H. Avakian, DPWG, Feb 271

Studies of Spin-Orbit Correlations with CLASStudies of Spin-Orbit Correlations with CLAS

Harut Avakian (JLab)Harut Avakian (JLab)

Deep PWG, Genova, Feb 27

H. Avakian, DPWG, Feb 272

•Physics motivation–spin-orbit correlations and widths of PDFs

•Spin asymmetries from eg1:–A1 measurements for pions–Extraction of g1 width from pi+ data

•Summary

OutlineOutline

H. Avakian, DPWG, Feb 273

Transverse Momentum Dependent (TMD) Distributions

Quark polarization

Nucleon polarization

Real and imaginary parts of the L≠0 interference contributions

•kT – leads to 3D description with 8PDFs

Factorization of kT-dependent PDFs proven at low PT of hadrons (Ji et al)

Twist-3

H. Avakian, DPWG, Feb 274

Polarized Semi-Inclusive DISCross section is a function of scale variables x,y,z

z

U unpolarized

L long.polarized

T trans.polarized

H. Avakian, DPWG, Feb 275

CLAS configurations with long.polarized target

e

ep→e’X

Polarizations:Beam: ~80%NH3 proton 80%

1) Polarized NH3/ND3 (no IC, ~5 days)2) Polarized NH3 with IC 60 days

Inner Calorimeter

H. Avakian, DPWG, Feb 276

Target fragmentation in SIDISUse PEPSI MC to define the kinematic region where the partonic description works

Pions from target fragments mainly at low energies, small z and PT

H. Avakian, DPWG, Feb 277

SSA with Longitudinal Target

quark polarization

Higher twist in fragmentation/or distribution

In jet SIDIS only contributions ~ D1 survive

With H1┴ (0)≈0 (or measured) Target (Beam) SSA can be a valuable source of info on HT T-odd distribution functions

H. Avakian, DPWG, Feb 278

Polarized target: HERMES vs CLAS at 5.7GeV

x dependence of CLAS A1

p (A┴=0) consistent with HERMES data

ep → e’ X ( Ee =5.7 GeV, MX > 1.1)

u/u from CLAS EG1 is consistent with GRV(GRVS) PDFs

H. Avakian, DPWG, Feb 279

A1-kinematic dependences

inbending

Ratio to inclusive asymmetry will account the x-dependence

outbending

H. Avakian, DPWG, Feb 2710

A1 PT-dependence in SIDIS

M.Anselmino et al hep-ph/0608048

+ ALL can be explained in terms of broader kT distributions for f1 compared to g1

02=0.25GeV2

D2=0.2GeV2

In perturbative limit predicted to be constant

Como-2005

constituent quark model (Pasquini et al).

H. Avakian, DPWG, Feb 2711

u/u

(dipole formfactor), J.Ellis, D-S.Hwang, A.Kotzinian

Helicity distributions: Diquark model

Difference in q+=f1+g1 (quark aligned with proton spin) and q-=f1-g1 - (anti-aligned) kT-dependences may lead to observable effects

JMR model

Jakob, Mulders, Rodrigues, Nucl. Phys. A 1997

q

DqMR , R=s,a

For given x the sign of the polarization is changing at large kT

H. Avakian, DPWG, Feb 2712

A1 PT-dependence in SIDIS

M.Anselmino et al hep-ph/0608048

+ A1 suggests broader kT distributions for f1 compared to g1

- A1 may require non-Gaussian kT-dependence for different helicities and/or flavors

02=0.25GeV2

D2=0.2GeV2

0.4<z<0.7

more data in 2009!

H. Avakian, DPWG, Feb 2713

cos moment in A1-PT-dependence

PT-dependence of cos moment of double spin asymmetry is most sensitive to kT-distributions of quarks with spin orientations along and opposite to the proton spin.

hep-ph/0608048

02=0.25GeV2

D2=0.2GeV2

CLAS PRELIMINARY

H. Avakian, DPWG, Feb 2714

Extracting widths from ALL

Assuming the widths of f1/g1 x,z and flavor independent

Anselmino et al

Collins et al

Fits to unpolarized data

H. Avakian, DPWG, Feb 2715

A1 PT-dependence

CLAS data suggests that width of g1 is less than the width of f1

AnselminoCollins

H. Avakian, DPWG, Feb 2716

Summary

double spin asymmetries measured at CLAS are consistent with HERMES and fits to world data, assuming the factorized picture

PT-dependence of the double spin asymmetry provides access to kT-widths of transverse momentum dependent distributions of quarks.

CLAS data suggests that the kT-width of the momentum distribution is wider than the width of the helicity distribution

The suggestions of the review committee have been applied and theanalysis note has been prepared for the next round of review.

H. Avakian, DPWG, Feb 2717

Support slides….

H. Avakian, DPWG, Feb 2718

Experimental Setup (CLAS EG1+IC)

Inner Calorimeter (424 PbWO4 crystals) for the detection of high energy photons at forward lab angles (e1-DVCS).

Polarized target (eg1)

13o

50o

solid NH3 polarized targetproton polarization ~80%high lumi ~ 21034 s-1cm-2

IC

H. Avakian, DPWG, Feb 2719

Collinear Fragmentation

quarkThe only fragmentation function at leading twist for pions in eN→e’X is D1(z)

Ee =5.7 GeV

No significant variation observed in z distributions of + for different x ranges (0.4<z<0.7, MX>1.5) and for A1p as a function of PT

q

qqq

qq

LLTLL zDxf

zDxg

DPA)()(

)()(

11

11

H. Avakian, DPWG, Feb 2720

0 multiplicitiesep→e’X

0 multiplicities consistent with SIDIS predictions

DSS (Q2=2.5GeV2)

DSS (Q2=25GeV2)

M.Aghasyan

H. Avakian, DPWG, Feb 2721

sin SSA analysis for pi0

With H1┴ (0)≈0 (or measured) Target (Beam) SSA can be a valuable source of info on HT T-odd distribution functions

Measure both for 3 pions and combine to separate different contributions.

H. Avakian, DPWG, Feb 2722

Dilution factor in SIDIS

Multiple scattering and attenuation in nuclear environment introduces

additional PT-dependence for hadrons

Fraction of events from polarized hydrogen in NH3

Nu,Np -total counts from NH3 and carbon normalized by lumi

u, p -total areal thickness of hydrogen (in NH3), and carbon target

Cn=Nitr/Carbon ratio (~0.98)Diff. symbols for diff x-bins

-