M. Ziembicki

Characterization and Simulation of the Response of Multi Pixel Photon Counters to Low Light Levels

The calorimeter, range detector and active target elements of the T2K near detectors rely on the Hamamatsu Photonics Multi-Pixel Photon Counters (MPPCs) to detect scintillation light produced by charged particles. Detailed measurements of the MPPC gain, afterpulsing, crosstalk, dark noise, and photon detection efficiency for low light levels are reported. In order to account for the impact of the MPPC behavior on T2K physics observables, a simulation program has been developed based on these measurements. The simulation is used to predict the energy resolution of the detector.

The T2K Side Muon Range Detector (SMRD)

The T2K experiment is a long baseline neutrino oscillation experiment aiming to observe the appearance ofe in a �µ beam. The �µ beam is produced at the Japan Proton Accelerator Research Complex (J-PARC), observed with the 295 km distant Super- Kamiokande Detector and monitored by a suite of near detectors at 280m from the proton target. The near detectors include a magnetized off-axis detector (ND280) which measures the un-oscillated neutrino flux and neutrino cross sections. The present paper describes the outermost component of ND280 which is a side muon range detector (SMRD) composed of scintillation counters with embedded wavelength shifting fibers and Multi-Pixel Photon Counter read-out. The components, performance and response of the SMRD are presented.

Scintillator counters with WLS fiber/MPPC readout for the side muon range detector (SMRD)of the T2K experiment

The T2K neutrino experiment at J-PARC uses a set of near detectors to measure the properties of an unoscillated neutrino beam and neutrino interaction cross-sections. One of the sub-detectors of the near-detector complex, the side muon range detector (SMRD), is described in the paper. The detector is designed to help measure the neutrino energy spectrum, to identify background and to calibrate the other detectors. The active elements of the SMRD consist of 0.7 cm thick extruded scintillator slabs inserted into air gaps of the UA1 magnet yokes. The readout of each scintillator slab is provided through a single WLS fiber embedded into a serpentine-shaped groove. Two Hamamatsu multi–pixel avalanche photodiodes (MPPCs) are coupled to both ends of the WLS fiber. This design allows us to achieve a high MIP detection efficiency of greater than 99%. A light yield of 25–50 p.e./MIP, a time resolution of about 1 ns and a spatial resolution along the slab better than 10 cm were obtained for the SMRD counters.

Monte Carlo study of the time resolution of scintillating fibre detectors

This paper presents the results of a Monte Carlo study of the time resolution of a scintillating fibre detector and analyses its dependence on the various aspects of detector construction. The estimations of the theoretical time resolutions for detectors with different numbers of fibre layers and different types of acrylic-based fibre coatings are presented. The method is suggested to decrease the rate counting effects encountered in high rate applications. It has been observed that for dual cladding fibres with a fluorinated polymer used for the outer cladding, the most significant factor contributing to the time resolution is the number of fibre layers, with the fibre coating being the marginal one. Another observation shows that the introduction of a gap between the fibre and the photomultiplier glass window allows the reduction of the number of photoelectrons by 25% with only a slight decrease in the time resolution, which may be helpful in decreasing the pulse pile-up effects and the photomultiplier gain, commonly observed under high rate conditions.

DEAD TIME MEASUREMENT BY TWO-SOURCE METHOD – OPTIMIZATION OF MEASUREMENT TIME DIVISION

The article presents the analysis of the dead time measurement using two sources for a non-paralyzable detector. It determined the optimum division of count rate measurement time between both source measurement and a single source one. Results of the work can be used to optimize dead time measurement for systems which count photons or particles.

GAIN PREDICTION THEORY OF SINGLE FOIL GAS ELECTRON MULTIPLIER DETECTOR

Gain prediction theory of single foil Gas Electron Multiplier detector was developed. Gas electron multiplier (GEM) detector with single foil was developed. Soft X-ray spectra with an energy of 5.9 keV emitted by the isotope Fe-55 were measured. On this basis, the dependence of gain and energy resolution from the detector voltage was determined. The simple theory of gain dependence on various detector parameters was developed. Preliminary results of the study confirmed the potential usefulness of the GEM detector as a substitute for the multiwire proportional chamber.

Fully Automated Machine for Scanning SIMP detectors

A fully automated measurement system has been built to measure uniformmity of the parameters of SiPM detectors with very high pixel densities. It has a light source with a microfocus spot (FWHM = 3 μm at the detector surface) and a precise positioning system (1 μm accuracy). A temperature control system with water cooling has been used to set the temperature of the measured detector. Finally, a low noise, custom made front-end amplifier has been designed to receive SiPM signals. This paper presents the MAPD-3N detector measurement results uniformity of gain and relative photon detection efficiency (PDE).

An automated system for scanning micropixel avalanche photodiodes with a fast amplifier

Silicon Photomultipliers (SiPMs) are rapidly developing photosensitive devices which are already used as an alternative to photomultipliers (PMT) in the newly developed calorimeters for high-energy physics. Many measurement results and SIPMs parameters based on signal amplitude histograms analysis have been published. Author presents a special automated system for scanning SIPMs surfaces with a fast amplifier. The system has been developed in order to examine shape of signal response dependency on position of photons hits on the surface of the detector.

Construction, performance and modeling of a compact SciFi hodoscope for use in detector testing at various test beams

It is quite common practice to test detectors for high energy physics experiments using test beams, produced at various accelerator facilities. A key component of every test setup is a trigger system, which usually has to be provided by the team preparing the test. Therefore, a compact scintillating fiber detector has been built, with the aim of working as a position sensitive trigger device for testing Shashlyk-type modules of a new electromagnetic calorimeter (ECAL0), being built for the COMPASS experiment. A description of the construction of the detector is presented, followed by its performance evaluation using a low-intensity electron beam from the ELSA accelerator and electrons at the T10 test beam in CERN. The detector was adapted for use with acquisition system based on an 80 MSPS, 12-bit analog-to-digital converters. An effort has been made to develop a full Monte-Carlo model of the system, which includes simulation of particle interactions, detector optics, photomultiplier, signal acquisition electronics (both ADC and shaping, incl. noise simulation) and finally signal quantization, ADC non-linearity and its clock jitter.

Study of a 3×3 module array of the ECAL0 calorimeter with an electron beam at the ELSA

ECAL0 is a new electromagnetic calorimeter designed for studying generalized parton distributions at the COMPASS II experiment at CERN. It will be located next to the target and will cover larger photon angles (up to 30 degrees). It is a modular high-granularity Shashlyk device with total number of individual channels of approx. 1700 and readout based on wavelength shifting fibers and micropixel avalanche photodiodes. Characterization of the calorimeter includes tests of particular sub-components, tests of complete modules and module arrays, as well as a pilot run of a fully-functional, quarter-size prototype in the COMPASS experiment. The main goals of the tests on low-intensity electron beam at the ELSA accelerator in Bonn were: to provide energy calibration using electrons, to measure angular response of the calorimeter and to perform an energy scan to cross-check previously collected data. A dedicated measurement setup was prepared for the tests, including a 3x3 array of the ECAL0 modules, a scintillating-fibre hodoscope and a remotely-controlled motorized movable platform. The measurements were performed using three electron energies: 3.2 GeV, 1.6 GeV and 0.8 GeV. They include a calibration of the whole detector array with a straight beam and multiple angular scans.