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 Preliminary results on: - -  q, -  G from D° and high-Pt pairs, - transversity, -  and polarizations. 4. Summary.

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

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

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

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

6 Single event Ring Imaging CHerenkov Counter (RICH) 5 m 6 m 3 m photondetectors: CsI MWPC mirrorwall vessel radiator: C 4 F 10

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

8 The polarized 6 LiD-Target 4 possible spin combinations: 1 2 or: 3 4 reversed every 8 hours reversed once a week Polarization: ~ 50%

9 nucleon spin structure Gluon Polarization  G/G transverse spin structure function h 1 (x) Flavor dependent polarized quark helicity densities  q(x) spin dependent fragmentation functions Diffractive VM-Production 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 COMPASS physics goals

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

11 COMPASS Acceptance Excellent for non-perturbative & perturbative physics  small x Bj  very small Q 2  Q 2 > 100 (GeV/c) 2

12 Virtual Photon-Deutron Asymmetry REMIND: precision data on g 1 are needed for QCD analysis,  q and  G

13 Virtual Photon Deuteron Asymmetry COMPASS: data only 6.5 Million DIS events Q 2 > 1 (GeV/c) < y < 0.9 expect * 4 statistics by end of 2004 by end of 2004 ( Data displayed at experimental of every x Bj 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 P T

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

16 Asymmetry for high p T pairs A  *d = ± ± (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: 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: h 1 (x) can be accessed via SIDIS

19 - Collins PFF Access to h 1

20 First Results on Collins Asymmetries

21 DIS & SIDIS: COMPASS will cover the small-x range to Q 2 >1 (GeV/c) 2 with > fourfold statistics of SMC High-p T : First results from COMPASS on deuterons Open charm: possibility for D 0 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. Summary 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: x min = HERMES: x min = 0.02

24 COMPASS HIGH P T PAIRS SELECTION Events have: incident , scattered , at least 2 high p T hadrons x F >0.1, Z>0.1 M (h 1, h 2 ) > 1.5 GeV/c < y < K (2002 data) after cuts

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

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

27  and Polarization