Backward Calorimetry For SuperB ____ _____ May 13, 2009

Introduction The original design for the backward endcap calorimeter consisted of tiles yielding 11520 readout channel Since on average only 1 particle is expected in the backward EC the segmentation can be substantially reduced Instead of using tiles one can use strips Dave Hitlin suggested to use spiral-shaped strips The new design will use 3 different shapes of strips: Right-handed spirals Left-handed spirals Sectors The 3 layers will alternate

SuperB: Baseline Design Rear endcap 3

Scintillator Planes Alternate 3 different strip shapes 8 times 24 layers in total There are 48 strips per layer yielding 1152 strips Due to the different strip shapes layer need to be mounted completely  no split into halves The sectors overlap 7 left-handed and 7 right-handed spirals

Strip Fabrication For practical reasons it is best not to produce individual strips but to start out with a rectangular scintillator sheet First outer and inner spiral edges as well as inner and outer circular edges Next we mill 5 grooves along the spiral lines to produce 6 strips We leave small bridges uncut so that the 6 strips are connected in a few places  we need to measure the cross talk to decide size of the bridges Gaps are filled with white diffuse reflector This procedure provides mechanical stability for each sheet 8 such sheets make one layer

Strip Readout The scintillator strips are 3 mm thick At the outer edge the strips are 9.8 cm wide, at the inner edge 4.1 cm In the center a 1mm deep spiral-shaped groove is cut into which the WLS fiber is inserted A SiPM (MPPC) is mounted at the outer edge A mirror is positioned at the inner edge of the fiber Thin boards with traces are placed on the outer edge to which the SiPM pins are soldered to SiPM mirror

R&D in Bergen We have started to test SiPMs and other pixelated avalanche photomultipliers in our laboratory Spectrum with light pulser and 106Ru source MEPHI/PULSAR 1156 pixels gainSiPM~4105 1pe 2pe 3pe pedestal MIP=4-5 pixels (33 cm2) 4pe 5pe

R&D in Bergen We have started gain and MIP measurements

Conclusion The new design reduces the number of channels to 1152 With the spiral design (sectors overlap 7 left-handed and 7 right- handed spirals) the position of the shower should be determined rather precisely In this design the entire calorimeter is built in one piece  it cannot be removed without removing the beam pipe