T476 report

A study of the fine segmented liquid scintillator detector
with wave-length shifting fiber readout for K2K upgrade
T. Nakaya, I. Kato, H. Maesaka, K. Nishikawa (Kyoto U.); T. Kobayashi (KEK)A primary purpose of T476 experiment is to study basic performance of a ﬁne segmented liquid scintillator detector with wave-length shifting (WLS) ﬁber readout. The detector is a possible candidateof a neutrino detector in K2K experiment with following advantages:• With liquid scintillator, a large full-active detector can be built inexpensively. In addition, anuniform response of each segment in the detector is expected.
• By using WLS ﬁber readout, the light correction from a large volume of the detector can be leadto small area of photo-detectors with high eﬃciency.
• A recent development of a multi-anode PMT makes it possible to read out many channels
inexpensively, and to provide the precise measurement of the light yield.
Recently, such a detector is also studied at CERN [1].
The schematic picture of the detector is shown in Figure 1. The liquid scintillators, ELJEN EJ39904 and Bicron BC517L were tested, both of which are proved not to attack a plastic ﬁber chemically.
The liquid scintillator container was optically segmented by Aluminum cells (2 × 2 × 20 cm3 ), each ofwhich was read out by two 1mm φ WLS ﬁbers. The two ﬁbers were attached to one multi-anode PMTchannel, Hamamatsu H6568-10. The detector can measure the track of a particle with energy depositin each cell. With the ﬁne granularity of the cell size, the detector had the ﬁne tracking capability.
As a consequence of the energy measurement, we proved that the detector can distinguish a proton
track from a pion one by dE/dx as shown in Figure 2. The positive identiﬁcation of a proton is crucial
as a neutrino detector to select quasi-elastic interaction. Separately, we also measure the attenuation
length of the ﬁber with a diﬀerent detector setup which had 2.6 × 2.6 × 300 cm3 cell size.
The results of T476 experiment [2] are:• Light yield of EJ399-04 for one 2 × 2 cm2 cell with two ﬁbers is measured to be 33 ± 2 photoelectrons for minimum ionized particles and 47 ± 3 for 1 GeV/c protons.
• With dE/dx measurement, we proved the performance to identify a proton track with the momentum between 0.6 and 1.2 GeV/c. The probability that a pion is misidentiﬁed as a proton ismeasured to be 3%.
• The attenuation length of the ﬁber in the liquid scintillator was measured to be 304 ± 1 cm.
T476 experiment is very successful and the new detector technology investigated here is promising
as a new neutrino detector. Currently, based on T476 measurement, the K2K detector update isintensively designed, developed, and carried out.

References[1] M. Doucet et al., Nucl. Instr. and meth. A459, 459 (2000).
M. Doucet et al., Nucl. Instr. and meth. A453, 545 (2000).
[2] I. Kato, master thesis, ’Kyoto University’ (2001), unpublished1

Photodetector
Wavelength Shifting Fiberµνµθp
Optical Separators
Liquid Scintillater Container
Figure 1: A schematic picture of the ﬁne segmented liquid scintillator detector. The incident particle
in T476 is a charged particle, either a pion or a proton.

Figure 2: The average energy deposit per cell for 1 GeV/c pions (blue) and 1 GeV/c protons (red).

2