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Studies of Spin-Orbit Correlations with CLAS. Harut Avakian (JLab). Deep PWG, Genova, Feb 27. Outline. 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. - PowerPoint PPT Presentation
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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
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
-