The K2K SciBar detector
Introduction
The KEK-to-Kamioka long-baseline neutrino experiment (K2K) [1] started taking data in 1999. An almost pure muon neutrino beam with average energy of 1.3 GeV is produced with the KEK 12 GeV proton synchrotron and directed toward the Super-Kamiokande detector (SK) located at Kamioka, 250 km away from KEK. The neutrino flux and energy spectrum at SK is estimated from the flux measured by near detectors located 300 m downstream of the production target. The number of events and the spectral shape at SK are compared with the expectations to study neutrino oscillations. The latest K2K results [2] indicate neutrino oscillation, and are consistent with the SK results [3]. In K2K, the neutrino energy at the oscillation maximum is expected to be 0.6 GeV.
A new near detector, Scintillator Bar (SciBar), was constructed in Summer 2003 to upgrade the near detectors. A main motivation of the new detector is to improve the measurement of the neutrino energy spectrum by using Charged Current Quasi Elastic interaction (CCQE, ). In order to select CCQE interaction with high purity and high efficiency and to suppress other interactions such as inelastic interactions with pions (), the detector is designed to have high efficiency for all charged particles produced in the interaction. The detector consists of plastic scintillator strips with fine segmentation. The scintillator itself is a neutrino target and has no dead region. Due to the fine segmentation of the detector, short tracks down to 10 cm long can be detected. The detector also has a capability of particle identification (especially for protons and pions) with information by measuring the energy deposition in each strip.
In addition, we expect to provide many new results for neutrino interactions in the 1 GeV region with SciBar.
Section snippets
The SciBar detector
Fig. 1 shows a schematic view of SciBar. SciBar consists of two components: a tracking calorimeter made of scintillator strips and an electromagnetic calorimeter called Electron Catcher. Table 1 shows the design for each component. The SciBar tracker consists of 14,848 extruded scintillator strips, each of dimension . The scintillator strips are arranged in 64 layers. Each layer consists of two planes, with 116 strips glued together to give horizontal and vertical position. The
Basic performance
SciBar is taking data since October 2003. Pedestal, LED and cosmic-ray data are taken simultaneously with beam data for calibration and monitoring. The gain is monitored and corrected by LED, so the energy deposition is measured within a stability better than 1% by the gain correction. By using cosmic-ray data the attenuation lengths of the WLS fibers are measured as shown in Fig. 2. The average attenuation length is 350 cm which is consistent with the measurement before installation. Fig. 3
Summary
The SciBar detector is designed and constructed to measure the neutrino energy spectrum around 1 GeV as the near detector of the K2K experiment, and has been commissioned successfully and on schedule. Now SciBar is working stably and with good performance.
Acknowledgements
We gratefully acknowledge the assistance of T. Haff and P. Rovegno during the construction of the detector. We would like to express our appreciation for support by M. Taino during the construction work. This work has been undertaken with the support of the Ministry of Education, Culture, Sports, Science and Technology, the Government of Japan and its grants for Scientific Research, the Japanese Society for the Promotion of Science, the US Department of Energy, the Korean Research Foundation,
References (6)
Nucl. Phys. Proc.
(1997)Phys. Lett. B
(2001)Atomospheric neutrino oscillations in SK-I