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HIGHLIGHTS FROM THE COMPASS EXPERIMENT @ CERN

HIGHLIGHTS FROM THE COMPASS EXPERIMENT @ CERN. F. Bradamante University of Trieste and INFN Trieste on behalf of the Collaboration WE Heraeus Seminar on Polarized Antiprotons Bad Honneff, June 23-25, 2008.

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HIGHLIGHTS FROM THE COMPASS EXPERIMENT @ CERN

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  1. HIGHLIGHTS FROM THE COMPASSEXPERIMENT @ CERN F. Bradamante University of Trieste and INFN Trieste on behalf of the Collaboration WE Heraeus Seminar on Polarized Antiprotons Bad Honneff, June 23-25, 2008

  2. COmmon Muon and Proton Apparatusfor Structureand Spectroscopy NA58 Czech Republic, Finland, France, Germany, India, Israel, Italy, Japan, Poland, Portugal, Russia Bielefeld, Bochum, Bonn, Burdwan, Calcutta, CERN, Dubna, Erlangen, Freiburg, Heidelberg, Helsinki, Lisbon, Mainz, Miyazaky, Moscow, Munich, Nagoya, Prague, Protvino, Saclay, Tel Aviv, Torino, Trieste, Warsaw 28 Institutes, ~230 physicists F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  3. COMPASS • since 2002 taking data with a new spectrometer with outstanding performances • merging of two programmes: F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  4. Experiments with muon beam ΔG/G g1 Transverse spin effects Flavor decomposition of spin distribution functions Vector meson production Spin transfer inΛ-hyperon production Experiments with hadron beams Pion and Kaon polarizabilities Diffractive production of exotic states Search for glueballs Light meson spectroscopy Production of double charmed baryons Physics program of COMPASS F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  5. luminosity: ~5 . 1032 cm-2 s-1 beam intensity: 2.108m+/spill (4.8s/16.2s) beam momentum: 160 GeV/c longitudinally polarised muon beam longitudinally or transversely polarised target calorimetry particle identification LHC SPS N F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  6. 160 GeVμ SM2 SM1 6LiD Target The Spectrometer for the Muon Programme Trigger-hodoscopes μFilter ECal & HCal 50 m RICH MWPC Straws TWO STAGE SPECTROMETER: Gems Drift chambers Polarized beam and target Micromegas SAT, LAT, PID Silicon SciFi 0.003 < x < 0.5 10-3 < Q2 < 10 GeV2 F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  7. the target system solid state target operated in frozen spin mode 2002-2004: 6LiD (polarised deuteron) dilution factor f = 0.38 polarization PT = 50% two 60 cm long cells with opposite polarisation (systematics) • 2006: • PTM replaced with the large acceptance COMPASS magnet (180 mrad) • 2 target cells  3 target cells 2007:NH3 (polarised protons) dilution factor f = 0.14 polarization PT = 90% during data taking with transverse polarisation, polarisation reversal in the cells after ~ 4-5 days F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  8. WHERE ARE WE ? • in 2002, 2003, 2004, 2006 and 2007 COMPASS has taken data in themuon programconfiguration 160 GeV, polarized m beam2002-2006 6LiD polarized target (~polarized deuterons) 2007 NH3 polarized target (~polarized protons) 2000 TB ~ 5·1010 events • pilot run in 2004 for hadron program • 2008: hadron beam at 190 GeV for diffractive and central production physics results • DG/G 1.pion polarizability • DS 2.PWA in diffractive • Transversity scattering • Cahn asymmetry • Pentaquark • Exclusive ρ0 • Λ physics F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  9. THE COMPASS MUON PROGRAM TWO CLASSES OF PHENOMENA: • LONGITUDINAL SPIN CASE • TRANSVERSE SPIN CASE F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  10. LONGITUDINAL SPIN CASE: the beginning  SPIN CRISIS F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  11. LONGITUDINAL SPIN CASE from polarised lepton – polarised nucleon DIS with and first moments: from measurement of EMC in 1988 and using complementary information from neutron and hyperon β–decay one obtained at variance with naïve expectation since necessity for measuring SMC, SLAC, HERMES and in SIDIS SMC, HERMES, COMPASS in SIDIS HERMES, COMPASS F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  12. A1d from COMPASS Inclusive DIS asymmetry Q2>1 (GeV/c)2 PLB 647(2007)8 • good agreement with previous experiments • significantly improved statistics at low x ! F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  13. COMPASS QCD fit using these results plus the same asymmetries on p and n from the other experiments F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  14. LONGITUDINAL SPIN CASE direct measurement of ΔG/G: main objective of the longitudinal run F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  15. MEASUREMENTS OF THEGLUON POLARIZATION FOUR LINES OF ATTACK: • Double spin asymmetry of the OPEN CHARM cross-section in high energy µD scattering • Double spin asymmetry of the HIGH-pt HADRON PAIRS in high energy µD DIS (Q2 > 1 GeV2) • Double spin asymmetry of the high-pt hadron pairs in high energy µD scattering (Q2 < 1 GeV2) • Measurement of g1 of the deuteron and QCD fit of all the world data F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  16. N DG/G at COMPASS Photon Gluon Fusion q = c cross section differencein charmed meson production → theory well understood → experiment challenging q = u,d,s cross section difference in 2+1 jet productionin COMPASS: events with 2 hadrons with high-pt → experiment easy → theory more difficult F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  17. ΔG/G from Open Charm F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  18. D mass spectra D0 → K π nD* = 8675 nD0 = 37398 D0 → K ππ0 APS, 13 April 2008 G.K. Mallot 18 F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  19. DG/G from open charm 2002 – 2006 data D0 + D* • ΔG/G = -0.49 ± 0.27 (stat) ± 0.11 (syst) • @ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2 preliminary 19 F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  20. ΔG/G from High-pt hadron pairs F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  21. QCD- Compton PGF LO DIS ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2 PGF and background F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  22. ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2 2002 – 2004 data: High pT, Q2 > 1 GeV/c2 • ΔG/G = 0.08 ± 0.10 (stat) ± 0.05(syst) • @ <xg> = 0.082 (range: 0.055 – 0.123), m2 ~ 3 (GeV/c)2 preliminary F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  23. QCD- Compton PGF LO DIS ΔG/G from High-pt hadrons all Q2 low Q2 resolved photon F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  24. ΔG/G from High-pt hadrons, Q2 < 1 (GeV/c)2 2002 – 2004 data: High pT, Q2 < 1 GeV/c2 ΔG/G = 0.016 ± 0.058 (stat) ± 0.055 (syst) • @ <xg> = 0.085, m2= 3 GeV2 preliminary F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  25. Gluon Polarization COMPASS preliminary results high-pT pairs, Q2>1GeV2 : 2002–2004 ΔG/G = 0.08 ± 0.10 (stat) ± 0.05(syst) • @ <xg> = 0.082 (range: 0.055 – 0.123), m2 ~ 3 (GeV/c)2 high-pt pairs, Q2< 1GeV2 : 2002–2004 ΔG/G = 0.016 ± 0.058 (stat) ± 0.055 (syst) • @ <xg> = 0.085, m2= 3 GeV2 open charm: 2002–2006 ΔG/G = -0.49 ± 0.27 (stat) ± 0.11 (syst) • @ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2 F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  26. Summary of results new high-pT point new charm point G.K. Mallot F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  27. CONCLUSION from ΔG MEASUREMENTS: ΔG SMALL more precise measurements will come soon COMPASS 2006 RHIC RUN6 …. interest in orbital angular momentum GPD’s Ji’s SUM RULE F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  28. The Transverse Spin Case F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  29. Transverse Spin case Large effects observed in hadronic interactions F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  30. q(x) Dq(x)DTq(x) Transverse Spin case at leading order a third PDF is necessary for a complete description of the structure of the nucleon Theoretical developments: Large effects observed in hadronic interactions • DTq(x) being chiral-odd, it can be measured only in conjunction • with another chiral-odd partner: Collins function SIDIS DY measurable in e+e- hadrons • relevance of transverse momentum dependent (TMD) PDF and FF Sivers function Many Workshops in recent years on Transverse Momentum, spin, and position distributions of partons in hadrons F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  31. Transversity – single hadron - 1 Collins and Sivers angles • C = h- S’ S = h- S S ’ azimuthal angle of spin vector of fragmenting quark (S’’ = p- S) hazimuthal angle of hadron momentum F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  32. Transversity – single hadron- 2 first measurements of transverse spin asymmetries in DIS of high energy muons on a transversely polarizeddeuteron target published single hadron asymmetries from 2002-2004 runs • Collins: related to transverse quark distributions • Sivers: related to intrinsic kT Phys Rev Lett 94 (2005) 202002 Nucl Phys B765 (2007) 31 F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  33. Collins asymmetry for pions and kaons preliminary 2002-2004 data proton (virtual photon asymm) (lepton beam 2002-05  DIS07) final CERN-PH-EP/2008-002hep-ex/0802.2160 (PRL) 2003-2004 data deuteron (virtual photon asymm) COMPASS sign convention F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  34. Independent Measurement of the Collins FF measurable in e+e– annihilation • first attempts to measured it from the correlation between the azimuthal angles of p‘s from e+e– annihilation using LEP data • 547 fb-1 charm corrected data sample, • UL and UC double ratios last years: great news from BELLE the Collins FF is being measured in e+e– annihilation, and it is different from zero! measurement of the correlation between the azimuthal angles of p‘s in the near jet and in the far jet from e+e– annihilation F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  35. Collins asymmetries: SUMMARY The facts: • HERMES has measured on a proton targetnon-zero Collins asymmetries for π+ and π- • COMPASS has measured on a deuteron targetCollins asymmetries compatible with zero • BELLE has produced the first results on Collins FF Conclusion: • Collins mechanism is a real phenomenon • universality of Collins FF • transversity can be measured in SIDIS Present picture • Collins:DTu ~ - DTd DT0D(fav.) ~ - DT0D(unfav) To extract TMD DF and FF GLOBAL ANALISYS are necessary F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  36. HERMES, COMPASS, BELLE F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  37. Sivers asymmetry for pions and kaons preliminary 2002-2005 data proton (DIS07) CERN-PH-EP/2008-002hep-ex/0802.2160 (PRL) 2003-2004 data deuteron F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  38. F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  39. conclusions from COMPASS deuteron data • the unpolarisedazimuthal asymmetries are different from zero and different for positive and negative hadrons HERMES, COMPASS, BELLE data: consistent picture first fits, extractions of the new DFs, and predictions for other experiments • still, a lot of expectation for the higher energy COMPASS proton data F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons all the transverse spin asymmetries have been measured to be compatible with zero

  40. 2007 Transverse data statistics Data used for these results • several stability tests have been performed • detectors and triggers performances • event reconstruction • K0 reconstruction • distributions of kinematical variables: • ( zvtx, Em’, fm’, xBj Q2,y, W, Ehad, fhadLab , qhadLab , fhadGNS , qhadGNS , pt) • ~20% of the total collected data has been used for this analysis F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons 2007 run: May to November equally shared between transverse and longitudinal Transverse polarization data taking:

  41. Collins asymmetry – proton data integrated over x and z statistical errors only; systematic errors ~ 0.3 sstat at small x, the asymmetries are compatible with zero in the valence region the asymmetries are different from zero, of opposite sign for positive and negative hadrons, and have the same strength and sign as HERMES F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  42. Collins asymmetry – proton data comparison with M. Anselmino et al. predictions F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  43. Sivers asymmetry – proton data integrated over x and z statistical errors only; systematic errors ~ 0.5 sstat the measured symmetries are small, compatible with zero F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  44. Sivers asymmetry– proton data comparison with the most recent predictions from M. Anselmino et al. arXiv:0805.2677 F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  45. Results: Sivers asymmetry comparison with predictions from S.Arnold, A.V.Efremov, K.Goeke, M.Schlegel and P.Schweitzer, arXiv:0805.2137 F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

  46. conclusions near future: analysis of the whole 2007 proton data sample longer term: transverse spin physics is one of the items being spelled out for the future COMPASS program the study of transverse spin effects needs further precise measurements and the COMPASS facility is the only place where SIDIS can be measured at high energy F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons COMPASS preliminary results on • unpolarised hadron asymmetries on deuteron for positive and negative hadrons • Collins and Sivers asymmetries on protons • Collins asymmetry different from zero the effect is there at COMPASS energies • Sivers asymmetry: smaller, compatible with zero to be understood

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