SIDIS and exclusive r production

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SIDIS and exclusive r production
H. Avakian
Jefferson Lab
JLab, May 26, 2004

• SIDIS factorization
• SIDIS partonic description at JLab energies
• SIDIS background from exclusive processes
• Summary Outlook

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SIDIS studies require

• Factorization in SIDIS into a distribution
  function f fragmentation function D and hard
  scattering part.

• Applicability of partonic description at JLab
  energies
• Low W and Q2
• Low MX in ep-gtehX
• Control over background processes
• Resonances in the t-channel
• Exclusive vector mesons

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SIDIS factorization
SIDIS (gp-gtpX) x-section at leading twist (Ji
et al. hep-ph/0405085)
Structure functions FUU,FLL factorize into TMD
distributions (hep-ph 0405085)
P- has contributions from distribution,
fragmentation and soft gluon radiation
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DSA show no significant Q2 dependence
ep ? e p X ( Ee 5.7 GeV, MX gt 1.1)
x dependence of CLAS A1p (A20) consistent with
HERMES data.
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Target SSA show no significant Q2 dependence
CLAS 5.7 GeV
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Beam SSA show no significant W,Q2 dependence
ssinfLU FLUHLT 1/Q (Twist-3)
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Missing mass of the pion
p0
p
p-
Mxgt1.4 applied to exclude the kinematics where
t-channel resonances may have significant
contribution
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ALU from CLAS 4.3 and 5.7GeV data
DIS-definition Q2gt1 GeV2 Wgt2 GeV y lt 0.85 MX gt1.4
GeV 0.5 lt z lt 0.8
5.7GeV
No significant dependence on beam energy
4.3 GeV
No significant ALU dependence on Mx beyond the
neutron.
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SSA in ep-gtepX
HERMES 27.5 GeV
CLAS 5.7 GeV
Strange pattern p0 SSA bigger at very low and
very large z
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2 pion electroproduction Kinematics
z-pion related to cosq
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Exclusive pp- and pp0
e p e p ?
p p-
r0 ID from missing p-
r ID from missing neutron
Simple BW fit with polin.background.
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SSA for p0 from ep-gtern
SSA from rn may affect SSA for SIDIS p0 at
large z
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p SSA from r
Modulation exist even for vanishing helicity
change amplitudes
r0
p SSA at large z may have a significant
contribution from r
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p from r
PYTHIA at 5.7 GeV
Larger fraction at low x and large z
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Summary

• SIDIS observables measured at JLab consistent
  within 10-15 with high energy measurements
  (HERMES, SMC) and theory predictions based on
  factorization (verified to one-loop order in pQCD
  for low P- )
• There is a significant (10-20) contribution in
  SIDIS pion sample from exclusive r at large z and
  low x.

• Realistic MC (PYTHIA-based) needed to control
  corrections to SIDIS observables from exclusive
  r,w production.
• Extract r,w cross sections, double and single
  spin asymmetries.

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Rho-MC ALU for gp-gtpX
E27.5 GeV
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Beam SSA for exclusive pp0
Missing mass
Invariant mass
Significant positive beam asymmetry in the r
region
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Beam SSA for r
HERMES r80.2/-0.1
striking difference with p0,p,r
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Exclusive r at 6 GeV
PYTIA-6
2p