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					    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:
                d
           - A1
           - q,
           - G from D° and high-Pt pairs,
           - transversity,
           -  and  polarizations.
4. Summary.
                                                      1
                             (230 Physicists from 12 Countries)




Dubna (LPP and LNP),                                              Bielefeld, Bochum, Bonn
Moscow (INR, LPI,                           CERN                  (ISKP & PI), Erlangen,
State University),                                                Freiburg, Heidelberg ,
Protvino                                                          Mainz, München (LMU & TU)




                                             Prag
 Warsaw (SINS),                                                            Helsinki
  Warsaw (TU)



                                                                                 Saclay
                                             Lisboa
     Nagoya

                                                                          Burdwan,
  Torino(University,INFN),                                                Calcutta
  Trieste(University,INFN)                                                                 2
                                             Tel Aviv
                                                             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                                                8. April 1999

     1999 – 2001 construction
                 & installation
     2001 technical run

     2002, 2003, 2004 data taking
     in long range planning @CERN at least
     until 2010                                                              3
                             COMPASS LAYOUT




    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              4
Luminosity:      ~5 . 1032 cm-2 s-1               Beam polarization: -76%
                      New technologies




                                            GEM
 Trigger-System           MicroMegas
                                                                  Straws




Readout electronics   Calorimeter readout                                  5
                                            Scintillating fiber trackers
   Ring Imaging CHerenkov Counter (RICH)



Single event
                                 vessel




                                                 mirror
                    photon                       wall




                                                          5m
                    detectors:
                    CsI MWPC

                                          radiator:
                                          C4F10


                                                           6
                 Hadron Identification          K
                                                    e
                                            p
                             By RICH
                                                        q(mrad)
                                 p(GeV/c)

…and   hadron calorimeters



                                                K
hadrons
                                       e
                                                    p
                 


                                                            7
          The polarized 6LiD-Target
                                   4 possible spin combinations:
    3He – 4He Dilution                 1
    refrigerator (T~50mK)
        superconductive
Solenoid (2.5 T)Dipole (0.5 T)
                                      2

                                       reversed every 8 hours

two 60 cm long Target-Containers    or:
    with opposite polarization
                                       3


                                       4

                                           reversed once a week


                                       Polarization: ~ 50%         8
                       COMPASS physics goals

nucleon spin structure                           hadron spectroscopy
    Gluon Polarization G/G
                                                  Primakoff-Reactions
    transverse spin structure
                                                   - polarizability of  and K
    function h1(x)

    Flavor dependent polarized                    glueballs and hybrids
    quark helicity densities q(x)
    spin dependent fragmentation                  charmed mesons and baryons
                
    functions Dq                                  - semi-leptonic decays
                                                   - double-charmed baryons
    Diffractive VM-Production
Continuation of spin physics studies initiated
                                                                                 9
at CERN by the EMC and SMC
               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 billions events on tapes per year   10
2004: in progress.
            COMPASS Acceptance




Excellent for non-perturbative & perturbative physics
 small xBj
 very small Q2  Q2 > 100 (GeV/c)2                     11
  Virtual Photon-Deutron Asymmetry




REMIND: precision data on g1 are needed for QCD analysis, q and G   12
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 )
                                    13
    GLUON CONTRIBUTION TO THE NUCLEON SPIN

Can be determined:
From QCD analysis of structure functions       g1p ( x, Q 2 , g1n ( x, Q 2 )
 (remind
           SMC:    G(1GeV 2 )  0.991..17
                                     0 31
                                                 0.42
                                                 0.22
                                                         1.43
                                                         0.45

                                         stat     syst     th

           E155:    G (5GeV 2 )  1.6  0.8  1.1   
 From SIDIS reactions on polarized targets induced by Photon-Gluon
  Fusion (PGF), particularly:

     •     production of charmed or strange particles,
     •     hadron pairs with high PT
                                                                                14
          PGF diagram


                 q=c: open charm
                 q=u,d,…: high pT pairs




                           Background
         QCD C
LO DIS                     for high pT pairs
                                               15
         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.


                                                          16
                     Open charm reconstruction
•Part of the 2002 data:




•2002-2004 data prospects: (G/G)  0.25        17
            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     N   ' h  X
                                                                        18
Access to h1

                  C   h     S 


          N   C   1  coeff .H ( x, z ) sin  C 

            H ( x, z )  h1 ( x)  H1 ( z ),

            H1 ( z ) - Collins PFF




                                                     19
First Results on Collins Asymmetries




                                       20
                                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
                                                                         21
Beam




   22
       Nucleon Flavor Decomposition from SIDIS

              u  u  d  d  s  s
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                              23
       COMPASS HIGH PT PAIRS SELECTION

Events have:
   •incident ,
   •scattered ,
   •at least 2 high pT hadrons
          PTh1 , PTh2  0.7GeV / c
         P   P 
            T
             h1 2
                      T
                       h2 2
                               2.5(GeV / c ) 2
     •xF>0.1, Z>0.1
     •M (h1, h2) > 1.5 GeV/c2
     •0.4 < y < 0.9
     •75K (2002 data) after cuts
                                                  24
                &
                                     N(7) ~ 2 * N(7)




Total statistics 2002: 12000  , 7000  * 2 in 2003
                                                       25
     &  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


                                                          26
 and  Polarization




                       27

				
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