SSA in SIDIS on the neutron

1
SSA in SIDIS on the neutron
H. Avakian
BONUS meeting March 11 JLab

• Physics Motivation
• Pion SSA
• Lambda SSA in target fragmentation
• Summary

2
Spin structure of the nucleon
½ ½ Sq DG Lq
Naïve quark model suggest DS DuDd1, D s
0 DIS experimentsDu 0.83, Dd -0.43, D s
-0.1

• Negative polarization of strange sea
• Positive polarization of gluons
• Orbital momentum

Origin of the negative sea polarization under
study
3
SIDIS target and current fragmentation
xFgt0 (current fragmentation)
xF - momentum in the CM frame
xFlt0 (target fragmentation, TFR)
probability of finding a parton q
with momentum fraction x and a hadron h with
energy fraction z in the proton (Trentadue
Veneziano).
Wide kinematic coverage of CLAS allows studies of
hadronization in the target fragmentation region
4
ALU x-dependence CLAS _at_ 4.3 and 5.7 GeV
0.5ltzlt0.8
Beam SSA analyzed in terms of the Collins effect
by Schweitzer et al. using e(x) from cQSM
5
Collins effect with Transversely polarized target
Hunf-1.2Hfav

• HERMES measurement of transverse SSA indicate
  large unfavored fragmentation function
  (Hunf-1.2Hfav) leading to strong suppression of
  p0 and pp- SSA

6
Flavor decomposition of T-odd g-
With SSA measurements for pp- and p0 on neutron
and proton (ppp-) assuming HfavHu?p
-Hu?p-Hunfav
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Flavor decomposition of T-odd g-
In jet SIDIS (ELIC) with massless quarks
contributions from H1-,E vanish
With SSA measurements for pp- on neutron and
proton (Dpp-p-)
8
? production
e
e
1
p
?
2
p
L unique tool for polarization study due to
self-analyzing parity violating decay
(ud)-diquark is a spin and isospin singlet ?
s-quark carries whole spin of L
L polarization in Target Fragmentation Region
(TFR) provides information on contribution of
strange sea to proton spin
6
W.Melnitchouk and A.W.Thomas 96 J.Ellis,
D.Kharzeev, A. Kotzinian 96
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? in target fragmentation
e
e
1
p
?
2
p
Accessing polarized PDFs with unpolarized target!
Ls accessible in CLAS (even at large z) are
mainly in the TFR region and can provide
information on contribution of strange sea to
proton spin
6
10
? mass resolution in e1f
Vertex constrains will further improve the
background
6
Lambda identified by a cut Mpp- - 1.115lt0.003
11
p- kinematics in ? production
e
e
1
p
?
2
p
E1fHDC
E1f(5.5GeV)
6
Low momentum, large angle p- detection with BONUS
will significantly increase the acceptance for
direct Lambdas
12
?s in target fragmentation
e
e
1
p
?
2
p
CLAS-5.7GeV
MC
data
HERMES

• Presence of large cosq from acceptance require
• Detailed MC simulation OR
• Spin asymmetry measurement to cancel the
  acceptance contribution

6
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?s in target fragmentation
e
e
1
p
?
2
p
6
Projections for Lambda polarization for 5.75 GeV
(600runs) with neutron target (predictions for
5.75 GeV from Ellis et al.)
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Summary

• Polarized beam with neutron target will allow
  studies of new observables, sensitive to the
  orbital motion and strange sea distributions.
• CLAS with central detection capabilities will
  significantly increase reconstruction efficiency
  of direct Lambdas allowing measurement of Lambda
  polarization with neutron target.
• Combination of pion SSA on proton and neutron may
  allow flavor decomposition of a new T-odd TMD
  distribution g-.

15
support slides..
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?s in target fragmentation
e
e
1
p
?
2
p
6
Predictions for Lambda polarization for 5.75 GeV
with neutron target from Ellis et al. (2 models
for spin transfer)
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? missing mass in e1f
K
K
6
Extraction of Lambda polarization as a function
of MX will study the transition from exclusive to
semi-inclusive production
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Photon Sivers Effect
Target SSA (Brodsky et al.)
Essential constituents
Light-cone spin wave function of a nucleon
Beam SSA (Afanasev Carlson)
Final state interaction from gluon exchange
Beam SSA has the same source and provides access
to essential parameters with less ambiguities