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Transversity & Hall-B at JLab

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1 Transversity & Hall-B at JLab
H. Avakian, L. Elouadrhiri Jefferson Lab International Workshop on Transversity Trento June 2004 Introduction Factorization and spin-azimuthal asymmetries at CLAS Transition from exclusive to semi-inclusive processes Summary & Outlook Note mes

2 Polarized Semi-Inclusive DIS
Cross section defined by scale variables x,y,z Hadron-Parton transition: by distribution function f1u(x): probability to find a u-quark with a momentum fraction x Parton-Hadron transition: by fragmentation function Dπ+ (z): probability for a u-quark to produce a p+ with a momentum fraction z. 1u

3 SIDIS studies require:
Factorization in SIDIS into a distribution function f fragmentation function D and hard scattering part. Applicability of partonic description at JLab energies Low W and Q^2 Low MX in ep->e’h+X Control over background processes Resonances in the t-channel Exclusive vector mesons H. Avakian, Trento, June 2004

4 SIDIS factorization SIDIS (g*p->pX) x-section at leading twist:
Ji et al. Structure functions FUU,FLL… factorize into TMD distributions (hep-ph ) P┴ has contributions from distribution, fragmentation and soft gluon radiation H. Avakian, Trento, June 2004

5 Contributions to s in Polarized SIDIS
Twist-2 TMDs from Mulders et al sUU ~ sLL ~ Sivers sUT ~ sUT ~ Collins sUL ~ KM Kinematic factors depend on the beam energy

6 Quantum Phase-Space Distributions of Quarks
Wpu(k,r) “Mother” Wigner distributions Same PDFs in exclusive and semi-inclusive analysis d2kT d3r IPDs Wpu(x,r) GPDs Hpu(x,x,t), GDAs Fudp+(x,x) dr|| FT TMD PDFs fpu(x,kT), TMD FFs Dup+(kT,z) IPDs Wpu(x,rT),… GPD d2r x=0,t=0 d2kT dx Measure momentum transfer to target Direct info about spatial distributions Measure momentum transfer to quark Direct info about momentum distributions PDFs fpu(x),… FFs Dup+(z) Form Factors F1pu(t),F2pu(t ).. H. Avakian, Trento, June 2004

7 The CLAS Detector Scattering of 5.7 GeV
polarized electrons off polarized NH3 and unpolarized hydrogen ~8M p+ in DIS kinematics,SIDIS Q2>1.5GeV2,W2>4,y<0.85, beam polarization 73% target polarization 72% (f=0.2) H. Avakian, Trento, June 2004

8 Missing mass of pions in ep→e’pX
D++ p- D0 MX>1.4 (Q2>1.5,W2>4) applied to exclude the kinematics where t-channel resonances may have significant contribution H. Avakian, Trento, June 2004

9 Multiplicities and Factorization
DIS: Q2>1 W2>4 MX>1.1 (1.4) y<0.85 Dup+ KKP (LO) The fraction of p from struck quark in a range 0.5<z<0.8 is not changing significantly with beam energy (LUND studies). No significant variation observed in z distributions of p+ for different x ranges H. Avakian, Trento, June 2004

10 A1p shows no significant Q2 and z dependence
ep → e’ p+ X ( Ee =5.7 GeV, MX > 1.1) A1p x dependence of CLAS A1p (A2=0) consistent with HERMES data and factorization. H. Avakian, Trento, June 2004

11 Longitudinally Pol Target: Twist-2 SSA for p+
SSA: x-dependence CLAS (5.7 GeV) is consistent with predictions for Collins effect from Efremov et al. hep-ph/ First indication of a non-zero sin2f moment (Kotzinian-Mulders asymmetry) AULsin2f is a clean source of Collins SSA H. Avakian, Trento, June 2004

12 Target SSA: sinf moment (HERMES effect)
Target SSA measured at different E,W consistent At least 3 possible sources! H. Avakian, Trento, June 2004

13 Beam SSA: sinf moment (CLAS @4.3 GeV)
ssinfLU ~FLU=HLT’~ 1/Q (Twist-3) Beam SSA shows no significant dependence on W,E H. Avakian, Trento, June 2004

14 ALU from CLAS 4.3 and 5.7GeV data
DIS-cuts Q2>1 GeV2 W>2 GeV y < 0.85 0.5 < z < 0.8 5.7GeV No significant dependence on beam energy 4.3 GeV No significant ALU dependence on Mx beyond the neutron. H. Avakian, Trento, June 2004

15 ALU x-dependence: CLAS @ 4.3 and 5.7 GeV
Photon Sivers Effect Afanasev & Carlson, Metz & Schlegel Beam SSA analyzed in terms of the Sivers effect by F.Yuan using h1┴ from MIT bag model 0.5<z<0.8 Beam SSA analyzed in terms of the Collins effect by Schweitzer et al. using e(x) from cQSM 4.3 GeV and 5.7 GeV data consistent H. Avakian, Trento, June 2004

16 ALU z-dependence: CLAS 4.3 vs. 5.7 GeV
Data also consistent with z-dependence of the Collins function from Efremov et al. Sivers effect by F.Yuan using h1┴ from MIT bag model z-dependence of ALU at 4.3 GeV and 5.7 GeV consistent with increase at low z H. Avakian, Trento, June 2004

17 2 pion electroproduction Kinematics
z-pion related to cosq H. Avakian, Trento, June 2004

18 Exclusive p+p- and p+p0 e p e p  e- p  e- nr+ π+π0 π+ π- n
r0 PID by Mpp and missing π- r+ PID by Mpp and missing neutron Fit Mpp with a BW + polinomial background. H. Avakian, Trento, June 2004

19 Beam SSA for exclusive p+p0
Missing mass Invariant mass Significant positive beam asymmetry for exclusive r+ H. Avakian, Trento, June 2004

20 p+ SSA from r(p+p-) r+ r0 (CLAS @5.7GeV)
Modulation exist even for vanishing helicity change amplitudes r+ r0 p+ SSA at large z may have a significant contribution from r H. Avakian, Trento, June 2004

21 SSA for p0 from ep->e’r+n
Different contributions from r for different pions SSA from r+n may affect SSA for SIDIS p0 at large z H. Avakian, Trento, June 2004

22 SSA in ep->e’pX PYTHIA at 5.7 GeV
Larger fraction of p+ from r at low x and large z r contribution to SSA (~20%) may be responsible for the difference in p+ and p0 beam SSA at large z H. Avakian, Trento, June 2004

23 SSA in ep->e’pX HERMES 27.5 GeV CLAS 5.7 GeV Strange pattern: p0 SSA bigger at very low and very large z H. Avakian, Trento, June 2004

24 Target SSA in exclusive p0 production
HERMES 27.5 GeV ep->e’p0p Large positive p0 target SSA in the exclusive limit confirmed by CLAS at 5.7 GeV H. Avakian, Trento, June 2004

25 LUND MC with Long. Pol. Target: SSA for p+
f distributions from MC vs 5.7 CLAS data. Fiducial cuts on e,p+ and smearing applied. sinf and sin2f moments arising from the Collins effect added in MC using predictions from Efremov et al. Phys.Rev.D67:063511,2003 Simulated and reconstructed SSA moments consistent H. Avakian, Trento, June 2004

26 Long. Pol. Target SSA for p+ at 12GeV
large x + high luminosity 6 GeV The sin 2f asymmetry for 2000 h of projected CLAS++ data. x,PT – dependence of AULsin2f may provide access to h1L(x,PT) Efremov et al. H. Avakian, Trento, June 2004

27 Transverse Target SSA at CLAS and CLAS++
5.7GeV Collins AUT ~ Expected precision of the AUT and extracted du/u from transverse spin asymmetry 0.5<z<0.8 Sivers AUT ~ Separate the Sivers effect using different kinematic dependences 11GeV Simultaneous measurement of SIDIS, exclusive r,r+,w and DVCS asymmetries with a transversely polarized target. H. Avakian, Trento, June 2004

28 Exclusive vector meson production at CLAS and CLAS++
Provide access to different combinations of orbital momentum contributions Ju,Jd r0 -> 2Ju + Jd r+ -> Ju - Jd w -> 2Ju - Jd Significant transverse target SSA predicted for exclusive r0, r+ (Goeke et al hep-ph/ ) H. Avakian, Trento, June 2004

29 Summary Current CLAS data are consistent with a partonic picture:
The data consistent with factorization (no x/z-dependence observed in single and double spin asymmetry measurements). Spin and azimuthal asymmetries extracted for SIDIS p+ are in agreement with theory predictions and measurements at higher energies. Measured asymmetries (<sin2f>, <sinf>, …), provide a unique access to new transverse momentum dependent distribution and fragmentation functions Global analysis of SSA for exclusive and semi-inclusive final states with polarized beam and target needed for separation of contributions from different mechanisms and precision measurements of underlying distribution functions. H. Avakian, Trento, June 2004

30 CLAS Transverse target at 5.7 GeV
“Chicane” magnets needed to re-steer the primary electron beam With the B field (5T) pointing perpendicular to the beam direction Mollers being focused into the torus coils between the sectors H. Avakian, Trento, June 2004

31 The CLAS Detector ++ Forward Cerenkov Forward EC Forward DC
Inner Cerenkov Central Detector Preshower EC Forward TOF Torus Cold Ring Coil Calorimeter H. Avakian, Trento, June 2004

32 DIS Cuts z Rapidity (h>1) and xF cuts related to z cut
H. Avakian, Trento, June 2004

33 CLAS ++ - Performance H. Avakian, Trento, June 2004
Forward Detector Central Detector Angular coverage: Tracks (inbending) 10o - 40o 42o - 135o Tracks (outbending) o - 40o o - 135o Photons 3o - 40o 42o - 135o Track resolution: dp (GeV/c) p p pT dq (mr) df (mr) Photon detection: Energy range > 100 MeV > 50 MeV dE/E (1 GeV) (1 GeV) dq (mr) (1 GeV) (1 GeV) Neutron detection: heff (p > 1.5 GeV/c) Particle id: e/p >>1000 ( < 5 GeV/c) >100 ( > 5 GeV/c) p/K (4s) < 3 GeV/c 0.6 GeV/c K/p (4s) < 5 GeV/c 1.1 GeV/c H. Avakian, Trento, June 2004

34 Q2 EIC clas (upgraded) compass hermes clas
H. Avakian, Trento, June 2004

35 Sivers and Boer (T-odd ) distribution functions
T-odd functions change sign from DIS to DY (Collins-02) Boer et al. scalar diquark f1T┴u=h1┴u f1T┴d=0 F. Yuan MIT bag model Bacchetta et al scalar+vector diquarks (non-0 f1T┴d) Anselmino et al (pp scattering) 0 in large class of chiral soliton models (cQSM) d-quark u-quark d-quark contribution suppressed H. Avakian, Trento, June 2004

36 Rho-MC: ALU for g*p->p+X
E=27.5 GeV H. Avakian, Trento, June 2004

37 Beam SSA for exclusive events
Beam SSA for p0,p+,r+ are consistent H. Avakian, Trento, June 2004

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