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SSA in BRAHMS

SSA in BRAHMS. Short Introduction Preliminary results on p ,K,p SSA from RHIC/Run-5 Summary/Prospects. J.H. Lee (BNL) for BRAHMS Collaboration. DIS2006, Tsukuba, April 2006. Single transverse Spin Asymmetry (SSA): Introduction.

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SSA in BRAHMS

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  1. SSA in BRAHMS • Short Introduction • Preliminary results on • p,K,p SSA from RHIC/Run-5 • Summary/Prospects J.H. Lee (BNL)for BRAHMS Collaboration DIS2006, Tsukuba, April 2006 J.H. Lee (BNL)

  2. Single transverse Spin Asymmetry (SSA): Introduction • Large SSAs have been observed at forward rapidities in hadronic reactions: E704/FNAL and STAR/RHIC • SSA is suppressed in naïve parton models (~smq/Q ) • Non-zero SSA at partonic level requires • Spin Flip Amplitude, and • Relative phase • SSA: Unravelling the spin-orbital motion of partons? J.H. Lee (BNL)

  3. Spin and Transverse-momentum-dependent parton distributions -Final state in Fragmentation (Collins effect), -Initial state in PDF (Sivers effect) Twist-3 matrix effects -Hadron spin-flip through gluons and hence the quark mass is replaced by ΛQCD -Efremov,Teryaev (final state) -Qiu,Sterman (initial state) Or combination of above -Ji, Qiu,Vogelsang,Yuan… Challenge to have a consistent partonic description: -Energy dependent SSA vs xF,pT, -Flavor dependent SSA -Cross-section Beyond Naïve Parton Models to accommodate large SSA J.H. Lee (BNL)

  4. BRAHMS measures identified hadrons (p,K,p,pbar) in kinematic ranges of 0<Y<3.5 and 0.2 <pT<4 pT dependent SSA in 0 < x < 0.35 (and -0.35 < x < 0) utilizing blue (and yellow) beam (xF, pT, flavor dependent AN) Cross-section of hadron production (Theoretical consistency) Data: Run-4: First SSA measurements in BRAHMS Run-5: pp at √s = 200 GeV 2.5 nb-1 recorded (this Talk) Run-6: pp at √s = 62 GeV planned (Energy dependence) This talk will focus on AN(p,K,p,pbar) in 0.1 < x < 0.35 from Run-5 SSA measurements in BRAHMS J.H. Lee (BNL)

  5. Braod RAnge Hadron Magnetic Spectrometers • Designed to study nuclear reactions in broad kinematic range (y-pT) • 2 movable spectrometers with small solid angle measuring charged identified hardrons precisely • Min-Bias Trigger Detector for pp (run05): ”CC” counter • Local polarimeter, SMD in Run-5 pp (analysis in progress) • 53 people from 12 institutions from 5 countries J.H. Lee (BNL)

  6. Kinematic Variables and Acceptances • The kinematic variables used for SSA: Feynman-x (xF) and pT • Shown is the BRAHMS acceptance for the data taken at  = 2.3°and the maximum field setting (7.2 Tm). • Strong xF-pT correlation due to limited spectrometer solid angle acceptance • The momentum resolution is dp/p~1% at 22 GeV/c J.H. Lee (BNL)

  7. RICH Particle Identification Multiple settings • PID for the analysis: Ring Image Cherenkov Counter • p,K identification < 30 GeV/c and proton,pbar > 17 GeV/c with efficiency ~ 97% J.H. Lee (BNL)

  8. Min-Bias Trigger / Normalization Counter:“CC” (Cherenkov Radiators) • Covers ~70% of pp inelastic cross-section (41mb) • 3.25 < |h|< 5.25 range • Vertex resolution s(z)~ 1.6cm • Main relative luminosity monitor for SSA analysis • ±80cm in z used in the analysis J.H. Lee (BNL)

  9. Determination of Single Spin Asymmetry: AN • Asymmetries are defined AN= (s+ - s- )/(s+ + s-) = e /P • For non-uniform bunch intensities e = (N+ /L+ - N-/L-) / (N+ /L+ + N-/L-) = (N+ - L*N-) / (N+ + L*N-) where L = relative luminosity = L+ / L- and the yield of in a given kinematic bin with the beam spin direction is N+ (up) and N- (down). • The polarization P of the beam was ~50% in the RHIC Run-5 (Blue beam) • Beam polarization P from on-line measurements: (systematic uncertainty ~15%) J.H. Lee (BNL)

  10. Relative luminosity L = L+ /L- determination • Using CC in spin scaler 80cm • Consistent with CC recorded in data stream • Relative luminosity calculated by Beam-Beam Counter and CC: < 0.3% • Systematic effect on bunch number dependent beam width: negligible J.H. Lee (BNL)

  11. AN of p+ and p- p+ p- • FS (Front+Back) setting: 2.3°+2.3° and 4°+4° • Statistical errors only • Systematic error estimated ~ 25% • AN(p+): positive ~(<) AN(p-): negative: 5-10% in 0.1 <xF< 0.3 • pT range is limited by PID and statistics J.H. Lee (BNL)

  12. Acceptance and Statistics in pT vs xF Counts FS(Front+Back) setting: 2.3o+2.3o 4o+4o FS(Front+Back) setting: 3o+2.3o AN • Statistically Challenging to do 2-d analysis • Indication of pT dependence: AN decrease with pT at fixed xF • Lower field settings to cover lower pT and extending PID is in progress J.H. Lee (BNL)

  13. Data vs Theory (Twist-3) for p+ Data (p+) Twist-3 (initial state) calculations by Qiu and Sterman: Extrapolated to lower pT region Phys. Rev D59 014004 (98) J.H. Lee (BNL)

  14. AN for Kaons BKK FF BKK FF rescaled K+ K- Anselmino and Murgia PLB442 (1998) 470-478 • Strong strangeness FF dependence in prediction • If main contribution to AN at large xF is from valence quarks: AN(K+)~AN(p+), K- ~0 • BKK (Binnewies, Kniehl, Kramer 1995) J.H. Lee (BNL)

  15. AN of Kaon K+ K- • AN(K+): positive ~ AN(K-): positive ≠ 0 for 0.2 <xF <0.3 • AN for lower and higher xF require including extended PID and lower field setting data: Work in progress but statistically challenging • Consistent with un-scaled BKK FF: in disagreement with naïve expectations J.H. Lee (BNL)

  16. Forward proton and pbar production in pp at √s=200 GeV BRAHMS Preliminary • Very different production mechanism (baryon transport) for p and pbar at forward • p/p+ >> pbar/p- (~x10) J.H. Lee (BNL)

  17. AN of proton and pbar • AN(pbar) ≠ 0 and positive • AN(pbar) ~ AN(K-)? Accidental? • AN(p) ~ 0: At this kinematic region, protons are mostly from polarized beam proton, but only ones showing AN ~0 • Need theoretical inputs J.H. Lee (BNL)

  18. Charged Hadron production at Forward vs NLO pQCD BRAHMS Preliminary • NLO pQCD describes data at forward rapidity at 200 GeV • p- ,K- are described best by KKP (Kniehl-Kramer-Potter) than Kretzer FF • pbar is described best by AKK (Albino-Kniehl-Kramer) FF (light flavor separated) (NLO pQCD Calculations done by W. Vogelsang. mKKP: “modified” KKP for charge separations for p and K) J.H. Lee (BNL)

  19. BRAHMS has obtained preliminary results for single transverse spin asymmetries for p±,K±, p, and pbar in √s =200 GeV pp collisions at RHIC in the xF range of 0.1 to 0.35 AN(p+): positive ~(<) AN(p-): negative: 5-10% in 0.1 < xF < 0.3 AN(p+) for 0.2 <x in agreement with Twist-3 calculations First SSA Results on K, p in 0.1 < xF < 0.3 - AN(K+) ~ AN(K-): positive - AN(p) ~0, AN(pbar): positive AN(K) in disagreement with naïve expectation from valence quark fragmentation. Need more theoretical inputs. BRAHMS Also measured cross-sections for p±,K±, p, and pbar in the same kinematic ranges described by NLO pQCD (with updated/modified FFs) Summary J.H. Lee (BNL)

  20. BRAHMS SSA Measurement at 62 GeV • BRAHMS will measure SSA at 62 GeV in RHIC/Run06 • Acceptance will reach kinematic limit, but SSA measurement up to xF~ 0.6 with statistical significance • Measurements at 62 GeV offers an opportunity to address an intermediate energy (RHIC-FNAL) to clarify to what degree the SSA are describable by pQCD, or is a ‘soft’ physics effect. J.H. Lee (BNL)

  21. BRAHMS xF, pT, flavor, and energy-dependent SSA and cross-section measurements: ingredient for consistent (partonic) description at RHIC energy regime: Exciting theoretical challenges We will work on our part: -Minimizing experimental systematic uncertainties -Extending kinematic coverage Theoretical Challenges J.H. Lee (BNL)

  22. The BRAHMS Collaboration I.Arsene7, I.G. Bearden6, D. Beavis1, S. Bekele6 , C. Besliu9, B. Budick5, H. Bøggild6 , C. Chasman1, C. H. Christensen6, P. Christiansen6, R. Clarke9, R.Debbe1, J. J. Gaardhøje6, K. Hagel7, H. Ito10, A. Jipa9, J. I. Jordre9, F. Jundt2, E.B. Johnson10, C.E.Jørgensen6, R. Karabowicz3, E. J. Kim4, T.M.Larsen11, J. H. Lee1, Y. K. Lee4, S.Lindal11, G. Løvhøjden2, Z. Majka3, M. Murray10, J. Natowitz7, B.S.Nielsen6, D. Ouerdane6, R.Planeta3, F. Rami2, C. Ristea6, O. Ristea9, D. Röhrich8, B. H. Samset11, D. Sandberg6, S. J. Sanders10, R.A.Sheetz1, P. Staszel3, T.S. Tveter11, F.Videbæk1, R. Wada7, H. Yang6, Z. Yin8,and I. S. Zgura9 1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France 3Jagiellonian University, Cracow, Poland, 4Johns Hopkins University, Baltimore, USA, 5New York University, USA 6Niels Bohr Institute, University of Copenhagen, Denmark 7Texas A&M University, College Station. USA, 8University of Bergen, Norway 9University of Bucharest, Romania,10University of Kansas, Lawrence,USA 11 University of Oslo Norway J.H. Lee (BNL)

  23. Backup Slides J.H. Lee (BNL)

  24. MRS: h- in 0.5<pT<1 GeV/c and 1<pT<1.5 GeV/c J.H. Lee (BNL)

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