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GLUON POLARISATION

GLUON POLARISATION. Fulvio Tessarotto INFN – Trieste. introduction Δ G from inclusive data analysis direct measurements of Δ G/G 1) method and previous measurements 2) recent results from COMPASS 3) measurements at RHIC outlook. EINN 2005.

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GLUON POLARISATION

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  1. GLUON POLARISATION Fulvio Tessarotto INFN – Trieste • introduction • ΔG from inclusive data analysis • direct measurements of ΔG/G • 1) method and previous measurements • 2) recent results from COMPASS • 3) measurements at RHIC • outlook EINN 2005

  2. In inclusive polarised DIS one can measure an asymmetry in the differential cross-section: and extract the struture function g1. In the QPM g1 has a simple interpretation: In QCD at NLO g1 may depend explicitely on DG: measuring Q2 variations of g1 we can try to get DG Milos, 23 09 2005

  3. The nucleon spin ½= ½ΔΣ + ΔG + Lq + Lg quarksgluons orb. mom. Ellis-Jaffe: ΔΣ = a0≈ 0.6 experimentally: a0 ≈ 0.25 ΔΣ = a0+ 3(s/2)ΔG Milos, 23 09 2005

  4. Two years ago … SLAC (E142, E143, E154, E155) CERN (EMC, SMC) DESY (HERMES) 185 exp. points DG not well constrained not extracted Spin-dependent PDFs 1/2 =½ 0.32 + 0.80 + Lz = 0.96 + Lz E. Leader, A. Sidorov, D. Stamenov Phys. Rev. D67 (2003) 074017  Lz is negative Milos, 23 09 2005

  5. ... Dg and Dq were largely unconstrained Direct Dg measurement Is this still true? Milos, 23 09 2005

  6. final g1 data - Very good statistics - Smearing (resolution and radiative corr.) → correlation between x bins Milos, 23 09 2005

  7. PRL 92, 012004 (2004) g1n(x) at high x from JLAB • pQCD + no Lz→ A1=Du/u= Dd/d=1 at high x • Very accurate A1n at high x A1n > 0 at x > 0.5 • + world A1p →Dd/d < 0 so Lz not negligible ? Du/u Dd/d Milos, 23 09 2005

  8. g1d(x) at low x PLB 612 (2005) 154 g1/F1 • new data : DS =0.202 (+0.042 -0.077) → 0.237 (+0.024 -0.029) • COMPASS systematically > SMC at low x Milos, 23 09 2005

  9. NLO QCD fits with new data + new unpolarised PDFs Milos, 23 09 2005

  10. possible trend toward smaller DG but the results are scattered: to know DG we still need to measure it Milos, 23 09 2005

  11. Direct Measurements: polarised p p collision: RHIC semi-inclusive deep inelastic scattering: DESY, CERN (Photon Gluon Fusion) History: Idea proposed by R.D.Carlitz, J.C.Collins and A.H.Mueller, Phys.Lett.B 214, 229 (1988) ……..and many more revisited by A.Bravar,D.von Harrach and A.Kotzinian, Phys.Lett.B 421, 349 (1998) Method used in HERMES for photoproduction HERMES, A.Airapetian et al., Phys.Rev.Lett.84, 2584 (2000) Applied for DIS region by SMC (data with Q2 >1GeV2) SMC, B.Adeva et al.., Phys.Rev.D70, 012002 (2004).

  12. ΔG/G from Photon-Gluon Fusion • Strategies to suppress background: • 1) Open charm production: • q = c unique, no background • charm fragmentation, 1.2 D0 per event • D0 -> K-π+ (BR 4%), D*+(~20%) -> D0π+ • 2) High-PT hadron pair production:q=u,d,s • skT(intr) = 450 MeV/c • spT(frag) = 350 MeV/c • pQCD scale set by: • 1) ŝ > 4mc2 or • 2) ŝ > (pt1+pt2)2 Photon-Gluon Fusion Milos, 23 09 2005

  13. HERMES & DESY • 27.5 GeV e • Pure atomic H or D targets • Spectrometer with complete • hadron identification Milos, 23 09 2005

  14. HERMES ALL from high pT hadron pairs photoproduction Proton target <xg> = 0.17 <Q2> = 0.06 (GeV/c)2 Promising channel, but … theoretical uncertainties may be large Statistics decreases with pT Milos, 23 09 2005

  15. ΔG/G from SMC DIS events Q2 > 1 GeV2, 0.4<y<0.9 xF > 0.1, S pT2 > 2.5 (GeV/c)2 1% of inclusive sample µ+ 190 GeV Pµ= -0.78±0.03 ∆G/G= -0.200.290.11 Milos, 23 09 2005

  16. COMPASS EXPERIMENT Beam: 2 . 108 µ+/ spill (4.8s / 16.2s) Luminosity: ~ 4 . 1032 cm-2 s-1 Beam polarisation: 76% Beam momentum: 160 GeV/c LHC SPS COMPASS Milos, 23 09 2005

  17. Spectrometer 2002 -> 2004 trigger-hodoscopes DW45 straws SM2 dipole Muon-filter2,MW2 HCAL1 RICH_1 Gem_11 ECAL2,HCAL2 SM1 dipole MWPC Gems Scifi Polarised Target SPS 160 GeV 2.108m/spill Muon-filter1,MW1 Veto straws,MWPC,Gems,SciFi Gems,SciFi,DCs,straws Silicon SciFi Micromegas,DC,SciFi Milos, 23 09 2005

  18. New detector technologies

  19. D0 K-π+ (BR 4%) D*+ D0π+ + c.c. c c ΔG/G from open charm Special trigger: quasi real photoproduction DsPGF at NLO: Bojak, Stratmann NPB 540 (1999) 345; A.P. Contogouris and G. Grispos, Phys. Rev. D 62 (2000). ŝ = m2cc Milos, 23 09 2005

  20. D* D0 π D0 K π D* tagging: D* D0π (Kπ)π Cuts: MKpps-MKp -Mp(MeV/c2) zD > 0.2 |cos q*| < 0.85 (Background) 10 < pK < 35 GeV/c(RICH PID) no vertex detector (solid target!) MKp -MD0(MeV/c2) Milos, 23 09 2005

  21. ΔG/G from open charm D0(untagged, 2003)4200 eventi D*+→D0π+(2003) 1100 eventi D0 → K ππ0 ΔG/G = -1.08 ± 0.73 <xg> ~0.15 0.73  0.43 with 2004 data MC: Aroma + PolDis Milos, 23 09 2005

  22. N Pairs of hadrons with high pt and Q2 > 1 GeV/c h1 h2 Photon Gluon Fusion • current fragmentation: • event cuts: xF > 0.1 z > 0.1 Q2 > 1 (GeV/c)2 xBj < 0.05 0.1 < y < 0.9 • 2 high pt hadrons: pt> 0.7 GeV/c pt12+pt22 > 2.5 (GeV/c)2 m(h1h2) > 1.5 GeV/c2 Milos, 23 09 2005

  23. Result for high pt asymmetry Asymmetry for high-pt hadron pairs at Q2 > 1 (GeV/c)2: Aγ*d = -0.015 ± 0.080 (stat.) ± 0.013 (syst.) 2002/03 data • Systematic uncertainty contains contributions from: • target and beam polarisation measurement (5% resp. 3%) • upper limit on false asymmetries (0.013) • determination of D and f (5% each) Milos, 23 09 2005

  24. determination of ΔG/G Leading Order Photon Gluon Fusion QCD-Compton cut on xBj < 0.05: Relative Fractions determined by Monte Carlo (LEPTO) Milos, 23 09 2005

  25. Data Monte Carlo comparision • Use LEPTO Monte Carlo for Q2>1 (GeV/c)2 including RADGEN Determination of the fraction of PGF events in LEPTO: σPGF/σtot = 0.34 ± 0.07 (syst.) • Variation of the cut on pt2 • Standard and modified* set of • fragmentation parameters * SMC, B. Adeva et al., Phys. Rev. D70:012002, 2004 Milos, 23 09 2005

  26. 10% of statistics COMPASS result for ΔG/G 2002/03 data Q2 > 1 (GeV/c)2 ΔG/G = 0.06 ± 0.31stat. ± 0.06syst. at <xg> = 0.13 ± 0.08 Milos, 23 09 2005 GSA,B,C: T. Gehrmann and W. Sterling, Z. Phys. C65 (1994) 461.

  27. Pairs of hadrons with high pt and Q2 < 1 GeV/c ALL/D = RpgfG/G aLLpgf all Q² + Rqcdcq/qaLLqcdc Milos, 23 09 2005

  28. Physical background ALL/D = RpgfG/G aLLpgf all Q² + Rqcdcq/q aLLqcdc + Rqqq/qaLLqq q/q  Q² < 1 Milos, 23 09 2005

  29. Physical background ALL/D = RpgfG/G aLLpgf all Q² + Rqcdcq/q aLLqcdc + Rqqq/q aLLqq q/q  Q² < 1 + RqgG/GaLLqg q/q  Milos, 23 09 2005

  30. Physical background ALL/D = RpgfG/G aLLpgf all Q² + Rqcdcq/q aLLqcdc + Rqqq/q aLLqq q/q + RqgG/G aLLqg q/q Q² < 1 + Rgqq/qaLLgq (G/G)  Milos, 23 09 2005

  31. Physical background ALL/D = RpgfG/G aLLpgf all Q² + Rqcdcq/qaLLqcdc + Rqqq/q aLLqq q/q + RqgG/G aLLqg q/q Q² < 1 + Rgqq/q aLLgq (G/G)  + RggG/GaLLgg (G/G)  Milos, 23 09 2005

  32. Physical background ALL/D = RpgfG/G aLLpgf + Rqcdcq/qaLLqcdc • Inputs: • generation of Monte Carlo evts • parametrization (world data) • pQCD calculations + Rqqq/qaLLqqq/q + RqgG/GaLLqgq/q + Rgqq/qaLLgq(G/G)  + RggG/GaLLgg (G/G)  Milos, 23 09 2005

  33. Resolved photon processes • polarised parton distribution functions of (virtual…) photon are unknown! BUT: -q(x,²) < q(x,²) < q(x,²) measured • leads to 2 extreme (min&max) scenarios  additional (theoretical) uncertainty Milos, 23 09 2005

  34. MC/data comparison PYTHIA generator is used for Q²<1GeV² GEANT is used for spectrometer simulation Q² .data - MC data/MC Milos, 23 09 2005

  35. MC/data comparison .data - MC .data - MC pT data/MC data/MC Milos, 23 09 2005

  36. Results from MC The Monte Carlo describes our data quite well! Rpgf≈ 31% Milos, 23 09 2005

  37. Gluon polarisation, high pT pairs Q2>1GeV2 : 2002-2003 data Q2<1GeV2: Milos, 23 09 2005

  38. Gluon polarisation results: G = 2.48 G = 0.62 G = 0.16 GRSV2000 NLO fits to g1 m2 = 3 Gev2 ΔG/G (xg≈ 0.1) is small DG>1 disfavoured Milos, 23 09 2005

  39. Milos, 23 09 2005

  40. ΔG/G from two jet events Leading hadron used as jet tag Hard Scattering Process qg+gq qq gg Pt [GeV/c] Milos, 23 09 2005

  41. Prompt photon production asymmetry • Gluon Compton Dominates • At LO no fragmentation function • Small contamination from annihilation A1 Milos, 23 09 2005

  42. 2 superconducting rings 3.8 km circumference NSRL Milos, 23 09 2005

  43. RHIC – first polarized hadron collider pC Polarimeters Absolute Polarimeter (H jet) BRAHMS PHOBOS Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin flipper Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake Pol. H- Source LINAC BOOSTER 5% Helical Partial Siberian Snake AGS 200 MeV Polarimeter Internal Polarimeter pC Polarimeter Rf Dipole 25% Helical Partial Siberian Snake Achieved ~ 50% beam polarization at 100 GeV Achieved ~ 30% beam polarization at 205 GeV on first try! Milos, 23 09 2005

  44. New AGS helical snakes 6 % helical snake build at Tokana Industries funded by RIKEN. 2.6 m • Warm snake avoids polarization mismatch at AGS injection and extraction. • Cold strong snake eliminates all depolarizing resonances in AGS. 2.6 m 25% s.c. helical snake build at BNL Milos, 23 09 2005

  45. STAR spin physics program: ∆G, ∆q/∆q, δq Large acceptance TPC and EMC -1<η<2 Milos, 23 09 2005

  46. 1.0 Inclusive Jets :LO W. Vogelsang 0.8 STAR qg 0.6 0.4 gg qq 0.2 0.0 0 5 10 15 20 25 30 ΔG – Star: ALL forjets (2005) 2005 pT (GeV) Milos, 23 09 2005

  47. PHENIX Detector • Philosophy: • High rate capability & granularity • Good mass resolution and particle ID • Sacrifice acceptance • Central Arms: • ||<0.35, =2900 • Charged particle ID and tracking; • photon ID • Muon Arm: 1.2<||<2.4 Muon ID and tracking • Global Detectors • Collision trigger • Collision vertex characterization • Relative luminosity • Local Polarimetry Milos, 23 09 2005

  48. π0 prompt γ pp -> π0/prompt g + X Excellent agreement with NLO & NLL calculation with collider data ! Milos, 23 09 2005

  49. Run 5 (April –June 2005): absolute polarimeter: ∆Pb/Pb~7% ∫Ldt ~ 3pb-1, <Pb>~0.45  reduces statistical error by factor 7 pp -> p0 + X 2003/4 PHENIX ALL for Inclusive p0 productionat √s=200 GeV, 2003 + 2004 data with about ∫Ldt~0.3pb-1 and <Pb>~0.3 Outlook 2005/7 Milos, 23 09 2005

  50. Y. Fukao, spin2004 B. Jaeger et al. Phys. Rev. D67, 054005 (2003) Milos, 23 09 2005

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