RESULTS FOR TRANSVERSE SPIN PHYSICS AT COMPASS Takahiro Iwata Yamagata University on behalf of the COMPASS Collaboration The 6th Circum-Pan-Pacific Symposium on High Energy Spin Physics, July 30 - August ２ 2007　@　Vancouver BC　Canada

The COMPASS Experiment Transverse Spin Physics at COMPASS Results on: OUTLINE The COMPASS Experiment Transverse Spin Physics at COMPASS Results on: SIDIS single hadron asymmetries Collins/Sivers asymmetries positive and negative hadrons p±, K± Two identified hadron asymmetries pp, pK, KK Other target transverse spin dependent asymmetries Summary Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

THE EXPERIMENTAL SETUP 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 acceptance 160GeV, polarised (PT>50%) Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

solid target operated in frozen spin mode THE POLARIZED TARGET SYSTEM superconductive Solenoid (2.5 T) 3He – 4He Dilution refrigerator (T~50mK) Dipole (0.5 T) two 60 cm long cells with opposite polarization (systematics) 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 Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

DATA TAKING HISTORY 2002 – 2007 Today’s Talk 2002 160 GeV m beam & 6LiD Long./Trans. Pol. PT (~ 80/20) 2003 ditto & (~ 80/20) 2004 ditto & (~ 80/20) 2004 pilot run with hadron beam ( for hadron program) 2005 NO SPS beam (several upgrades) 2006 160 GeV m beam & 6LiD Long. Pol. 2007 ditto & NH3 Trans. / Long. Pol. PT Today’s Talk Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

TRANSVERSE SPIN PHYSICS AT COMPASS Transversity quark with spin parallel to the nucleon spin in a transversely polarized nucleon DTq(x) = q↑↑(x) - q↑↓(x) h1q(x), dq(x), dTq(x) from Collins asym. In single hadron production of SIDIS, and two hadron asym. , L transverse polarization TMD asymmetries an intrinsic asymmetry in the parton transverse momentum distribution induced by the nucleon spin related to orbital angular momentum of quarks from Sivers asym. in SIDIS single hadron production 　　　　and other transverse spin dependent asymmetries Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

SIDIS SINGLE HADRON ASYMMETRIES angular distribution of a hadron wrt nucleon spin Collins Sivers fS = azim. angle of initial quark spin fS’ = azim. angle of struck quark spin fS= p- fS’ （due to helicity conservation) fh = azim. angle of produced hadron initial quark spin (nucleon spin) struck quark spin Collins angle: Azim. angle of a hadron wrt the struck quark spin FC = fh - fS’ (= fh +fS- p) Sivers angle: Azim. angle of a hadron wrt the initial quark spin (=nucleon spin) FS= fh - fS Scattering plane quark direction hadron （Breit frame） modulation of angular distribution Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

COLLINS & SIVERS ASYMMETRIES Collins Asymmetry ± refer to the opposite orientation of the transverse spin of the nucleon PT is the target polarisation; DNN is the transverse spin transfer coefficient initial  struck quark, given by QED Transvesity Collins fragmentation function non-zero Collins function gives transversity Sivers Asymmetry Sivers PDF (TMD) orbital angular momentum of quarks Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

DISTRIBUTIONS & EVENT SELECTION 2004 leading hadron DIS events Q2 > (1 GeV/c)2 W2 > 25 GeV2 0.1 < y < 0.9 hadrons pht > 0.1 GeV/c z > 0.2 (all h) z > 0.25 (leading h) Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

COLLINS ASYMMETRIES 2002-2004 small errors (~1%) small asymmetries deuteron target Published: NP B765 (2007) 31-70 small errors (~1%) small asymmetries 2002 data [ PRL94 (2005) 202002] confirmed cancellation between p and n Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

HADRON IDENTIFICATION same DIS event selection and hadron definition as before Plus PID based on RICH Threshold pions ~ 3 GeV/c kaons ~ 9 GeV/c protons ~ 17 GeV/c 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 Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

p±, K± Collins Asymmetries 2003-2004 deuteron target again, difficult to see an effect … Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

INTERPRETATION (COLLINS ASYMMETRY) In valence region, neglecting sea quark contribution HERMES proton data Non zero Collins asymmetry　observed u-quark dominance (d-quark not constrained) COMPASS deuteron data sensitive to both u- and d-quark with opposite sign Transversities for u- & d-quark Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

SIVERS ASYMMETRIES 2002-2004 small errors (~1%) small asymmetries deuteron target Published in NP B765 (2007) 31-70 2002 data [ PRL94 (2005) 202002] confirmed small errors (~1%) small asymmetries cancellation between p and n Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

p±, K± SIVERS ASYMMETRIES 2003-2004 deuteron target Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

INTERPRETATION (SIVERS ASYMMETRY) In valence region, neglecting sea quark contribution HERMES proton data with COMPASS deuteron data Consistent with models based on the HERMES data J.C.Collins et al., Phys.Rev.D73(2006)01402, M.Anselmino et al.,Phys.Rev.D72(2005)054028, W.Vogelsang and Yuan,Phys.Rev.D72(2005)054028 Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

TWO HADRON ASYMMETRIES modulation of the number of events in fRS fS = angle of initial quark spin (=target spin) fS’ = angle of final (struck) quark spin fS= p - fS’ （due to helicity conservation) fR = angle of two-hadron plane fRS =fR –fS’ = fR +fS- p i f h l-l’ transversity : interference fragmentation function( presently unknown) initial quark spin quark direction Trento conventions see hep-ph/0407345 Breit frame Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

TWO IDENTIFIED HADRON ASYMMETRIES Event selection DIS: Q2>1GeV2 0.1<y<0.9 W>5GeV Hadrons: positive(h1) & negative(h2) hadrons z= zh1+zh2 < 0.9 ( remove diffractiv r) PID by RICH Pth(p)+0.5 GeV/c < Pp < 50 GeV/c Pth(K)+1.0 GeV/c < PK < 50 GeV/c Statistics from 2003 & 2004 data p+ p- pairs 3.7 M events p+ K- pairs 0.24 M events K+ p- pairs 0.30 M events K+ K- pairs 0.086 M events Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

p+ p- ASYMMETRIES r r 3.7 M (70%) z=z1+z2 Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

K+ p- ASYMMETRIES K* 0.3 M (5.8%) K* Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

p+ K- ASYMMETRIES K* 0.25 M (4.5%) K* Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

K+ K- ASYMMETRIES f f 0.09 M (1.6%) small asymmetries compatible with 0 Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

TRANSVERSE SPIN DEPENDENT ASYMMETRIES. SIDIS (1-hadron) cross-section based on one photon exchange 18 structure functions Azimuthal modulation genrated by 14 functions 2 pol. independent 1 beam pol. dependent 2 target longitudinal pol. dependent 1 beam + target longitudinal pol. dependent 5 target transverse pol. dependent 3 double beam + target transverse pol. dependent Sivers ‘Collins’ Asymmetries Beam Target Virtual photon Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

Interpretation in QCD parton model ASYMMETRIES I Interpretation in QCD parton model TMD leading twist Sivers + Collins subleading twist Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

ASYMMETRIES II Sivers subleading twist TMD long.beam & trans. target Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

ASYMMETRIES III long. beam & trans. target subleading twist again cancellation between the p and n for the deuteron ? Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

SUMMARY All the measured asymmetries are very small, New precise deuteron data from COMPASS are available Collins and Sivers asymmetries for h±, p±, K± (published : h±2002: PRL94(2005)202002, h±2002-2004: NPB765(2007)31) Two identified hadron asymmetries All other target transverse spin dependent asymmetries All the measured asymmetries are very small, compatible with zero PRESENT PICTURE Collins: Sivers: from COMPASS from COMPASS Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

OUTLOOK near future: COMPASS will complete the analysis of the recorded deuteron data K0 asymmetries exclusive  asymmetries on transversely polarised target  GPD E transverse effects from longitudinal data Cahn and Boer-Mulders effect 2007: COMPASS data available with a transversely polarised proton target (NH3) with 50 days expected , same precision at small x as for deuteron, better at “large” x for the new PT magnet on a longer time scale: good perspective for a measurement of polarized Drell-Yan process in COMPASS to study transversity & Sivers & Boer-Mulders PDFs and further measurements of transverse spin effects in SIDIS Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

TRANSVERSE MOMENTUM DEPENDENT PDFs Nucleon unpol. long. pol. trans. pol. number density Sivers unpol. Nucleon Parton T-odd helicity long. pol. RICH + AGS annual Users’ Meeting June 6, 2006, www.bnl.gov/rhic ags/users meetings/workshops/basp , and paper in preparation. Quark transversity Boer-Mulders survive after integration over kT trans. pol. T-odd Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

L TRANSVERSE POLARIZATION Transversity PT : target polarization; f : target dilution factor D(y): transverse spin transfer coefficient initial  struck quark, given by QED Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

L TRANSVERSE POLARIZATION systematic errors not larger than statistical errors RICH ID not used yet Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

RUN WITH TRANSVERSE POL. TARGET transversely polarised deuteron target ~ 20% of the running time 2002 11 days of data taking, 2 periods 2003 9 days of data taking, 1 period 2004 14 days of data taking, 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) Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

COLLINS ASYMMETRY & GLOBAL FIT SIDIS (deuteron COMPASS/ proton HERMES) & Belle data RICH + AGS annual Users’ Meeting June 6, 2006, www.bnl.gov/rhic ags/users meetings/workshops/basp , and paper in preparation. GLOBAL FIT　 Ｂy　Anselmino et al., PRD 75,054032(2007) PRESENT PICTURE DT0D(fav.) ~ - DT0D(unfav) DTd not well constrained from the global fit Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

SIVERS ASYMMETRIES & MODELS model calculations　to be compared with the COMPASS 2002-04 data preliminary COMPASS 2002-2004 preliminary COMPASS 2002-2004 Collins et al Vogelsang and Yuan RICH + AGS annual Users’ Meeting June 6, 2006, www.bnl.gov/rhic ags/users meetings/workshops/basp , and paper in preparation. preliminary COMPASS 2002-2004 PRESENT PICTURE Anselmino et al Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

TWO HADRON ASYMMETRIES (all hadrons) DNN : transverse spin transfer coefficient initial  struck quark f : target dilution factor PT : target polarization; Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata

TWO HADRON ASYMMETRIES z ordered pairs Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007 Takahiro Iwata