Title: Determination of the gluon polarization from spin asymmetries for events with highpT hadrons in DIS
1Determination 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
2PGF 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
3Neural 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)
4Neural 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
5Monte 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
6The criteria to judge the selection
Best result of cut selection based on ?pT2
compared to NN
7Beam 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
9Results 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
11Input 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
12Data and Monte Carlo comparison
Data MC
Event kinematics
Hadron variables
Data and Monte Carlo agree at the level of
10-25
13Gluon polarisation
?G/G determined for a given fraction of nucleon
momentum carried by gluons ?
???
14Systematic uncertainty on ?G/G
Changing only R or aLL
15Summary
- 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