1. CLAS12 Pre-shower Calorimeter (PCAL) project Fall of 2010 to fall of 2014, a lot of person-hours S. Stepanyan (JLAB) Hall-B Meeting, March 24, 2014

2. CLAS12 Hall-B Meeting, March 24, 20142

3. CLAS Electromagnetic Calorimeter Hall-B Meeting, March 24, 20143

4. CLAS EC at high energies Two problems will arise at high energies Separation of clusters from high energy  0 ’  decay Diminishing energy resolution due to leakage from the back Both are important for successful execution of the CLAS12 physics program One cluster with E=E  4

5. Hall-B Meeting, March 24, 2014 EC with additional finer segmented 5 layers Energy resolution for electrons Efficiency of two photon cluster reconstruction  0   decays 5

6. CLAS12 PCAL  Lead-scintillator sandwich with three stereo readout views, UVW (5 layers per readout view), 14 layers of 2.2 mm lead - total of 5.5 r.l.  Extruded scintillator strips with Titanium dioxide cover. Cross section 4.5x1 cm 2, two holes along the strip for light readout  84 strips in U-layer, 78 strips in V- and W-layers  Light transport from the scintillator to PMT via 1 mm diameter green wave- shifting fibers inserted inside the holes in the scintillator (2 fibers per hole)  Total number of readout channels 1152 (6x192) Hall-B Meeting, March 24, 20146

7. 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 7 78 strips = 46s + 32d=62PMTs 84 strips = 52s + 32d=68PMTs

8. PCAL construction  Assembly of PCAL modules started on April of 2011  It took 2.5 years to assemble and test all 6 modules  The assembly process included the following steps (at JLAB):  Load test and mechanical assembly of the box, followed by assembly fiber retainers  Cutting scintillator strips (JLAB/W&M)  QC of long (>2.5 meters) strips and 20% of wave-length shifting fibers  Test and assembly of PMTs and dividers are in progress (JMU)  Stacking of scintillator strips and lead sheets, and assembly of fibers  Fiber polishing and assembly of PMTs  Fabrication of signal and HV cables is completed (OU)  Fabrication of electronics cables is in progress (NSU) Procedures were developed for each stage of the construction based on experience gained during prototyping Hall-B Meeting, March 24, 20148

9. Mechanical assembly of modules Dimensional checks and test fit of sidewalls on the window have been done before load test Hall-B Meeting, March 24, 20149 The PCAL box consists of – two composite windows, 2’’ ROHACELL structural foam core sandwiched between two 2mm thick stainless steel sheets. The set is kept together by a stainless steel “L” frame welded around the perimeter Three aluminum (~2’’) sidewalls attached to the window’s frame Retaining assembly inside the box to keep the lead and scintillator layers in place and to allow enough space for the fibers to be routed out of the box

10. Hall-B Meeting, March 24, 2014 Scintillator strips 10 Scintillator strips were extruded at FNAL in two lengths, 420 cm (1450 strips) and 450cm (2710 strips). Strips have 0.25mm titanium dioxide cover. The shorter strips were used for U-view, the longer strips were for V- and W-views. PCAL layer has an isosceles triangular shape, strips in a layer have different lengths and ends of strips must be cut in an angle From each original strip, two PCAL strips were cut

11. QC of scintillator strip dimensions Full width of strip thickness distribution is <0.3mm, requirement is 1mm Full width of strip width distribution is <0.6mm, requirement is 1mm Hall-B Meeting, March 24, 201411

12. Relative light yield and attenuation measurements Light yield along the strip was measured for each strip with length > 2 m Light yield and attenuation of 20% of fibers fro each batch is measured measured as well. Total of 3600 strips and ~3000 fibers have been tested Hall-B Meeting, March 24, 201412

13. Stacking of scintillators and fiber assembly Stacking of each modules starts from scintillators of U-layer After scintillators are laid, fibers are inserted. Ends of fibers (opposite to the readout) are glued to the scintillator, then scintillator strips are shimmed in place with springs Hall-B Meeting, March 24, 201413

14. Lead sheets Pre-cut lead shits have been used, 2 right angle triangular pieces per layer. Total of 168 sheets (about 175 sheets have been processed) Lifting fixture with suction caps and a gantry crane were used to stack led sheets in the box. While in the box, couple of mm thick shims have been used to fix the position of the lead layer Hall-B Meeting, March 24, 201414

15. QC of lead sheets Hall-B Meeting, March 24, 201415 Before installing each sheet was examined for damage, dimensions (length and straightness of sides, and the thickness) have been measure. If required, sheets were cut to match the requirements. Only less than 5% of sheets found to be defective.

16. Cutting and polishing of fibers Hall-B Meeting, March 24, 201416 PCAL fiber cutter-polisher is a custom built small 3-axis milling machine with a diamond- cutting tip (from ATLAS Tilecal) Process was fully automated: U-view had to be cut in 3-4 settings, W,V-views were cut at the same time in two settings After cut no further processing was required

17. PCAL Cosmic Ray Test Runs Hall-B Meeting, March 24, 201417

18. PCAL Cosmic Ray Test Runs Hall-B Meeting, March 24, 201418

19. Hall-B Meeting, March 24, 2014 Signal readout and electronics PMT Spliter FADCFADC TDCTDC Discriminator Scaler HV Each PMT (Hamamatsu R6095) will be furnished with HV power supply, ADC, discriminator and TDC channel Anode signal of the PMT will be split with 1:2 split PCAL response will be measured in FADC Time of the signal will be measure in multi-hit TDC Fast readout of FADC will be used in the trigger logic Trigger logic 19

20. Hall-B Meeting, March 24, 2014 Few thing to consider for simulation and reconstruction CLAS EC:  U-, V-, and W-readout from each side of the triangle  fixed width of transvers segmentation along the readout view  fixed distance from scintillator strips to PMTs PCAL:  V-, and W-readout from the same side of the triangle (top)  variable width of transverse segmentation  length of fibers from end of scintillator to PMT depends on location of the scintillator strip 20 All single strips U-double V&W-single W-single, U&V-double V-single, U&W-double U V W V W U

21. PCAL Transport Custom made rollers are used to move modules out of the assembly area First modules went for storage in ESB on a fork lift Then were transported into Hall on a trailer Hall-B Meeting, March 24, 201421

22. PCAL installation Hall-B Meeting, March 24, 201422 o On November 12, first PCAL module has been installed on Sector 5 o The last one was install on December 2 in Sector 4

23. CLAS12 PCAL - Summary It took four years for the whole project Construction itself started in April of 2011 During 2.5 years of construction students, postdocs, scientist, and staff of the collaborating institutions processed and assembled – 7200 scintillator strips – 28800 wave-length shifting fibers – 200 lead sheets – 1152 PMTs, voltage dividers, and housing Hall-B Meeting, March 24, 201423

24. CLAS12 PCAL project (WBS 1.4.2.2.2) has been successfully completed Efforts of 10 undergraduate (from JMU and NSU) and 4 graduate (from OU, W&M, and AANL) students, and number scientists and staff from participating institutions paid off  Jefferson Lab – overall design, work space, R&D, and module construction  The Collage of William and Mary –design and module assembly, scintillator processing, and purchase of fibers  Ohio University – purchase and fabrication of signal and HV cables, module assembly  James Madison University –PMTs and voltage dividers, PMT housing assembly, module assembly  Norfolk State University – purchase and assembly of electronic cables and signal splitters  Artem Alikhanian National Lab (formerly known as Yerevan Physics Institute) – simulation and reconstruction, R&D,, design, and module construction  University of Virginia – cosmic tests, installation Thanks to JLAB 12 GeV project team for continuous support Many thanks to NSF for MRI funds granted to PCAL consortium, OU, W&M, JMU, and NSU, in 2009. Special recognition to be given to the Hall-B engineering group for an excellent support Hall-B Meeting, March 24, 201424