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 2x1034 cm2 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 (> 4o), 424 channel PbWO4 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 Q2 (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 electronicsPixels of 1 cm thick 3.8x3.8 cm2

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) – S10362-11-100U by Hamamatsu

Gai

n

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 S10362-11-100U 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)

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

.75..1 channep

~15p.e.

First beam run during April-May ’08. Photon beam with up to 5.7 GeV energy, 40 cm long LH2 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

ADC

TDC

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 cm2 scintillator plates (pixels) with embedded 1 mm diameter green WS fibers for light transport

As photo detectors, HAMAMATSU MPPC S10362-11-100U with average gain of 2x106 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 PbWO4 calorimeter for electron detection at small angles