F. Pilo

The AMS-02 electromagnetic calorimeter

Abstract The Electromagnetic Calorimeter (ECAL) of the AMS-02 experiment is a lead-scintillanting fibers sampling calorimeter characterized by high granularity that allows to image the longitudinal and lateral showers development, a key issue to provide high electron/hadron discrimination. The light collection system and the FE electronics are designed to let the calorimeter operate over a wide energy range from few GeV up to 1 TeV. A full-scale prototype of the e.m. calorimeter was tested at Cern in October 2001 using electrons and pions beams with energy ranging from 3 to 100 GeV. Effective sampling thickness, linearity and energy resolution were measured.

The Electromagnetic Calorimeter Trigger System for the AMS-02 Experiment

AMS-02 is an astroparticle experiment designed for a very precise measurement of the primary cosmic rays spectrum. The experiment will operate on board the ISS at a 400 km altitude for a period of about 3 years. The main scientific goals of the experiment are the search for antimatter, for dark matter and the study of gamma rays. In AMS-02 the electromagnetic calorimeter plays a key role for its high capability to measure e+, e- and gamma spectra and to suppress the background generated by p and He nuclei. To directly detect photons the calorimeter must provide a stand alone trigger. The proposed trigger, presented in this article, will have the capability to detect photons with energy above 4 GeV with an efficiency of about 100%. The hardware implementation comprises an analog section, comparing the photomultiplier signal with a given threshold, and a digital section applying the trigger selection algorithm.

A reduced scale e.m. calorimeter prototype for the AMS-02 experiment

A reduced scale prototype of the Pb-SciFi sampling e.m. calorimeter for the AMS-02 experiment was tested at CERN SPS beam line X5 at energies from 5 to 250 GeV. The detector was equalized with minimum ionizing particles and calibrated with electron beams. Effective sampling thickness, linearity and energy resolution were measured (C) 2002 Elsevier Science B.V. All rights reserved.

The Space Qualified Read-Out Electronics for the e.m. Calorimeter (ECAL) of the AMS-02 Experiment

The Electromagnetic Calorimeter (ECAL) of the AMS-02 experiment is a fine grained lead-scintillating fiber sampling calorimeter that allows precise, 3-dimensional imaging of the longitudinal and lateral shower development, providing high electron/hadron discrimination ( ~ 106) in combination with the other AMS-02 detectors and a good energy resolution: ¿E/E ¿ 10%/¿(E( GeV)). The ECAL is instrumented with several custom developed electronics subsystems. In addition to the front-end electronics mounted directly on the calorimeter, specific custom boards were developed for supplying high and low voltages and for data acquisition, slow control and trigger. In this article, the ECAL data acquisition, slow control and trigger electronics are described. These boards are composed of two completely independent and separately powered sectors, each capable of carrying out the same functionality. In the case of any fault it is possible to switch from one sector to the other while maintaining full functionality of the ECAL. As for the entire AMS detector, these cards are Space qualified and have been constructed to meet the performance requirements on orbits during 3-5 years of operation.

Experimental test of a new technique of background suppression in digital mammography

A multiple-exposure technique in digital mammography has been developed to suppress the physical background in the image due to Compton scattering in the body. A pair of X-ray masks, shaped in a projective geometry and positioned upstream and downstream the patient, are coupled mechanically and moved in four steps along a square pattern in order to irradiate the full area in four consecutive short exposures. A proof-of-principle apparatus is under test with a breast phantom and a standard mammographic X-ray unit. Results are reported.

A low-power high dynamic range front-end ASIC for imaging calorimeters

High granularity calorimeters with shower imaging capabilities require dedicated front-end electronics. The ICON_4CH and VA4_PMT chip-set is suitable for very high dynamic range systems with strict noise requirements. The ICON-4CH is a 4 channel input, 12 channel output ASIC designed for use in a multi-anode photomultiplier system with very large dynamic range and low-noise requirements. Each of the four input signals to the ASIC is split equally into three branches by a current conveyor. Each of the three branches is scaled differently: 1:1, 1:8 and 1:80. The signal is read out by a 12 channel low noise / low power high dynamic range charge sensitive preamplifiershaper circuit (VA4-PMT chip), with simultaneous sampleand-hold, multiplexed analog read-out, calibration facilities. Tests performed in our lab with a PMT are reported in terms of linearity, dynamic range and cross-talk of the system.

ELECTROMAGNETIC CALORIMETER FOR THE AMS-02 EXPERIMENT

The electromagnetic calorimeter (ECAL) of the AMS-02 experiment is a 3-dimensional sampling calorimeter, made of lead and scintillating fibers. The detector allows for a high granularity, with 18 samplings in the longitudinal direction, and 72 sampling in the lateral direction. The ECAL primary goal is to measure the energy of cosmic rays up to few TeV, however, thanks to the fine grained structure, it can also provide the separation of positrons from protons, in the GeV to TeV region. A direct measurement of high energy photons with accurate energy and direction determination can also be provided.

Continuum gamma spectra from neutralino annihilation

Abstract Direct observations of cosmic photon spectra from neutralino annihilation at energies above EGRET data might reveal the presence of dark matter in the Universe. Calculations of the rates for the continuum γ channel are reviewed together with the large theoretical uncertainties associated to a number of possible supersymmetric scenarios and different halo models. From an experimental point of view, a very selective rejection of the abundant cosmic ray background is a key issue.