Preparation of the EG1DVCS run

1
Preparation of the EG1-DVCS run
Latifa Elouadrhiri, JLab (on behalf of the
eg1-dvcs run group)
2
Eg1-dvcs setup and schedule

• First dedicated DVCS experiment with polarized
  target
• Solid longitudinally polarized target
• Polarized electron beam
• IC to detect low-angle photons
• Hodoscope

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• 60 PAC days
• According to the current accelerator schedule
• Feb 4th Mar 11th _at_ 5.9 Gev,
• Apr 9th May 31st _at_ 6.1 GeV
• Rest of the run, about 30 PAC days TBA

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3
Preparation for the run

• Polarized target (Chris Keith, Peter Bosted)
• Simulations to study Moeller and Drift Chamber
  Occupancy (Alex Vlassov, Hovanes Egyian - Moeller
  only)
• Simulations to study IC and Target position
  (Silvia Niccolai, F.X. Girod)
• Simulations to study best configuration for the
  SIDIS experiment (Harut Avakian)
• Work on gsim to simulate the eg1 targetIC
  configuration (Angela Biselli)

Both e1 and eg1-dvcs
For DVCS analysis, it is useful and important to
have the same configuration as the e1-dvcs
experiment, for technical (backgrounds,
engineering) and physics reasons (equal kinematic
coverage)
4
Status of the work on the polarized target

• A new insert has been built
• Cell length 1.5 cm instead of 1.0 cm ? dilution
  factor 7 better (less helium). We can lower beam
  current so higher average polarization.
  Equivalent to gt14 more beam time.
• Use 14NH3 instead of 15NH3. Equivalent to 14
  more running time.
• Cryostat has been assembled
• Start cooling to 4K in these days

5
Simulations for DC occupancy and Moller dose on
the IC

• Performed by Alex Vlassov
• Testing different configurations
• Many parameters IC/Target position, different
  shielding geometry, different materials
• Simulation so far only for e1- dvcs
• For eg1-dvcs need raster and eg1 polarized
  target magnet

New shielding
Original design
Foam chamber
DC occupancy 4.2
DC occupancy 2.49
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Changing IC-target distance IC dose changes as
well
Studied shieldings to reduce the dose on the IC,
but they increase DC occupancy, and dont help
much decrease the dose
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Simulations with Gemc for Moller dose on the IC
Hovanes Egyian

• eg1-dvcs target density r 0.73 g/cm3 ? L
  1.21034 s-1 cm-2
• beam rastering simulated by Gaussian with s 3
  mm
• magnetic field file for eg1 polarized target
  magnet from Harut/Sebastian
• compared IC energy deposits for e1-dvcs and
  eg1-dvcs (at 55 cm) as a function of x, y, z

e1-dvcs
e1-dvcs
eg1-dvcs
eg1-dvcs
e1/eg1
e1/eg1
e1/eg1
e1/eg1
E1-dvcs and eg1-dvcs, for the same IC-target
distance, see similar energy deposits by Moller
electrons in IC
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Simulations with Gemc for Moller dose on the IC
Hovanes Egyian

• eg1-dvcs target density r 0.73 g/cm3 ? L
  1.21034 s-1 cm-2
• beam rastering simulated by Gaussian with s 3
  mm
• magnetic field file for eg1 polarized target
  magnet from Harut/Sebastian
• compared IC energy deposits e1-dvcs and eg1-dvcs
  (at 55 cm) as a function of x, y, z
• tested three IC-target distances for eg1-dvcs
  55 cm, 65 cm, (75 cm)

55 cm
55 cm
65 cm
65 cm
55/65

• Increasing the separation to 65cm will increase
  the background rate
• by a factor of 4 in the second and the third
  rings
• The question still remains if the absolute
  rates, which seem to be consistent
• with the rates e1-dvcs seen, for larger
  separations in eg1-dvcs can be tolerated in the
  analysis

55/65
55/65
55/65
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Simulation to study DVCS photon acceptance for
different IC/Target positions

• GPD-based DVCS/BH event generator
• E(beam) 5.775 GeV
• Q2 gt 0.8 GeV2
• Wgt1.3 GeV
• e1-dvcs configuration (solenoid e1-dvcs target)
• Events are processed with GSIM, GPP (using the
  parameters calculated for the first e1-dvcs run),
  recsis and data analysis (PID epg final state).
• 2 configurations
• target at -66, distance target-IC 55 cm
• target at -66, distance target-IC 67 cm

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Comparison of f distributions for the two
IC-target distances
Loss of events at 120o and 240o increases with
t (from 20 to a factor 2)
Integrated over t

• At 120o and 240o statistic
• are poor (DVCS only)
• At 0 and 360o statistics
• are high (BH cross section
• peaks), BSA and TSA are 0

• Larger distance
• 20-30 less events at the angles between f
  120o and 240o
• 40 increase at 0 and 360o

Silvia Niccolai
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Increasing IC-target distance is useful to
increase forward-angles acceptance for charged
particles
EG1 data/MC
Elastic events
Proton angular distributions for DVCS events
Harut Avakian
Elastic events with 5.7 GeV beam (important for
target polarization measurement)
Polarized target magnet cuts protons above 50
degrees Fraction of elastic events significant
for electrons lt20 degrees
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Semi-Inclusive Pion Electroproduction

• Concurrent to eg1-dvcs
• ep?ep0(, -) X
• Studied the acceptance for pions in PTGIC
  acceptance and resolution studies for different
  configurations

And 40 more events for charged pions
Harut Avakian
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• The optimal IC-target distance for eg1-dvcs is
  still under debate.
• For the DVCS analysis 55 cm are OK, because
• IC background rates are under control (known
  from e1-dvcs)
• acceptance is the same as e1-dvcs (same
  kinematics,
• cross sections can be compared, cross section
  difference can be
• extracted from eg1-dvcs using cross section
  measured in e1-dvcs)
• no loss of photons where the statistics are
  already low (and DVCS
• is dominant over BH)
• it works fine for e1-dvcs why change?
• However
• a larger coverage for electrons could improve
  statistical error on PbPt
• (7 with 55 cm, 4 with 65 cm, according to Peter
  Bosteds estimation)
• improved acceptance for SIDIS channels