on behalf of the COMPASS collaboration New target transverse spin dependent azimuthal asymmetries from COMPASS experiment Bakur Parsamyan INFN & University of Turin on behalf of the COMPASS collaboration SPIN - Praha - 2007 Prague, July 08 – 14, 2007

Outline General expression of polarized SIDIS cross-section Target transverse spin asymmetries COMPASS experimental setup Event selection Extraction 1D method Systematic checks 2D method Correlation Coefficients Results asymmetry, comparison with the model Conclusions SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

General expression of polarized SIDIS cross-section A.Kotzinian, Nucl. Phys. B441, 234 (1995). Bacchetta, Diehl, Goeke, Metz, Mulders and Schlegel JHEP 0702:093,2007 This is a general, model independent expression which is also valid for exclusive reactions and for entire phase space of SIDIS (TFR, CFR) Azimuthal modulations: 2 polarization independent 1 single beam polarization dependent 2 single target longitudinal polarization dependent 1 double beam + target longitudinal polarization dependent 5 single target transverse polarization dependent 3 double beam + target transverse polarization dependent SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Target transverse spin dependent azimuthal modulations General expression of polarized SIDIS cross-section Target transverse spin dependent azimuthal modulations Published by HERMES & COMPASS For Collins and Sivers asymmetries from COMPASS see next talk by Girisan Venugopal SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Transverse spin dependent azimuthal modulations LT 8 – modulations. 5 – single spin 3 – double spin ST - target polarization, Pbeam – beam polarization – Depolarization factor SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Twist-2 + kT/Q kinematical corrections: Interpretation of the transverse asymmetries Twist-2: double spin single spin Twist-2 + kT/Q kinematical corrections: SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Definition of the UT asymmetries “raw” – indicates number event asymmetry extracted as an amplitude of the corresponding modulation f - target dilution factor, ST - target polarization – Depolarization factor SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Definition of the LT asymmetries f - target dilution factor, ST - target polarization – Depolarization factor - Single Spin Asymmetries - Double Spin Asymmetries SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

COmmon Muon Proton Apparatus for Structure and Spectroscopy The COMPASS Experimental Setup COmmon Muon Proton Apparatus for Structure and Spectroscopy Longitudinally polarized µ+ beam (160 Gev/c). Longitudinally or Transversely polarized 6LiD target Momentum, tracking and calorimetric measurements, PID High energy beam Large angular acceptance Broad kinematical range CERN SPS North Area. Two stages spectrometer Large Angle Spectrometer (SM1) Small Angle Spectrometer (SM2) Hadron & Muon high energy beams. Beam rates: 108 muons/s, 5·107 hadrons/s. SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Polarized target 2002-2004 6LiD: Target Polarization ±50% superconductive Solenoid (2.5 T) Dipole (0.5 T) 2002-2004 6LiD: Target Polarization ±50% dilution factor f ≈ 0.4 ~20% of the time transversely polarized For transverse runs polarization reversal in two cells each ~ 5days Two 60 cm long 6LiD cells with opposite polarization Data collected simultaneously for the two target spin orientations. Longitudinal polarization Transverse polarization SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Event selection (2002-2004 deuteron data) DIS cuts : Q2 > 1 GeV2 0.1 < y < 0.9 W > 5 GeV All Hadrons : z > 0.2 pt > 0.1 GeV/c Year Period Positive hadrons Negative hadrons 2002 P2B/P2C 0.71·106 0.59·106 P2H 0.48·106 0.40·106 2003 P1G/P1H 2.46·106 2.03·106 2004 W33/W34 2.12·106 1.74·106 W35/W36 2.75·106 2.26·106 Sum 8.52·106 7.02·106 SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

The number-of-event asymmetries Azimuthal modulations Extraction of the asymmetries The number-of-event asymmetries 8 modulations 5 combinations of φh and φS Independent angles Azimuthal modulations SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Double Ratio method (NP B765 (2007) 31) For each data taking period, each cell and polarization state the Φj distribution of the number of events can be presented like: u - Up Stream cell, d - Down Stream cell, +/- - target polarization “ratio product” quantities Under the reasonable assumption on the ratio of the acceptances - to be constant before and after polarization reversal in each Φj bin: Acceptance differences cancel out minimizes acceptance effects spin independent terms cancel at 1st order (Cahn) SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

1-D fitting procedure (MINUIT with minimization method) 9 – XBj, 8 – z, 9 - PhT bins and 16 Φj bins. Fitting the “ratio product” quantities Newly extracted Collins & Sivers asymmetries gave the same result as published (NP B765 (2007) 31) SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Periods compatibility Systematic checks Periods compatibility Asymmetries from each period were compared with the weighed mean from all periods. Par[0] test Extracted from the fit par[0] ≈ 1 (acceptance cancellation) Stability of the acceptance in Φj angles The quality of the fit - distribution (acceptance assumption) Systematic errors are smaller than statistical SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

2-D fitting procedure (9 parameter fit using MINUIT) 9 – XBj, 8 - z, 9 - PhT bins and 8x8 – φh,φS bins. Fitting function Fitting the “ratio product” quantities Results from 1D and 2D fits are in good agreement, only 1D results have been released SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Correlation Coefficients (positive hadrons, x) - Correlation between Collins and Sivers asymmetries For the most of the pairs of parameters ρ≈0 and always < 0.4 Only some correlation coefficients are larger than 0.1 Correlations are small or negligible x preliminary SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Correlation Coefficients (+/- hadrons, x, z and PT) SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Results for (2002-2004 deuteron data, 1D fit) SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Results for (2002-2004 deuteron data, 1D fit) SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Results for (2002-2004 deuteron data, 1D fit) SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

asymmetry (PRD73:114017,2006) First estimations by A.Kotzinian & P.Mulders, PRD 54, 1229 (1996) A.Kotzinian, B.Parsamyan & A.Prokudin, PRD73:114017,(2006) Deuteron Proton Lorentz Invariance Relations: Deuteron Proton Predicted for COMPASS kinematical range and deuteron target asymmetry is small ≈ 1-2% Measured is small, compatible with zero. SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

ALT asymmetry (COMPASS) PRD73:114017,(2006) Kinematical cuts: Q2>1.0 (GeV/c)2, W2>25 GeV2, 0.05<xBj<0.6, 0.5 < y < 0.9, 0.4 < z < 0.9 The predicted asymmetries are small (few % for deuteron target) in COMPASS “preferable” (with sizable statistics) kinematical regions. SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

ALT asymmetry (HERMES & JLab) PRD73:114017,(2006) Kinematical cuts (HERMES): - Q2>1.0 (GeV/c)2, W2>10 GeV2, 0.1<xBj<0.6, 0.45 < y < 0.85, 0.4 < z < 0.9 Kinematical cuts (JLab): - Q2>1.0 (GeV/c)2, W2>4 GeV2, 0.2<xBj<0.6, 0.4 < y < 0.7, 0.4 < z < 0.7 The predicted asymmetries can reach up to ~10% for proton target and up to ~6-7% for deuteron target with high x, y, z and pT cuts at HERMES and JLab kinematics. SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Conclusions 6 new asymmetries were measured in COMPASS (2002-2004 deuteron data) Analysis was done using 1 dimensional and 2 dimensional fitting procedures Asymmetries obtained from both methods are in agreement and point to the same physical result. Only 1D results have been released Correlation coefficients obtained from 2 dimensional fit are negligible or small In most of the cases ρ ≈ 0 and always < 0.4 Results have been checked for systematic effects Systematical errors appears to be smaller than statistical All measured asymmetries are compatible with zero within statistical accuracy… SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

The end Thank you!!! SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

Additional slides SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

All ingredients (DFs & FFs) are known! ALT asymmetry PRD 54, 1229 (1996) First estimations by A.Kotzinian & P.Mulders, PRD 54, 1229 (1996) Weighted asymmetry is related to the first kT-momentum of g1T: There exists a relation between first momentum of g1T and g2 (follows from Lorentz invariance, Tangerman & Mulders) : All ingredients (DFs & FFs) are known! SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

ALT asymmetry PRD73:114017,(2006) A.Kotzinian, B.Parsamyan & A. Prokudin, Phys.Rev. D73 (2006) From analysis of unpolarized PhT dependence and Cahn effect Naïve positivity constraint: N is fixed by holds if Predictions done for: SPIN – Praha – 2007, July 08-14 Bakur Parsamyan

ALT asymmetry, kinematical cuts PRD73:114017,(2006) + Low x, y, z & pT High ATMD= GRV98+GRSV2000 LO, std DFs Kretzer FFs COMPASS - Q2>1.0 (GeV/c)2, W2>25 GeV2, 0.05<xBj<0.6, 0.5 < y < 0.9, 0.4 < z < 0.9, |Ph,T| > 0.5GeV/c HERMES - Q2>1.0 (GeV/c)2, W2>10 GeV2, 0.1<xBj<0.6, 0.45 < y < 0.85, 0.4 < z < 0.9, |Ph,T| > 0.5GeV/c JLab - Q2>1.0 (GeV/c)2, W2>4 GeV2, 0.2<xBj<0.6, 0.4 < y < 0.7, 0.4 < z < 0.7, |Ph,T| > 0.5GeV/c SPIN – Praha – 2007, July 08-14 Bakur Parsamyan