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BRAHMS Spin and p+p results

BRAHMS Spin and p+p results. Short Introduction Preliminary Results on p ,K,p Single Spin Asymmetries and Spectra from Run5 at high-x F /rapidities Summary/Prospects. J.H. Lee (BNL) for BRAHMS Collaboration. June 8 th 2006 RHIC Users’ Meeting.

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BRAHMS Spin and p+p results

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  1. BRAHMS Spin and p+p results • Short Introduction • Preliminary Results on • p,K,p Single Spin Asymmetries • and Spectra from Run5 • at high-xF/rapidities • Summary/Prospects J.H. Lee (BNL)for BRAHMS Collaboration June 8th 2006 RHIC Users’ Meeting

  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?

  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

  4. Determination of Single Spin Asymmetry: AN • Asymmetries are defined as • 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%)

  5. 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 pb-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 Run5 SSA measurements in BRAHMS

  6. 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

  7. Particle Identification using RICH 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%

  8. 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% • point-to-point variations include pT-dependence of AN from <pT> variations in xF bins • AN(p+): positive ~(<) AN(p-): negative: 5-10% in 0.1 <xF< 0.3 • pT range is limited by PID and statistics

  9. 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

  10. pT dependent AN of p+ and p- p+ p- • xF and pT dependence: • increasing with xF and decreasing with pT

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

  12. 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)

  13. 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

  14. Forward proton and pbar production in pp at √s=200 GeV BRAHMS Preliminary • proton and pbar production at high-y, pT :Very different production mechanism (fragmentation vs. baryon transport) • p/p+ >> pbar/p- (~x10)

  15. AN of proton and pbar pbar p • AN(pbar) ≠ 0 and positive • AN(p) ~ 0: At this kinematic region, protons are mostly from polarized beam proton, but only ones showing AN ~0 • Need theoretical inputs

  16. 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 mKKP (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)

  17. BRAHMS has obtained particle spectra and 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 Cross-section described by NLO pQCD (with updated/modified FFs) Proton production requires extra production mechanism in addition to fragmentation even at high-pT AN(p+): positive ~(<) AN(p-): negative: 5-10% in 0.1 < xF < 0.3 increasing with xF and decreasing with pT AN(p+) 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 of small sea quark polarization. Lack of understanding of p, pbar polarization: Need more theoretical inputs. Summary

  18. BRAHMS SSA Measurements at 62 GeV • BRAHMS will measure SSA at 62 GeV in RHIC/Run6 • 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.

  19. 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: -Expect to have interesting results from 62 GeV Run6 -Minimizing experimental systematic uncertainties -Extending kinematic coverage Theoretical Challenges

  20. 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

  21. Back-Up Slides

  22. 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

  23. 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

  24. 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

  25. Anti-particle/Particle ratios at y~3 and NLO comparisons

  26. p- Spin-Up/Spin-Down

  27. p- / -xF

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