SiPM and front-end electronics development for Cherenkov light detection

The Italian Institute of Nuclear Physics (INFN) is involved in the development of a demonstrator for a SiPM-based camera for the Cherenkov Telescope Array (CTA) experiment, with a pixel size of 6$\times$6 mm$^2$. The camera houses about two thousands electronics channels and is both light and compact. In this framework, a R&D program for the development of SiPMs suitable for Cherenkov light detection (so called NUV SiPMs) is ongoing. Different photosensors have been produced at Fondazione Bruno Kessler (FBK), with different micro-cell dimensions and fill factors, in different geometrical arrangements. At the same time, INFN is developing front-end electronics based on the waveform sampling technique optimized for the new NUV SiPM. Measurements on 1$\times$1 mm$^2$, 3$\times$3 mm$^2$, and 6$\times$6 mm$^2$ NUV SiPMs coupled to the front-end electronics are presentedComment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

Internal alignment and position resolution of the silicon tracker of DAMPE determined with orbit data

The DArk Matter Particle Explorer (DAMPE) is a space-borne particle detector designed to probe electrons and gamma-rays in the few GeV to 10 TeV energy range, as well as cosmic-ray proton and nuclei components between 10 GeV and 100 TeV. The silicon-tungsten tracker-converter is a crucial component of DAMPE. It allows the direction of incoming photons converting into electron-positron pairs to be estimated, and the trajectory and charge (Z) of cosmic-ray particles to be identified. It consists of 768 silicon micro-strip sensors assembled in 6 double layers with a total active area of 6.6 m$^2$. Silicon planes are interleaved with three layers of tungsten plates, resulting in about one radiation length of material in the tracker. Internal alignment parameters of the tracker have been determined on orbit, with non-showering protons and helium nuclei. We describe the alignment procedure and present the position resolution and alignment stability measurements

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 $6\times6$ mm$^2$ lead to a very compact design with challenging problems of thermal dissipation. A modular structure, made by copper frames hosting one PSM and the corresponding FEE, has been conceived, with a water cooling system to keep the required working temperature. The actual design, the adopted technical solutions and the achieved results for this demonstrator are presented and discussed.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons

High energy cosmic ray electrons plus positrons (CREs), which lose energy quickly during their propagation, provide an ideal probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been directly measured up to $\sim 2$ TeV in previous balloon- or space-borne experiments, and indirectly up to $\sim 5$ TeV by ground-based Cherenkov $\gamma$-ray telescope arrays. Evidence for a spectral break in the TeV energy range has been provided by indirect measurements of H.E.S.S., although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range $25~{\rm GeV}-4.6~{\rm TeV}$ by the DArk Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The majority of the spectrum can be properly fitted by a smoothly broken power-law model rather than a single power-law model. The direct detection of a spectral break at $E \sim0.9$ TeV confirms the evidence found by H.E.S.S., clarifies the behavior of the CRE spectrum at energies above 1 TeV and sheds light on the physical origin of the sub-TeV CREs.Comment: 18 pages, 6 figures, Nature in press, doi:10.1038/nature2447

Precision Measurement of the Boron to Carbon Flux Ratio in Cosmic Rays from 1.9 GV to 2.6 TV with the Alpha Magnetic Spectrometer on the International Space Station

Knowledge of the rigidity dependence of the boron to carbon flux ratio (B/C) is important in understanding the propagation of cosmic rays. The precise measurement of the B/C ratio from 1.9 GV to 2.6 TV, based on 2.3 million boron and 8.3 million carbon nuclei collected by AMS during the first 5 years of operation, is presented. The detailed variation with rigidity of the B/C spectral index is reported for the first time. The B/C ratio does not show any significant structures in contrast to many cosmic ray models that require such structures at high rigidities. Remarkably, above 65 GV, the B/C ratio is well described by a single power law R[superscript Δ] with index Δ=-0.333±0.014(fit)±0.005(syst), in good agreement with the Kolmogorov theory of turbulence which predicts Δ=-1/3 asymptotically.National Science Foundation (U.S.) (Grants 1455202 and 1551980)Wyle Research (Firm) (Grant 2014/T72497)United States. National Aeronautics and Space Administration (NASA Earth and Space Science Fellowship Grant HELIO15F-0005

The Gamma-Flash Program: high-energy radiation and particles in thunderstorms, lightning, and terrestrial gamma-ray flashes

The Gamma-Flash program, funded by the Italian Space Agency (ASI) and led by the National Institute for Astrophysics (INAF), aims to study high-energy emissions related to thunderstorms, such as terrestrial gamma-ray flashes (TGFs) and gamma-ray glows. The program led to the development of two main detection systems: a ground-based system, installed at the “O. Vittori” Observatory on top of Mt. Cimone (Northern-Central Italy), and an airborne payload, installed on a Cessna Citation Mustang aircraft, for in-flight campaigns. The ground-based detection system consists of five γ-ray and three neutron detectors, and it has been collecting data from Jul 2022 to Oct 2023, overall experiencing 95 days of thunderstorm activity (36% of the total experiment lifetime). During this first observational survey, a gamma-ray glow of ∼ 1.5 min was revealed. The event light curve shows an abrupt interruption at the end, coinciding with the occurrence of a CG lightning discharge, that took place within 2 km from the detectors. The avionic payload consists of 6 γ-ray and 2 neutron detectors. The purpose of this second payload is to collect additional data by flying nearby convective systems, in order to reveal high-energy emissions directly from the sky. To date, two flights have been conducted: the first was an operational test flight on December 22, 2023, lasting 2 hours under clear sky conditions. The second flight, on June 4, 2024, lasted approximately 2.5 hours and took place during thunderstorm activity in Northern Italy. Additional flights are planned for the summer of 2024

Assembly and performance of SiPM arrays for the prototype SCT proposed for CTA

The Near Ultraviolet High Density (NUV-HD) SiPMs produced by Fondazione Bruno Kessler have been employed to develop 16-pixel optical units to equip the focal plane of the prototype Schwarzschild–Couder Telescope (pSCT) proposed as a possible design for the Medium-Sized Telescope of the Cherenkov Telescope Array Observatory. After the assembly procedure, the optical units were tested and characterized to study their performance and homogeneity in terms of gain and dark count rate. In this work, we report on the assembly procedure and on the laboratory tests performed on different production of NUV-HD and the selection we made for the best quality sensors to be used in the installation on the telescope camera. Currently 36 NUV-HD3 optical units have been successfully integrated on the pSCT camera, together with 64 HAMAMATSU MPPCs. An upgrade of the pSCT camera is foreseen over the next years when the full focal plane is expected to be equipped entirely with FBK NUV-HD3 SiPMs, for a total of 11328 pixels

Upgrading the prototype Schwarzschild-Couder telescope camera to a wide-field, high-resolution instrument

The Schwarzschild-Couder Telescope (SCT) is a candidate technology for a medium-sized telescope within the Cherenkov Telescope Array. It is expected to yield substantial improvements in field of view and image resolution compared to traditional telescopes based on Davies-Cotton optics. To match the improved optical resolution, challenging requirements of high channel count and density at low power consumption have to be met by the camera. An initial prototype camera, with 1600 pixels spanning a 2.7? field of view, was installed on the prototype SCT in 2018. A project is now underway to upgrade the camera by increasing its pixel count and field of view by factors of 7 and 3, respectively (to 11,328 pixels and 8.0?). At the same time, the electronics design is being improved in order to lower the gamma-ray energy threshold and thereby provide an instrument especially well-suited for scientific studies related to extended sources and multimessenger astronomy