s spin Forward (backward) lepton measurement Blue beam toward endcap Yellow beam away from endcap W select spin and flavor Spin parity-violated asymmetry Detect W ± in STAR via isolated high-p T daughter lepton, without away-side jet   u,  d determination via A L PV in p + p  W ± + X @  s = 500 GeV –

30. STAR Summary Single spin asymmetry A N 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 x F region at s 1/2 =200 GeV. First single and double 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 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 A N is reduced when P beam calibration exp’t is done. p  + p  “   ”+ X,  s = 200 GeV STAR Spin Results: Forward Pion Asymmetry and Cross Section Forward Pion Asymmetry and Cross Section STAR PRELIMINARY