Determination of the gluon polarization from spin asymmetries for events with highpT hadrons in DIS - PowerPoint PPT Presentation

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Determination of the gluon polarization from spin asymmetries for events with highpT hadrons in DIS

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1. Determination of the gluon polarization. from spin asymmetries for events ... PTd ~ 0.50. Beam: 190 GeV. P = -0.78 0.03. Measured asymmetry: where: beam, target ... – PowerPoint PPT presentation

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Title: Determination of the gluon polarization from spin asymmetries for events with highpT hadrons in DIS


1
Determination of the gluon polarization from
spin asymmetries for events with high-pT hadrons
in DIS
K.Kowalik, SINS Warsaw
  • Idea proposed by R.D.Carlitz, J.C.Collins and
    A.H.Mueller,
  • Phys.Lett.B 214, 229 (1988)
  • Discussed by A.Bravar,D.von Harrach and
    A.Kotzinian,
  • Phys.Lett.B 421, 349 (1998)
  • Method used in HERMES for photoproduction
  • HERMES, A.Airapetian et al., Phys.Rev.Lett.84,
    2584 (2000)
  • Here application for DIS region, SMC data with
    Q2 gt1GeV2

2
PGF with high-pT hadrons
PGF
LP
QCDC
  • Two high-pT hadrons more likely in QCDC and PGF
  • Study of PGF contribution on MC sample using
    methods of selection based on neural network or
    kinematic cuts

3
Neural network

Architecture multi-layer feed-forward
configuration
NN response
  • input layer event kinematics (x, y, Q2) and
    hadron variables (E1,2, pT1,2, charge, azimutal
    angle between pT of two selected hadrons)
  • output layer single unit number within range
    (0,1)

4
Neural Network (NN) response
LP QCDC PGF
  • number within range lt0,1.gt events at high
    values of NN response are more likely to be PGF
  • PGF enriched sample selected by setting
    the threshold on the NN response


NN response
5
Monte Carlo studies
  • studies for DIS µN interactions at 190 GeV
  • LEPTO generator, Q2 ?1 GeV2
  • detector and reconstruction effects
  • geometrical acceptance for hadrons
  • simulations of trigger conditions
  • looses in reconstruction
  • smearing for scattered µ and hadrons
  • secondary interaction in target for hadrons
  • generated sample LP 67 QCDC22
    PGF11
  • selection of 2 hadrons
  • with pT ? 0.7 GeV LP40 QCDC35
    PGF25
  • Input sample for selections which further
    increase PGF

6
The criteria to judge the selection
Best result of cut selection based on ?pT2
compared to NN
7
Beam µ 190 GeV Pµ -0.780.03
  • Target
  • butanol,ammonia proton
  • d-butanol deuteron
  • PTp 0.89
  • PTd 0.50

Measured asymmetry
where ? beam, ?? target
8
Data sample selection
  • Full SMC statistics with longitudinal target
    polarization was used in this analysis
  • µ µ and at least 2 hadrons at primary vertex
  • Q2?1GeV2 , y?0.4
  • for both hadrons with pT?0.7GeV
  • - xF?0.1, z?0.1 reject target
    fragmentation region
  • - increase PGF contribution
  • ? pT2?2.5 GeV2 or NN
    response ? 0.26
  • finally selected about 1 of the inclusive
    sample

9
Results on Asymmetry
AlN?lhhX
pT?0.7GeV ?pT2?2.5GeV2 NN?0.26
Interpretation of A lN? lhhX in terms of ?G/G
requires additional information from MC
simulation.
10
?G/G evaluation from measured asymmetry
LP
PGF
QCDC
where AlN?lhhX measured asymmetry, A1
asymmetry ?N, ?aLL? partonic
asymmetry, R fraction of
contributed processes
11
Input for calculation of ?G/G
  • From other measurements
  • A1 asymmetry taken from fit to all
    experimental data
  • From MC simulations
  • aLL calculated in POLDIS
  • ?aLL?LP?0.8 ?aLL?QCDC ? 0.6
    ?aLL?PGF ? -0.44
  • fractions of processes in the selected
    sample

Important consistency between data and MC
12
Data and Monte Carlo comparison
Data MC
Event kinematics
Hadron variables
Data and Monte Carlo agree at the level of
10-25
13
Gluon polarisation
?G/G determined for a given fraction of nucleon
momentum carried by gluons ?
???
14
Systematic uncertainty on ?G/G
Changing only R or aLL
15
Summary
  • The method of ?G/G evaluation from asymmetry for
    events with high-pT hadrons was applied to SMC
    data in DIS region
  • Results obtained for cut selection and neural
    network
  • ?G/G?stat. ?sys. -0.07 0.40 0.11 cut
    ?pT2
  • ?G/G?stat. ?sys. -0.20 ?0.29 ? 0.11 NN
  • precision of ?G/G limited by the statistical
    error, however, this was unique possibility to
    test algorithms and procedure
  • Improvment in accuarncy of ?G/G in DIS region
  • COMPASS at CERN, RHIC at BNL, E161 at SLAC
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