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) A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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 … A.Magnon IWHSS ‘08 – Torino March 31, 2008

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) A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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

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

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

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

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

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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

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

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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

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

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

 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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

 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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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; A.Magnon IWHSS ‘08 – Torino March 31, 2008

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

From pT to xgluon (PHENIX, p0X) √s=200 GeV 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 Log10(xgluon) G.Bunce Dubna Spin07 A.Magnon IWHSS ‘08 – Torino March 31, 2008

Calc. by W.Vogelsang and M.Stratmann 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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

Conclusion, possible scenarios From COMPASS & RHIC: DG =|∫DG(xG)| ≤ 0.4 ? DS ≈ a0 = 0.3 a0 = DS DG 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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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

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 A.Magnon IWHSS ‘08 – Torino March 31, 2008

DG from scaling violations DGLAP evolution equations rule ∂/∂ lnQ2 dependence 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) A.Magnon IWHSS ‘08 – Torino March 31, 2008

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

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