First Results on Large Cerium Fluoride Crystals in A Test Beam
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Introduction
The need for very high resolution calorimetry at the forthcoming LHC (the Large Hadron Collider to be built at CERN) has been stressed many times in the past. Such high precision can be achieved with homogeneous calorimeters made from dense, scintillating crystals. At LHC only crystals with fast scintillation and good radiation hardness can be used. CeF 3 is a good candidate to meet these requirements. In a calorimeter, high energy electrons and gammas are stopped by creating an electromagnetic shower (fig. 1). To measure the scintillation light, which is created by the shower and is proportional to the energy deposit, the scintillator has to be read out by a photodetector. electromagmetic shower (mainly bremsstrahlung and pair production)
scintillation light
photodetictor
high energetic particle(e, '7)
scintillator
Figure 1: Electromagnetic shower ')
CERN, Geneva, Switzerland
2) Vrije Universiteit, Brussel, Belgium
CE Saclay, DAPNIA, France Universitd Claude Bernard, IPNL, Lyon, France 5) RWTH, I. Physics Institute, Aachen, Germany 6) CAS, Institute of Physiscs, Praha, Czeck Republik 7) TIFR, Tata Institute of Fundamental Research, Bombay, India s) LAPP, Annecy, France *) Now at CERN 3) 4)
117 Mat. Res. Soc. Symp. Proc. Vol. 348. ©1994 Materials Research Society
To provide spatial resolution in addition to the energy measurement, crystal scintillators are commonly assembled in a matrix structure (fig. 2). In order to assess the possibility of using CeFs for a calorimeter at LHC, it is essential to test this material in a high energy electron beam.
high enrergetic parti le(e,)) -y-){--i.I
Figure 2: Matrix of crystals 2 The test setup Our studies were performed in the H2-beam line of the CERN SPS, using electrons and muons of different energies. Five scintillators allow to define beam widths of 2x2 cm 2 or 0.5x0.5 cm' (fig.
3). Black box
/
Movable table
JSI
S2
electron beams (20, 50, 80, 150 GeV) muon beam (225 GeV)
H2 beam
Figure 3: Test setup The test setup itself was built as a long parallelopipedic central crystal tower (fig. 4) with a total length of 26 radiation lengths (44 cm) and four side towers with somewhat shorter crystals. The central tower, to which the results mainly refer, was made out of three crystals with the back two glued together. The readout of the crystals was performed by silicon photodiodes (Hamamatsu S3590-04) of 1cm 2 sensitive area and a depletion thickness of 300um. The quantum efficiency of these diodes in the emission range of CeF 3 is 35-40%. For the optical coupling we used an optical glue based on silicon oil (Oken 6262A), which is transparent in the UV-region.
118
,e
SH2 beamn 1.5x2x17 cm3
i P1) lx II cm
2
glue
2 2 2x2xl4 cm
3
3 2x2x13 cm
PD i x I cm
Figure 4: Side view of the central tower
2
The electronic chain associated with the photodiodes consists of charge sensitive preamplifiers and standard RC-CR amplifiers with a shaping time of 2ps. The readout was done by CAMAC peak-sensing ADCs (Ortec 811, see fig. 5). The electronic no
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