CLAS12

Pre-shower Calorimeter (PCAL) projectFall of 2010 to fall of 2014, a lot of person-hours

S. Stepanyan (JLAB)

Hall-B Meeting, March 24, 2014

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CLAS12

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CLAS Electromagnetic Calorimeter

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CLAS EC at high energies

Two problems will arise at high energiesSeparation of clusters from high energy p0’ gg 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=Ep

Hall-B Meeting, March 24, 2014 5

EC with additional finer segmented 5 layers

Energy resolution for electrons

EEE 1.0

Efficiency of two photon cluster reconstruction p0ggg decays

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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 cm2, 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)

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All single stripsU-double V&W-single

W-single V-singleU-

singl

e

W-single, U&V-doubleV-single, U&W-double

Readout with variable segmentation Beam

78 strips = 46s + 32d=62PMTs 78 strips = 46s + 32d=62PMTs

84 strips = 52s + 32d=68PMTs

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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

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Mechanical assembly of modules

Dimensional checks and test fit of sidewalls on the window have been done before load test

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

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

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QC of scintillator strip dimensionsFull width of strip thickness distribution is <0.3mm, requirement is 1mm

Full width of strip width distribution is <0.6mm, requirement is 1mm

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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

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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

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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

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QC of lead sheetsBefore 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.

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Cutting and polishing of fibers• 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

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PCAL Cosmic Ray Test Runs

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PCAL Cosmic Ray Test Runs

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Signal readout and electronics

PMT Spliter FADC

TDC

DiscriminatorScaler

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

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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

All single strips U-double V&W-single

W-single, U&V-double V-single, U&W-double

U

V

W V W

U

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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

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PCAL installationo On November 12, first PCAL module has been

installed on Sector 5o The last one was install on December 2 in

Sector 4

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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

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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