Physics Hall B preshower WBS 1.4.2.2.2.3

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PhysicsHall B pre-showerWBS 1.4.2.2.2.3

Stepan Stepanyan

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CLAS Forward Electromagnetic Shower Detector

• CLAS12 physics program requires reliable
  detection of photons and p0s and photons with
  momenta lt10 GeV/c
• With increase of the pion energy the spatial
  distance between the two photons will decrease
  and at energies gt 5 GeV that distance will be too
  small to reconstruct two photons as separate hits
  in the existing forward electromagnetic
  calorimeter (FEC)
• A pre-shower with finer transverse granularity
  will be build and mounted on the front of the
  existing calorimeter
• The pre-shower will cover at least 60 in angle
  (30 in area) of the forward part of present FEC
• It will be lead-scintillator sandwich with three
  stereo readout planes
• the number of layers and the number of
  scintillator strips per layer will be defined
  during the RD stage of the project
• The light transmission to a photo-detector will
  be performed via 1-2mm diameter wave-shifting
  fibers, embedded in the surface of the
  scintillator strips

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Pre-shower layers and a scintillator strip
Scintillator strip
1 mm, 1.5 mm or 2 mm diameter WLS fiber
Final dimensions will be determined at the end
of RD work
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Status of Simulations

• For simulations, the existing GEANT model for the
  CLAS detector (GSIM) is used

• the pre-shower is inserted before the forward
  electromagnetic calorimeter
• each layer has 108 scintillator strips (3cm wide
  and 1 cm thick)
• there are total of 12 alternating layers of lead
  and scintillator (4U, 4V, and 4W)
• CLAS event reconstruction algorithm is modified
  to include reconstruction of the pre-shower
  information

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Preliminary results
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Preliminary Results

• Two cluster reconstruction efficiency

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Status of a light readout tests
The optimal combination of the scintillator-fiber-
PMT system will be chosen based on the studies of
the photoelectron yield for several possible
types of a scintillator material, wave shifting
fibers (with double and single cladding), and
PMTs.

• Studies will include
• measurements of the light yield with short
  scintillator strips
• for scintillator-fiber-PMT combinations with the
  highest light yield, study the light attenuation
  and the time characteristics
• for a final combination study the sensitivity of
  the individual fiber readout to the transverse
  position of the ionization
• design and build a prototype with selected types
  of scintillator material, wave shifting fiber,
  and the PMT. Test the prototype with cosmic muons
  and possibly with the beam
• A dark box for the measurements is ready in EEL
  building
• Building fixtures, the PMT housing, and the fiber
  holders is in process
• 70 of orders (scintillator strips, fibers, PMTs,
  and accessories) are received
• Building a DAQ system is in progress
• Measurements will start in couple of weeks

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Status of orders for RD
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CLAS12 Pre-shower RD and PED

• GEANT simulations and reconstruction will
  determine the number of layers and the number of
  scintillator strips per layer, optimized for
  reliable p0 reconstruction and the minum number
  of channels. The first results will be ready by
  the end of June 2006.
• The type of scintillator strips, fibers, and PMTs
  will be selected based on the studies of the
  photoelectron yield and the cost
• scintillator strips will chosen from
  FNAL-NICADD, AMCRYS-PLAST, and ELJEN
  TECNOLOGY
• fibers will be chosen from two vendors, BICRON
  and KURARY
• PMTs will be selected from three vendors
  HAMAMATSU, PHOTONIS, and ELECTRON TUBES
• Preliminary results of measurements will be ready
  by the end of September 2006.
• The final selection of materials for a prototype
  will be performed in December 2006
• after additional tests with few of selected
  samples.
• A design of prototype will start in October.
  Purchase orders for fibers, PMTs, and the
  scintillator strips should start in January 2007.
  Purchase orders for mechanical parts for the
  prototype should start in February 2007.