Exclusive p Production from Deuterium

1
Exclusive p? Production from Deuterium

• Jixie Zhang
• Old Dominion University
• (for the CLAS Collaboration)

2
Motivation

• Proton resonances have been studied in detail
  with high statistics.
• Neutron resonances are also very interesting. It
  has different isospin (Iz) than the proton.
• However, we have almost no data yet because
  there are no free neutron targets.
• Most of the data we have were taken with
  deuteron targets, so we do not know the initial
  state of the neutron (binding and Fermi motion
  effects) .

K.Park et al, CLAS collaboration, submitted to
physics review C
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Solution
Scatter the electron from a neutron in the
deuteron and detect the spectator proton.
Low momentum spectator proton
Conservation of energy and momentum allows
determine the initial state of the neutron.
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Jefferson Lab Experiment E03-012Barely off-shell
Nucleon Structure (BoNuS)

• Electron beam energies 2.1, 4.2, 5.3 GeV
• Spectator protons were detected by the newly
  built Radial Time Projection Chamber (RTPC)
• Scattered electrons and other final state
  particles were detected by CEBAF Large Acceptance
  Spectrometer (CLAS)
• Target 7 atm D2 gas
• Data were taken from Sep. to Dec. in 2005

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BoNuS RTPC Detector

• Low momentum protons from the target ionize
  He/DME gas in the drift region (30 to 60 mm from
  the target)
• Ionization electrons drift to the three layers of
  Gaseous Electron Multipliers (GEMs)
• Sensitive to proton momenta between 66 and 200
  MeV/c
• GEMs are read out by 3200 channels (pads) in 114
  ns time windows
• 3-Dimensional Tracking
• time of flight -gt R
• 2D channel position -gt q, z

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CEBAF Large Acceptance Spectrometer
EC
TOF
CC
DC 3
DC 2
e-
DC 1
Beam Line
BoNuS RTPC
Target 7 atm. D2 gas
low energy backwards proton
CLAS
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p- Production Kinematics
g n -gt p- p
p-
q
Q2 momentum transfer to the target W
invariant mass of virtual photon target neutron
(not at rest)
n
Leptonic plane
hadronic plane
q angle of emitted p- with respect to
direction of virtual photon in the CM frame f
angle between the leptonic and hadronic
scattering planes
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Missing Mass, E 5.3GeV, No momentum calibration
N(e,e?p-)X
D(e,e?p-pCLAS)X
PRELIMINARY
D(e,e?p-pRTPC)X
D(e,e?p-pRTPCpCLAS)X
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Spectator momentum spectrum
D(e, e? p- p)p
D(e, e? p- pCLAS)ps
D(e, e? p- pRTPC)pCLAS
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Kinematics coverage, D(e,e?p-p)p , E 5.3 GeV
q Vs f
f(degree)
W Vs Q2
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Baryonic resonances, D(e,e?p-p)p E 5.2 GeV,
Accepance and momentum not corrected yet
N(1520)D13, N(1535)S11
D(1620)S31, N(1650)S11 N(1675)D15, N(1680)D15
D(1700)D33, N(1720)P13
D(1232)P33
PRELIMINARY
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Summary

• The Bonus RTPC detector, together with the CLAS
  detector, allows us to study the neutron
  resonances clearly.
• We have taken data for D(e,e?p-p)p over a large
  kinematic range in q and f, Q2 and W
• We presented preliminary results for the p-p
  invariant mass showing N resonances
• Momentum and acceptance corrections still need to
  be applied.
• Results from other beam energies are coming soon
  2.1, 4.2 GeV

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Final States Interaction
quasi-free D(e,e?p-ps)p process
primary background
This final state interaction is small for low
momentum ps and has a very strong angular
dependence on qpq, which is the angle between q
and p- in cm frame.
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Angular Acceptance (q and f)
PRELIMINARY
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Missing Mass, E5.3 GeV
N(e,e?p-)X
D(e,e?p-p)X
PRELIMINARY
D(e,e?p-prtpc)p
D(e,e?p-prtpcpCLAS)X
?0
p0
r0/ w0
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W in Q2 bin, E5.3 GeV, No acceptance calibration
PRELIMINARY
PRELIMINARY
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BoNuS RTPC Detector
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Baryonic resonances, D(e, e? p- pCLAS)pE 5.3
GeV, Accepance and momentum not corrected yet
Invariant mass of p- and pCLAS
D13(1520), S11(1535)
S31(1620), S11(1650), D15(1675), F15(1680),
D33(1700), P11(1710)
P33 (1232)
PRELIMINARY
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Data on the proton - nothing comparable exists
for the neutron
p(e,e?np)
CLAS
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Resonance Transition Amplitudes(compared to a
quark-model description)

• Proton
• Neutron