Y. Musienko

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.

Characterization of avalanche photodiodes for calorimetry applications

Silicon avalanche photodiodes (APDs) have been studied extensively as photosensor candidates for the electromagnetic calorimeter of the CMS detector at LHC. This work presents the measurements of APDs from Hamamatsu and EG&G, with particular emphasis on multiplication factor, spectral response, excess noise factor as well as their dependence on wavelength. The results are compared to the theoretical predictions. Results on the stability of APD gain to bias and temperature drift are also presented. ( 1999 Elsevier Science B.V. All rights reserved.

On the limited amplitude resolution of multipixel Geiger-mode APDs

The limited number of active pixels in a Geiger-mode Avalanche Photodiode (G-APD) results not only in a non-linearity but also in an additional fluctuation of its response. Both these effects are taken into account to calculate the amplitude resolution of an ideal G-APD, which is shown to be finite. As one of the consequences, the energy resolution of a scintillation detector based on a G-APD is shown to be limited to some minimum value defined by the number of pixels in the G-APD. PACS numbers: 85.60.GzThe limited number of active pixels in a Geiger-mode Avalanche Photodiode (G-APD) results not only in a non-linearity but also in an additional fluctuation of its response. Both these effects are taken into account to calculate the amplitude resolution of an ideal G-APD, which is shown to be finite. As one of the consequences, the energy resolution of a scintillation detector based on a G-APD is shown to be limited to some minimum value defined by the number of pixels in the G-APD.

Beam tests of lead tungstate crystal matrices and a silicon strip preshower detector for the CMS electromagnetic calorimeter

Tests of lead tungstate crystal matrices carried out in high-energy electron beams in 1996, using new crystals, new APDs and an improved test set-up, confirm that an energy resolution of better than 0.6% at 100 GeV can be obtained when the longitudinal uniformity of the struck crystal is adequate. Light loss measurements under low dose irradiation are reported. It is shown that there is no loss of energy resolution after irradiation and that the calibration change due to light loss can be tracked with a precision monitoring system. Finally, successful tests with a preshower device, equipped with silicon strip detector readout, are described.

Investigation of the avalanche photodiodes for the CMS electromagnetic calorimeter operated at high gain

Abstract Avalanche Photodiodes (APD) with improved characteristics were developed by Hamamatsu Photonics for the Electromagnetic Calorimeter of the CMS experiment. This report presents measurements of the latest generation of APDs, which are capable to operate at high gains (∼2000).

The CMS electromagnetic calorimeter

The CMS electromagnetic calorimeter, containing 80,000 scintillating lead tungstate crystals is designed to give excellent energy resolution in the LHC environment. An overview of the design is given and the current status of the project presented.

SSPM Readout of LSO, (Lu-Y)AP:Ce and PWO-II Pixels for PET Detector Modules

We have studied the performance of recently developed solid state photomultipliers (SSPMs) with 2.1times2.1 mm2 sensitive area as a readout for small LSO, (Lu-Y)AP:Ce and PWO-II scintillator crystals. The SSPM is based on the p+-p-n+ structure which was optimized for blue/UV light detection. It operates at a gain of >105 and shows >25% photon detection efficiency in the 380-600 nm spectral range. Energy and timing spectra were measured using a 22Na gamma source. Energy resolutions of 13%, 25% and 50% FWHM were measured for 511 keV gammas with the LSO, (Lu-Y)AP:Ce and PWO-II scintillator crystals respectively. A coincidence timing resolution of 710 ps (FWHM) was measured between two identical LSO+SSPM modules.

Studies of Lead Tungstate Crystal Matrices in High-Energy Beams for the CMS Electromagnetic Calorimeter at the LHC

Using matrices of lead tungstate crystals, energy resolutions better than 0.6% at 100 GeV have been achieved in the test beam in 1995. It has been demonstrated that a lead tungstate electromagnetic calorimeter read out by avalanche photodiodes can consistently achieve the excellent energy resolutions necessary to justify its construction in the CMS detector. The performance achieved has been understood in terms of the properties of the crystals and photodetectors.

Recent progress on cooled avalanche photodiodes for single photon detection

Abstract Recent results on the properties of cooled avalanche photodiodes for single photon detection are presented. Results from Hamamatsu silicon photodiodes, originally developed as radiation-hard photodetectors for high energy physics experiments, are extremely encouraging. Gains of approximately 10,000 can be achieved with the APD operating in proportional mode. Together with a low noise amplifier they allow photon counting with extremely high efficiency and very low noise making cold APDs almost ideal single photon detectors. Operation of APDs in Geiger mode is also reported, together with measurements of detection efficiency and noise as function of operating voltage. Prospects and hopes for future work are briefly summarized.

Studies of neutron irradiation of avalanche photodiodes using 252Cf

Abstract Results on the radiation hardness of photodiodes to fast neutrons are presented. Four photodiodes (three avalanche photodiodes from two manufacturers, and one PIN photodiode) were exposed to neutrons from a 252 Cf source at Oak Ridge National Laboratory. The effects of this radiation on many parameters such as gain, intrinsic dark current, quantum efficiency, noise, capacitance, and voltage and temperature coefficients of the gain for these devices for fluences up to ∼2×10 13 neutrons/cm 2 are shown and discussed. While degradation of APDs occurred during neutron irradiation, they remained photosensitive devices with gain.