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「 COMPASS での核子スピン構造の研究」 STUDY OF SPIN STRUCTURE OF NUCLEON IN COMPASS

「 COMPASS での核子スピン構造の研究」 STUDY OF SPIN STRUCTURE OF NUCLEON IN COMPASS. Takahiro Iwata Yamagata University. on behalf of the COMPASS Collaboration. KEK Nucleon Structure 2007 , January 12 , 200 7. OUTLINE. COMPASS apparatus Data taking history

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「 COMPASS での核子スピン構造の研究」 STUDY OF SPIN STRUCTURE OF NUCLEON IN COMPASS

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  1. 「COMPASSでの核子スピン構造の研究」STUDY OF SPIN STRUCTURE OF NUCLEON IN COMPASS Takahiro IwataYamagata University on behalf of the COMPASS Collaboration KEK Nucleon Structure 2007, January 12, 2007

  2. OUTLINE • COMPASS apparatus • Data taking history • DG/G from high pT hadron pairs & open charm • g1D, new COMPASS QCD fit, DG evaluation • Transverse spin effects: • single-hadron asymmetries • two-hadron asymmetries • L transverse polarization • Upgrades in 2006 • Prospects Nucleon Structure Function 2007 @KEK, January 11-12 2007

  3. COMPASSSETUP 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 SM1 MuonWall Polarised Target RICH mbeam • high energy beam (160 GeV) • broad kinematical range • large angular acceptance X(min.)~0.002 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  4. dN/dz 4000 3He – 4He Dilution refrigerator (T~50mK) 2000 superconductive Solenoid (2.5 T) Dipole (0.5 T) 0 -1000 0 1000 zvtx (mm) two 60 cm long cells with opposite polarization (systematics) 3 m 6 m photon detectors 5 m C4F10 THE TARGET SYSTEM THE RICH DETECTOR solid target operated in frozen spin mode Target material: 6LiD threshold momenta • pp = 2 GeV/c • pK = 9 GeV/c • pP =17 GeV/c Nucleon Structure Function 2007 @KEK, January 11-12 2007

  5. DATA TAKING HISTORY 2002 - 2006 • 2002160 GeV m beam & 6LiD Long./Transv. Pol. • 2003 ditto (~ 80/20) • 2004 ditto (~ 80/20) • 2004 test run with hadron beam • 2005 NO SPS beam (Several upgrades) • 2006 160 GeV m beam & 6LiD Long. Pol. Nucleon Structure Function 2007 @KEK, January 11-12 2007

  6. DIRECT MEASUREMENT OF DG/G Photon Gluon Fusion:gg-> qq two ways to access DG/G q= u,d,s“HIGH pT HADRON PAIRS”2 hadrons with high pT  Large statistics physical background: „model” (MC) dependent, q= c“OPEN CHARM” charm production  less background, less MC dependent. small statistics Leading order analysis in the moment.. Nucleon Structure Function 2007 @KEK, January 11-12 2007

  7. HIGH PT HADRON PAIRS measure extracted Monte Carlo(LO) SIGNAL BACKGROUND + Resolvedg Q2 < 1 (GeV/c)2 Photon Gluon Fusion Leading Order DIS QCD compton Nucleon Structure Function 2007 @KEK, January 11-12 2007

  8. HIGH PT HADRON PAIRS : Q2>1 GeV2 • pT1, pT2 > 0.7 GeV/c, • ΣpT2 > 2.5 (GeV/c)2 • 0.1 < y < 0.9 • small x : small A1d  LODIS and QCDC neglected • LEPTO Monte Carlo low Q2 high Q2 2002-2003 data result: (prelim.) systematic error: false asymmetry mainly contributes Nucleon Structure Function 2007 @KEK, January 11-12 2007

  9. PGF QCDC LO DIS HIGH PT HADRON PAIRS : Q2<1 GeV2 Resolved photon Direct neglect neglect PYTHIA-Monte Carlo for low Q² Nucleon Structure Function 2007 @KEK, January 11-12 2007

  10. 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.) Nucleon Structure Function 2007 @KEK, January 11-12 2007

  11. DG/G FROM OPEN CHARM Photon Gluon Fusion:gg-> cc hard scale m2 = 4mc2 Theory understood c Kaon ID with RICH c Combinatorial background Limited statistics Challenging measurement. Nucleon Structure Function 2007 @KEK, January 11-12 2007

  12. DG/G FROM OPEN CHARM BR:68% BR:4% D* tagging with slow pion D0Kp untagged D0Kpp0 D0Kp Nucleon Structure Function 2007 @KEK, January 11-12 2007

  13. DG/G FROM OPEN CHARM from Neural Network (parameterization) trained with AROMA Monte Carlo (full kinematics) • f : dilution factor ~0.4 • Pb : beam polarization ~0.8 • Pt : target polarization ~0.5 • S/(S+B): determined from fit AROMA MC VS. Neural Network • 2002 – 2004 data D0 + D* • DG/G = - 0.57 ± 0.41 (stat) ± (syst ≤ stat) • @ xg ~ 0.15, m2 ~ 13 GeV2 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  14. DIRECT MEASUREMENTS OF DG/G ∫G(x) = 2. 5 GRSV2000 NLO fits to g1 m2= 3 Gev2 ∫G(x) = 0.6 (GRSV stdr) ∫G(x) = 0.2 ΔG/G is small(xg ≈ 0.1) ∫DG>1unlikely Consistent also with RHIC ALL (p0 channel) measurements Nucleon Structure Function 2007 @KEK, January 11-12 2007

  15. COMPASS g1D(2002-2004) precise data at low x , 3~4 better than SMC NEGATIVE TREND NOT OBSERVED hep-ex/060938, CERN-PH-EP/2006-029 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  16. QCD FIT OF WORLD DATA WITH COMPASS g1D Input data usual cut : Q2>1GeV2 MS-bar renormalization and factorization scheme in NLO SU(3) flavor symmetry Nucleon Structure Function 2007 @KEK, January 11-12 2007

  17. COMPASS g1D WITH NLO QCD FIT Two equally possible solutions: DG>0 and DG<0 Previous fits do not show the trend of the data at low x Nucleon Structure Function 2007 @KEK, January 11-12 2007

  18. RESULTS OF NLO QCD FIT • solutions :DG > 0DG < 0 • ∫G(x)dx=+0.26 +0.04,-0.06-0.31 +0.10,-0.14 • ∫S(x)dx= +0.28± 0.01+0.32 ± 0.01 @ Q2=3(GeV)2 Both give 0.2-0.3 for the absolute value of the gluon spin contribution (∫G(x)dx) Gluon spin contribution is not large Nucleon Structure Function 2007 @KEK, January 11-12 2007

  19. QCD FIT & DIRECT MEASUREMENTS ∫G(x) = 0.3 NLO fit to g1 Q2 = 3 Gev2 ∫G(x) = -0.3 COMPASS high PT, Q2<1(GeV)2 data : good agreement with DG>0 , but only 1.3s away from DG<0. Nucleon Structure Function 2007 @KEK, January 11-12 2007

  20. DG/G SUMMARY • DG/G (xg ≈ 0.1) is small from the direct measurement ( high Pt hadron pairs ,Q2<1GeV2) • Global QCD fit to g1 data gives two solutions. • DG>0 and DG<0 • |DG| not large (0.2-0.3) • DG>0 is in better agreement to the direct measurement. • Large DG unlikely Nucleon Structure Function 2007 @KEK, January 11-12 2007

  21. TRANSVERSE SPIN EFFECTS 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 and two hadron asym. , L transverse polarization TMD PDFs an intrinsic asymmetry in the parton transverse momentum distribution induced by the nucleon spin related to orbital angular momentum of quark Sivers PDF from Sivers asym. in SIDIS single hadron production Nucleon Structure Function 2007 @KEK, January 11-12 2007

  22. DIS events (106) RUN WITH TRANSVERSE POL. TARGET transversely polarised deuteron target~ 20% of the running time Collins and Sivers asymmetries published results 2002 prel results 2002-2004 with RICH PID Two hadron asymmetries prel results 2002-2004 Λ polarimetry prel results 2002-2003 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  23. SINGLE HADRON ASYMMETRIES SIDIS cross-section for transv. PT 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 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） Nucleon Structure Function 2007 @KEK, January 11-12 2007

  24. 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 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  25. 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 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  26. DIS2006 DIS2006 COLLINS ASYMMETRIES FOR DEUTERON • small errors (~1%) • small asymmetries 2002-2004 CERN-PH-EP/2006-036 • cancellation between p and n (lh and ah) Nucleon Structure Function 2007 @KEK, January 11-12 2007

  27. COLLINS ASYMMETRY & GLOBAL FIT Belle(e+e- hh’X) • 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 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  28. DIS2006 DIS2006 SIVERS ASYMMETRIES FOR DEUTERON 2002-2004 • small errors (~1%) • small asymmetries CERN-PH-EP/2006-036 • cancellation between p and n (lh and ah) Nucleon Structure Function 2007 @KEK, January 11-12 2007

  29. SIVERS ASYMMETRIES & MODELS model calculationsconsistent with HERMES proton DATA to 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 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  30. hadrons 100% no RICH information 5% pions 77% after all cuts kaons 12% protons 3% p±, K± ASYMMETRIES 2003-2004 • same DIS event selection and hadron definition as before • plus • PID based on RICH final sample Nucleon Structure Function 2007 @KEK, January 11-12 2007

  31. p±, K± Collins Asymmetries 2003-2004 again, difficult to see an effect … Nucleon Structure Function 2007 @KEK, January 11-12 2007

  32. p±, K± SIVERS ASYMMETRIES 2003-2004 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  33. 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 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  34. 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 Nucleon Structure Function 2007 @KEK, January 11-12 2007

  35. TWO HADRON ASYMMETRIES DNN: transverse spin transfer coefficient initial  struck quark f : target dilution factor PT : target polarization; Nucleon Structure Function 2007 @KEK, January 11-12 2007

  36. TWO HADRON ASYMMETRIES z ordered pairs Nucleon Structure Function 2007 @KEK, January 11-12 2007

  37. L TRANSVERSEPOLARIZATION Transversity PT: target polarization; f : target dilution factor D(y): transverse spin transfer coefficient initial  struck quark, given by QED Nucleon Structure Function 2007 @KEK, January 11-12 2007

  38. L TRANSVERSEPOLARIZATION systematic errors not larger than statistical errors RICH ID not used yet Nucleon Structure Function 2007 @KEK, January 11-12 2007

  39. TRANSVERSE SPIN EFFECTS SUMMARY New deuteron data from COMPASS are available the measured asymmetries and polarizations are very small, compatible with zero Collins and Sivers asymmetries for positive and negative hadrons, p±, K± Two hadron asymmetries L transverse polarization PRESENT PICTURE Collins:DT0D(fav.) ~ - DT0D(unfav) DTd not well constrained Sivers: D0Tu ~ - D0Td Nucleon Structure Function 2007 @KEK, January 11-12 2007

  40. UPGRADES IN 2006 upgrade of polarized target Old SMC Magnet New magnet with a large aperture 60 cm 30 cm hadron acceptance increased Nucleon Structure Function 2007 @KEK, January 11-12 2007

  41. field lenses UPGRADES IN 2006 RICH upgrade field lens concentrator 3 m 6 m MAPMT 5 m photon detectors ¼ of inner part C4F10 mass spectrum upgrade of RICH p K previoussystem upgraded RICH inner part : 576 MAPMTs with indiv. Telescope HAMAMATSU R7600-M16-03, 16 ch PID performance raised up Nucleon Structure Function 2007 @KEK, January 11-12 2007

  42. PROSPECTS • 2007 • Transverse polarization run with pol. proton target • Hadron program with p/p beam + Liq.H2 target • 2008/2009 • longitudinal(+transverse) polarization run & hadron program • 2010- • DVCS measurements with muon beam & Liq.H2 target • Polarized Drell-Yan measurements with p- beam & pol. target Nucleon Structure Function 2007 @KEK, January 11-12 2007

  43. BACKUP SLIDES Nucleon Structure Function 2007 @KEK, January 11-12 2007

  44. HERMES DG/G from single hadron P.Liebing (HERMES) SPIN2006, Kyoto Nucleon Structure Function 2007 @KEK, January 11-12 2007

  45. TRANSVERSE MOMENTUM DEPENDENT PDFs Nucleon unpol. long. pol. trans. pol. number density Sivers unpol. Nucleon T-odd Parton helicity long. pol. Quark transversity Boer-Mulders survive after integration over kT trans. pol. T-odd Nucleon Structure Function 2007 @KEK, January 11-12 2007

  46. SINGLE HADRON ASYMMETRIES unpol B and T transvely polarised target SIDIS cross-section long pol B and/or T hazimuthal angle of the hadron s’ azimuthal angle of the transverse spin of the struck quark sazimuthal angle of the transverse spin of the initial quark s’ = p - s FS at leading order Sivers Collins beam polarization independent angles  independent extraction of the asymmetries Nucleon Structure Function 2007 @KEK, January 11-12 2007

  47. ASYMMETRIES 2003-2004 vs 2002 2003-2004 data released in April 2006 (DIS2006) comparison with the published 2002 data increase in statistics by a factor of 7! PRL 94 (2005) 202002 Nucleon Structure Function 2007 @KEK, January 11-12 2007

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