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Recent results on Polarized Quark and Gluon Distributions at COMPASS I.Savin, JINR, Dubna

Recent results on Polarized Quark and Gluon Distributions at COMPASS I.Savin, JINR, Dubna on behalf of the COMPASS Collaboration Outline 1. Introduction. 2. COMPASS status and data taking in 2002 and 2003. 3. Preliminary results on: - - q, - G from D ° and high-Pt pairs,

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Recent results on Polarized Quark and Gluon Distributions at COMPASS I.Savin, JINR, Dubna

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  1. Recent results on Polarized Quark and Gluon Distributions at COMPASS I.Savin, JINR, Dubna on behalf of the COMPASS Collaboration Outline 1. Introduction. 2. COMPASS status and data taking in 2002 and 2003. 3. Preliminary results on: - - q, - G from D°and high-Pt pairs, - transversity, -  and polarizations. 4. Summary.

  2. (230 Physicists from 12 Countries) Dubna (LPP and LNP), Moscow (INR, LPI, State University), Protvino Bielefeld, Bochum, Bonn (ISKP & PI), Erlangen, Freiburg, Heidelberg , Mainz, München (LMU & TU) CERN Prag Warsaw (SINS), Warsaw (TU) Helsinki Saclay Lisboa Nagoya Burdwan, Calcutta Torino(University,INFN), Trieste(University,INFN) Tel Aviv

  3. 26. June 1998 COMPASS: COmmon Muon and Proton Apparatus for Structure and Spectroscopy - the new fixed target facility at CERN ! • 1996 COMPASS proposal • 1997 conditional approval • 1998 MoU • 1999 – 2001 construction & installation • 2001 technical run • 2002, 2003, 2004 data taking • in long range planning @CERN at least until 2010 8. April 1999

  4. C O M P A S S L A Y O U T Double arm spectrometer, each with own magnet (SM1 and SM2), various trackers and PID for muons, electrons and hadrons Beam:2 . 108 µ+/ spill (4.8s / 16.2s) Beam momentum: 160 GeV/c Luminosity:~5 . 1032 cm-2 s-1Beam polarization: -76%

  5. New technologies GEM Trigger-System MicroMegas Straws Readout electronics Calorimeter readout Scintillating fiber trackers

  6. 3 m 6 m Single event vessel mirror wall photon detectors: CsI MWPC 5 m radiator: C4F10 Ring Imaging CHerenkov Counter (RICH)

  7. K e   p hadrons  Hadron Identification K e   p By RICH q(mrad) p(GeV/c) …and hadron calorimeters

  8. 3He – 4He Dilution refrigerator (T~50mK) superconductive Solenoid (2.5 T) Dipole (0.5 T) 1 2 two 60 cm long Target-Containers with opposite polarization 3 4 The polarized 6LiD-Target 4 possible spin combinations: reversed every 8 hours or: reversed once a week Polarization: ~50%

  9. nucleon spin structure • Gluon Polarization G/G • transverse spin structure function h1(x) • Flavor dependent polarized quark helicity densities q(x) • spin dependent fragmentation functions • Diffractive VM-Production COMPASS physics goals hadron spectroscopy • Primakoff-Reactions • polarizability of  and K • glueballs and hybrids • charmed mesons and baryons • semi-leptonic decays • double-charmed baryons Continuation of spin physics studies initiated at CERN by the EMC and SMC

  10. DATA TAKING IN 2002-2004 FOR SPIN PHYSICS • 2002 & 2003: • 500 TByte Data • 1010 Events • longitudinal polarization • 3.109 Events • transverse polarization • 0.1%with Q²>1 (GeV/c)² • (after all cuts) 2002: 80 days, 80% eff. spectrometer&beam 2003: 100 days, 80% eff. spectrometer. 60% beam 5 billionsevents on tapes per year 2004: in progress.

  11. COMPASS Acceptance • Excellent for non-perturbative & perturbative physics • small xBj • very small Q2  Q2 > 100 (GeV/c)2

  12. Virtual Photon-Deutron Asymmetry REMIND: precision data on g1 are needed for QCD analysis, q and G

  13. Virtual Photon Deuteron Asymmetry COMPASS: - 2002 data only 6.5 Million DIS events Q2 > 1 (GeV/c)2 0.1 < y < 0.9 expect *4 statistics by end of 2004 ( Data displayed at experimental <Q2> of every xBj bin )

  14. GLUON CONTRIBUTION TO THE NUCLEON SPIN • Can be determined: • From QCD analysis of structure functions (remind SMC: stat syst th E155: • From SIDIS reactions on polarized targets induced by Photon-Gluon Fusion (PGF), particularly: • production of charmed or strange particles, • hadron pairs with high PT

  15. LO DIS QCD C PGF diagram q=c: open charm q=u,d,…: high pT pairs Background for high pT pairs

  16. Asymmetry for high pT pairs A*d = -0.065 ± 0.036 ± 0.010 (syst)  experimental false asymm. MC studies are needed to subtract the background before estimations of G/G. But assuming R_PGF~1/4: (G/G) ~ 0.17 … G > 0.

  17. Open charm reconstruction • Part of the 2002 data: • 2002-2004 data prospects: (G/G)  0.25

  18. Transverse Spin Physics 3 structure functions are necessary to describe the spin structure of the nucleon at LO: h1(x) can be accessed via SIDIS

  19. Access to h1 - Collins PFF

  20. First Results on Collins Asymmetries

  21. Summary • DIS & SIDIS: • COMPASS will cover the small-x range to x=0.003 @ Q2>1 (GeV/c)2 • with > fourfold statistics of SMC • High-pT: • First results from COMPASS on deuterons • Open charm: • possibility for D0 reconstruction in massive target demonstrated •  collect more statistics • Transversity: • first measurement of Collins Asymmetry on • transverse polarized deuteron target • production: • extraction of spin transfer on its way • Many other channels are in progress. COMPASS IS ON GOOD TRACK TO ACCOMPLISH ITS GOALS

  22. Beam

  23. Nucleon Flavor Decomposition from SIDIS • Light quark distributions are measured before by SMC and HERMES • s(x) is particular interest since famous EMC results • s(x) can be measured at COMPASS using d target only and h+, h-, K+, K- and K°s SIDIS asymmetries • Kinematics range: of Q²>1 • COMPASS: xmin = 0.003 • HERMES: xmin = 0.02

  24. COMPASS HIGH PT PAIRS SELECTION • Events have: • incident , • scattered , • at least 2 high pT hadrons • xF>0.1, Z>0.1 • M (h1, h2) > 1.5 GeV/c2 • 0.4 < y < 0.9 • 75K (2002 data) after cuts

  25. N(7) ~ 2 * N(7) Total statistics 2002: 12000  , 7000 * 2 in 2003

  26. Physics objectives • Target Fragmentation region (xF < 0): • negative longitudinal polarization of  predicted • Ellis, Kharzeev, Kotzinian Z. Physik C69 (1996) 467 • - may test polarized strangeness content of nucleon • BUT: acceptance poor for COMPASS • Current fragmentation region (xF > 0): • Study of spin transfer from photon to baryon • measure  Spin structure

  27. and Polarization

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