44Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 41 (2008)(LNS Experiment : #2608)

Performance Test of a Wire Sampling Calorimeter withPositron Beam
K.Y. Baik1 , T. Kamibayashi2 , G.Y. Lim3 , L. Ogata4 , T. Shimogawa4 ,and Y. Tajima2
12

Department of Physics, Pusan University, Busan Korea, 609-735

Department of physics, Yamagara University, Yamagata, 990-8560
34IPNS, KEK, Tsukuba,305-0801

Department of Physics, Saga University, Saga, 840-8502

We have performed a beam test for a wire sampling calorimeter made of alternating tungsten wires
and scintillating ﬁbers. The calorimeter shows energy resolution as σ/E=13.2 % at the 1 GeV, which ismainly due to sampling ﬂuctuation of electromagnetic shower.

§ 1. Introduction
The motivation of a wire sampling calorimeter is to make a dense calorimeter (short radiation
length (X0 )) having a high detection efﬁciency for low energy photons. By using tungsten wires as aconverter, we can achieve its radiation length (X0 )) as 0.7cm shorter than that of the PWO crystal. We
use scintillating ﬁbers as an active detector that enables us to extract the scintillation light to the PMTwith small attenuation. By using small cross-sectional ﬁbers, we can achieve high detection efﬁciency
especially for the low energy photons. It is another attractive feature of the wire calorimeter to adjust
radiation length by proper selecting of the converter material and to produce a long calorimeter module
quickly with low cost.

§ 2. Module Fabrication and Beam Test
Figure 1 shows a photograph of fabricated module consisting of alternating 1mm-square tungsten
wires and scintillation ﬁbers. Figure 2 shows energy resolution of the calorimeter as a function of incident positron energy. We got the energy resolution as σ/E = 13.2 % at 1 GeV, which is mainly determined by a sampling ﬂuctuation due to poor visible ratio. The attenuation length of the calorimeter wasobtained 102 cm, which agreed with the result of the single ﬁber test with a radioactive source.

§ 3. PWO Test
An additional test was performed during the beam time: a measurement of position dependency atthe glued PWO crystal. A 50-cm long PWO crystal is a candidate of a beam collar calorimeter. Instead offabricating such a long crystal, we try to glue two crystals that is an effective way. Since the light output
is very sensitive to the condition of glue, we have tested several candidates of glues. The result of bench

45

Fig.1. Cross-section of the wire sampling
calorimeter made of 1mm-square tungsten wires and scintillation ﬁbers.

Fig.2. Energy resolution of the wire sampling
calorimeter responding to the incident
positrons.

test by using the cosmic rays was not conclusive due to its small energy deposit and poor statistics. With
the positron beam, we could check the position dependency of the light yield. As shown in Fig. 3, thelight output was dropped by 12% due to the joint, which will guide us to further study.

Fig.3. Position dependency of light yield. At the boundary of two adjoint crystals, 12% of lightwas lost.

Acknowledgment
The authors are grateful to Prof. H. Shimizu, Dr. T. Ishikawa and other LNS staffs for their various
help and stable operation of the accelerator during the beam test. This work has been supported by aGrant-in-Aid (#18540302) from JSPS.