Development of a tracking detector system with multichannel scintillation fibers and PPD
Introduction
An experiment for a measurement of cross-sections for elastic scatterings has been proposed (J-PARC E40). The hyperon–nucleon (YN) scattering experiment has been technically difficult because the life time of hyperons is so short that a hyperon decays before reaching detectors. Therefore, in the past experiments at KEK [1], [2], an imaging device that was a scintillation fiber active target recorded trajectories of a hyperon and a scattered proton. However, statistics is still poor due to several technical problems such as a slow response of the image recording device, backgrounds from carbons in the active target and the difficulty associated with the image analysis. To overcome these problems, a liquid hydrogen target and a detector surrounding the target with Multi-Pixel Photon Counter (MPPC) will be used instead of the active target. There is no backgrounds from carbons by using the liquid hydrogen target. We can solve the kinematics to identify a scattering from detector informations. The new detectors with MPPC are keys of E40.
Fig. 1 shows two key detectors for E40, namely a beamline tracker and a proton detection system, which consist of scintillation fibers with a MPPC readout. E40 will be performed at the K1.8 beamline with Superconducting Kaon Spectrometer (SKS). The entire scheme is shown in Ref. [3]. A beamline fiber tracker with the MPPC readout will be used as a beam particle position detector of the K1.8 beamline spectrometer. The fast time response of a scintillation fiber and MPPC enables us to handle a high intensity beam up to a few tens of MHz. A proton detection system composed of scintillation fiber trackers and BGO calorimeters will be installed around the target to measure scattered particles. In experiment, elastic scattering events are identified from the scattering angle and energy of a scattered proton. For the particle identification, we use a method using an energy deposit () at the fiber tracker and a total energy (E) at BGO. Therefore, the fiber tracker has to measure both the trajectory and . Each fiber and BGO crystal are read by a MPPC. The detection system will be installed in front of the SKS magnet and thus needs to be compact and operational under a magnetic field. MPPC is suited, therefore, for the current system.
A total of five thousand of MPPCs will be used for the beamline fiber tracker and the proton detection system. Such a large number of the readout channel necessitates a readout electronics for handling MPPCs. It is desirable to use an ASIC as a front-end part of the readout. We adopted an ASIC, Extended Analogue Silicon PM Integrated Read-Out Chip (EASIROC) [4], which is developed by Omega group in IN2P3. EASIROC has functions such as a bias adjustment, amplifier, shaper, discriminator and one analog buffer. Data transfer via a network is also required since the data acquisition (DAQ) system in the K1.8 beamline is based on TCP/Ethernet [5]. For this purpose, SiTCP [6] that is an implementation of TCP with a hardware was used as a communication interface.
We developed and tested a prototype proton detection system and a readout electronics with EASIROC. In Section 2, we describe details of the prototype of the proton detection system and its performance obtained from a test experiment. In Section 3, we describe the development of the readout electronics with EASIROC.
Section snippets
Prototype proton detection system and test experiment
The proton detection system has to measure and a kinetic energy of a scattered proton by the fiber tracker and the calorimeter, respectively. To identify scatterings with sufficient signal to noise ratio, their energy resolutions are required to be better than 20% () for 1 MeV and 4% () for 70 MeV, respectively. We made a prototype of the proton detection system to evaluate the performance. Configuration of the prototype detector is shown in Fig. 2. The fiber tracker was constructed from
Prototype readout electronics
Since the proton detection system will have four or five thousand channels, it is difficult to read all MPPCs with a conventional method by using the NIM and VME modules. The readout electronics also must satisfy the following requirements from E40. Since the J-PARC accelerator supplies a continuous beam for the slow extraction, the readout electronics has to be operated in an asynchronous mode. In addition, a function to generate trigger signal is required for the readout electronics because
Summary
We are planning an experiment on scattering as J-PARC E40 with new detectors which consist of scintillation fibers and MPPCs. We developed the prototype of the proton detection system and its readout electronics with EASIROC and SiTCP. The prototype consists of the fiber tracker, which has 24 segments, and a small BGO calorimeter. As the result of the test experiment with a proton beam at CYRIC, the energy resolution of the calorimeter was obtained to be 1.0% () for 70 MeV. On the other
Acknowledgments
We would like to express our thanks to all members of Tohoku University who supported our test experiment. We acknowledge all members involved in electronics development and all members in Omega group in IN2P3 in France. We also acknowledge N. Chiga for his technical supports. The readout electronics project is supported by Open Source Consortium and Detector Technology Project in KEK in Japan. This work was supported by dean's Grant for Exploratory Research (Graduate School of Science at
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