Determination of the gluon polarization from spin asymmetries for events with high-p T hadrons in DIS

1. Determinationof 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 >1GeV2

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 sampleusing 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 unitnumber within range (0,1)

4. Neural Network (NN) response LP QCDC PGF • number within range <0,1.> 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%QCDC=22%PGF=11% • selection of 2 hadrons with pT 0.7 GeVLP=40%QCDC=35%PGF=25% 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 = -0.78±0.03 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 • µµ ‘ 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 GeV2or 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 allexperimental 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 gluonsη 

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/Glimited 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