GLUON POLARIZATION MEASUREMENTS AT COMPASS

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GLUON POLARIZATION MEASUREMENTS AT COMPASS

• F. Bradamante
• University of Trieste and INFN Trieste
• on behalf of the COMPASS Collaboration
• RIKEN Workshop on Gluon Polarization
  December 3, 2005

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COmmon Muon and Proton
Apparatus for
Structure and
Spectroscopy NA58

• Czech Republic, Finland, France, Germany, India,
  Israel, Italy, Japan, Poland, Portugal, Russia
• Bielefeld, Bochum, Bonn, Burdwan, Calcutta, CERN,
  
• Dubna, Erlangen, Freiburg, Heidelberg, Helsinki,
  Lisbon,
• Mainz, Miyazaky, Moscow, Munich, Nagoya, Prague,
  Protvino,
• Saclay, Tel Aviv, Torino, Trieste, Warsaw
• 28 Institutes, 230 physicists

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• longitudinally polarised muon beam
• longitudinally or transversely polarised
  deuteron (6LiD) target
• momentum and calorimetry measurement
• particle identification

LHC
SPS
N
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The COMPASS Spectrometer
Trigger-hodoscopes
µ Filter
ECal HCal
50 m
RICH
MWPC
Straws
TWO STAGE SPECTROMETER
Gems
Drift chambers
Polarized beam and target
Micromegas
SAT,
LAT,
PID
Silicon
SciFi
0.003 lt x lt 0.5 10-3 lt Q2 lt 10 GeV2
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THE TARGET SYSTEM
two 60 cm long cells with opposite
polarization 6LiD Polarization 50 Dilution
factor 0.38
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NEW TECHNOLOGIES
DAQ, off-line system
MicroMegas
GEM
Straws
Trigger-System
Readout electronics
Scintillating fiber trackers
RICH1 readout
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MEASUREMENTS OF GLUON POLARIZATION

• FOUR LINES OF ATTACK
• Double spin asymmetry of the OPEN CHARM
  cross-section in high energy µD scattering
• Double spin asymmetry of the HIGH-pt HADRON PAIRS
  in high energy µD DIS (Q2 gt 1 GeV2)
• Double spin asymmetry of the high-pt hadron pairs
  in high energy µD scattering (Q2 lt 1 GeV2)
• Measurement of g1 of the deuteron and QCD fit of
  all the world data

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Photon-Gluon fusion
q c OPEN CHARMcross section
differencein charmed meson production ? theory
well understood ? experiment challenging q
u,d,s HIGH pT HADRON PAIRScross section
difference in 21 jet production in COMPASS
events with 2 hadrons with high pT ? experiment
easy ? theory more difficult
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?G/G and counting rate asymmetry

• Asymmetrytarget polarisation PT 0.50
  dilution factor f 0.40beam polarisation Pb
  0.76depolarisation factor D
• ?G/G
• Different background contributions for the
  different channels

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DG/G from OPEN CHARM
PID crucial
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RICH1

• Photon detectors (PD) 5.3 m2 of CsI MWPCs,
• 84,000 analogic read-out channels

VUV mirror wall, 20 m2, 116 mirror pieces
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RICH response for DIS events

• Threshold momenta
• Pp 2 GeV/c
• pK 9 GeV/c
• pP 17 GeV/c

p
K
p
Hadron masses calculated from the measured
Cherenkov angle
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Open Charm Selection

• zD gt 0.2 (0.25 for D0)cosq lt 0.85 (0.5 for
  D0)
• RICH identification for K 9 GeV/c lt p (K ) lt
  50 GeV/c
• 3.1 MeV/c2 lt MKpp (MKp mp ) lt 9.1 MeV/c2

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?G/G from Open Charm
MKpp - (MKp Mp) MeV/c2

MKp - MD0(PDG) MeV/c2
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?G/G from Open Charm
MKpp - (MKp Mp) MeV/c2

MKp - MD0(PDG) MeV/c2
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?G/G from Open Charm
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?G/G from Open Charm

• no asymmetry contribution from background
• s PGF/s tot S/(SB) determined from the fit
• aLL ( m (gg ), y, Q2,) parametrised for data by
  pt, zD, y with Monte Carlo (AROMA with POLDIS)

POLDIS A.Bravar et al., Comput. Phys. Commun.
105 (1997) 42
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?G/G from Open Charm

• aLL parametrised by pt, zD, y

comparison of background-subtracted data and
AROMA Monte Carlo
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?G/G from Open Charm

• First measurement
• of ?G/G with
• Open Charm tagging

with 2004 data 0.73 ? 0.43
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DG/G from HIGH pt HADRON PAIRSQ2 gt 1 GeV2
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High-pt Hadron Pairs

• enrich photon-gluon fusion events with high-pt
  cuts pt gt 0.7 GeV/c pt12 pt22 gt 2.5
  (GeV/c)2 xF, z gt 0.1 m(h1,h2) gt 1.5 GeV/c2
• asymmetry contributions from background
  events aLL and si/stot from Monte Carlo

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High-pt Hadrons, Q2 gt 1 (GeV/c)2

• PGF and background

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High-pt Hadrons, Q2 gt 1 (GeV/c)2

• PGF and background

xB lt 0.05 ? in this region A1 0 and LO DIS
QCD-Compton contributions can be neglected
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High-pt Hadrons, Q2 gt 1 (GeV/c)2

• PGF and background

0
xB lt 0.05 ? in this region A1 0 and LO DIS
QCD-Compton contributions can be neglected
Asymmetry ALL/D -0.015 0.080 stat. 0.013
syst. (2002 2003)
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High-pt Hadrons, Q2 gt 1 (GeV/c)2

• Data Monte Carlo (LEPTO) comparison

Q2
leading hadron p
leading hadron pt
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High-pt Hadrons, Q2 gt 1 (GeV/c)2
Results from Monte Carlo Ratio of PGF events
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DG/G from HIGH pT HADRON PAIRSQ2 lt 1 GeV2
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High-pt Hadrons, Q2 gt 1 (GeV/c)2
all Q2
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High-pt Hadrons, Q2 lt 1 (GeV/c)2
all Q2
low Q2
resolved photon
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High-pt Hadrons, Q2 lt 1 (GeV/c)2

• Results from PYTHIA
• Background
• as forQ2 gt 1 (GeV/c)2
• additional background from resolvedphoton
  events
• additional processes sensitive to gluonsin the
  nucleon

neglect LO DIS and low pt
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High-pt Hadrons, Q2 lt 1 (GeV/c)2
Determination of ?G/G
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High-pt Hadrons, Q2 lt 1 (GeV/c)2
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High-pt Hadrons, Q2 lt 1 (GeV/c)2

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High-pt Hadrons, Q2 lt 1 (GeV/c)2

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High-pt Hadrons, Q2 lt 1 (GeV/c)2
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High-pt Hadrons, Q2 lt 1 (GeV/c)2

• Contribution from resolved photons
• unknown polarised PDFs of the photon
• known unpolarised PDFs of the photon
• ? use unpolarised PDFs to constrain polarised
  PDFs
• ? additional theoretical uncertainty

Glück, Reya, Sieg, Eur. Phys. J. C20 (2001) 271
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High-pt Hadrons, Q2 lt 1 (GeV/c)2

• Determination of ?G/G
• 2002 2003 ALL/D 0.002 0.019stat.
  0.003syst

hep-ex/0511028, CERN-PH-EP/2005-049, Phys. Lett. B
with 2004 data 0.089 ? 0.06
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High-pt Hadrons - 2002-2003 data
hep-ex/0511028 accepted PLB
preliminary
Glück et al.,Phys. Rev. D63(2001) 094005

• results favour small ?G or
• ?G crosses 0 around xg 0.1

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DG/G from QCD EVOLUTION
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Polarized DIS
Parton Model
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New measurement of g1 of the deuteron
COMPASS 2002-2003 data PLB 612 (2005) 154

• most precise measurement for 0.004 lt x lt 0.03
• new NLO QCD fit, precision of a0 improves factor
  2 (Q2 4 GeV2)

?G 0.4 0.2 (stat) ?? (syst) COMPASS
SPIN2005
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Results from QCD anaysis of g1 data
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Asymmetry Analysis Collaboration, M. Hirai, S.
Kumano and N. Saito, PRD (2004)
Results from QCD anaysis of g1 data

• Valence Dists are determined well
• Sea Dist is poorly constrained
• Gluon can be either gt0, 0, lt0

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Results on ?G
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PERSPECTIVES for ?G
from collected COMPASS data
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NEAR FUTURE (2006-2010)

• Workshop on Future Physics _at_ COMPASS
• Yellow Report CERN-2004-011, 22 Nov. 2004
• IMPORTANT UPGRADE of the SPECTROMETER ONGOING
• RICH
• TRACKING
• E.M. CALORIMETERS
• O. D. P.T. MAGNET
• Veto System
• 2006 MUON RUNNING
• 100 days 6LiD Longitudinal Polarization
• 30 days NH3 Transverse Polarization
• 2007 HADRON RUNNING
• CENTRAL PRODUCTION
• with 300 GeV hadron beam and LH2 target

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COMPASS upgrades for 2006

• New solenoid magnet
• 70 mrad ? 180 mrad
• RICH upgrade
• Central region MAPMT system
• More photons
• Improved S/N
• Outer region New faster electronics
• Improved S/N
• Other important upgrades
• Large Drift Chamber
• RICHWall
• Full ECAL coverage
• trigger

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