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Delta G from high p T events at SMC and high p T analysis at COMPASS

Delta G from high p T events at SMC and high p T analysis at COMPASS. Krzysztof Kurek, Andrzej So ł tan Institute for Nuclear Studies, Warsaw, Poland On behalf of SMC and COMPASS Collaborations. 10 th International Conference. B a r y n s 4. Ecole Polytechnique

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Delta G from high p T events at SMC and high p T analysis at COMPASS

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  1. Delta G from high pT events at SMCandhigh pT analysis at COMPASS Krzysztof Kurek, Andrzej Sołtan Institute for Nuclear Studies, Warsaw, Poland On behalf of SMC and COMPASS Collaborations 10th International Conference B a r y n s 4 Ecole Polytechnique Palaiseau (France) October 25-29 2004

  2. G/G from measured asymmetryAlNlhhX LP QCD-C PGF taken from inclusive DIS measurements the asymmetry for hard sub-process Provided by MonteCarlo R the fraction of events Idea proposed by R.D.Carlitz, J.C.Collins and A.H.Mueller, Phys.Lett.B 214, 229 (1988) ……..and many more

  3. Beam: µ+ 190 GeV , Pµ = -0.78 ± 0.03 Targets: butanol,ammonia –proton ,d-butanol - deuteron Measured asymmetry:  beam, target

  4. Data sample selection: • Full SMC statistics with longitudinal target polarization was used in thisanalysis • Q21GeV2 , 0.4 y0.9 • µµ ‘ and at least 2 hadrons at primary vertex • for both hadrons : • - xF0.1, z0.1 reject target fragmentation region • - pT0.7GeV • After these selections data sample consisted of: • 80 k interactions on target with pol. protons and 70 k with deuterons • -additional selections toincrease PGF contribution – input from MC • finally selected about 1% of the inclusive sample

  5. Simulation of experimental conditionsLEPTO generator with JETSET fragmentation Good description after inclusion of hadron secondary interactions Modification of fragmentation function: a=0.5, b=0.1 (stand.)

  6. Data and Monte Carlo comparison Hadron variables: Sensitive to smearing and MCgeneration (ff) Event kinematics: Sensitive to trigger mixture, smearing Data MC Data and Monte Carlo agree at the level of 10-25% To be used for selections of PGF and ∆G evaluation

  7. Contribution of PGF process For SMC experimental conditions Lepto at generation level: RPGF = 8% events with two hadrons (phad>5GeV): RPGF = 12% additionally pThad > 0.7 GeV: RPGF = 24% How to get more? Two methods tried: • kinematical selections (cuts) • Neural Network classification(NN)

  8. Neural network Architecture: multi-layer feed-forward configuration • input layer: event kinematics (x, y, Q2) and hadron variables • (E1,2, pT1,2, charge, azimuthal angle between pT of two selected hadrons), • best way to use correlations • trained on simulated sample to select wanted category • of events (here PGF)

  9. The criteria to judge the selection: Cuts on hadron variables: Several variables tried, Opposite chargesof hadrons – small effect, 1/3 events lost Azimuthal anglebetween hadrons – no improvement Best - ∑p2T

  10. Selections used for final asymmetry calculation Cut on pT2>2.5 GeV2 Purity = 33% Efficiency = 30% NN threshold > 0.26 Purity = 33% Efficiency = 56%

  11. Asymmetry AlNlhhX With selection to increase PGF fraction 1. Cut on pT2> 2.5 GeV2 2. NN threshold > 0.26 • Systematic uncertainties:: • False asymmetries from acceptance variation • Calculation of radiative effects (unpolarized and polarized part) • effect due to restricted phace space • Polarization of beam and target • Target material

  12. Results on Asymmetry AlNlhhX pT0.7GeV pT22.5GeV2NN0.26 Interpretation of A lN→ lhhX in terms of ∆G/G requires additional information

  13. Input for calculation of ∆G/G • From MC simulations: • aLL calculated in POLDIS • aLLLP0.8 • aLLQCDC 0.6 • aLLPGF -0.44 • fractions of processes aLLLP0.8 aLLQCDC 0.6 aLLPGF -0.44 Important: consistency between data and MC

  14. Gluon polarization SpT2 NN  ∆G/G determined for a given fraction of nucleon momentum carried by gluons η final SMC result on∆G/G =-0.200.290.11 Averaged: all SMC data

  15. The COMPASS spectrometer Beam: µ+ 160 GeV , Pµ -0.76, high intensity beam (>5*SMC) Target: polarised 6LiD-deuteron ,polarization: 0.5, higher dilution factor Particle indentification: Rich detector (not present in SMC) LAS - Large angle spectrometer (SM1 region, not present in SMC) Most data from small Q2 (photoproduction)

  16. Pairs of hadrons with high pT in COMPASS(cuts and data selection) • current fragmentation: • event cuts: • 2 high pT hadrons: xF > 0.1 z > 0.1 Q2 > 1 (GeV/c)2 xBj < 0.05 0.1 < y < 0.9 pT> 0.7 GeV/c pT12+pT22 > 2.5 (GeV/c)2 m(h1h2) > 1.5 GeV/c2

  17. Result for high pT asymmetry Asymmetry for high-pt hadron pairs at Q2 > 1 (GeV/c)2 2002/03 data, 28 k events: AlNlhhX /D = -0.015 ± 0.080 (stat.) ± 0.013 (syst.) • Systematic uncertainty contains contributions from: • target and beam polarisation measurement (5%, 3% resp.) • upper limit on false asymmetries (0.013) • determination of D and f (depolarization and dilution factors,5% each)

  18. Input for ΔG/G from Monte Carlo Data and Monte Carlo comparison Determination of thefraction of PGF eventsin LEPTO: LEPTO Monte Carlo for Q2>1 (GeV/c)2 including RADGEN RPGF = 0.34 ± 0.07 (syst.) • Variation of the cut on pT2 • Standard and modified set of • fragmentation parameters • a la SMC

  19. Preliminary COMPASS result for ΔG/G ΔG/G = 0.06 ± 0.31stat. ± 0.06syst. 2002/03 data Q2 > 1 (GeV/c)2 at <xg> = 0.13 ± 0.08 COMPASS – preliminary SMC, B.Adeva et al.., Phys.Rev.D70:012002,2004. hep-ex/0402010 Hermes, A.Airapetian et al., Phys.Rev.Lett.84, 2584 (2000) , photoproduction GSA,B,C: T. Gehrmann and W. Sterling, Z. Phys. C65 (1994) 461.

  20. 10% of statistics Complete statistics of events with high pT hadron pairs Asymmetry from 2002 data (all Q2 ): AlNlhhX /D = -0.065 ± 0.036 (stat.) ± 0.010 (syst.) • Determination of ΔG/G from this asymmetry is more difficult; • resolved photon and VDM contribution, • unknown asymmetries for these processes. • work in progress

  21. Future prospects Expected precision on ΔG/G • 2004 run double data • 10 times more data at Q2<1 (GeV/c)2 • COMPASS will resume data • taking 2006 and continue • until ≥ 2010 • More information on ΔG/G • expected from RHIC.

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