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Review of results on polarized glue from fixed-target DIS experiments

This review examines the results of polarized glue measurements in fixed-target deep inelastic scattering (DIS) experiments. It discusses scaling violations of g1, inclusive DIS, hadron production via photon-gluon fusion (PGF), hadron pairs, single hadrons, and charmed hadrons. The review covers data from EMC, SMC, SLAC, HERMES, COMPASS, and JLab experiments, as well as QCD fits and the determination of polarization distributions. Potential scenarios and uncertainty sources are also discussed.

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Review of results on polarized glue from fixed-target DIS experiments

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  1. Review of results on polarized glue from fixed-target DIS experiments G. K. Mallot CERN/PH APS Meeting, St. Louis, MO, 12-15 April , 2008

  2. EMC 1987/88 20th anniversary G.K. Mallot

  3. Lepton-Photon 1989 G. Ross 1989 possible scenario: ∆G ≈ 6 (Q2=10 GeV2) ∆g/g(x) = 1 for xg > 0.1 Let’s measure it! G.K. Mallot

  4. ∆g in fixed-target DIS exp. • scaling violations of g1 • inclusive DIS • hadron production via PGF • hadron pairs • single hadrons • charmed hadrons • EMC, SMC, SLAC, HERMES, COMPASS, JLab • SMC, HERMES, COMPASS • HERMES, (COMPASS) • COMPASS G.K. Mallot

  5. F2(x,Q2) g1(x,Q2) proton G.K. Mallot

  6. World data on xg1 (x,Q2) p d G.K. Mallot

  7. World data on neutron g1 from p and d n from 3He G.K. Mallot

  8. Scaling violations: QCD fits NLO DGLAP: • choose scheme MS, AB, jet and Q02 • optionally fix ns moments from hyperon decays (a3, a8) • fit PDFs for quark non-singlet and singlet and gluon to g1 data • functional form of PDFs biases error band • extra problems in polarized case: • no positivity condition, no momentum sum rule • higher twist, … G.K. Mallot

  9. QCD fits • many groups performing World Data fits • most recent and complete DSSV → De Florian • here: AAC, LSS06, COMPASS AAC Singlet gluon note: errors of AAC account for simultaneous deviation of all parameters G.K. Mallot

  10. Fit with new deuteron g1 ΔG = - 0.309 ΔG = 0.336 ΔG • two solutions with ∆G > 0 and ∆G < 0 • uncertainty due to parametrization not included MS Q02=3 GeV2 ∆G > 0 ∆G < 0 PLB 647 (2007) 8-17 G.K. Mallot

  11. COMPASS deuteron g1 Q2 = 3 GeV2 G.K. Mallot

  12. LSS06 / COMPASS06 ∆G > 0 • LSS06 also finds two solutions with small ∆G > 0 and∆G < 0 • includes HT and Clas data • How to tell sign of ∆G? ∆G < 0 G.K. Mallot

  13. Sign of ∆G and low g1 at small x measurable at a polarized ep collider (EIC) ∆G > 0 ∆G < 0 LSS06 g1 p Leader, DIS2008 x x G.K. Mallot

  14. Δg/g from hadron production in DIS G.K. Mallot

  15. Hadron production in DIS via PGF Principle: Gluon polarization enters via photon-gluon fusion (PGF) q • measure • calculate , and • background by Monte Carlo q G.K. Mallot

  16. Analysed channels analysed data sets: • high-pThadron pairs (no ID, pions/kaons) • Q2 > 1 GeV2 Lepto • Q2 < 1 GeV2 or unmeasured Pythia • high-pTsingle hadron • small Q2 or unmeasured Pythia • single charmed meson • quasi-real photons Aroma, Rapgap All analyses in LO till now (plus parton showers) G.K. Mallot

  17. Why is small Q2 interesting • much larger cross section • Hermes cannot measure Q2 for most events • scattered e out of acceptance • dominated by small Q2 • hard scale given by • high-pT hadrons: • charmed hadron: G.K. Mallot

  18. Hermes high-pThadrons e+ 27.5 GeV • scattered electron: • “tagged” • inside acceptance • Q2 measured • pTwrtγ* • “anti-tagged” • outside acceptance • Q2 small, unmeasured • pTwrt beam • 3 samples for p/d, h+/h-: • single hadrons • tagged ~ 4% • anti-tagged ~92% • hadron pairs • combined ~ 4% • rough percentages for events after respective cuts: pT>1 GeV/c see: N.Bianchi, Pacific SPIN07, Vancouver BC G.K. Mallot

  19. ALL for single hadrons h+ tagged h- h+ untagged h- ALL p d pT (beam) pT Q2>0.1 GeV2, W2>4 GeV2 MC plus asymmetry model with Δg/g(x) = -1, 0, 1 for upper, middle and lower curve G.K. Mallot

  20. Subprocesses in MC anti-tagged, charge combined, deuteron PYTHIA 6.2 VMD(elast.+diffr., soft low-pT): decreasing with pT DIS: increasing (dominating) with pT QCDC/QCD2->2(q): increasing with pT Signal processes are PGF and QCD2>2(g) (resolved photon) G.K. Mallot

  21. Direct Method (I) from Monte Carlo statistical errors only ▲ pairs: G.K. Mallot

  22. Indirect Method (II) Fit parameters of polynomial function to A║ using MC h++h- data G.K. Mallot

  23. MC tuning/systematics varied: MC parameters, PDFs, low pT asymmetry G.K. Mallot

  24. Original HERMES measurement • proton data only, high-pT pairs • missing generator processes (Pythia 5.7 vs 6.3) Phys. Rev. Lett. 84 (2000) 2584 G.K. Mallot N.Bianchi, Pacific SPIN07, Vancouver BC

  25. Results for ∆g/g Method I +0.125 g/g(x,2) = 0.078 ± 0.034(stat) ± 0.011(syst-exp) (syst-model) -0.082 Method II -0.127 g/g(x,2) = 0.071 ± 0.034(stat) ± 0.010(syst-exp) (syst-model) -0.105 G.K. Mallot

  26. ΔG/G from high-pT pairs all Q2 Q2 < 1 GeV2 qg,gg + g q q q,g Photon Gluon Fusion ~ 30% Resolved g ~50% Leading Order QCD Compton use also inclusive ALL G.K. Mallot

  27. High-pT pairs, low Q2 Resolved photons Ratios for hadron pairs with for Q2 < 1 signal G.K. Mallot

  28. Resolved photons • More than 50%, however assuming a min and maxscenario, shows little difference. • Probing photon at large x, where photon PDF rather well determined u/u Glück, Reya, Sieg G.K. Mallot

  29. Data versus MC, low Q2 • excellent to good agreement for all kinematics variables pT G.K. Mallot

  30. Systematics: e.g. kTtuning, low Q2 nucleon photon • systematic error: • determined using 15 independent MC simulations • exploring the parameter space • in kT of nucleon and photon • fragmentation functions • parton shower on/off, • renormalization scale G.K. Mallot

  31. Δg/g from high-pT hadron pairs, low Q2 • 2002 – 2004 data: high-pT, Q2 < 1 GeV2 DG/G = 0.016 ± 0.058 (stat) ± 0.055 (syst) • @ <xg> = 0.085, m2 = 3 GeV2 G.K. Mallot

  32. High-pT pairs, Q2 >1 GeV2 • tune MC (Lepto) to reproduce data • estimate relative fractions R on event-by-event basis using NN trained with MC events (kin. variables) • use in NN output as event weight • looser cuts possible • Q2 > 1 GeV2 • pT1,2 > 0.7 GeV • xF > 0, inv. mass 2h > 1.5 GeV2 • for details see M. Stolarski DIS2008 G.K. Mallot

  33. Monte Carlo Leading hadron Sub-leading hadron G.K. Mallot

  34. NN description G.K. Mallot

  35. NN output inclusive hadron pairs G.K. Mallot

  36. Can we learn about xg? here Lepto and Q2>1 All processes PGF events (MC) G.K. Mallot

  37. Δg/g from high-pT hadron pairs • 2002 – 2004 data: High pT, Q2 > 1 GeV/c2 • DG/G = 0.08 ± 0.10 (stat) ± 0.05(syst) • @ <xg> = 0.082, (range: 0.055 – 0.123)m2 ~ 3 (GeV/c)2 G.K. Mallot

  38. Δg/g from open charm • cleanest process (“golden channel”) • no or little physics background (LO, QCDC) • observe asymmetry in D meson production • strongly statistics limited • only one D meson via D→πK (BR ~ 4%) • combinatorial background large • drastically reduced when looking to D* decay in coincidencewith slow pion • for details see F. Robinet DIS2008 G.K. Mallot

  39. D mass spectra D0 → K π nD* = 8675 nD0 = 37398 D0 → K ππ0 G.K. Mallot

  40. DG/G from open charm • Analysis uses both aLLand S/(S+B) weighting • aLL obtained from Neural Network trained on MC (AROMA) using: Q2, xbj, y, pT, zD • S/(S+B) given by a parameterization in fPμaLL, pK, θK, zD, cosθ*, pT, RICH likelihoods • weighting brings significant improvement in statistics due to large variations of aLL and S/(S+B) in phase-space G.K. Mallot

  41. aLL variation G.K. Mallot

  42. S/S+B weighting D0 -untagged D* -tagged G.K. Mallot 5 bins in S = S/(S+B)

  43. DG/G from open charm • 2002 – 2006 data D0 + D* • DG/G = -0.49 ± 0.27 (stat) ± 0.11 (syst) • @ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2 G.K. Mallot

  44. Summary of results new high-pT point new charm point G.K. Mallot

  45. DIS-FT G/G measurements GRSV, DG max, 2.5 std, 0.6 min, 0.2 QCD Fits |DG| ~ 0.3 G.K. Mallot

  46. Summary • all results point to small Δg/g • DIS results are very precise • NLO analysis urgently needed • use results in global fits G.K. Mallot

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