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RISULTATI RECENTI DI COMPASS

RISULTATI RECENTI DI COMPASS. Two classes of phenomena. Longitudinal Spin Case Transverse Spin Case. Δ G Measurements in COMPASS. Open charm – D 0 and D* events. All deuterium data analyzed (2002-2006). D 0 selection: K p invariant mass + cuts on kinematics + RICH PID.

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RISULTATI RECENTI DI COMPASS

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  1. RISULTATI RECENTI DI COMPASS

  2. Two classes of phenomena • Longitudinal Spin Case • Transverse Spin Case

  3. ΔG Measurements in COMPASS

  4. Open charm – D0 and D* events All deuterium data analyzed (2002-2006) D0 selection: Kp invariant mass + cuts on kinematics + RICH PID

  5. ΔG/G da open-charm NEW: PRESENTED @ DIS2008

  6. ΔG/G da adroni ad alto pT Q2 > 1 (GeV/c)2 Photon Gluon Fusion ~ 30% Leading Order QCD Compton

  7. adroni ad alto pT: data/MC Data /MC

  8. Sommario ΔG/G da COMPASS COMPASS QCD fits to g1 |DG| ~ 0.2-0.3 Q2=3 (GeV/c)2 New high pT New open charm

  9. Transverse Spin effects in COMPASS

  10. What we are after? (Trans) three quark distribution functions (DF) are necessary to describe the structure of the nucleon at LO q(x) f1q (x) unpolarised DF quark with momentum xP in a nucleon well known – unpolarised DIS • vector charge Dq(x) g1q(x) helicity DF quark with spin parallel to the nucleon spinin a longitudinally polarised nucleon known – polarised DIS  axial charge DTq(x) = q↑↑(x) - q↑↓(x) h1q(x), transversity DF quark with spin parallel to the nucleon spinin a transversely polarised nucleon  tensor charge largely unknown ALL 3 OF EQUAL IMPORTANCE

  11. Single hadron asymms. Collins and Sivers terms in SIDIS cross sections depend on different combination of angles: • C = h- s’ • Collins angle S = h- sSivers angle hazimuthal angle of the hadron sazimuthal angle of the transverse spin of the initial quark s’ azimuthal angle of the transverse spin of the fragmenting quark s’ = p -s (spin flip)

  12. Proton 2007 data… • 450 TB collected (by november)! • ~20% of the data processed quasi on-line! • First data crunching! All 459 TB processed end by January-Febrary • Stability cheks done! • Systematic studies done! • First results by May!

  13. 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) 2007 run: May to November equally shared between transverse and longitudinal Transverse polarization data taking:

  14. Collins asymmetry – proton data NEW: PRESENTED @ TRANSVERSITY2008 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 Anna Martin

  15. Comparison with predictions

  16. SIVERS Mechanism • The Sivers DF is probably the most famous between TMDs… • gives a measure of the correlation between the transverse momentum and the transverse spin • Requires final/initial state interactions of the struck quark with the spectator system and the interference between different helicityFock states to survive time-reversal invariance • Time-reversal invariance implies: • …to be checked – Drell-Yan program in COMPASS • In SIDIS:

  17. Sivers asymmetry – proton data NEW: PRESENTED @TRANSVERSITY2008 statistical errors only; systematic errors ~ 0.5 sstat the measured symmetries are small, compatible with zero Anna Martin

  18. Sivers asymmetry– proton data comparison with the most recent predictions from M. Anselmino et al. arXiv:0805.2677 Anna Martin

  19. Results: Sivers asymmetry comparison with predictions from S.Arnold, A.V.Efremov, K.Goeke, M.Schlegel and P.Schweitzer, arXiv:0805.2137 Anna Martin

  20. UNPOLARIZED ASYMMETRIES

  21. unpolarised target SIDIS cross-section 3 independent azimuthal modulationsin h , the hadron azimuthal angle in GNS Anna Martin

  22. acceptance unpolarised target SIDIS cross-section to extract the asymmetries the azimuthal distributions have to be corrected by the apparatus acceptancededicated MC simulations for L and T target polarisation data final azimuthal distribution initial azimuthal distribution

  23. results: sinmodulation error bars: statistical errors bands: systematical errors Anna Martin

  24. results: cosΦmodulation Anna Martin

  25. results: cos 2Φmodulation Anna Martin

  26. COMPASS FUTURE PROGRAM • Proposal to CERN in preparation (deadline December 2008) • Transverse SPIN effects • Drell-Yan with p- • SIDIS on protons • GPD via DVCS

  27. FOTORIVELATORI basati su TH(ick) GEM R&D per lo sviluppo di fotorivelatori a gas di terza generazione basati su MPGD (Micro Pattern Gaseous Detector) P1: D=0.8 mm Pitch=2 mm Rim=0.04 mm Thick=1mm R3 W2 si veda, ad esempio, il poster presentato a Phyisics@UNITS “ The quest for a third generation of gaseous photon detectors for Cherenkov Imaging Counters” , F. Tessarotto P1 R3: D=0.2 mm Pitch=0.5 mm Rim=0.01 mm Thick=0.2mm W2: D=0.3 mm Pitch=0.7 mm Rim=0.1 mm Thick=0.4mm necessita’ future di COMPASS tradizione ed interesse per rivelatori di frontiera

  28. Over !

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