SINGLE HADRON TRANSVERSE SPIN ASYMMETRIES FROM COMPASS Franco Bradamante University of Trieste and INFN Trieste on behalf of the COMPASS Collaboration Kyoto, October 3, 2006

THE SPECTROMETER two stages spectrometer Large Angle Spectrometer (SM1) Small Angle Spectrometer (SM2) tracking, calorimetry, PID SciFi Silicon Micromegas GEMs Straws SDC MWPC W45 MuonWall SM2 E/HCAL E/HCAL SM1 Polarised Target MuonWall RICH m beam high energy beam broad kinematical range large angular acceptance Franco Bradamante

solid target operated in frozen spin mode superconductive Solenoid (2.5 T) 3He – 4He Dilution refrigerator (T~50mK) Dipole (0.5 T) two 60 cm long cells with opposite polarization (systematics) THE TARGET SYSTEM solid target operated in frozen spin mode dN/dz 2000 zvtx (mm) -1000 1000 4000 THE RICH DETECTOR 5 m 6 m 3 m C4F10 photon detectors threshold momenta pp = 2 GeV/c pK = 9 GeV/c pP =17 GeV/c fully efficient for transverse data in 2003 and 2004 Franco Bradamante

DATA TAKING 2002-2004 transversely polarised deuteron target ~ 20% of the running time 2002 11 days of data taking (19), 2 periods 2003 9 days of data taking (14), 1 period 2004 14 days of data taking (24), Collins and Sivers asymmetries published results 2002 prel results 2002-2004 with RICH PID Two hadron asymmetries Λ polarimetry prel results 2002-2003 trigger (large x, Q2) DAQ, on line filter DIS events (106) Franco Bradamante

SINGLE HADRON ASYMMETRIES unpol B and T transvely polarised target SIDIS cross-section long pol B and/or T h azimuthal angle of the hadron s’ azimuthal angle of the transverse spin of the struck quark s azimuthal angle of the transverse spin of the initial quark s’ = p - s FS at leading order Collins Sivers beam polarization independent angles  independent extraction of the asymmetries Franco Bradamante

EVENT SELECTION DIS events Q2 > 1 GeV2 W2 > 25 GeV2 0.1 < y < 0.9 hadrons pht > 0.1 GeV/c z > 0.2 (all h) z > 0.25 (leading h) Q2 = 2.4 (GeV/c)2 W = 9.4 GeV/c2 xBj  0.035 2002 data Franco Bradamante

increase in statistics by a factor of 7! ASYMMETRIES 2003-2004 vs 2002 results from 2003-2004 data released in April (DIS2006) comparison with the published 2002 data PRL 94 (2005) 202002 increase in statistics by a factor of 7! Franco Bradamante

COLLINS ASYMMETRIES 2002-2004 small errors (~1%) small asymmetries DIS2006 DIS2006 small errors (~1%) small asymmetries cancellation between p and n (lh and ah) Franco Bradamante

COLLINS ASYMMETRY results from model calculations: good fits to the proton HERMES DATA with Collins FF: favoured ~ – unfavored, at variance with unpolarised case comparison with BELLE DATA ok: universality of the Collins effect, hints on Tu comparison with the deuteron COMPASS 2002 DATA ok Td ~ unconstrained comparison with the new COMPASS 2002-2004 data Vogelsang and Yuan preliminary COMPASS 2002-2004 Efremov et al preliminary COMPASS 2002-2004 Anselmino et al, Tq = q preliminary COMPASS 2002-2004 Anselmino et al, SB preliminary COMPASS 2002-2004 agreement not so good as with COMPASS 2002 data from a global fit of all the present data probably stronger constrains on the transversity PDFs and in particular on Td (x) RICH + AGS annual Users’ Meeting June 6, 2006, www.bnl.gov/rhic ags/users meetings/workshops/basp , and paper in preparation. Franco Bradamante

SIVERS ASYMMETRIES 2002-2004 small errors (~1%) small asymmetries DIS2006 DIS2006 small errors (~1%) small asymmetries cancellation between p and n (lh and ah) Franco Bradamante

What have we learnt over the past 2 years ? Sivers Asymmetry comparison of the same calculations with the COMPASS 2002-04 data preliminary COMPASS 2002-2004 preliminary COMPASS 2002-2004 Collins et al Vogelsang and Yuan preliminary COMPASS 2002-2004 as in the Collins case, agreement not always so good as for 2002 data from a global fit of the present HERMES and COMPASS data probably stronger constrains on the Sivers DFs RICH + AGS annual Users’ Meeting June 6, 2006, www.bnl.gov/rhic ags/users meetings/workshops/basp , and paper in preparation. Anselmino et al Franco Bradamante

p±, K± ASYMMETRIES 2003-2004 same DIS event selection and hadron definition as before plus PID based on RICH response 3% protons 12% kaons 77% pions 5% no RICH information 100% hadrons after all cuts final sample positive all leading pions 5.3 M 3.4 M kaons 0.9 M 0.7 M negative all leading pions 4.2 M 2.8 M kaons 0.6 M 0.4 M additional systematic tests: RICH stability  systematic errors smaller than statistical ones Franco Bradamante

p±, K± SIVERS ASYMMETRIES 2003-2004 GPD2006 Franco Bradamante

p±, K± Collins Asymmetries 2003-2004 GPD2006 again, difficult to see an effect … Franco Bradamante

SUMMARY New precise DIS deuteron data from COMPASS are now available In all the channels investigated in so far the measured deuteron asymmetries are very small, compatible with zero Collins and Sivers asymmetries for positive and negative hadrons, p±, K± PRESENT PICTURE Collins: u quark dominance DT0D(fav.) ~ - DT0D(unfav) for u quark DTd from global analysis (NEW COMPASS DATA) Sivers: D0Tu ~ - D0Td Franco Bradamante

One of the most recent citations COMPASS 2002 data Evidence for the Absence of Gluon Orbital Angular Momentum in the Nucleon S.J. Brodsky, S. Gardner SLAC-PUB-12062, Aug 2006. Subm. Phys.Lett.B, hep-ph/0608219 Due to the smallness of the anomalous magnetic moment of the deuteron the orbital motion of the quarks should not contribute to the Sivers SSA of the deuteron. Thus Franco Bradamante

riserva Franco Bradamante

COLLINS ASYMMETRY important theoretical work on the interpretation of the data assumptions on Tq and fit of HERMES 2002-2004 data to exctract the Collins FF Vogelsang Yuan, PRD 72, 054028 (2005) Soffer bound Efremov et al, PRD 73, 094025 (2006) chiral quark-soliton model Anselmino et al, BNL UM 2006 Soffer bound & Tq = q RICH + AGS annual Users’ Meeting June 6, 2006, www.bnl.gov/rhic ags/users meetings/workshops/basp , and paper in preparation. Franco Bradamante

SIVERS ASYMMETRY important theoretical work on the interpretation of the data use of the HERMES 2002-2004 data to exctract/check the Sivers DF Vogelsang Yuan, PRD 72, 054028 (2005) result: d SDF ~ -2 u SDF Collins et al, PRD 73, 014021 (2006) input: d SDF = - u SDF Anselmino et al, PRD 72, 094007 (2005) u SDF ~ - d SDF fit using the COMPASS 2002 data too RICH + AGS annual Users’ Meeting June 6, 2006, www.bnl.gov/rhic ags/users meetings/workshops/basp , and paper in preparation. Franco Bradamante