R. Rando

Pre-launch estimates for GLAST sensitivity to dark matter annihilation signals

We investigate the sensitivity of the Gamma-ray Large Area Space Telescope (GLAST) for indirectly detecting weakly interacting massive particles (WIMPs) through the γ-ray signal that their pair ann ...

Cosmic-ray electron-positron spectrum from 7 GeV to 2 TeV with the Fermi Large Area Telescope

We present a measurement of the cosmic-ray electron+positron spectrum between 7 GeV and 2 TeV performed with almost seven years of data collected with the Fermi Large Area Telescope. We find that the spectrum is well fit by a broken power law with a break energy at about 50 GeV. Above 50 GeV, the spectrum is well described by a single power law with a spectral index of 3.07 ± 0.02 (stat+syst) ± 0.04 (energy measurement). An exponential cutoff lower than 1.8 TeV is excluded at 95% CL. PACS numbers: 98.70.Sa, 96.50.sb, 95.85.Ry, 95.55.Vj

Search for Cosmic-Ray Electron and Positron Anisotropies with Seven Years of Fermi Large Area Telescope Data

The Large Area Telescope on board the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events since the beginning of its operation. Potential anisotropies in the arrival directions of cosmic-ray electrons or positrons could be a signature of the presence of nearby sources. We use almost seven years of data with energies above 42xa0GeV processed with the Pass 8 reconstruction. The present data sample can probe dipole anisotropies down to a level of 10^{-3}. We take into account systematic effects that could mimic true anisotropies at this level. We present a detailed study of the event selection optimization of the cosmic-ray electrons and positrons to be used for anisotropy searches. Since no significant anisotropies have been detected on any angular scale, we present upper limits on the dipole anisotropy. The present constraints are among the strongest to date probing the presence of nearby young and middle-aged sources.

Radiation testing of GLAST LAT tracker ASICs

GLAST is a next generation high-energy gamma-ray space observatory designed for observations of celestial gamma-ray sources in the energy band extending from 10 MeV to more than 100 GeV. The main instrument, the Large Area Telescope (LAT), consists of a microstrip silicon Tracker, a Calorimeter, an Anticoincidence Detector and the DAQ system. This study summarizes the results obtained during the radiation testing of the ASIC chips used in the LAT Tracker. Both Single Event Effects (SEE) and Total Dose (TID) tests have been performed, as part of the Radiation Hardness Assurance (RHA) for the planned 5 year mission. Heavy ion SEE tests have been performed at the SIRAD irradiation facility at the INFN Laboratories of Legnaro, Italy (LNL) and at the Texas A&M University (TAMU) Cyclotron Institute, with LET values ranging up to /spl sim/80 MeV/spl middot/cm/sup 2//mg. The tolerance of the chips to ionizing radiation has been evaluated with heavy ions, and by irradiating chips with the spherical /sup 60/Co gamma source of the LNL CNR-FRAE laboratory.

Lithium ion irradiation of standard and oxygenated silicon diodes

The next generation silicon detectors for future very high luminosity colliders or a possible LHC upgrade scenario will require radiation-hard detectors for fluences up to 10/sup 16/ 1-MeV equivalent neutrons/cm/sup 2/. These high fluences present strong constraints because long irradiation times are required at the currently available proton irradiation facilities. Energetic (58 MeV) Lithium ions present a nonionizing energy loss higher than protons and neutrons, and could consequently be a new promising radiation source for investigating the radiation hardness of silicon detectors up to very high particle fluences. Starting from this premise, we have investigated the degradation, as measured by the leakage current density increase and depletion voltage variations in the short- and long-term characteristics, induced by 58 MeV Li ions in state-of-the-art silicon diodes processed by two different manufacturers on standard and oxygenated silicon substrates. Finally, the correlation between the radiation damage induced by 58 MeV Li ions and 27 MeV protons is discussed.

Neutron irradiation effects on standard and oxygenated silicon diodes

Silicon diodes processed on standard and oxygenated silicon substrates by two different manufacturers have been irradiated by neutrons in a nuclear reactor and by the /sup 9/Be(d,n)/sup 10/B nuclear reaction. The leakage current density (J/sub D/) increase is linear with the neutron fluence. J/sub D/ and its annealing curve at 80/spl deg/C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. On the contrary, standard devices from one manufacturer present the lowest acceptor introduction rate (/spl beta/) for the effective substrate doping concentration (N/sub eff/), showing that the /spl beta/ dependence on the particular process can be important, overtaking the small substrate oxygenation effect. Finally, the average saturation value of the N/sub eff/ reverse annealing is slightly lower for the oxygenated samples, pointing out a positive effect of the substrate oxygenation even for devices irradiated by neutrons.

New evidence of dominant processing effects in standard and oxygenated silicon diodes after neutron irradiation

Abstract Silicon diodes processed on standard and oxygenated silicon substrates by three different manufacturers have been irradiated by neutrons in a nuclear reactor. The leakage current density ( J D ) increase is linear with the neutron fluence. J D and its annealing curve at 80°C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. The acceptor introduction rate ( β ) of the effective substrate doping concentration ( N eff ) is independent from the oxygen concentration when standard and oxygenated devices from the same manufacturer are considered. On the contrary, β significantly varies from one manufacturer to another showing that the β dependence on the particular process can be important, overtaking the small substrate oxygenation effect. Finally, the average saturation value of the N eff reverse annealing is slightly lower for the oxygenated samples, pointing out a positive effect of the substrate oxygenation even for devices irradiated by neutrons.

INFN Camera demonstrator for the Cherenkov Telescope Array

The Cherenkov Telescope Array is a world-wide project for a new generation of ground-based Cherenkov telescopes of the Imaging class with the aim of exploring the highest energy region of the electromagnetic spectrum. With two planned arrays, one for each hemisphere, it will guarantee a good sky coverage in the energy range from a few tens of GeV to hundreds of TeV, with improved angular resolution and a sensitivity in the TeV energy region better by one order of magnitude than the currently operating arrays. In order to cover this wide energy range, three different telescope types are envisaged, with different mirror sizes and focal plane features. In particular, for the highest energies a possible design is a dual-mirror Schwarzschild-Couder optical scheme, with a compact focal plane. A silicon photomultiplier (SiPM) based camera is being proposed as a solution to match the dimensions of the pixel (angular size of ~ 0.17 degrees). INFN is developing a camera demonstrator made by 9 Photo Sensor Modules (PSMs, 64 pixels each, with total coverage 1/4 of the focal plane) equipped with FBK (Fondazione Bruno Kessler, Italy) Near UltraViolet High Fill factor SiPMs and Front-End Electronics (FEE) based on a Target 7 ASIC, a 16 channels fast sampler (up to 2GS/s) with deep buffer, self-trigger and on-demand digitization capabilities specifically developed for this purpose. The pixel dimensions of

Energy Calibration of Cherenkov Telescopes using GLAST Data

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Silicon detectors for γ-ray and β-spectroscopy

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