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1
Recent results on Polarized Quark and Gluon Distributions at COMPASS
I.Savin, JINR, Dubnaon behalf of the COMPASS Collaboration
Outline1. 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.
dA1
2
Bielefeld, Bochum, Bonn
(ISKP & PI), Erlangen,
Freiburg, Heidelberg ,
Mainz, München (LMU & TU)
Helsinki
Saclay
Tel Aviv
Burdwan, CalcuttaTorino(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)
3
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
COMPASSCOMPASS: : COCOmmon mmon MMuon and uon and PProton roton AApparatus pparatus for for SStructure and tructure and SSpectroscopy - the new fixed target pectroscopy - the new fixed target facility at CERN !facility at CERN !
8. April 1999
26. June 1998
4Beam: 2 . 108 µ+/ spill (4.8s / 16.2s) Beam momentum: 160 GeV/cLuminosity: ~5 . 1032 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 readoutScintillating fiber trackers
Straws
GEM
New technologies
6
Single Single eventevent
Ring Imaging CHerenkov Counter (RICH)
5 m5 m
6 m6 m3 m3 m
photon photon detectors:detectors:CsI MWPCCsI MWPC
mirrormirrorwallwall
vesselvessel
radiator:radiator:
CC44FF1010
7
Hadron Identification
…and hadron calorimeters
hadronhadronss
e e
(mrad)(mrad)By RICH
pp
ppe e
p(GeV/c)p(GeV/c)
8
The polarized 6LiD-Target
two 60 cm long Target-Containerswith opposite polarization
superconductive Solenoid (2.5 T)
3He – 4He Dilution refrigerator (T~50mK)
Dipole (0.5 T)
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 h1(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
qD
10
2002: 80 days, 80% eff. spectrometer&beam
2003: 100 days, 80% eff. spectrometer. 60% beam 5 billions events on tapes per year2004: in progress.
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)
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 expect **4 statistics 4 statistics by end of 2004by 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 ),(,,( 2
12
1 QxgQxg np
(remind
SMC:
stat syst th
43.142.017.145.022.031.0
2 99.0)1( GeVG
E155: 1.18.06.1)5( 2 GeVG
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 DISQCD C
q=c: open charm
q=u,d,…: high pT pairs
Background
for high pT pairs
PGF diagram
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 Physics3 structure functions are necessary to describe the spin structure of the nucleon at LO:
h1(x) can be accessed via SIDIS XhN '
19
CC
ShC
zxHcoeffN
sin.1 ),(
),()(),( 11 zHxhzxH
)(1 zH - Collins PFF
Access to h1
20
First Results on Collins Asymmetries
21
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.
Summary
&
COMPASS IS ON GOOD TRACK TO ACCOMPLISH ITS GOALS
23
Nucleon Flavor Decomposition from SIDIS
ssdduu 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
222)/(5.2
/7.0,
21
21
cGeVPP
cGeVPP
hT
hT
hT
hT
•xF>0.1, Z>0.1
•M (h1, h2) > 1.5 GeV/c2
•0.4 < y < 0.9
•75K (2002 data) after cuts
26
Physics objectives
&
Target Fragmentation region (xF < 0):
negative longitudinal polarization of predictedEllis, 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