Scintillation hodoscope with SiPM readout for the CLAS detector S. Stepanyan (JLAB) IEEE conference, Dresden, October 21, 2008

S. Stepanyan, Jefferson Lab (USA) TOF counters Drift chambers Beam line and the target Electromagnetic calorimeters 6 Superconducting toroidal coils Cherenkov counters CEBAF Large Acceptance Spectrometer at JLAB Multipurpose spectrometer based on a superconducting toroidal magnet. Managed by the CLAS collaboration (170 scientists from 40 institutions) Conducts experiments in the field of high energy nuclear and particle physics using high energy electron and tagged photon beams at luminosities of up to 2x10 34 cm 2 sec -1, with variety of liquid and solid targets Best suited for multi-particle final states

S. Stepanyan, Jefferson Lab (USA) Small angle electromagnetic calorimeter For detection of high energy photons in forward region (  > 4 o ), 424 channel PbWO 4 crystal calorimeter (IC) installed inside the CLAS boar is used In the IC APDs are used as a photodetector due to tight space constraints and the presence of 5T solenoid field Calorimeter performed well during the high luminosity electron run. However, lack of ability of separating electromagnetic showers induced by electrons and photons limited access to an interesting physics at low Q 2 (small electron scattering angle) For electron identification, highly segmented, lightweight charged particle detector with compact readout, immune to magnetic field is necessary in front of IC Solenoid Calorimeter

S. Stepanyan, Jefferson Lab (USA) Charged particle detector in front of IC Thin scintillation pixel hodoscope with light readout via green wave shifting fibers embedded in the surface of scintillator plates Location of photo- detectors Rohacell back plate Location of readout electronics Pixels of 1 cm thick 3.8x3.8 cm 2 scintillator plates arranged in octagonal shape to match the calorimeter acceptance (projected from the target) Each pixel has one spiral and one straight grove in each side Group of 3(4) pixels have one common fiber running through the straight groove Total number of pixels 56, total number of fiber readout 72 Arrangement of pixels and readout in ¼ of the detector. Photo-detectors and electronics are in the “shadow” of the coils of toroidal magnet

S. Stepanyan, Jefferson Lab (USA) Photodetectors for the hodoscope Traditional PMTs are big and difficult to operate in high magnetic field APDs have very low gain and hard to use in low light yield detectors Newly developed, high gain SiPMs are ideal for a single [1mm] fiber readout Our choice: Multi Pixel Photon Counter (MPPC) – S U by Hamamatsu Gain

S. Stepanyan, Jefferson Lab (USA) Light yield measurements MIP Cosmic ray muons were selected by a coincidence between a scintillator counter positioned above the test pixel and the PMT connected directly to the test pixel Light yield of16 photo-electrons for 2 MeV energy deposition from both, spiral and straight fibers are measured

S. Stepanyan, Jefferson Lab (USA) MPPC grouping Manufactures suggested voltage Range of linear operation Each readout corner contains 18 MPPCs, divided into two groups of 9 MPPCs Group of 9 MPPCs have common bias voltage Gain vs. V for 100 samples of S U were measured Manufacture provided and measured gains were in good agreement MPPCs with closest median bias voltages of linear region were grouped in groups of 12

S. Stepanyan, Jefferson Lab (USA)

Pixel and fiber assembly Place for readout electronicsScintillator pixels

S. Stepanyan, Jefferson Lab (USA) Final assembly

S. Stepanyan, Jefferson Lab (USA) Photon beam run No selection cuts After timing cut ~15p.e. First beam run during April-May ’08. Photon beam with up to 5.7 GeV energy, 40 cm long LH 2 target Hodoscope covered forward scattering angles between 2 to 6.5 degrees ADC distributions of hits in the coincidence window with CLAS selects hits from high energy charged particles. LV Amp Disc ADCADC TDCTDC Scal Delay MPPC

S. Stepanyan, Jefferson Lab (USA) Summery Scintillation pixel detector for the forward region of the CLAS detector was built using 1cm thick, 3.8x3.8 cm 2 scintillator plates (pixels) with embedded 1 mm diameter green WS fibers for light transport As photo detectors, HAMAMATSU MPPC S U with average gain of 2x10 6 were used During the beam run detector showed stable performance. Preliminary analysis showed good agreement between expected (16 p.e.) and measured (15 p.e.) light yields corresponding to high energy charged particles Gain vs. V dependences of all 72 MPPCs were measured after two months of high luminosity beam run. No visible change in the dark currents or in the gains were observed Scintillation detector will be used in upcoming CLAS electroproduction experiment together with PbWO 4 calorimeter for electron detection at small angles