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Gluon Polarisation Overview

Gluon Polarisation Overview. DS, quark contribution to nucleon spin. Why D G ? D G from scaling violations D G from hadron production - Open charm - COMPASS - High p T hadrons pairs & single - COMPASS/HERMES D G from pp collisions - RHIC A. Magnon (CEA-Saclay/IRFU & COMPASS).

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Gluon Polarisation Overview

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  1. Gluon Polarisation Overview • DS, quark contribution to nucleon spin. Why DG ? • DG from scaling violations • DG from hadron production - Open charm - COMPASS - High pT hadrons pairs & single - COMPASS/HERMES • DG from pp collisions - RHIC A. Magnon (CEA-Saclay/IRFU & COMPASS) IWHSS ‘08 – Torino March 31, 2008

  2. SLAC g1p Compatible with DS=0.6 xBj Ellis-Jaffe DS = 0.6 EMC ∫g1p xBjg1p xBj Early measurements of DS (1) SLAC Polarized electrons DS large, “as expected” 1976-1983 EMC @ CERN polarized m Access lower x, DS = 0.12 ± 0.17 → ” Spin crisis ’’1988 IWHSS ‘08 – Torino March 31, 2008

  3. Early measurements of DS (2) HERMES, SLAC high precision, SMC @ CERN lower x • g1 for proton & neutron (deuteron) … • Bjorken Sum Rule relates proton & neutron g1=∫g1dx DS = 0.2 - 0.3 confirmed to be small Theory, Q2=5 GeV2 SMC 1998 Bjorken OK + as determination + first flavor separation … IWHSS ‘08 – Torino March 31, 2008

  4. Recent measurements of DS • COMPASS @ CERN, m 160 GeV COMPASS fit to g1 p, n, d world data, MS scheme, Q2 = 3 (GeV/c)2 PLB 647 (2007) 8 DS = 0.30 ± 0.01 (stat) ± 0.02 (evol) Ds + Ds= - 0.08 ± 0.01 (stat) ± 0.02 (syst) COMPASS data alone • HERMES @ DESY, e- 27 GeV HERMES from g1d data, MS scheme, Q2=5 (GeV/c)2, neglecting x < 0.02 contrib., PRD75 (2007) 012007 DS =0.33 ± 0.011 (stat) ± 0.025 (theo) ± 0.028 (evol) Ds + Ds= - 0.085 ± 0.013 (th) ± 0.008 (exp) ± 0.009(evol) IWHSS ‘08 – Torino March 31, 2008

  5. Why measure DG ? ½ = ½ΔΣ + ΔG+ <Lq> + <Lg> Measurement ofDGimportant : 1 – How are gluons polarized ? 2- Low value of a0 could be due to axial anomaly ifDG is large. (A. Efremov O.Teryaev, G. Altarelli – G. Ross) 3 – How large is parton orbital angular momentum a0 = IWHSS ‘08 – Torino March 31, 2008

  6. How to measure DG ? • DG from scaling violations • DG from hadron production - Open charm - High pT hadrons (pairs, single) • DG from pp collision IWHSS ‘08 – Torino March 31, 2008

  7. COMPASS NLO QCD fit Q2 = 3 GeV2 Comparison of fits - disagreement of data with previous QCD fits (LSS05,GRSV, BB) IWHSS ‘08 – Torino March 31, 2008

  8. ΔG = - 0.31 ΔG = 0.34 ΔG COMPASS NLO QCD fit DG = 0.34 Q2 = 3 GeV2 DG = - 0.31 New COMPASS g1d  G > 0 or  G < 0, |G| ~ 0.3 a0 = 0.33 ± 0.03 ± 0.05 s = -0.08 ± 0.01 ± 0.02 2006 IWHSS ‘08 – Torino March 31, 2008

  9. How to measure DG ? • DG from scaling violations • DG from hadron production (PGF) - Open charm - High pT hadrons (pairs, single) • DG from pp collision IWHSS ‘08 – Torino March 31, 2008

  10. Photon-gluon fusion (PGF) • Gluon polarisation is measurable in PGF • measure • calculate and using Monte Carlo N IWHSS ‘08 – Torino March 31, 2008

  11. DG/G from open charm Open charm, single D meson c -> (D*) -> (ps) D0 -> Kp(ps) c • cleanest process wrt physical bkgr • combinatorial bkgr, limited statistics • so far LO analysis, NLO in progress c N IWHSS ‘08 – Torino March 31, 2008

  12. DG/G from open charm COMPASS Data: 2002,2003,2004 & 2006 160 GeV m beam & 6LiD target nD* = 8675 nD0 = 37398 IWHSS ‘08 – Torino March 31, 2008

  13. DG/G from open charm • Analysis uses both aLL and S/(S+B) weighting • aLL obtained from Neural Network trained on MC (AROMA): input variables : Q2, xbj, y, pT, zD • S/(S+B) given by a parameterization: input variables : target cell, fPμaLL, pK, θK, zD, cosθ*, pT, RICH Likelihoods • Weighting brings significant improvement in statistics due to large variations of aLL and S/(S+B) in phase-space IWHSS ‘08 – Torino March 31, 2008

  14. DG/G from open charm D0 -untagged D* -tagged IWHSS ‘08 – Torino March 31, 2008 5 bins in S = S/(S+B)

  15. DG/G from open charm 2006 aLL parameterization aLL generated aLL reconstructed IWHSS ‘08 – Torino March 31, 2008

  16. DG/G from open charm “ New ” • 2002 – 2006 data D0 + D* • DG/G = -0.49 ± 0.27 (stat) ± 0.11 (syst) • @ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2 IWHSS ‘08 – Torino March 31, 2008

  17. How to measure DG ? • DG from scaling violations • DG from hadron production (PGF) - Open charm - High pT hadrons pairs, Q2 > 1 GeV/c2 • DG from pp collision IWHSS ‘08 – Torino March 31, 2008

  18. Q2 < 1 (GeV/c)2 qg,gg + q,g Resolved g ~50% ΔG/G from high pT hadron pairs Q2 > 1 (GeV/c)2 g q q Photon Gluon Fusion ~ 30% Leading Order QCD Compton IWHSS ‘08 – Torino March 31, 2008

  19. ΔG/G from high pT hadron pairs • Analysis uses parameterization of RPGF, RQCDC, RLO, aLLPGF, aLLQCDC, aLLincl, xg, xC, … etc based on Neural Network trained on MC (LEPTO for Q2 > 1). • No cut on NN which assigns to each evt. a probability to originate from LO, PGF or COMPTON. • Dependence on PDFs studied • Parton shower (NLO process) added • Detailed studies of systematics IWHSS ‘08 – Torino March 31, 2008

  20. ΔG/G from high pT hadron pairs Two parameters: O1 & O2 to express fractions R (PGF, LO or QCDC) for each high pT event IWHSS ‘08 – Torino March 31, 2008

  21. ΔG/G from high pT hadron pairs Leading hadron Sub-leading hadron IWHSS ‘08 – Torino March 31, 2008

  22. ΔG/G from high pT hadron pairs Probabilities (fractions) of LO, QCDC, PGF : Monte Carlo vs Neural Network IWHSS ‘08 – Torino March 31, 2008

  23. ΔG/G from high pT hadron pairs “ New ” • 2002 – 2004 data: High pT, Q2 > 1 GeV/c2 • DG/G = 0.08 ± 0.10 (stat) ± 0.05(syst) • @ <xg> = 0.082, (range: 0.055 – 0.123)m2 ~ 3 (GeV/c)2 IWHSS ‘08 – Torino March 31, 2008

  24. ΔG/G from high pT hadron pairs (Released 2 Oct. 2006, SPIN2006) • 2002 – 2004 data: High pT, Q2 < 1 GeV/c2 DG/G = 0.016 ± 0.058 (stat) ± 0.055 (syst) • @ <xg> = 0.085, m2 = 3 (GeV/c)2 IWHSS ‘08 – Torino March 31, 2008

  25. G/G, direct measurements GRSV, DG max, 2.5 std, 0.6 New high pT min, 0.2 QCD Fits |DG| ~ 0.3 New open charm IWHSS ‘08 – Torino March 31, 2008

  26.  G/G, direct measurements • Accurate DG/G from COMPASS data (2002 – 2004) from high pT hadron pairs, Q2 < 1 GeV/c2 and Q2 > 1 GeV/c2(new) DG/G small (~ 0) @ <xg> = 0.08 • Significant improvement for DG/G from open charm (2002 – 2004 + 2006) and aLL + S/B weighting. Also DG/G (~ 0) @ <xg> = 0.11 • Similar conclusion from new HERMES analysis IWHSS ‘08 – Torino March 31, 2008

  27. How to measure DG ? • DG from scaling violations • DG from hadron production - Open charm - high pT hadrons (pairs, single) • DG from pp collision IWHSS ‘08 – Torino March 31, 2008

  28. RHIC: polarized pp collider YearP L(pb-1) P4L(*) 2004 40% 3 0.08 2005 50% 13 0.8 2006 60% 46 6 (*)G.Bunce Dubna Spin07 IWHSS ‘08 – Torino March 31, 2008

  29. pp collisions @ PHENIX & STAR Reactions pp -> pX, jet X, gX, cc X, probe gluon • Measure always product of 2 observables • MC required to determine fraction of process IWHSS ‘08 – Torino March 31, 2008

  30. pp collisions @ PHENIX & STAR Considerable progress in pQCD NLO calculations Jäger,Schäfer, Stratmann,Vogelsang; de Florian Jäger,Schäfer, Stratmann,Vogelsang; Signer et al. Gordon,Vogelsang; Contogouriset al.; Gordon, Coriano Bojak, Stratmann; IWHSS ‘08 – Torino March 31, 2008

  31. Unpol. Cross Section in pp Good agreement between NLO pQCD calculations and data confirmation that theory can be used to extract spin dependent pdf’s from RHIC data pp0 X : hep-ex-0704.3599 PHENIX data pp X: PRL 98, 012002 IWHSS ‘08 – Torino March 31, 2008

  32. From pT to xgluon (PHENIX, p0X) √s=200 GeV Log10(xgluon) NLO pQCD: 0 pT=29 GeV/c  xgluon=0.020.3 • GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 ) Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins. • These data is not much sensitive to variation of G(xgluon) within our x range. • Any quantitative analysis should assume some G(xgluon) shape G.Bunce Dubna Spin07 IWHSS ‘08 – Torino March 31, 2008

  33. From ALL to DG(PHENIX, p0 with GRSV) Calc. by W.Vogelsang and M.Stratmann  “3 sigma” GRSV “standard”, G(Q2=1GeV2)=0.4, is excluded by data on >3 sigma level: 2(std)2min>9 • Only exp. stat. uncertainties are included (the effect of syst. uncertainties is expected to be small in the final results) • Theoretical uncertainties are not included G.Bunce Dubna Spin07 IWHSS ‘08 – Torino March 31, 2008

  34. 2005 STAR preliminary GRSV DIS Systematic error band Measured Jet PT (GeV) From ALL to DG(STAR, jetX with GRSV) Large gluon polarisation scenario is not consistent with data J.C.Dunlop Dubna Spin07 IWHSS ‘08 – Torino March 31, 2008

  35. STAR STAR, inclusive p± production (mid - η) Different sensitivity of p+ and p- to the sign of G …. e.g. G > 0  No constraint on DG yet … Dramatic increase in precision in Run 2006 J.C.Dunlop Dubna Spin07 IWHSS ‘08 – Torino March 31, 2008

  36. DG from RHIC • High statistics available to constrain DG in xg range (0.02 – 0.3) • DG not large (consistent with zero) • “Standard” scenario, G (Q2=1GeV2) = 0.4, is excluded by data on > 3 sigma level: 2(std)2min > 9 (PHENIX ?) • Theoretical uncertainties might be significant IWHSS ‘08 – Torino March 31, 2008

  37. RHIC, prospects • Improve exp. (stat.) uncertainties, move to higher pT - more precise DG in probed x range - probe (lower) and higher x and constrain DG vs x • Different channels - different systematics - different x, - gq -> qg (pp -> g jet), sensitive to DG sign, parton kinematics well constrained, theoretically clean • Different √s, 62 GeV, 200 GeV,500 GeV Substantial FOM = P4L needed IWHSS ‘08 – Torino March 31, 2008

  38. Conclusion, possible scenarios From COMPASS & RHIC: • DG =|∫DG(xG)| ≤ 0.4 ? • DS ≈ a0 = 0.3 a0 = DSDG Lq Lg ½ = 1/2 × 0.3 + 0.35 + 0 + 0 ½ = 1/2 × 0.3 + 0.0 + 0.35 ½ = 1/2 × 0.3 - 0.35 + 0.70 COMPASS/RHIC JLab/HERMES/COMPASS IWHSS ‘08 – Torino March 31, 2008

  39. Additional slides IWHSS ‘08 – Torino March 31, 2008

  40. Measurements of DG/G xg binning High pT in 2006 IWHSS ‘08 – Torino March 31, 2008

  41. PHENIX, different s s=62 GeV 0 cross section described by NLO pQCD within theoretical uncertainties Sensitivity of Run6 s=62 GeV data collected in one week is comparable to Run5 s=200 GeV data collected in two months, for the same xT=2pT/s s=500 GeV will give access to lower x; starts in 2009 IWHSS ‘08 – Torino March 31, 2008

  42. DG from scaling violations DGLAP evolution equations rule ∂/∂ lnQ2dependence of parton distribution functions Method - parameterize polarised parton distributions at Q02 e.g. Dqi ~ xai (1-x)bi(1+gix) - DGLAP evolution to measured Q2 - calculate g1 and fit all existing g1 data together DS and DG coupled in the evolution → Extract DG(x) IWHSS ‘08 – Torino March 31, 2008

  43. Global QCD analysis: AAC - NLO xDuv xDG DG = 0.31 ± 0.32 at Q2=1 GeV2 xDq xDdv Dq = - 0.050 ± 0.32 AAC – NLO, hep-ph/0603213 including g1 new data from HERMES, COMPASS and JLAB + PHENIX ALL p0 IWHSS ‘08 – Torino March 31, 2008

  44. New COMPASS A1d data PLB647 (2007) 8 IWHSS ‘08 – Torino March 31, 2008

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