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STUDY OF SPIN STRUCTURE OF NUCLEON AT COMPASS AND ITS CHALLENGES

STUDY OF SPIN STRUCTURE OF NUCLEON AT COMPASS AND ITS CHALLENGES. Takahiro Iwata Yamagata University. on behalf of the COMPASS Collaboration. KEK Workshop on Nucleon Structure, January 10, 2009. OUTLINE. COMPASS apparatus Data taking history Direct measurements of D G/G

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STUDY OF SPIN STRUCTURE OF NUCLEON AT COMPASS AND ITS CHALLENGES

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  1. STUDY OF SPIN STRUCTURE OF NUCLEON AT COMPASSANDITS CHALLENGES Takahiro IwataYamagata University on behalf of the COMPASS Collaboration KEK Workshop on Nucleon Structure, January 10, 2009

  2. OUTLINE • COMPASS apparatus • Data taking history • Direct measurements of DG/G • high pT hadron pairs & open charm • Dq from SI-DIS • Transverse spin effects • asymmetries with proton target • Plans and Challenges KEK Workshop on Nucleon Structure 2009, January 10, 2009

  3. THE SPECTROMETER • two stages spectrometer • Large Angle Spectrometer (SM1) • Small Angle Spectrometer (SM2) • tracking, calorimetry, PID SciFi Silicon Micromegas GEMs Straws SDC MWPC W45 MuonWall SM2 E/HCAL E/HCAL 0.003 < x < 0.5 10-3 < Q2 < 10 GeV2 SM1 MuonWall Polarised Target RICH Pol. mbeam • high energy beam • broad kinematical range • large angular acceptance KEK Workshop on Nucleon Structure 2009, January 10, 2009

  4. THE TARGET SYSTEM Solid polarized target operated in Dynamic Nuclear Polarization technique with a dilution refrigerator New COMPASS target magnet: +180~-180 mrad geometrical acceptance The world largest polarized target To match larger acceptance: new microwave cavity 3 target cells: reduction of false asymmetries Target: NH3 for proton , 6LiD for deuteron  longitudinal & transverse mode available very long relaxation time (∼ 4000 h) magnetic field rotation without polarization loss  Polarization of NH3-92%, +88%, -83%

  5. 3 m 6 m photon detectors 5 m C4F10 THE RICH DETECTOR • radiator gas: C4F10 • mirror wall: 20 m2 surface • photon-detectors: • outer part (75%) MWPC(pad RO) with CsI cathode • inner part(25%) 576 MAPMTs with indiv. telescope threshold momenta • pp = 2 GeV/c • pK = 9 GeV/c • pP =17 GeV/c Installed in 2005, Used in data taking from 2006 KEK Workshop on Nucleon Structure 2009, January 10, 2009

  6. DATA TAKING HISTORY 2002 - 2008 • in 2002, 2003, 2004, 2006 and 2007 • COMPASS has taken data in muon program configuration • 160 GeV, polarized muon • 2002-20066LiD polarized target ( ~pol. deuterons) • L-mode: 80 / T-mode: 20 • 2005 no data taking, new target system installed • 2007NH3 polarized target (~ pol. protons) • L-mode: 50 /T-mode: 50 • 2008: hadron beam at 190 GeV for the hadron program KEK Workshop on Nucleon Structure 2009, January 10, 2009

  7. Direct Measurements of Gluon Polarization DG/G KEK Workshop on Nucleon Structure 2009, January 10, 2009

  8. DIRECT MEASUREMENTS OF DG/G access to DG/G Photon Gluon Fusion:gg-> qq q= u,d,s“HIGH pT HADRON PAIRS”2 hadrons with high pT  Large statistics physical background: „model” (MC) dependent ・hard scale given by pT q= c“OPEN CHARM” charm hadrons ( one hadron detected)  no background, less MC dependent. small statistics 　　・　hard scale charm mass: m2 = 4mc2 Leading order analysis in the moment.. KEK Workshop on Nucleon Structure 2009, January 10, 2009

  9. HIGH PT HADRON PAIRS measure extracted Monte Carlo + Photon Gluon Fusion QCD Compton Leading Order DIS Resolvedg Q2 < 1 GeV2 • Data divided into two data sets • High Q2 : Q2>1GeV2 • Low Q2 : Q2<1GeV2 cross-section ratio analyzing power KEK Workshop on Nucleon Structure 2009, January 10, 2009

  10. HIGH PT HADRON PAIRS : Q2>1 GeV2 In previous analysis Abkg neglected , because A1,d~0 at small x • Q2>1GeV2, 0.1 < y < 0.9 • pT1, pT2 > 0.7 GeV, XF1,2>0,z1,2>0, z1+z2<0.95 • M2h1,h2>1.5GeV2 • Monte Carlo • LEPTO with MRST2004LO & JETSET fragmentation • R & a for PGF, QCDC and LO determiend • Neural Network parametrization • Good agreement with the data averaged values New method Reduced by 1/3 from 2002-2003 2002-2004 data result: New result (prelim.) systematic error: false asymmetry mainly contributes KEK Workshop on Nucleon Structure 2009, January 10, 2009

  11. PGF QCDC LO DIS HIGH PT HADRON PAIRS : Q2<1 GeV2 PYTHIA-Monte Carlo for low Q² Resolved photon Direct neglect neglect KEK Workshop on Nucleon Structure 2009, January 10, 2009

  12. Resolved photon processes HIGH PT HADRON PAIRS : Q2<1 GeV2 photon PDFs : unknown point like: perturbative(calculable) VMD: non-pertarbative  extream scenarios M.Gluck et al., Eur.Phys.J. C20:272(2001) 2002-2004 data result: (prelim.) Stat. error reduced by 30% compared to COMPASS 2002-03 data published PL B 633 (2006) 25 KEK Workshop on Nucleon Structure 2009, January 10, 2009

  13. nD* = 8675 nD0 = 37398 DG/G FROM OPEN CHARM BR:68% BR:4% D* tagged by slow pion untagged D0Kpp0 D0Kp D0Kp KEK Workshop on Nucleon Structure 2009, January 10, 2009

  14. DG/G FROM OPEN CHARM Kinematics not fully given in the experiment (only one charm detected)  need efficient way to determine aLL • f : dilution factor ~0.4 • Pb : beam polarization ~0.8 • Pt : target polarization ~0.5 • S/(S+B): determined from fit • Calculation with event weighting • Neural network trained with AROMA Monte Carlo • good description of data • 2002 – 2006 (full deuteron statistics) D0+D* • DG/G = - 0.49 ± 0.27 (stat) ± 0.11(syst) • @ xg ~ 0.11, m2 ~ 13 GeV2 New result False asymmetry & S/S+B determination KEK Workshop on Nucleon Structure 2009, January 10, 2009

  15. RESULTS FOR DG/G ∫DG=+0.26 QCD Fit to g1 COMPASS06 m2= 3 Gev2 ∫DG=-0.31 new high-pT point high Q2 HERMES Single hadron new open charm ΔG/G ≈0 @ xg ≈ 0.1 RECALL: charm point atlarger scale (m2= 13 Gev2 ) KEK Workshop on Nucleon Structure 2009, January 10, 2009

  16. DG/G SUMMARY & PROSPECTS • New preliminary results have been obtained • DG/G ≈0 at xg ≈ 0.1 likely • Prospects: • open charm: • including 2007 proton data, but not much improvement • high-Pt hadron pairs: • include data from 2006, 2007 • use single high-Pt hadron, • determine DG/G in 2-3 bins of xg KEK Workshop on Nucleon Structure 2009, January 10, 2009

  17. Polarized PDF, Dq from Semi-Inclusive DIS KEK Workshop on Nucleon Structure 2009, January 10, 2009

  18. Dq from SI-DIS at LO QCD Inclusive asymmetry Semi-inclusive hadron identified asymmetries flavor dependent fragmentation functions  flavor & valence/sea decomposition for Dq COMPASS 2002-2006 data on deuteron (full statistics on deuteron) Evaluation of , , KEK Workshop on Nucleon Structure 2009, January 10, 2009

  19. ASYMMETRIES deuteron data 2002-2006 ( full statistics on deuteron) Q2>1GeV2, 0.004<x<0.3, 10<p<50GeV, 0.2<z<0.85 Statistics: New data at small x Impurities corrected; although the correction is very small KEK Workshop on Nucleon Structure 2009, January 10, 2009

  20. BASES OF EVALUATION • Asymmetries to be independent on Q2 : • Assume • Un-polarized PDF: MRST04 • Fragmentation Functions: two parameterizations • DSS-FF • from e+e-, SI-DIS , pp collision • EMC-FF • charge/isospin symmetry • all un-favored FFs are equal • Assume • No Q2 dependence • s-quark favored FF is large • Least square fit in each x bin main difference in favored FF of strange quark KEK Workshop on Nucleon Structure 2009, January 10, 2009

  21. RESULTS OF FIT Similar results with different FFs; agreement with LO DNS-PDF valence DNS-PDF: global fit to e+e-, SIDIS & pp Phys.Rev.D71:094018,2005 (comparable to typical QCD fits to g1) sea Compatible with 0; Not sensitive to FFs DNS-PDF: EMC-FF gives larger stat. errors strange small contribution from large x KEK Workshop on Nucleon Structure 2009, January 10, 2009

  22. Ds FROM CHARGED KAON ASYMMETRY Alternative way to access Ds well constrained by K+ and K- cross-section data DNS-FF not constrained ! KRE-FF agreement between two evaluations EMC-FF DNS-FF KEK Workshop on Nucleon Structure 2009, January 10, 2009

  23. Ds V.S. RSF from SI-DIS from inclusive DIS only 2sdifference COMPASS,QCD-fits to g1 Phys.Lett. B 660 (2008) 458 • 1st moment strongly depends on RSF • With a large RSF, Ds<0 expected in unmeasured lower x region • Comparison between SI-DIS and inclusive DIS is limited by the errors KEK Workshop on Nucleon Structure 2009, January 10, 2009

  24. Dq FROM SI-DIS SUMMARY • SI-DIS asymmetries from full deuteron data shown • Evaluation of valence, sea, strange polarized PDFs • Valence component is consistent with inclusive DIS data • Sea polarization is 0 over the measured range • Strange component strongly depends on s-quark FF (RSF ) • Comparison between SI-DIS and incl. DIS is limited by errors • Prospects: • analysis of 2007 proton data • extraction of RUF and RSF form COMPASS KEK Workshop on Nucleon Structure 2009, January 10, 2009

  25. Transverse Spin Effects KEK Workshop on Nucleon Structure 2009, January 10, 2009

  26. TRANSVERSE SPIN EFFECTS IN COMPASS DTq(x) = q↑↑(x) - q↑↓(x) h1q(x), dq(x), dTq(x) Transversity PDF quark with spin parallel to the nucleon spinin a transversely polarized nucleon from Collins asym. in SIDIS single hadron production L transverse polarization, two hadron asym. , ,,, TMD PDF an intrinsic asymmetry in the parton transverse momentum distribution induced by the nucleon spin • related to orbital angular momentum of quark from Sivers asym. in SIDIS single hadron production • New COMPASS data for Collins & Sivers Asymmetries on Proton KEK Workshop on Nucleon Structure 2009, January 10, 2009

  27. fS= azim. angle of initial quark spin fS’= azim. angle of struck quark spin fS= p-fS’（due to helicity conservation) fh= azim. angle of leading hadron SINGLE HADRON ASYMMETRIES SIDIS cross-section for transv. PT Sivers Collins initial quark spin (nucleon spin) struck quark spin • Collins angle: Azim. angle of a hadron wrt the struck quark spin • FC =fh - fS’ (=fh +fS-p) • Sivers angle:Azim. angle of a hadron wrt the initial quark spin (=nucleon spin) • FS=fh - fS Scattering plane quark direction hadron （Breit frame） KEK Workshop on Nucleon Structure 2009, January 10, 2009

  28. COLLINS & SIVERS ASYMMETRIES Collins Asymmetry ± refer to the opposite orientation of the transverse spin of the nucleon PT is the target polarisation; DNNis the transverse spin transfer coefficient initial  struck quark, given by QED Transvesity Collins fragmentation function Sivers Asymmetry Sivers PDF KEK Workshop on Nucleon Structure 2009, January 10, 2009

  29. PROTON DATA EVENT SELECTION • Proton data in 2007, ~20% analyzed • DIS cuts: • Q2>1 (GeV/c)2,0.1<y<0.9, W>5 GeV/c2 • Cut for hadrons • Track Length<10 X0 • Energy Deposit in HCALs • pT>0.1 GeV/c • Z>0.2 • Statistics h+ : 5.7M h-: 4.5M KEK Workshop on Nucleon Structure 2009, January 10, 2009

  30. COLLINS ASYMMETRY ON PROTON • 20% statistics systematic errors ~ 0.3 sstat at small x, the asymmetries are compatible with zero in the valence region the asymmetries are different from zero, opposite sign for positive and negative hadrons, and the same strength and sign as HERMES KEK Workshop on Nucleon Structure 2009, January 10, 2009

  31. COLLINS ASYM. DATA V.S. PREDICTION comparison with M. Anselmino et al. predictions arXiv:0805.2677 good agreement KEK Workshop on Nucleon Structure 2009, January 10, 2009

  32. SIVERS ASYMMETRY FOR PROTON systematic errors ~ 0.5 sstat the measured asymmetries are small, compatible with zero KEK Workshop on Nucleon Structure 2009, January 10, 2009

  33. SIVERS ASYM. DATA V.S. PREDICTION comparison with recent M. Anselmino et al. predictions arXiv:0805.2677 HERMES proton data COMPASS deuteron data marginal agreement with COMPASS proton data KEK Workshop on Nucleon Structure 2009, January 10, 2009

  34. TRANSVERSE L POLARIZATION Another way to access Transversity Transversity PT: target polarization; f : target dilution factor D(y): transverse spin transfer coefficient initial  struck quark, given by QED • 2002-2004 deuteron data (no RICH ID) already reported • Small tendency seen for anti-Λ L L KEK Workshop on Nucleon Structure 2009, January 10, 2009

  35. NEW L DATA ON PROTON TARGET • Secondary vertex downstream of primary vertex. • PT > 23 MeV/c to exclude e+e− pairs • Protonand pion momenta > 1 GeV/c • Q2 > 1 (GeV/c)2, 0.1 < y < 0.9 • Λ decay distance DΛ > 7 σD • Collinearity < 10 mrad • Pid by RICH • 60% higher statistics w.r.t. deuteron data KEK Workshop on Nucleon Structure 2009, January 10, 2009

  36. L POLARIZATION ON PROTON TARGET • Systematic errors have been estimated to be smaller than statistical errors from false polarization. • No dependence on x. KEK Workshop on Nucleon Structure 2009, January 10, 2009

  37. New preliminary results of 2007 proton transverse run: TRANSVERSE SPIN EFFECTS SUMMARY • Collins Asymmetry: • different from zero • Agreement with predictions of Anselmino et al. (consistent with HERMES, Belle) • Sivers Asymmetry: • Small and compatible with zero within present statistical errors • Marginal agreement with the prediction • Transverse L polarization: • small and compatible with zero within present statistics KEK Workshop on Nucleon Structure 2009, January 10, 2009

  38. Plans and Challenges in COMPASS KEK Workshop on Nucleon Structure 2009, January 10, 2009

  39. 2009 Run for Hadron program 190 GeV hadron beam & Liq.H2 target (partly test with the muon beam) 2010~ Run for Muon program(with pol. proton target)? PLANS & CHALLENGES IN COMPASS • Challenges • Polarized Drell-Yan program • 200 GeV p- Beam & Polarized Target • TMD PDFs(Boer-Mulders, Sivers) • Transversity • GPD program • 100GeV polarized m+/- Beam & Liq.H2 Target(+ Pol.T) • DVCS(Deeply Virtual Compton Scattering) • HEMP(Hard Exclusive Meson Production) KEK Workshop on Nucleon Structure 2009, January 10, 2009

  40. BACKUP SLIDES KEK Workshop on Nucleon Structure 2009, January 10, 2009

  41. EVENT SELECTION DIS events Q2 > 1 GeV2 W2> 25 GeV2 0.1 < y < 0.9 hadrons pht > 0.1 GeV/c z > 0.2 (all h) z > 0.25 (leading h) Q2 = 2.4 (GeV/c)2 W = 9.4 GeV/c2 xBj  0.035 2002 data KEK Workshop on Nucleon Structure 2009, January 10, 2009

  42. increase in statistics by a factor of 7! ASYMMETRIES 2003-2004 vs 2002 2003-2004 data released in April 2006 (DIS2006) comparison with the published 2002 data PRL 94 (2005) 202002 KEK Workshop on Nucleon Structure 2009, January 10, 2009

  43. DIS2006 small errors (~1%) small asymmetries DIS2006 COLLINS ASYMMETRIES 2002-2004 CERN-PH-EP/2006-036 • cancellation between p and n • (lh and ah) KEK Workshop on Nucleon Structure 2009, January 10, 2009

  44. COLLINS ASYMMETRY & GLOBAL FIT • SIDIS(deuteron COMPASS/ proton HERMES) & Belle data Anselmino et al., hep-ph/0701006v1 PRESENT PICTURE DT0D(fav.) ~ - DT0D(unfav) DTd not well constrained from the global fit KEK Workshop on Nucleon Structure 2009, January 10, 2009

  45. DIS2006 DIS2006 SIVERS ASYMMETRIES 2002-2004 • small errors (~1%) • small asymmetries CERN-PH-EP/2006-036 • cancellation between p and n • (lh and ah) KEK Workshop on Nucleon Structure 2009, January 10, 2009

  46. SIVERS ASYMMETRIES & MODELS model calculationsto be compared with the COMPASS 2002-04 data preliminary COMPASS 2002-2004 preliminary COMPASS 2002-2004 Collins et al Vogelsang and Yuan PRESENT PICTURE preliminary COMPASS 2002-2004 Anselmino et al KEK Workshop on Nucleon Structure 2009, January 10, 2009

  47. p±, K± Collins Asymmetries 2003-2004 again, difficult to see an effect … KEK Workshop on Nucleon Structure 2009, January 10, 2009

  48. p±, K± SIVERS ASYMMETRIES 2003-2004 KEK Workshop on Nucleon Structure 2009, January 10, 2009

  49. f i h l-l’ TWO HADRON ASYMMETRIES modulation of the number of events infRS • fS= angle of initial quark spin (=target spin) • fS’= angle of final (struck) quark spin • fS=p - fS’（due to helicity conservation) • fR = angle of two-hadron plane • fRS=fR –fS’= fR+fS-p transversity : interference fragmentation function( presently unknown) initial quark spin quark direction Trento conventions see hep-ph/0407345 Breit frame KEK Workshop on Nucleon Structure 2009, January 10, 2009

  50. TWO HADRON ASYMMETRIES Event selection z1> 0.1 & z2>0.1 xf1>0.1 & xf2>0.1 z=z1+z2<0.9 diffractive r production 2002-2004 6.1x106 combinations KEK Workshop on Nucleon Structure 2009, January 10, 2009

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