Studies of Lambda polarization

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Studies of Lambda polarization
H. Avakian )
Jefferson Lab
CLAS Collaboration Meeting, JLAB March, 2005
) in collaboration with L. Elouadrhiri, A.
Kotzinian, M. Mestayer and L.C. Smith
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Outline

• Lambda production in target fragmentation
• Data sample and cuts
• Invariant and missing mass distributions
• Lambda Polarization
• Summary

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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
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? 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

L polarization in Target Fragmentation Region
(TFR) probes the strange sea, as the s-quark
carries whole spin of L
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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
6
p- kinematics in ? production
e
e
1
p
?
2
p
Total
E1f(accepted)
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Good acceptance for low momentum, large angle p-
detection compared to e16 data set
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? resolution and background
No spin asymmetry for background
Lambda identified by a cut Mpp- - 1.115lt0.003
6
8
Missing mass of e?X
K
K
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No energy loss and momentum corrections
applied. Masses of K and K consistent with PDG
values (MK493.7, MK891.7)
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Missing mass of e?X
K
6
Invarian and missing mass resolutions better for
e16, but few events left
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?s in target fragmentation
e
e
1
p
?
2
p
Raw asymmetry
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No sign flip is visible in transition from
exclusive to semi-inclusive Lambda production for
the polarization transfer
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?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

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?s in target fragmentation
e
e
1
p
?
2
p
PRELIMINARY
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Lambda polarization for 5.75 GeV with proton
target (predictions for 5.75 GeV from Ellis,
Kotzinian and Naumov)
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Summary

• Direct production of Lambdas studied using the
  e1f data set
• For the first time the polarization transfer was
  extracted for semi-inclusive Lambda production
  in the target fragmentation region.
• The measured Lambda polarization is consistent
  Studies of hard exclusive photon and vector meson
  production underway, allowing access to GPDs and
  also providing important info for the
  interpretation of SIDIS SSAs.
• Measure Lambda polarization using other methods
  and estimate the systematic errors.
• Study transition from exclusive to
  semi-inclusive Lambda production.

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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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? mass resolution in e1f
Vertex constrains will further improve the
background
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Lambda identified by a cut Mpp- - 1.115lt0.003