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Recent measurement of ΔG/G at COMPASS

Recent measurement of ΔG/G at COMPASS. Sébastien Procureur – CEA Saclay on behalf of the COMPASS collaboration. EPS2005 23/07/2005. The Nucleon spin. ½= ½ ΔΣ + ΔG + L q + L g. Sébastien Procureur EPS2005. quarks gluons orb. mom. The Nucleon spin.

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Recent measurement of ΔG/G at COMPASS

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  1. Recent measurement of ΔG/G at COMPASS Sébastien Procureur – CEA Saclay on behalf of the COMPASS collaboration EPS2005 23/07/2005

  2. The Nucleon spin ½= ½ΔΣ + ΔG + Lq + Lg Sébastien Procureur EPS2005

  3. quarksgluons orb. mom. The Nucleon spin ½= ½ΔΣ + ΔG + Lq + Lg • Quark model: ΔΣ ≈ 0.75 - QCD + s = 0 (Ellis-Jaffe): ΔΣ ≈ 0.6 - Experimentaly: a0 (=ΔΣ?) ≈ 0.2 ΔΣ = a0+ 3(s/2)ΔG Sébastien Procureur EPS2005

  4. The Nucleon spin ½= ½ΔΣ + ΔG + Lq + Lg quarksgluons orb. mom. • Quark model: ΔΣ ≈ 0.75 - QCD + s = 0 (Ellis-Jaffe): ΔΣ ≈ 0.6 - Experimentaly: a0 (=ΔΣ?) ≈ 0.2 ΔΣ = a0+ 3(s/2)ΔG Necessary to measure ΔG Sébastien Procureur EPS2005

  5. ΔG/G measurement main DIS diagrams (up to 1st order): PGF QCDC LO  only PGF is sensitive to ΔG/G Sébastien Procureur EPS2005

  6. ΔG/G measurement hard part if factorization holds (need a hard scale): Apgf = ΔG/G * aLLpgf soft part  we need to select PGF events(S suppressed)… with a hard scale Sébastien Procureur EPS2005

  7. PGF selections • Open charm channel  J.Pretz’s talk • 2 high pT hadrons channel: (q,q) (h1,h2) with high pT h1 • large stat, suppress LO, but still physical background scale: pT², Q² h2 ? ALL/D = RpgfG/G aLLpgf + (ALL/D)back Sébastien Procureur EPS2005

  8. Physical background ALL/D = RpgfG/G aLLpgf all Q² + Rqcdcq/qaLLqcdc Sébastien Procureur EPS2005

  9. Physical background ALL/D = RpgfG/G aLLpgf all Q² + Rqcdcq/q aLLqcdc + Rqqq/qaLLqq q/q  Q² < 1 Sébastien Procureur EPS2005

  10. 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  Sébastien Procureur EPS2005

  11. 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)  Sébastien Procureur EPS2005

  12. 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)  Sébastien Procureur EPS2005

  13. 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)  … what about the rest (Q² < 1GeV²)?? Sébastien Procureur EPS2005

  14. 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, but we can continue! Sébastien Procureur EPS2005

  15. MC/data comparison Generator PYTHIA is used for Q²<1GeV² (+ GEANT for spectrometer simulation) Q² .data - MC data/MC Sébastien Procureur EPS2005

  16. MC/data comparison .data - MC .data - MC pT data/MC data/MC Sébastien Procureur EPS2005

  17. Results from MC The Monte Carlo describes our data quite well! Rpgf≈ 31% Sébastien Procureur EPS2005

  18. Systematics due to MC • Relevant parameters of the MC were varied to study the dependence of our results with MC model a typical one the critical one Sébastien Procureur EPS2005

  19. Results for high pT low Q² • Asymmetry for 2002+2003 (pT > 0.7 GeV, pT² > 2.5 GeV²): • G/G: ALL/D = 0.002 ± 0.019(stat) ± 0.003 (syst) ΔG/G(xg=0.1,²=3GeV²) = +0.024 ± 0.089(stat.) ± 0.014(exp.syst) ± 0.052(MC.syst) ± 0.018(photon) 0.057 Sébastien Procureur EPS2005

  20. Comparison with other results G = 2.48 G = 0.62 G = 0.16 (GRSV param.) Sébastien Procureur EPS2005

  21. Summary • Most precise measurement of ΔG/G up to now: ΔG/G(xg=0.1,²=3GeV²) = +0.024 ± 0.089(stat.) ± 0.052(syst.)  ΔG is small or ΔG(xg) crosses 0 around xg = 0.1 • For the 1st time, Res. Phot. asym. taken into account • Next steps: • 2004 data analysis  (ΔG/G)0.05 (also 2006 run) • NLO analysis • Other channel: single high pT hadron Sébastien Procureur EPS2005

  22. Spares Sébastien Procureur EPS2005

  23. COMPASS acceptance Sébastien Procureur EPS2005

  24. Results from RHIC-PHENIX Sébastien Procureur EPS2005

  25. Asymmetry versus pT Sébastien Procureur EPS2005

  26. Experimental systematics • Asymmetries calculated with low pT events • Aexp = AAfalse according to microwave setting A-Af  1% of false asymmetries in 2003 data A+Af Sébastien Procureur EPS2005

  27. Polarised 6LiDTarget PD: 50% Dilution factor: 40% 3He – 4He dilution refrigerator (T~50mK) Superconducting Solenoid (2.5 T) Dipole (0.5 T) Two 60 cm long target cells with opposite polarisation Reconstructed interaction vertices Sébastien Procureur EPS2005

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