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Collins and Sivers asymmetries on the deuteron from C O M P A S S

Collins and Sivers asymmetries on the deuteron from C O M P A S S. Andrea Bressan (University and I.N.F.N. Trieste) on behalf of the COMPASS Collaboration. PANIC05 Particles and Nuclei International Conference Santa Fe, NM - October 24-28, 2005. LHC. COMPASS. SPS. COMPASS data sample.

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Collins and Sivers asymmetries on the deuteron from C O M P A S S

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  1. Collins and Sivers asymmetries on the deuteron from COMPASS Andrea Bressan (University and I.N.F.N. Trieste) on behalf of the COMPASS Collaboration PANIC05 Particles and Nuclei International Conference Santa Fe, NM - October 24-28, 2005

  2. LHC COMPASS SPS Andrea Bressan University -INFN Trieste

  3. COMPASS data sample RICH PID • In so far ( 3 years ) • only DIS off 6LiD • 20% of the time with transverse target polarization • only runs with transverse polarized target being analyzed E-Calorimetry Andrea Bressan University -INFN Trieste

  4. Target 3He – 4He Dilution refrigerator (T~50mK) superconductive Solenoid (2.5 T) Dipole (0.5 T) For transversity: 1 2 reversed once a week Polarization: 50% Dilution factor: 0.38 two 60 cm long Target-Containers with opposite polarization During data taking for transversity dipole field always  Relaxation time > 2000 hrs Andrea Bressan University -INFN Trieste

  5. COMPASS acceptance Q21(GeVc)2 Excellent for non-perturbative & perturbative physics - small xBj & very small Q2  Q2 > 100 (GeV/c)2 Andrea Bressan University -INFN Trieste

  6. Transverse Spin Effects in SIDIS • 3 possible polarimeters to measure ΔTq are explored in COMPASS: • Azimuthal dependence of the plane containing hadrons pairs • Preliminary results on 02-03 data (Rainer Joosten) • Collins effects of (leading) h± • Published results on 2002 data • (PRL 94 (2005) 202002 – Collins and Sivers) • Transverse polarization of Λ hyperon • First results on 02-03 data Andrea Bressan University -INFN Trieste

  7. Azimuthal asymmetries of single hadrons • Collinseffect predicts an azimuthal asymmetry infragmentation of transversely polarized quarks with finite transverse momentum to unpolarized hadrons 2) Siverseffect predicts an azimuthal asymmetry from the un-polarized quarks, i.e. an azimuthal modulation of initial quark transverse momentum for a transversely polarized nucleon Andrea Bressan University -INFN Trieste

  8. Collins and Sivers Asymmetries S = azimuthal angle of spin vector of incident quark (nucleon) S’ = azimuthal angle of spin vector of fragmenting quark (after scattering) h=azimuthal angle of hadron Andrea Bressan University -INFN Trieste

  9. Event Selection • Leading Hadron • 0.25<z<1 • Pt>0.1 GeV/c • z-missing cut • All Hadrons • z>0.2 • Pt>0.1 GeV/c • DIS cuts: • Q2>1 (GeV/c)2 • 0.1<y<0.9 • W>5 GeV/c2 • Hadrons • Track Length<10 X0 • Energy Deposit in HCALs > 5(8) GeV Q2=2.4 (GeV/c)2 pT0.51 GeV/c z0.45 xBj0.035 Andrea Bressan University -INFN Trieste

  10. Collins and Sivers effects Only statistical errors shown Phys. Rev. Lett. 94, 202002 (2005) Systematic errors are smaller than the quoted statistical errors. Andrea Bressan University -INFN Trieste

  11. Collins and Sivers effects Only statistical errors shown Phys. Rev. Lett. 94, 202002 (2005) Systematic errors are smaller than the quoted statistical errors. Andrea Bressan University -INFN Trieste

  12. Interpretations • Small asymmetries, some explanations: • Cancellation between proton and neutron; • Too small Collins mechanism. • and large (as from preliminary measurement by BELLE, hep-ex/0507063) means evidence for cancellation in isoscalar target; • Phenomenological fits of the data from HERMES and prediction for COMPASS by Vogelsang and Yuan (hep-ph/0507266), Efremov et al. (hep-ph/0412353, Phys.Part.Nucl.35:S139-S142,2004) and Anselmino et al. (hep-ph/0507181) Andrea Bressan University -INFN Trieste

  13. Just a flash: fits and calculations • M. Anselmino et al. • Sivers on Deuterium • W. Vogelsang and F. Yuan Deuterium • Set I for CFF Andrea Bressan University -INFN Trieste

  14. Expected accuracy for transversity Andrea Bressan University -INFN Trieste

  15. RICH response Hadron masses calculated from the measured Cherenkov angle Threshold momenta: • pp=2 GeV/c • pK=9 GeV/c • pP=17 GeV/c For single leading (z) hadrons, with additional cut: z > 0.25 Andrea Bressan University -INFN Trieste

  16. ΔTq(x) from Λ polarization Informations on ΔTq(x) can be access also in μN μ’ΛX • Alternative approch to Collins single hadron asymmetries • The chiral-odd partner of ΔTq(x) is the fragmentation function Andrea Bressan University -INFN Trieste

  17. ΔTq(x) from Λ polarization • Negative trend but, not very significand deviation from zero yet. • Systematic effects not larger than statistical errors. • Factor 2 in statistics expected from 2004 data. Andrea Bressan University -INFN Trieste

  18. 2006: proton run for transverse PT • New magnet: larger acceptance • Higher statistics at large x Andrea Bressan University -INFN Trieste

  19. Expected accuracy for transversity • 30 days of running For Sivers expected errors are almost the same • M. Anselmino et al. Protons Andrea Bressan University -INFN Trieste

  20. Summary and Outlook • The 2002 single hadron asymmetries (Collins and Sivers) are small and compatible with the zero • Both COMPASS (deuteron) and HERMES (protons) can be described by the same model, implying for deuteron a cancellation between protons and neutrons. Existing phenomenological models are in a good agreement with COMPASS and HERMES data; • Making use of existing deuteron data (2002-2004), accuracy will improve by a factor ~ 3, results are coming soon; • Data (of comparable statistics) will be collected on a transversely polarized proton target (NH3) in 2006 and will allow a flavor separation. Andrea Bressan University -INFN Trieste

  21. THANK YOU

  22. Save slides Andrea Bressan University -INFN Trieste

  23. Flavor decomposition To measure the shape of Andrea Bressan University -INFN Trieste

  24. Estimators Weaker assumptions on acceptance effects less sensitive to distorsions set by Cahn effects Reconstruction time independent in the solid angle Andrea Bressan University -INFN Trieste

  25. Extraction of Collins (Sivers) asym’s • Evaluating the population as a function of Φ, independently in both target cells; • Extracting 2 asymmetries and calculating the weighted mean; j = C, S, (Φj calculated always with spin = ↑)and F is the muon flux, n the number of target particles, σ the spin averaged cross-section, and aj the product of angular acceptance and efficiency of the spectrometer; Andrea Bressan University -INFN Trieste

  26. Spectrometer 2002  2004 Beam:160 GeV µ+ 2 . 108 µ/spill (4.8s/16.2s) Pm ~ 80% trigger-hodoscopes DW45 straws SM2 dipole Muon-filter2,MW2 HCAL1 RICH_1 Gem_11 ECAL2,HCAL2 SM1 dipole MWPC Gems Scifi Polarised Target Muon-filter1,MW1 Veto straws,MWPC,Gems,SciFi Gems,SciFi,DCs,straws Silicon SciFi Micromegas,DC,SciFi BMS Andrea Bressan University -INFN Trieste

  27. Measuring ΔTq(x) Tq(x) is chiral odd: decouples from leading twist DIS because helicity of quark must flip. It doesn’t play any role in inclusive DIS; How to access it? Andrea Bressan University -INFN Trieste

  28. Measuring ΔTq(x) Convolution with fragmentation functions (measurements of ff ongoing at BELLE) Direct Measurement Chiral-odd: requires another chiral-odd partner ppl+l-X epe’hX Andrea Bressan University -INFN Trieste

  29. SIDIS off transversely polarized target Collins effect predicts an azimuthal asymmetry in the quark fragmentation The quark prefers to fragment in one direction; Look at leading hadron (it comes from the struck quark); The larger is “z” (fraction of the available energy carried by the hadron), the stronger is the signal ; But an azimuthal asymmetry can also come from the un-polarised quarks; namely from an azimuthal modulation of quark transverse momentum for a transversely polarized nucleon (Sivers effect) y x h z q y x q kT z Andrea Bressan University -INFN Trieste

  30. Collins single-spin asymmetries on deuterons • W. Vogelsang and F. Yuan hep-ph/0507266 • Fit Parameters: Set II for CFF Andrea Bressan University -INFN Trieste

  31. Theoretical work on the subject • “The role of Cahn and Sivers effects in DIS” M. Anselmino et al. (hep-ph/0501196) • Phenomelogical model whose parameters are constrained by HERMES proton measurements; • COMPASS preliminary results for Sivers effect (shown at SPIN04) are in agreement with the model. • Interpretation of Collins effect in progress. Andrea Bressan University -INFN Trieste

  32. 2hadron case using RICH Pairs of hadrons to be analyzed: pp, pK, KK K0 r0 K* f Andrea Bressan University -INFN Trieste

  33. 2hadron case using RICH Identification for “standard” cuts (zh1>0.1 & zh2>0.1) Better SNR for zh1>0.25 and zh2>0.25 Andrea Bressan University -INFN Trieste

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