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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

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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)

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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

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Trigger-System

Readout electronics

MicroMegas

Calorimeter readoutScintillating fiber trackers

Straws

GEM

New technologies

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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

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Hadron Identification

…and hadron calorimeters

hadronhadronss

e e

(mrad)(mrad)By RICH

pp

ppe e

p(GeV/c)p(GeV/c)

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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%

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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

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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)

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COMPASS Acceptance

Excellent for non-perturbative & perturbative physics small xBj

very small Q2 Q2 > 100 (GeV/c)2

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Virtual Photon-Deutron Asymmetry

REMIND: precision data on g1 are needed for QCD analysis, q and G

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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 )

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GLUON CONTRIBUTION TO THE NUCLEON SPIN

Can be determined:From QCD analysis of structure functions ),(,,( 2

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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

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LO DISQCD C

q=c: open charm

q=u,d,…: high pT pairs

Background

for high pT pairs

PGF diagram

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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.

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Open charm reconstruction

•Part of the 2002 data:

•2002-2004 data prospects: (G/G) 0.25

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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 '

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CC

ShC

zxHcoeffN

sin.1 ),(

),()(),( 11 zHxhzxH

)(1 zH - Collins PFF

Access to h1

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First Results on Collins Asymmetries

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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

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COMPASS IS ON GOOD TRACK TO ACCOMPLISH ITS GOALS

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Beam

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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

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COMPASS HIGH PT PAIRS SELECTION

Events have:

•incident ,

•scattered ,

•at least 2 high pT hadrons

222)/(5.2

/7.0,

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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

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N() ~ 2 * N()

Total statistics 2002: 12000 , 7000 * 2 in 2003

&

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Physics objectives

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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

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and Polarization