1. F.-H. Heinsius (Universität Freiburg/CERN) Introduction Gluon polarization in the nucleon Transverse spin distribution Newest Results from the Experiment Graduiertenkolleg Freiburg, 24.5.2006

2. Fritz-Herbert Heinsius GK Freiburg 2006 Towards understanding nonperturbative QCD Nucleon is fundamental in understanding QCD –confinement –asymptotic freedom –spontaneous chiral symmetry breaking Mass around us mostly due to nucleons –quark mass accounts for only about 1% –mostly due to dynamics of gluons and quarks Do we understand the structure of baryons? –measurements unpolarized: ≈40% of momentum: gluons → DIS polarized: ≈30% of helicity: quarks –cannot be calculated from QCD (yet) lattice gauge calculation Study of special bound states: –double charmed baryons: 2 heavy & 1 light quark –hybrids: q  q & gluon –glueballs: gluon bound state allowed by QCD, but do they exist? Study QCD at the low energy end using chiral perturbation theory: –light meson sector: polarisability of  and K

3. Fritz-Herbert Heinsius GK Freiburg 2006 Deep Inelastic Scattering Probing the content of the proton 1968 Friedman, Kendall, Taylor: Nobel prize 1990 DESY: highest Q² –no further substructure Q² = negative momentum transfer squared

4. Fritz-Herbert Heinsius GK Freiburg 2006 Structure Functions parton carries all momentum parton carries 1/3 of momentum gluon contribution reduces momentum carried by quarks including sea quarks x = momentum fraction of the nucleon carried by the parton

5. Fritz-Herbert Heinsius GK Freiburg 2006 Parton Density Distributions 40% of the momentum carried by gluons

6. Fritz-Herbert Heinsius GK Freiburg 2006 Towards understanding nonperturbative QCD Nucleon is fundamental in understanding QCD –confinement –asymptotic freedom –spontaneous chiral symmetry breaking Mass around us mostly due to nucleons –quark mass accounts for only about 1% –mostly due to dynamics of gluons and quarks Do we understand the structure of baryons? –measurements unpolarized: ≈40% of momentum: gluons polarized: ≈30% of helicity: quarks –cannot be calculated from QCD (yet) lattice gauge calculation Study of special bound states: –double charmed baryons: 2 heavy & 1 light quark –hybrids: q  q & gluon –glueballs: gluon bound state allowed by QCD, but do they exist? Study QCD at the low energy end using chiral perturbation theory: –light meson sector: polarisability of  and K

7. Fritz-Herbert Heinsius GK Freiburg 2006 COMPASS SPS LHC COMPASS: A Facility to study QCD  p, or  /K beam 230 physicists, 10 countries, 25 institutes

8. Fritz-Herbert Heinsius GK Freiburg 2006 COMPASS: A Facility to study QCD Experiments with muon beam  Gluon polarization  G/G in the nucleon –Flavor dependent quark helicity density distributions  q  Transverse quark spin distribution functions h 1 (x) –Spin transfer in  -hyperon production –Vector meson production –Generalised parton distributions Experiments with hadron beams –Pion and kaon polarizabilities –Diffractive production of exotic states –Search for glueballs –Light meson spectroscopy –Production of double charmed baryons Application and test of perturbative QCD nonperturbative QCD –effective theories –chiral perturbation theory –lattice QCD

9. Fritz-Herbert Heinsius GK Freiburg 2006 The COMPASS SpectrometerSM1 SM2 RICH ECal & HCal μ Filter Trigger-hodoscopes Silicon Micromegas SciFi GEMs Drift chambers Straws MWPC Two stage spectrometer Polarized beam and target ~80% ≥50% SAT,LAT,PID 10 -5 <x<0.5, 10 -3 <Q 2 <100 (GeV/c) 2 50 m 6LiD Target 160 GeV μ

10. Fritz-Herbert Heinsius GK Freiburg 2006 Many new technologies for tracking and PID Scintillating fiber trackers GEM MicroMegas Readout electronics Trigger-System Straws RICH readout

11. Fritz-Herbert Heinsius GK Freiburg 2006 The polarized 6 LiD-Target 4 possible spin combinations: 1 2 reversed every 8 hrs Polarization: ~ 50% 3 4 or: reversed once a week

12. Fritz-Herbert Heinsius GK Freiburg 2006 Probing the Spin Structure of the Nucleon  ´´ Nukleon x = fraction of nucleon momentum carried by quark

13. Fritz-Herbert Heinsius GK Freiburg 2006 A 1 of the deuteron COMPASS, Phys. Lett. B 612 (2005) 154

14. Fritz-Herbert Heinsius GK Freiburg 2006 g 1 of the deuteron COMPASS, Phys. Lett. B 612 (2005) 154 COMPASS 2002/2003

15. Fritz-Herbert Heinsius GK Freiburg 2006 QCD analysis of g 1 fit to world data:  =0.22 ± 0.03 stat. Q²=3 (GeV/c)² incl. COMPASS:  =0.25 ± 0.02 stat. Q²=3 (GeV/c)²  G=0.4±0.2 stat. Systematic uncertainties: - fit parametrisation - extrapolation x→0

16. Fritz-Herbert Heinsius GK Freiburg 2006 What makes up the Nucleon‘s Spin? Naive quark model: valence quarks CERN, SLAC, DESY, JLAB:   0.30 … and angular momentum ! QCD: …additional contributions from Gluons … GΣ 2 1 2 1  ΔG = ?

17. Fritz-Herbert Heinsius GK Freiburg 2006 Polarization of Gluons  G/G in the Nucleon q = c cross section difference in charmed meson production → cross section known to NLO → experiment challenging q = u,d,s cross section difference in 2+1 jet production. In COMPASS: events with 2 hadrons with high p T → experiment easy → background difficult use two complementary measurements: Q²>1 (GeV/c)² and LEPTO MC Q²<1 (GeV/c)² and PYTHIA MC Photon gluon fusion N

18. Fritz-Herbert Heinsius GK Freiburg 2006  G/G from Open Charm (D-mesons) Photon gluon fusion N D z D > 0.2 (0.25 for D 0 ) |cos  *| < 0.85 (0.5 for D 0 ) RICH identification for K ± 9 GeV/c < p (K ± ) < 50 GeV/c

19. Fritz-Herbert Heinsius GK Freiburg 2006 m D 0 with D * tagging m D 0 without D * tagging  G/G from Open Charm (D-mesons) 2002 - 2004  2 ≈13 (GeV/c) 2

20. Fritz-Herbert Heinsius GK Freiburg 2006  G/G from high- p T meson pairs Q 2 > 1 (GeV/c) 2 LEPTO Monte Carlo Photon Gluon Fusion h1h1 h2h2 N Q 2 < 1 (GeV/c) 2 PYTHIA Monte Carlo

21. Fritz-Herbert Heinsius GK Freiburg 2006 How to get ΔG/G Q 2 >1 (GeV/c) 2 Photon Gluon Fusion QCD-Compton Leading Order fractions of cross section determined by Monte Carlo

22. Fritz-Herbert Heinsius GK Freiburg 2006  G/G from high- p T meson pairs ΔG/G = 0.06 ± 0.31 stat. ± 0.06 syst. Q 2 > 1 (GeV/c) 2 LEPTO Monte Carlo at = 0.13 ± 0.08 2002/2003 Photon Gluon Fusion h1h1 h2h2 N

23. Fritz-Herbert Heinsius GK Freiburg 2006 Background for Q 2 <1 (GeV/c) 2 PYTHIA:

24. Fritz-Herbert Heinsius GK Freiburg 2006 Uncertainty due to the unknown spin distribution in the hadronic structure of the photon Background for Q 2 <1 (GeV/c) 2 PYTHIA:

25. Fritz-Herbert Heinsius GK Freiburg 2006 Monte Carlo Tuning scrutinize systematic error: 15 independent simulations map the parameter space, i.e. for k T in nucleon and photon Fragmentation functions „parton shower“ on/off, renormalization scale Nucleon Photon

26. Fritz-Herbert Heinsius GK Freiburg 2006  G/G from high- p T meson pairs ΔG/G = 0.06 ± 0.31 stat. ± 0.06 syst. Q 2 > 1 (GeV/c) 2 LEPTO Monte Carlo at = 0.13 ± 0.08 2002/2003 Photon Gluon Fusion h1h1 h2h2 N ΔG/G = 0.016 ± 0.058 stat. ± 0.055 syst. Q 2 < 1 (GeV/c) 2 PYTHIA Monte Carlo at = 0.085 2002-2004 +0.071 - 0.035

27. Fritz-Herbert Heinsius GK Freiburg 2006  G/G summary GRSV: Glück et al.,Phys. Rev. D63 (2001) 094005  G=2.5  G=0.6  G=0.2 NLO fits to g 1  2 = 3 Gev 2

28. Fritz-Herbert Heinsius GK Freiburg 2006 Transverse Spin Distributions 3 independent structure functions are necessary to describe the spin structure of the nucleon at leading order: All of equal importance ! h 1 (x) decouples from leading twist DIS because helicity of quark must flip No mixture with Gluon

29. Fritz-Herbert Heinsius GK Freiburg 2006 3 possible quark polarimeters suggested: Azimuthal distribution of hadrons Azimuthal dependence of the plane containing 2 hadrons Measure transverse polarization of  COMPASS studies all of them  S’ = azimuthal angle of target spin vector after scattering  h = azimuthal angle of hadron  C =  h -  S’ ‚ h ‚ Transverse Spin Physics muon beam transverse target polarisation

30. Fritz-Herbert Heinsius GK Freiburg 2006 Azimuthal distribution of hadrons Transverse Spin Physics Collins: spin dependent fragmentation of transversely polarised quarks into hadrons Efremov, Goeke, Scheitzer, hep-ph/060354 (fit to BELLE & HERMES data)

31. Fritz-Herbert Heinsius GK Freiburg 2006 Transverse Spin Physics Collins fragmentation function extracted from HERMES / BELLE From: Efremov, Goeke, Schweitzer hep-ph/0603054 COMPASS 2002 data compatible with fit deuteron essential to determine h 1 d

32. Fritz-Herbert Heinsius GK Freiburg 2006 Azimuthal distribution of hadrons Transverse Spin Physics Efremov, Goeke, Scheitzer, hep-ph/060354 (fit to BELLE & HERMES data) Anselmino et. al hep-ph/0507181 Sivers : intrinsic k T dependence of the quark distribution

33. Fritz-Herbert Heinsius GK Freiburg 2006 Azimuthal dependence of the plane containing 2 hadrons Transverse Spin Physics precise measurement of few % systematics seems well under control also compatible with zero interesting to see proton in 2006 1 +/- combination per event: p t ordering all +/- combination per event

34. Fritz-Herbert Heinsius GK Freiburg 2006 Measure transverse polarization of  Transverse Spin Physics

35. Fritz-Herbert Heinsius GK Freiburg 2006 Results not covered semi-inclusive asymmetries,  single hadron high-p T  spin-density matrix elements  polarisation pentaquark search diffractive processes J/  production Ξ(1530) 0

36. Fritz-Herbert Heinsius GK Freiburg 2006 COMPASS upgrades for this year New solenoid magnet –Larger acceptance –70 mrad  180 mrad RICH upgrade –Central region: MAPMT system –Outer region: new faster electronics Other upgrades: –Large Drift Chamber –ECAL1 –…

37. Fritz-Herbert Heinsius GK Freiburg 2006 Summary / Outlook COMPASS results (2002-2004) –polarisation of gluons in the nucleon –transversity: small asymmetries on deuteron Many more results not covered Major upgrade of spectrometer for this year Next year: start spectroscopy –hybrids, glueballs, … Long term future (2010+): generalised parton distributions (DVCS,…)