1. Electromagnetic Calorimeter for the CLAS12 Forward Detector S. Stepanyan (JLAB) Collaborating institutions: Yerevan Physics Institute (Armenia) James Madison University Ohio University Norfolk State University Orsay-IPN (France) Jefferson Lab 12 GeV IPR Lehman Review, April 26-29, 2007, JLAB

2. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Proposal for the CLAS12 calorimetery Install a pre-shower calorimeter in front of the existing EC, with full coverage of the EC acceptance Basic structure - similar to the CLAS EC: –lead-scintillator sandwich –about 5-6 radiation lengths thick –three stereo readout planes –finer transverse segmentation of readout planes than in EC Light transport from scintillator to a photo-detector via green wave-shifting fibers, embedded in the grooves on the surface of the scintillator strips The main requirements for the pre-shower are: –high detection efficiency for showering particles (e,  ) –good accuracy for electromagnetic shower energy reconstruction –separation of two photon clusters from high energy (~10 GeV)  0 decay Adding more scintillator layers will increase neutron detection efficiency

3. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB GEANT simulation of the PCAL N. Dashyan (YerPhI), K. Whitlow (SULI) Goals :  establish design parameters of PCAL  determine characteristics of electromagnetic shower and  0 ’  reconstruction in the CLAS12 forward electromagnetic calorimeter Tools:  GEANT simulation package for the CLAS detector, GSIM, with PCAL positioned in front of EC  CLAS event reconstruction package, RECSIS. Modified EC package for cluster reconstruction

4. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Pre-shower in GSIM The pre-shower (PCAL) was inserted in front of EC Internal geometry of the PCAL:  alternating layers of scintillators and lead  10 mm thick scintillator, 2.2 mm thick lead  triangular shape layers to match the geometry of the EC  three stereo readout views (U, V, and W) In the initial simulations:  15 layers of scintillators (5 per view) and 14 layers of lead  the whole stack was sandwiched between two end plates, constructed from composite foam and 2mm thick SS sheets  scintillator layers were sliced into 108 strips of equal width

5. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB PCAL+EC simulations (15 layers and 108 strips) Energy resolution for electrons thrown in the center of the of the calorimeter Efficiency of two photon cluster reconstruction from high energy  0 ’  decays

6. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Configurations with 9, 12, and 15 layers   0 reconstruction efficiency decreases at high energies for 12 and 9 layer modules – not enough radiator thickness and some of high energy photons do not convert  12 layers configuration with first 3 layers of lead with double thickness had comparable efficiency but ~10% worse energy resolution 1 module = 3 layers of scintillator-lead

7. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Different readout segmentations  Efficiency of reconstruction of two clusters from  0 ’  decay decreases for small number of readout segments  For  0 energies up to 10 GeV efficiency of two cluster separation is reasonably high for 4.5 cm wide segmentation Simulations with 15 layers of scintillators and 14 layer of lead

8. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB All single strips U-double V&W-single W-singleV-single U-single W-single, U&V-double V-single, U&W-double Readout with variable segmentation Beam

9. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Variable segmentation with 196PMTs/sector  Total of 86x4.5 cm wide strips in each readout view (U, V, and W)  Finer segmentation (4.5 cm) of short U strips and long V and W strips will allow to achieve desired results with smaller number of readout channels  Final number of strips per layer and arrangement of the readout will be performed after design is completed Simulations with15 layers, 4.5 cm strip width 86 single strip readout Single strip readout 66 U, 30 V, 30 W 58 U, 34 V, 34 W 50 U, 38 V, 38 W 42 U, 42 V, 42 W Two cluster reconstruction efficiency  0 momentum (GeV/c)

10. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Summary of simulations  Initial design parameters of the pre-shower are established using a full GEANT simulations of the CLAS12 electromagnetic calorimeter system  Proposed configuration for the pre-shower:  15 layers of the lead and scintillator, 2.2mm lead, 10mm scintillator  three stereo readout views, UVW (5 layers per readout view)  4.5 cm segmentation of the scintillator layers in the forward region for all three UVW views. In the backward region, double-strip (9 cm) readout for U view (perpendicular to the beam direction) and single- or double-strip readout for V or W  Simulations will continue -  final arrangement of the readout segmentation  photoelectron statistics  realistic attenuation of light in the fibers  integration of the PCAL+EC configuration into the CLAS12 simulation package

11. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Light collection system Does not require high performance scintillator strips Light gets absorbed locally and transported through fibers Low cost extruded scintillator strips with grooves made in the extrusion process can be used Technique is widely used in several large detectors (MINOS, MINERvA …) Light transport from scintillator to PMT via 1 mm diameter green wave- shifting fibers embedded in grooves on the surface of the scintillator strips

12. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Test setup (in the EEL) Trigger PMT XP2262 Test scintillator with grove(s) FNAL, Kharkov, ELJEN Test PMTs R7899, R6095, R1450 XP1912, XP2802 9224B Test WS fibers Y11(sc-1mm, 1.5mm, 2mm; mc-1mm) BC-91A, BC-92 (1mm) Rad.Sources: 90 Sr and 207 Bi Cosmic muons with second trigger PMT 4 m long dark box with moving cart and support fixtures (Hall B engineering) Simple DAQ (CODA) – FASTBUS with LeCroy ADC

13. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Selection of the PCAL components Choice for the scintillator, WLS fiber, and PMT is : Fermi Lab extruded scintillators, 4.5x1 cm 2 with 3 grooves Kuraray, 1mm diameter Y11 single clad HAMAMATSU R6095 selected with Q.E.>16% @ 500 nm Expected photo-electron yield ~11p.e./MeV for 3 fibers (yield for EC readout from the test measurements was ~8.4p.e./MeV) Scintillator-WLSF- PMT combination with reasonably high photo-electron statistics at low cost

14. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB The Geometry of the PCAL Sc layers Y X yhyh ylyl  15.24 The last layer of PCAL scintillators projected from the EC will be: h U =360.3 cm, b U =368.97 cm Height for V/W h V =328.43 cm The same size layers and 4.5 cm scintillator strips – Area S=66477.4 cm 2 Strip length for a layer S/4.5=14773 cm Total length for a sector 2216 meters The total length of Sc strips: 13296 meters The total length of fibers: 41040 meters (3x13296+1152x5x0.2) EC PCALPCAL hUhU bUbU hVhV Design details will be discussed in D. Kashy’s presentation

15. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB PCAL Construction: cost and manpower

16. S. Stepanyan, 12 GeV IPR Lehman Review, June 26-29, 2007, JLAB Summary  Pre-shower R&D and PED are in progress  Main design parameters are established using the full GEANT simulations  Components of the PCAL (scintillator-fiber-PMT) are selected  More measurements of the light yield and the light attenuation will be done using the new extruded scintillators from Fermi Lab  Design and construction of a small prototype is in progress  Design and construction details can be worked out with building of a full scale prototype  Cost estimate for whole project is completed  Contingency and risk analysis are performed  Construction stages for the main detector are identified