RESULTS FOR TRANSVERSE SPIN PHYSICS AT COMPASS Takahiro

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

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, p. K, KK Other target transverse spin dependent asymmetries § Summary Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

THE EXPERIMENTAL SETUP two stages spectrometer • Large Angle Spectrometer (SM 1) • Small Angle Spectrometer (SM 2) tracking, calorimetry, PID Sci. Fi Silicon Micromegas GEMs Straws SDC MWPC W 45 E/HCAL Muon. Wall SM 2 E/HCAL SM 1 Muon. Wall Polarised Target RICH m beam 160 Ge. V, polarised (PT>50%) Takahiro Iwata • high energy beam • broad kinematical range • large acceptance Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

THE POLARIZED TARGET SYSTEM solid target operated in frozen spin mode 3 He – 4 He Dilution refrigerator (T~50 m. K) superconductive Solenoid (2. 5 T) Dipole (0. 5 T) d. N/dz 4000 2000 0 two 60 cm long cells with opposite polarization (systematics) -1000 0 1000 zvtx (mm) THE RICH DETECTOR 3 m 6 m 5 m photon detectors threshold momenta ● p = 2 Ge. V/c p ● p = 9 Ge. V/c K ● p =17 Ge. V/c P C 4 F 10 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

DATA TAKING HISTORY 2002 – 2007 § 2002 160 Ge. V m beam & 6 Li. D Long. /Trans. Pol. PT (~ 80/20) § 2003 ditto & (~ 80/20) § 2004 ditto & (~ 80/20) Today’s Talk § 2004 pilot run with hadron beam ( for hadron program) § 2005 NO SPS beam (several upgrades) § 2006 160 Ge. V m beam & 6 Li. D Long. Pol. § 2007 ditto Takahiro Iwata & NH 3 Trans. / Long. Pol. PT Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

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) h 1 q(x), d. Tq(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 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

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

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 Sivers Asymmetry Collins fragmentation function non-zero Collins function gives transversity Sivers PDF (TMD) orbital angular momentum of quarks Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

DISTRIBUTIONS & EVENT SELECTION 2004 leading hadron DIS events Q 2 > (1 Ge. V/c)2 W 2 > 25 Ge. V 2 0. 1 < y < 0. 9 hadrons pht > 0. 1 Ge. V/c z > 0. 2 (all h) z > 0. 25 (leading h) Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

COLLINS ASYMMETRIES 2002 -2004 deuteron target Published: NP B 765 (2007) 31 -70 • small errors (~1%) • small asymmetries 2002 data [ PRL 94 (2005) 202002] confirmed • cancellation between p and n Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

HADRON IDENTIFICATION same DIS event selection and hadron definition as before Plus PID based on RICH Threshold pions ~ 3 Ge. V/c kaons ~ 9 Ge. V/c protons ~ 17 Ge. V/c hadrons 100% no RICH information after all cuts pions 77% kaons 12% protons final sample positive Takahiro Iwata all leading 5% negative 3% all leading pions 5. 3 M 3. 4 M pions 4. 2 M 2. 8 M kaons 0. 9 M 0. 7 M kaons 0. 6 M 0. 4 M Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

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

INTERPRETATION (COLLINS ASYMMETRY) In valence region, neglecting sea quark contribution Non zero Collins asymmetry observed HERMES proton data 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 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

SIVERS ASYMMETRIES 2002 -2004 deuteron target Published in NP B 765 (2007) 31 -70 • small errors (~1%) • small asymmetries 2002 data [ PRL 94 (2005) 202002] confirmed • cancellation between p and n Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

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

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. D 73(2006)01402, M. Anselmino et al. , Phys. Rev. D 72(2005)054028, W. Vogelsang and Yuan, Phys. Rev. D 72(2005)054028 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

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

TWO IDENTIFIED HADRON ASYMMETRIES Event selection DIS: Hadrons: • Q 2>1 Ge. V 2 • positive(h 1) & negative(h 2) hadrons • 0. 1<y<0. 9 • z= zh 1+zh 2 < 0. 9 ( remove diffractiv r) • W>5 Ge. V • PID by RICH • Pth(p)+0. 5 Ge. V/c < Pp < 50 Ge. V/c • Pth(K)+1. 0 Ge. V/c < PK < 50 Ge. V/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 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

p+ p- ASYMMETRIES r 3. 7 M (70%) r z=z 1+z 2 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

K+ p- ASYMMETRIES K* 0. 3 M (5. 8%) K* Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

p+ K- ASYMMETRIES K* 0. 25 M (4. 5%) K* Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

K+ K- ASYMMETRIES f 0. 09 M (1. 6%) f small asymmetries compatible with 0 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

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

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

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

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

SUMMARY New precise deuteron data from COMPASS are available Collins and Sivers asymmetries for h±, p±, K± (published : h± 2002: PRL 94(2005)202002, h± 2002 -2004: NPB 765(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 Takahiro Iwata Collins: from COMPASS Sivers: from COMPASS Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

OUTLOOK near future: COMPASS will complete the analysis of the recorded deuteron data § K 0 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 (NH 3) 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 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

TRANSVERSE MOMENTUM DEPENDENT PDFs unpol. Nucleon long. pol. unpol. number density Nucleon Parton trans. pol. Sivers T-odd Quark long. pol. helicity trans. pol. Boer. Mulders transversity survive after integration over k. T 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 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

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

RUN WITH TRANSVERSE POL. TARGET transversely polarised deuteron target ~ 20% of the running time 2002 11 days of data taking, 2003 9 days of data taking, 2004 14 days of data taking, DIS events (106) 2 periods 1 period 2 periods 2) trigger (large x, Q Collins and Sivers asymmetries DAQ, on line filter published results 2002 prel results 2002 -2004 with RICH PID Two hadron asymmetries prel results 2002 -2004 Λ polarimetry prel results 2002 -2003 Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

COLLINS ASYMMETRY & GLOBAL FIT • SIDIS (deuteron COMPASS/ proton HERMES) & Belle data GLOBAL FIT Ｂy Anselmino et al. , PRD 75, 054032(2007) PRESENT PICTURE DT 0 D(fav. ) ~ - DT 0 D(unfav) DTd not well constrained from the global fit Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

SIVERS ASYMMETRIES & MODELS model calculations to be compared with the COMPASS 2002 -04 data preliminary COMPASS 2002 -2004 Vogelsang and Yuan preliminary COMPASS 2002 -2004 Collins et al PRESENT PICTURE Anselmino et al Takahiro Iwata Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007

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

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