1 / 27

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.

mab
Download Presentation

Recent measurement of ΔG/G at COMPASS

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. 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

More Related