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D G/G from high-p T events in SMC

D G/G from high-p T events in SMC. E.Rondio for Spin Muon Collaboration (SMC) Sołtan Institute for Nuclear Studies Warsaw, Poland. Determination of ∆G/G from Photon Gluon Fusion Analysis in Leading Order where it can be separated based on simulations with LEPTO

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D G/G from high-p T events in SMC

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  1. DG/G from high-pT events in SMC E.Rondio for Spin Muon Collaboration (SMC) Sołtan Institute for Nuclear Studies Warsaw, Poland Determination of ∆G/G from Photon Gluon Fusion Analysis in Leading Order where it can be separated based on simulations with LEPTO Search for sample with high PGF contribution application for DIS region, SMC data with Q2 >1GeV2 Workshop on Hadron Structure and Spectroscopy, Paris, March 1st to 3rd 2004

  2. History Idea proposed by R.D.Carlitz, J.C.Collins and A.H.Mueller, Phys.Lett.B 214, 229 (1988) Revisited 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 SMC, B.Adeva et al.., submitted to Phys.Rev.D, hep-ex/0402010

  3. G/G evaluation from measured asymmetry where:AlNlhhXmeasuredasymmetry, Dq/q approximated by A1/Dasymmetry N, aLL partonic asymmetry, R fraction of contributing processes

  4. Applicability and restrictions Splitting between processes only in LO >>> when higher order effects expected to be important it can not be used >>> here scale dependence was checked and found small, so no clear signal of such strong dependence Using information which is not an observable (which type of interaction given event is) >>> so it has to be taken from simulation >>> the above makes analysis model dependent (using Lepto or eg. Pythia can give different results) but … a tool to check reliability is comparison of data with MC Spin effects do not have to be simulated >>>measurement is independent of assumptions about polarized parton distributions and spin effects in fragmentation

  5. Why events with high-pT hadrons ? PGF signal LP QCDC background • Two high-pT hadrons more likely in QCDC and PGF • because • in LP source of pT only fragmentation • in PGF and QCDC in addition pT from hard scattering

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

  7. Event selection for asymmetry vertex in target half, beam through full target length, stable conditions Selected events cover following x, y, Q2 region Kinematic cuts andregions:Q2>1GeV2, 0.4<y<0.9, acceptance for  and h Q2 [GeV] y xBj xBj Conditions on hadrons in the final state 2 hadrons: pT> 0.7GeV, z>0.1, xF>0.1 (no electron contamination observed after these cuts) Statistics after selections proton deuteron 81 178 75 266 below 0.5% of the inclusive sample

  8. Monte Carlo studies • studies for DIS µp interactions at 190 GeV • LEPTO simulations, Q2 1 GeV2 • detector and reconstruction effects • geometrical acceptance for hadrons • simulations of trigger conditions • looses in reconstruction (chamber efficiencies) • smearing for scattered µ and hadrons (1/p, angles) • secondary interaction in target for hadrons • conditions in MC generation scale for hard processes (syst.errors only) cut-off’s in matrix element calculation parameters of symmetric fragmentation function

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

  10. Simulation of exp.conditions Sensitive to details of target: position, angle Good description after inclusion of hadron secondary interactions a=0.5, b=0.1 (stand.) Modification of fragm. function

  11. Contribution of PGFprocess 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) and • Neural Network classification (NN)

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

  13. 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, azimuthal angle between pT of two selected hadrons), • best way to use correlations • output layer:single unit number within range (0,1)

  14. Neural Network response 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

  15. Processes contributions for two selection method LO PDG QCDC QCDC PGF LO NN treshold Best result of cut selection based on pT2 compared to NN

  16. Asymmetry AlNlhhX • 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

  17. 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 from MC simulation.

  18. Input for calculation of ∆G/G Hermes • ∆q/q approximated by A1·D • neglecting PGF contribution in inclusive • A1 measurements, • ok. only if RPDG(incl)<< RPDG(selected) • From other measurements: • A1 asymmetry taken from fit • to all experimental data • f(x)=xa·(1-ebx)+c , • Q2 dependence neglected proton Hermes deuteron

  19. 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 Important consistency between data and MC

  20. Statistical precision of ∆G/G

  21. Gluon polarization Separately for proton and deuteron ∆G/G determined for a given fraction of nucleon momentum carried by gluons η 

  22. Average value final SMC result on∆G/G=-0.200.290.11 • comparison • Difference < 2 σ • Different process • DIS vs. Photoproduction • Factor 2 difference • in ηgluon Hermes SMC pT12+pT22 NN

  23. Systematic uncertainty on ∆G/G Contribution to the systematic due to uncertainty on parameters used in MC : • sensitivity to fragmentation, • cutoffs in matrix elements calculations • scale dependence (2Q2,Q2/2), Changes in RPGF< 5% Similar effect for pT of faster hadron

  24. Systematic uncertainty on ∆G/G Changing only R or aLL

  25. 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  0.11NN points to rather small value of gluon polarization • precision of ∆G/Glimited by the statistical error, • systematic error controlable (and can be reduced for high statistics by precise data/MC comparison) • Improvement on accuracy of ∆G/G in future: COMPASS at CERN, RHIC at BNL, E161 at SLAC

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