Simulation Procedure

1
Exclusive p- Electro-production from the Neutron
in the Resonance Region Jixie Zhang for the BoNuS
CollaborationOld Dominion University
LOGO
LOGO
Radial Time Projection Chamber
D(e,ep-p)p Study
Neutron Resonances
Simulation
The study of baryon resonances is crucial to our
under-standing of nuclear structure and dynamics.
The excited states of the proton have been
studied in great detail. We are interested in
study the neutron as well.
However, there is not a free neutron target due
to its instability. Most of the neutron data
were taken with deuteron targets, so we do not
know the initial state of the neutron due to the
binding, Fermi motion, and other effects. Thus
the spectator tagging technique may help.
Missing Mass spectrum The figure on the top right
shows events one proton detected by CLAS The
figure on the bottom left plots events one proton
detected by the RTPC The bottom right figure
shows the case 2 protons have been respectively
detected by the RTPC and CLAS. The purple area is
under the proton mass cut from 0.838 to 1.038 GeV
Simulation Procedure Event Generator ? Geant4
RTPC ? gsim (CLAS) ? RECSIS (reconstruct)

• A long and thin target of deuterium gas at 7 atm
  with a diameter of 6 mm and a length of 20 cm.
• Drift region locates at 3 to 6 cm from the target
  and is filled with a drift gas (helium-DME).
• The ionized electrons are avalanched by the 3
  layer of Gaseous Electron Multipliers (GEMs) and
  finally collected by 3200 readout channels
• 5 tesla magnetic filed point to the opposite
  direction to the beam line.

Simulation is one of my major contribution to
BoNuS experiment. A complete simulation code was
developed to simulate RTPC and CLAS detectors
step by step. We used Geant4 toolkit to simulate
RTPC, then used gsim (Geant3) code to simulate
CLAS detector and finally ran RECSIS to
reconstruct the data. Base on the fake tracks
from the simulation we checked the RTPC tracking
(reconstruction) software . I have also developed
the energy loss correction for particles measured
by CLAS or RTPC. Currently I am running to
simulation to finish the acceptance correction.
Kinematic
Spectator proton momentum spectrum. Black curve
is the momentum measured by RTPC red curve is
the momentum of a spectator proton infer from the
measurement of CLAS blue curve is the summation
of black and red.
CLAS detector
W (mn2 2mnw - Q2)1/2 q2 -Q2
4ee'sin2(qe/2) q angle between the emitted p-
and the virtual photon in the CM frame f angle
between the leptonic and hadronic scattering
planes
Primary Background

• Conclusion
• RTPC effectively reconstructed and identified
  slow protons
• Spectator tagging technique works
• RTPC can save 20 more date for exclusive p-
  channel

• The Continuous Beam Electron Accelerator
  Facility (CEBAF) at Jefferson Lab is based on a
  recirculation electron linear accelerator.
  Located in the Hall-B is CEBAF Large Acceptance
  Spectrometer (CLAS), which is designed to study
  multi-particle final state reactions induced by
  electron or tagged photon beams.
• CLAS is constructed around 6 iron-free
  superconducting coils which provide a toroidal
  magnetic field.
• The particle detection system consists of drift
  chambers, Cherenkov counters, scintillator
  counters and electromagnetic calorimeters.
• The RTPC detector was placed in the center of
  Hall-B to work conjugate with CLAS.

preliminary
Acknowledgements
Ratio of total to quasi-free cross section
against the theta angle of the recoil proton. The
2 peaks cor-respond to p-p and pp rescattering.
Ratio of total to quasi-free cross section
against the momentum of the recoil proton, at the
top of p-p rescattering peak.
I would like to express my sincere gratitude to
the DOE and the entire CLAS and BoNuS
collaborations. I am very grateful to my
advisors G. Dodge and S. Kuhn for all of their
encouragement, guidance, suggestion and patience.
Also I would like to thank several colleagues
for their significant contributions. They include
N. Baillie, N. Kalantarians, S. Tkachenko and T.
Vladas.
The full and dashed lines include the hadron
scattering without and with the color
transparency effect, respectively. The dotted
curve corresponds to the quasi-free process.
Calculation from Laget This final state
interaction has a very strong ?R angular
dependence and is small for low momentum PR .