HPS – ECal Detector - TECHNICAL PARAMETERS The experimental apparatus includes two main detectors: a silicon vertex tracker (SVT) for precise momentum vertex determination and and an electromagnetic calorimeter (ECal) to trigger on e + e - pairs produced by A’ decay. The ECal consists of 442 lead-tungstate PbWO4 crystals (16 cm long, tapered, with front/back face of 1.3x1.3/1.6x1.6 cm 2 ) with avalanche photodiode (APD) readout and on-detector amplifiers. INFN contributed to the APD/crystal assembly, the LED gain Monitoring system and the connection motherboards design and manufacturing other than electromagnetic shower software reconstruction. The Heavy Photon Search (HPS) is an experiment proposed for Jefferson Laboratory to search for new heavy vector boson(s), "dark photons”, in the mass range of 20 MeV/c2 to 1000 MeV/c2. HPS uses both invariant mass and separated decay vertex signatures using a compact, large acceptance forward spectrometer. After a test run in Spring 2012, the full HPS experiment, capable of searching for heavy photons over a wide and unchartered region in parameter space, is currently running. PARAMETERDESIGN VALUE HPS-ECal Calorimeter typePbWO4, homogeneous Crystal number and size442, tapered 15x15 (front) 16x16 (back) x160 mm 3 Readout sensorsHamamatsu LAAPD s Working Temperature T = 20 o C (  T ≤ 0.5 o C) HPS-SVT Tracking technology Silicon microstrips, single-sided, 60  m sense pitch Detector type6 layers, axial + stereo Spatial resolution  X,  Y ≤ 10  m Expected Performance VALUE Azimuthal angular coverage1.0 o to 5.0 o EM shower energy rangeE max –E min = (0.5 – 5.0) GeV Energy resolution  E /E ≤ 4.5 %/√E(GeV) ⊕ 1% Vertex resolution  X,  Y ≤ 300  m Time resolution≤500 ps

Upgrade Strategy and Project Leadership: –INFN units of Cagliari, Catania, Genova, Roma, Genova, Padova and Torino contributed to the HPS-ECal upgrade –Project is lead by IN2P3-Orsay, JLab and INFN (lead scientists R.Dupre, S.Stepanyan and M.Battaglieri). –The Large Area APD has been tested individually and glued to the crystals. –Every crystal/APD assembly has been tested before mounting. –The LED gain monitoring system has been fully designed, assembled and tested under responsibility of JLab12 Collaboration. Project Status The HPS-ECal has been gone under a major upgrade concerning the readout (LAAPD), the electrical/signal connection plane (motherboard), the LED gain monitoring system. The JLAB12 Collaboration played a major role in the upgrade contributing both to the construction funds and manpower. The Ecal installation has been on-schedule and on-cost. Preliminary results from data collected in the two run periods show that the design specs were met. Significant dates –ECal refurnishing started in 2013 –LAAPD received tested and qualified in early 2014 –Crystal/APD assembled in spring 2014 –The motherboard have been designed manufactured and tested in Spring 2014 –The LED gain monitoring system designed, assembled and tested in Summer 2014 –ECal reassembled in September 2014 –Cosmic ray run in Fall 2014 –ECal fully operational for December 2014 run –ECal is currently tacking data in Spring 2015 ruC