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Spin and azimuthal asymmetries in SIDIS at JLAB

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hard exclusive vector meson cross section - pp p0X (E704,RHIC) cross sections ... Require z 0.7 to avoid diffractive rho meson. contributions (and keep Mx 1.4 GeV) ... – PowerPoint PPT presentation

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Title: Spin and azimuthal asymmetries in SIDIS at JLAB


1
Spin and azimuthal asymmetries in SIDIS at JLAB
P. Bosted
Jefferson Lab
DNP-2005
  • Physics Motivation
  • Jlab kinematics and factorization
  • Single Spin Asymmetries
  • Future measurements
  • Summary

In collaboration with H. Avakian, V.Burkert and
L.Elouadrhiri
2
Single pion production in hard scattering
xFgt0 (current fragmentation)
h
xFlt0 (target fragmentation)
xF - momentum in the CM frame
Target fragmentation
Current fragmentation
h
h
h
h
M
PDF
PDF
GPD
1
-1
0
xF
Fracture Functions
kT-dependent PDFs
Generalized PDFs
Wide kinematic coverage of large acceptance
detectors allows studies of hadronization both in
the target and current fragmentation regions
3
Polarized Semi-Inclusive DIS
Cross section is a function of scale variables
x,y,z
n E-E y n /E x Q2 /2Mn z Eh /n
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 Dp(p-) (z) probability for a u-quark
to produce a p(p-) with momentum fraction z
z
1u
4
Transverse momentum of quarks
  • kT led to introduction of kT dependent PDFs
    (TMDs)
  • kT crucial for orbital momentum and spin
    structure studies
  • led to SSA in hard scattering processes
  • kT - important for cross section description
  • - PT distributions of hadrons in DIS
  • exclusive photon production (DVCS)
  • - hard exclusive vector meson cross section
  • - pp ? p0X (E704,RHIC) cross sections

Spin-Azimuthal Asymmetries sensitive to kT
To study orbital motion of quarks in
semi-inclusive DIS measurements in a wide range
of x,z,PT, f are required.
5
SIDIS (gp?pX) cross section at leading twist (Ji
et al.)
e
Boer-Mulders 1998
Kotzinian-Mulders 1996
Collins-1993
structure functions pdf fragm hard soft
(all universal)
Off diagonal PDFs related to interference between
L0 and L1 light-cone wave functions.
To observe the transverse polarization of quarks
in SIDIS spin dependent fragmentation is required!
6
JLab Kinematics and Facorization
  • Traditional DIS Wgt2 GeV, Q2gt1.1 GeV2
  • Berger criteriium for current fragmentation
  • dominance is zgt0.4
  • Require zlt0.7 to avoid diffractive rho meson
  • contributions (and keep Mxgt1.4 GeV)
  • Ptlt1 GeV (approximately exponential region)
  • Study if factorization broken for these cuts
    using
  • unpolarized data from E00-108 in Hall C

7
Z-Dependence of unpolarized cross sections
Jlab E00-108, Preliminary, E5.5 GeV
Pretty good agreement with prediction using
CTEQ5M PDFs and Binnewies fragmentation
functions, except for zgt0.7, or Mxgt1.4 GeV.
X0.3, Q22.5 GeV2, W2.5 GeV
8
CLAS Experiment Setup and Kinematics
Scattering of 5.7 GeV polarized electrons off
polarized NH3, ND3
  • 8M p in SIDIS kinematics

x
x
9
Experimental Overview
  • Target polarization PT about 0.7 (0.3) for NH3
    (ND3)
  • Beam polarization PB about 0.7
  • Dilution factor f varies from 0.1 to 0.3 used
    Lund
  • model for n/p ratio and preliminary Hall B data
  • for A-dependence
  • Depolarization factor DLL(y) evaluated assuming
    R
  • same as for inclusive.
  • Assumed Aperp0 (not measured, probably small)
  • No radiative corrections applied (expected to be
    small)
  • p and p- include some K, K- for Pgt1.5 GeV
  • p0 events cleanly identified with two photons

10
SIDIS factorization studies
GRVS
g1/F1 inclusive, for the sum of p ,p- , and for
p0 are consistent with each other in the range
0.4ltzlt0.7, as expected in LO if factorization
works and current fragmentation dominance. Data
at 6 GeV with Mxgt1.4 GeV support this.
11
z-depenence of SIDIS g1/F1
No significant z-dependence seen 0.3ltzlt0.7,
as expected for factorization and current
fragmentation dominance Good agreement with
PEPSI predictions (including dropoff at high
z for p-)
CLAS 5.7 GeV
PRELIMINARY
12
Longitudinally Polarized Target SSA
  • Clear f dependence
  • seen for proton
  • target and p, p0
  • Fit Asin(f) Bsin(2f)
  • for Twist-3 and Twist-2
  • respectively

13
SSA measurements at CLAS
ep?epX
W2gt4 GeV2
CLAS PRELIMINARY
p1sinfp2sin2f
Q2gt1.1 GeV2
ylt0.85
0.4ltzlt0.7
MXgt1.4 GeV
PTlt1 GeV
0.12ltxlt0.48
p1 0.0590.010 p2-0.0410.010
p1-0.0420.015 p2-0.0520.016
p10.0820.018 p20.0120.019
  • Significant SSA measured for pions with
    longitudinally polarized target
  • Complete azimuthal coverage crucial separation
    of sinf, sin2f moments

14
SSA x-dependence
Twist-2
Higher Twist
Data in rough agreement with Efremov et
al. predictions, except for p0 sin(f)
term (evidence for terms not involving
Collins fragmentation?)
5.7 GeV
PRELIMINARY
15
First glimpse of Twist-2 TMD h1L-
For Collins fragmentation function use HERMES data
Distribution functions from cQSM from Efremov et
al
PRELIMINARY
CLAS-5.7GeV
Systematic error only from unknown ratio of
favored and unfavored Collins functions (R
H1d?p/H1u?p), band correspond to -2.5ltRlt0
  • More data required with p- p0
  • Exclusive 2 pion background may be important
    analysis in progress.

16
AULSSA PT-dependence
HT SSA significant for p and p 0
CLAS PRELIMINARY
  • sinf SSA p increases with PT and is consistent
    with HERMES measurement.

17
Higher Twist SSAs
Discussed as main sources of SSA due to the
Collins fragmentation
Target sinf SSA (Bacchetta et al. 0405154)
In jet SIDIS only contributions D1 survive
Beam sinf SSA
With H1- (p0)0 (or measured) Target and Beam SSA
can be a valuable source of info on HT T-odd
distribution functions
18
Future more p0 data in SIDIS
advantages
  1. SIDIS p0 production is not contaminated by
    diffractive r
  2. HT effects and exclusive p0 suppressed
  3. Simple PID by p0-mass (no kaon contamination)
  4. Provides complementary to p/- information on PDFs

disadvantages reconstruction efficiency
(requires detection of 2g)
19
CLASInner Calorimeter (IC)
424 PbWO4 ..crystals
IC
IC sE/E0.0034/E0.038/vE0.022
CLASIC
CLAS
Reconstruction efficiency of high energy p0 with
IC increases 4 times due to small angle coverage
CLAS
IC at CLAS opens new avenue for studies of spin
and azimuthal asymmetries of exclusive and
semi-inclusive g, p0,h,r
20
Longitudinally polarized target SSA using CLASIC
50 days of CLASIC
curves, cQSM from Efremov et al
Hunf-5Hfav
Hunf-1.2Hfav
Hunf0
  • Provide measurement of SSA for all 3 pions,
    extract the Mulders TMD and study Collins
    fragmentation with longitudinally polarized
    target
  • Allows also measurements of 2 pion asymmetries

21
CLAS12
High luminosity polarized (80) CW beam
Wide physics acceptance (exclusive,
semi-inclusive current and target fragmentation)
Wide geometric acceptance
12GeV significantly increase the kinematic
acceptance (x10 lumi)
22
Summary
  • Spin and azimuthal asymmetries measured at 5.7
    GeV with longitudinally polarized target.
  • Double spin asymmetries of pions are consistent
    with factorization and partonic picture may be
    used in future NLO QCD fits.
  • sinf and sin2f SSA measured, providing access to
    the twist-2 TMD h1L distribution and testing the
    Collins fragmentation function
  • Future measurements with IC will greatly improve
    p0 data, and charged pions too. Much greater
    improvements for all reactions possible with 12
    GeV upgrade due to much larger coverage of DIS
    kinematics.

23
support slides..
24
AULSSA z-dependence
CLAS PRELIMINARY
25
Missing mass of pions in ep?epX
p0
p-
p
n
D
D0
In accessible kinematics (Q2gt1.5,W2gt4) low
MX(large z) for p0 are suppressed by current CLAS
acceptance.
26
Collinear Fragmentation
The only fragmentation function at leading twist
for pions in eN?epX is D1(z)
Ee 5.7 GeV
No significant variation observed in z
distributions of p for different x ranges
(0.4ltzlt0.7, MXgt1.5) and for A1p as a function of
PT
27
SIDIS factorization studies
P.Bosted
JLab data at 6GeV are consistent with
factorization and partonic description for
variety of ratio observables
28
Collins Effect azimuthal modulation of the
fragmentation function
FUT8h1H1-
sT(qPT)? H1-
y
fC
PT
fC
sT
D(z,PT)D1(z,PT)H1-(z,PT) sin(fh- fS)
fh
fS
x
fC
fS p/2fh
x
fS p-fS p-fh
sin(2fh)
fS p-fS p/2-fh
sin(2fh)
29
Flavor decomposition of T-odd f-
L
In jet SIDIS with massless quarks contributions
from H1- vanish
gauge link contribution
With SSA measurements for pp- and p0 on neutron
and proton (ppp-) assuming HfavHu?p
-Hu?p--Hunfav
With H1- (p0)0 (or measured) target and beam HT
SSAs can be a valuable source of info on HT T-odd
distribution functions
30
Collins effect and 2 pion production
Sub-leading pion opposite to leading (into page)
Simple string fragmentation (Artru model)
L1
Leading r opposite to leading p(into page)
r production may produce an opposite sign AUT
r
r
Understanding of 2 pion asymmetries will help to
understand single pion mesurements
r0
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