1 / 33

SSA in BRAHMS

SSA in BRAHMS. Preliminary Results on p ,K,p Transverse Single Spin Asymmetries at 200 GeV and 62 GeV at high-x F. J.H. Lee (BNL) for BRAHMS Collaboration. Sep. 29 th 2006 RHIC-SPIN Collaboration Meeting. Single transverse Spin Asymmetry (SSA): Introduction.

jeneil
Download Presentation

SSA in BRAHMS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. SSA in BRAHMS Preliminary Results on • p,K,p Transverse Single Spin Asymmetries • at 200 GeV and 62 GeV • at high-xF J.H. Lee (BNL)for BRAHMS Collaboration Sep. 29th 2006 RHIC-SPIN Collaboration 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. BRAHMS measures identified hadrons (p,K,p,pbar) in kinematic ranges of 0<Y<3.5 and 0.2 <pT<4 GeV/c pT dependent SSA in xF 0 - ±0.35 (xF, pT, flavor-dependent AN) Cross-section of hadron production (Theoretical consistency) Data: Run-5: pp at √s = 200 GeV 2.5 pb-1 recorded SSA measurements in BRAHMS at 200 GeV

  5. 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. pT dependent SSA in xF 0 – ±0.6 (xF, pT, flavor-dependent AN) Cross-section (not shown today) Data: Run-6: pp at √s = 62 GeV 0.21 pb-1 recorded with polarization at 50-65% (see Vadim’s talk) SSA measurements in BRAHMS at 62 GeV

  6. 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 ~18%)

  7. Min-Bias Trigger / Normalization Counter:“CC” (Cherenkov Radiators) • Covers ~70% (~45%) of pp inelastic cross-section 41mb (36 mb) at 200 GeV (62 GeV) • 3.25 < |h|< 5.25 range • Vertex resolution • s(z)~ 1.6cm • Main relative luminosity monitor for SSA analysis

  8. 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

  9. 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%

  10. AN (p±,K±,p,pbar) presented at DIS2006 (April 2006)

  11. 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)

  12. 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 at DIS2006

  13. <pT> vs xF (200 GeV) at 2.3 and 4 deg with various field settings

  14. BRAHMS FS Acceptance at 2.3 deg. and 4 deg./Full Field (7.2 Tm) 4deg. 2.3deg. • Strong xF-pT correlation due to limited spectrometer solid angle acceptance

  15. Twist-3 calculation provide by F. Yuan - Kouvarius, Qiu, Vogelsang, Yuan - “Extended” with non-derivative terms (“moderate” effects at BRAHMS kinematics) - Two flavor (u,d) and valence+sea+antiquarks Fits Sivers effect calculation provided by U. D’Alesio - Anselmino, Boglione, Leader, Melis, Murgia “Sivers effect with complete and consistent kT kinematics plus description of unpolarized cross-section” (Details: Talks at this afternoon: D’Alesio, Vogelsang) Calculations compared at the BRAHMS kinematic region

  16. AN(p) at 2.3 deg. at 200 GeV

  17. AN(p) at 2.3 deg. at 200 GeV + Twist-3 • Solid line: two-flavor (u, d) fit • Dashed line: valence + sea, anti-quark • Calculations shown only for pT(p) > 1 GeV/c

  18. AN(p) at 2.3 deg. at 200 GeV + Sivers

  19. AN(p) at 4 deg. at 200 GeV (high-pt setting)

  20. AN(p) at 4 deg. at 200 GeV (high-pt setting) + Twist-3

  21. AN(p) at 4 deg. at 200 GeV (high-pt setting) + Sivers

  22. AN(K) at 2.3 deg at 200 GeV

  23. AN(K) at 2.3 deg at 200 GeV + Twist-3

  24. proton 2.3 deg at 200 GeV

  25. 62 GeV kinematic coverage at 2.3+3deg/half field setting

  26. AN(p) at 62 GeV

  27. AN(p) at 62 GeV + Twist-3

  28. AN(p) vs –xF at 62 GeV

  29. AN(K) at 62 GeV

  30. AN(K) at 62 GeV + Twist-3

  31. AN(K) vs –xF at 62 GeV

  32. BRAHMS measures AN of identified hadrons at 62 GeV and 200 GeV Large SSAs seen for pions and kaons Suggesting: - Sivers mechanism plays an important role. - described (qualitatively) by Twist-3 - main contributions are from leading (favored) quarks - power-suppression 1/pT set the scale Questioning: - where the large positive AN(K-) come from then? - Sea quark contributions not well understood: AN(K-) and AN(pbar) - how well pQCD applicable at 62 GeV (cross-sections at 62 GeV will be delivered) - what can (not) be learned from AN at pT < 1 GeV/c - AN(-xF) ~ 0 set limits on Sivers-gluon contribution? - can AN (p, pbar) be described in the consistent framework? We plan to finalize the SSA analysis (+ cross-section analysis) in the next few months Summary

  33. “Despite the conceptual simplicity of AN, the theoretical analysis of SSA of hadronic scattering is remarkably complex.” (hep-ph/0609242) Looks like theorists are having all the fun. Enjoy!

More Related