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RESULTS FOR TRANSVERSE SPIN PHYSICS AT COMPASS

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1 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 BC　Canada

2 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 July 30 - Aug Takahiro Iwata

3 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 July 30 - Aug Takahiro Iwata

4 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 July 30 - Aug Takahiro Iwata

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

6 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 July 30 - Aug Takahiro Iwata

7 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 July 30 - Aug Takahiro Iwata

8 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 July 30 - Aug Takahiro Iwata

9 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 > (all h) z > (leading h) Pan-Pacific July 30 - Aug Takahiro Iwata

10 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) ] confirmed cancellation between p and n Pan-Pacific July 30 - Aug Takahiro Iwata

11 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 July 30 - Aug Takahiro Iwata

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

13 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 July 30 - Aug Takahiro Iwata

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

15 p±, K± SIVERS ASYMMETRIES 2003-2004
deuteron target Pan-Pacific July 30 - Aug Takahiro Iwata

16 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 July 30 - Aug Takahiro Iwata

17 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/ Breit frame Pan-Pacific July 30 - Aug Takahiro Iwata

18 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 M events p+ K- pairs M events K+ p- pairs M events K+ K- pairs M events Pan-Pacific July 30 - Aug Takahiro Iwata

19 p+ p- ASYMMETRIES r r 3.7 M (70%) z=z1+z2
Pan-Pacific July 30 - Aug Takahiro Iwata

20 K+ p- ASYMMETRIES K* 0.3 M (5.8%) K*
Pan-Pacific July 30 - Aug Takahiro Iwata

21 p+ K- ASYMMETRIES K* 0.25 M (4.5%) K*
Pan-Pacific July 30 - Aug Takahiro Iwata

22 K+ K- ASYMMETRIES f f 0.09 M (1.6%)
small asymmetries compatible with 0 Pan-Pacific July 30 - Aug Takahiro Iwata

23 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 July 30 - Aug Takahiro Iwata

24 Interpretation in QCD parton model
ASYMMETRIES I Interpretation in QCD parton model TMD leading twist Sivers + Collins subleading twist Pan-Pacific July 30 - Aug Takahiro Iwata

25 ASYMMETRIES II Sivers subleading twist TMD long.beam & trans. target
Pan-Pacific July 30 - Aug Takahiro Iwata

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

27 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± : 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 July 30 - Aug Takahiro Iwata

28 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 July 30 - Aug Takahiro Iwata

29 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, 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 July 30 - Aug

30 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 July 30 - Aug Takahiro Iwata

31 L TRANSVERSE POLARIZATION
systematic errors not larger than statistical errors RICH ID not used yet Pan-Pacific July 30 - Aug Takahiro Iwata

32 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 with RICH PID Two hadron asymmetries Λ polarimetry prel results trigger (large x, Q2) DAQ, on line filter DIS events (106) Pan-Pacific July 30 - Aug Takahiro Iwata

33 COLLINS ASYMMETRY & GLOBAL FIT
SIDIS (deuteron COMPASS/ proton HERMES) & Belle data RICH + AGS annual Users’ Meeting June 6, 2006, 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 July 30 - Aug Takahiro Iwata

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

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

36 TWO HADRON ASYMMETRIES
z ordered pairs Pan-Pacific July 30 - Aug Takahiro Iwata

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