Luca Ghislotti

GAPS (General AntiParticle Spectrometer) is a stratospheric balloon experiment designed to detect low-energy cosmic ray antinuclei (<0.25 GeV) as an indirect signature of dark matter. The experiment exploits an innovative particle identification approach based on the formation of an excited atom and its consequent de-excitation and decay. GAPS will provide unprecedented sensitivity to cosmic antideuterons, an antiproton spectrum in a hitherto unexplored energy range and high sensitivity to cosmic antihelium. The first flight is foreseen to take place from the McMurdo Station in Antarctica during the austral summer of 2024. The instrument is currently undergoing integration and calibration in anticipation of launch. In this paper, the latest tracker electronics energy threshold calibration results will be presented.

The General Antiparticle Spectrometer (GAPS) is a balloon-borne experiment designed to search for low-energy cosmic-ray antinuclei as a potential indirect signature of dark matter. Over the course of at least three long-duration flights over Antarctica, it will explore the sub-250 MeV/n energy range with sensitivity to antideuterons and antihelium, while also extending antiproton measurements below 100 MeV. The instrument features a tracker built from more than one thousand lithium-drifted silicon detectors, each read out by a dedicated custom integrated circuit. With the first flight scheduled for the austral summer of 2025, a new prototype chip, ANTARES4, has been developed using a commercial 65 nm complementary metal-oxide semiconductor process for use in the second flight. It integrates eight independent analog channels, each incorporating a low-noise charge-sensitive amplifier with dynamic signal compression, a CR–RC shaping stage with eight selectable peaking times, and on-chip calibration circuitry. The charge-sensitive amplifier uses metal-oxide semiconductor feedback elements with voltage-dependent capacitance to support the wide input energy range from 10 keV to 100 MeV. Four alternative feedback implementations are included to compare performance and design trade-offs. Leakage current compensation up to 200 nA per detector strip is provided by a Krummenacher current-feedback network. This paper presents the design and architecture of ANTARES4, highlighting the motivations, design drivers, and performance requirements that guided its development.

The General Antiparticle Spectrometer (GAPS) is a balloon-borne experiment designed to perform three long-duration flights from Antarctica to search for low-energy cosmic antinuclei, in particular antideuterons, as an indirect probe of dark matter. Its detection method is based on the formation and decay of exotic atoms, identified through the emission of characteristic X-rays and subsequent annihilation into secondary particles. At the core of the instrument is the silicon tracker, composed of lithium-drifted silicon detectors operated at −40 °C and read out by a custom application-specific integrated circuit (ASIC), SLIDER32, implemented in a 180 nm CMOS technology. This thesis reports on the integration, calibration, and validation of the SLIDER32-based tracker readout electronics. Laboratory characterization of a single tracker module with an Americium-241 source and cosmic muons was complemented by calibration and testing of the full tracker in its flight configuration, leading to the first X-ray spectrum acquisition from a Cadmium-109 source. These activities formed part of the integration and testing phase for the first flight, culminating in full instrument assembly and validation during the 2024 Antarctic campaign. Building on this experience, the work presents the design and characterization of a new prototype integrated circuit conceived as an upgrade to SLIDER32: the ANTARES4 chip, fabricated in 65 nm CMOS technology. The device integrates eight analog channels up to the shaping stage and implements dynamic signal compression techniques based on dynamic-threshold MOS transistors, together with an improved detector leakage current compensation circuit at the preamplifier input. Laboratory characterization provides an initial validation of these design choices, laying the foundations for the next-generation tracker readout system to be adopted in the second flight of the experiment.

This paper presents the design and experimental characterization of a low-noise analog readout channel implemented in a commercial 65 nm CMOS technology. The circuit is intended for the readout of large-area silicon-strip detectors used in astroparticle physics tracker applications and is based on a charge-sensitive amplifier followed by a unipolar semi-Gaussian shaping filter. Dynamic signal compression is achieved by exploiting the nonlinear behavior of a dynamic-threshold MOS (DTMOS) capacitor in the amplifier feedback network, resulting in a gain that decreases with increasing input signal and enabling a wide dynamic range while preserving high resolution at low deposited charge. The amplifier also incorporates an enhanced Krummenacher feedback network that, through an additional bulk-controlled device, compensates detector leakage currents up to 200 nA. The design criteria and circuit architecture are described, with particular emphasis on the DTMOS feedback capacitor and the improved charge restoration network. Experimental results are presented to validate the proposed design and support the adopted architectural choices.