TRANSVERSE SPIN EFFECTS IN COMPASS

1. TRANSVERSE SPIN EFFECTS IN COMPASS

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

3. 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

4. 160 GeVμ SM2 SM1 6LiD Target The Spectrometer for the Muon Programme Trigger-hodoscopes μFilter ECal & HCal 50 m TWO STAGE SPECTROMETER: RICH MWPC 0.003 < x < 0.5 10-3 < Q2 < 10 (GeV/c)2 Straws Gems Drift chambers Micromegas LAT, PID Silicon SciFi

5. Polarized Target New COMPASS target magnet: 180 mrad geometrical acceptance excellent field homogeneity To match larger acceptance: new microwave cavity 3 target cells: reduction of false asymmetries Target material: NH3 high polarisation very long relaxation time (∼ 4000 h) magnetic field rotation without polarisation loss  Polarisation of NH3 in 2007: -92%, +88%, -83% Target Polarization reversed every week

6. 2007 Transverse data taking statistics • 2007 Compass Data taking Begin of run: 18 May 2007 End of run: 11 November 2007 • Split between transverse and longitudinal target polarization: - m on tape for transverse (40.0 x1012) - m on tape for longitudinal (41.5 x1012) • For the extraction of the asymmetries (this analysis) only a fraction of the full statistic available has been used : nearly 20% of the whole data sample available.

7. DIS Event Selection DIS cuts: • Q2>1 (GeV/c)2 • 0.1<y<0.9 • W>5 GeV/c2

8. Hadron Selection • All hadrons • Track Length<10 X0 • Energy Deposit in HCALs>Thr. ( 4 GeV HCal1 and 5 GeV Hcal2 ) • Only 1 HCAL fired • pT>0.1 GeV/c • z>0.2

9. Data quality checks • Data taking stability is needed: A dedicated set of quality checks have been developed and applied to fulfill this condition Different estimators have been considered: • the detector profiles stability • the number of primary vertices per event • the number of tracks per primary vertex • beam particles per primary vertex • the number of K0 per primary vertex • the reconstructed mass of the K0 meson • stability of many kinematical variables: ( zvtx, Em’, fm’, xBj Q2,y, W, Ehad, fhadLab, qhadLab, fhadGNS, qhadGNS, pt)

10. Mean of kinematical quantities

11. Collins and Sivers angles Azimuthal modulations • C = h- S’ S = h- S S ’ azimuthal angle of spin vector of fragmenting quark (S’ = p- S) hazimuthal angle of hadron momentum

12. SIDIS azimuthal asymmetries All possible 8 azimuthal asymmetries extracted at once. ... Sivers Collins 6 further modulations M. Diehl, S. Sapeta, Eur.Phys.J C41 (2005) 515-533 hep-ph/0503023

13. Asymmetry Extraction Splitting middle cell into two parts • two couples of cells with opposite polarization • two independent values for the asymmetries per period Extraction: 2D Binned Maximum Log-Likelihood Fit: eight by eight grid in fh and fS; in each bin of the matrix one expects Nj counts :

14. Asymmetry Extraction - II Separation of acceptance and spin dependent modulations: Coupling of two cells (u,d) with opposite polarization () and two periods (p1,p2) with opposite target polarization: Reasonable assumption: 4 · 64 = 256 nonlinear equations 1 + 8 + 3 · 64 = 201 fit parameter, Poisson distribution to account for low statistics: • Tests for systematic errors: • For false asymmetries: combination of cells with same polarization • Comparison of 5 estimators for asymmetry extraction included the one used in previous analysis (deuteron data) • For this analysis: overall systematic error is 30% and 50% of the • statistical error for Collins and Sivers respectively

15. Collins asymmetry – proton data 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

16. Compass proton data comparison with M. Anselmino et al. predictions

17. Collins Final on Deuteron

18. Sivers asymmetry – proton data systematic errors ~ 0.5 sstat the measured symmetries are small, compatible with zero

19. Sivers Final on Deuteron from COMPASS

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

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

22. Transverse L polarization

23. Data Selection • Secondary vertex downstream of primary vertex. • PT > 23 MeV/c to exclude e+e− pairs • Proton and pion momenta > 1 GeV/c • Q2 > 1 (GeV/c)2 • 0.1 < y < 0.9 • Use of RICH (2007 data) • Λ decay distance DΛ > 7 σD • Collinearity < 10 mrad

24. Results with proton target • ~60% higher statistics with respect deuteron data (after) • Systematic errors have been estimated to be smaller than statistical errors from false polarization. • No dependence on x.

25. (Old) Results on Deuteron L L • Analysis for 2002-2004 deuteron data (and no RICH ID) • Only statistical errors are shown (systematic effects not larger than the statistical errors). • Small tendency for Λ, but not significant for deuteron target.

26. Summary First preliminary results of COMPASS 2007 proton transverse run: • Collins Asymmetry: • different from zero, comparable to HERMES • agreement with predictions of Anselmino et al • Sivers Asymmetry: • small and compatible with zero within present statistical errors • Accessing Collins from L: • small and compatible with zero within present statistical errors

27. Thank You

28. The 3rd Twist-2 structure function 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

29. Inclusive DIS ppl+l-X lpl’hX impossible direct measurement ΣΔTq(x) ·ΔTq(x) convolution with spin dependent fragment. func. Misura di ΔTq(x) Chiral-odd: requires another chiral-odd partner lpl’h1h2X lpl’ΛX

30. Transversity DF q=uv, dv, qsea quark with spin parallel to the nucleon spinin a transversely polarised nucleon DTq(x) = q↑↑(x) - q↑↓(x) h1q(x), dq(x), dTq(x) • Properties: • probes the relativistic nature of quark dynamics • no contribution from the gluons  simple Q2 evolution • Positivity: Soffer bound…………….. • first moments: tensor charge………. • sum rule for transverse spinin Parton Model framework………… • it is related to GPD’s • is chiral-odd: decouples from inclusive DIS Soffer, PRL 74 (1995) Bakker, Leader, Trueman, PRD 70 (04)

31. 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 • In SIDIS:

32. Global Fits

33. Global Fit

34. First Extraction of DTq HERMES, COMPASSBELLE

35. Global Analysis Stefano Melis DIS

36. Sivers PDF

37. 2007 Transverse data taking statistics • 2007 Compass Data taking Begin of run: 18 May 2007 End of run: 11 November 2007 • Split between transverse and longitudinal target polarization: - m on tape for transverse (40.0 x1012) - m on tape for longitudinal (41.5 x1012) • For the extraction of the asymmetries (this analysis) only a fraction of the full statistic available has been used : nearly 20% of the whole data sample available.