General Antiparticle Spectrometer Research Articles

Design and application of multi-loop capillary heat pipes to cool GAPS silicon detectors

This paper presents the basic design of a thermal control system that can cool the >1000 semiconducting silicon detectors for the General Anti-Particle Spectrometer (GAPS) balloon-borne cosmic antiparticle mission. To identify antiparticles with sufficient energy resolution, it is essential to cool the detectors to operating temperatures below −40°C. To provide such cooling, we developed a novel multi-loop capillary heat pipe (MCHP) which merges gravitational force, capillary force, and self-oscillating driving force to flow a refrigerant effectively in thin tubes. The MCHP is suitable to cool a number of widely distributed detectors with a minimum mass, minimum power consumption, and large thermal conductivity, compared to any other techniques such as traditional pumped circulating systems. Experimental results using a two-meter-scale full-size model verified that the MCHP can meet all the requirements. The unique MCHP technique can be applied to thermally controlling other large particle/nuclear instruments.

The GAPS experiment: Low-energy antinuclei measurements for dark matter searches

GAPS (General Anti-Particle Spectrometer) is a balloon-borne experiment designed to measure low-energy (<0.25 GeV/n) cosmic antinuclei (i.e., antiprotons, antideuterons, and antihelium nuclei) as a signature of dark matter annihilation or decay. According to viable beyond-the-Standard Model theories, the predicted dark matter signal in the low-energy antideuterons and antihelium nuclei channels is several orders of magnitude higher than the astrophysical background. The experiment will conduct a series of at least three long-duration balloon flights at high altitudes from Antarctica. The instrument is composed of a Si(Li) tracker surrounded by a Time-of-Flight system made of plastic scintillators. GAPS uses the novel exotic-atom detection technique in which an antinucleus is captured by the tracker material and forms an exotic atom. This excited exotic atom decays within the order of nanoseconds emitting X-rays at specific energies defined by the atomic transitions and annihilates emitting secondary particles (mainly pions and protons). The measured quantities (e.g., dE/dx, time of flight, annihilation vertex position, X-rays energies, etc.) allow for identifying antinuclei with high precision.

Sensitivity of the GAPS experiment to low-energy cosmic-ray antiprotons

The General Antiparticle Spectrometer (GAPS) is an upcoming balloon mission to measure low-energy cosmic-ray antinuclei during at least three ∼35-day Antarctic flights. With its large geometric acceptance and novel exotic atom-based particle identification, GAPS will detect ∼500 cosmic antiprotons per flight and produce a precision cosmic antiproton spectrum in the kinetic energy range of ∼0.07−0.21GeV/n at the top of the atmosphere. With these high statistics extending to lower energies than any previous experiment, and with complementary sources of experimental uncertainty compared to traditional magnetic spectrometers, the GAPS antiproton measurement will be sensitive to dark matter, primordial black holes, and cosmic ray propagation. The antiproton measurement will also validate the GAPS antinucleus identification technique for the antideuteron and antihelium rare-event searches. This analysis demonstrates the GAPS sensitivity to cosmic-ray antiprotons using a full instrument simulation and event reconstruction, and including solar and atmospheric effects.

A mixed-signal processor for X-ray spectrometry and tracking in the GAPS experiment

This paper reports the design and experimental results from the characterization of an integrated circuit developed for the readout of the X-ray spectrometer and tracking system of the General AntiParticle Spectrometer (GAPS) balloon mission. GAPS will search for an indirect signature of dark matter through the detection of low-energy (<0.25 GeV/n) cosmic-ray antiprotons, antideuterons and antihelium nuclei. The ASIC, named SLIDER32 (32 channels Si-LI DEtector Readout ASIC), was fabricated in a 180 nm CMOS technology and is comprised of 32 analog readout channels, an 11-bit SAR ADC and a digital back-end section which is responsible for defining channel settings and for sending digital information to the data acquisition system. The core of the ASIC is a low-noise analog channel implementing a dynamic signal compression which makes the chip suitable for resolving both X-rays in the range of 20 to 100 keV and charged particles with energy deposition of up to 100 MeV. It features an energy resolution of 4 keV FWHM in the 20–100 keV range with a 40 pF detector capacitance, to clearly distinguish X-rays from antiprotonic or antideuteronic exotic atoms. The readout electronics of the ASIC will run at a temperature of about –40 °C, complying with a detector leakage current of the order of 5–10 nA per strip.

Statistical investigation of the large-area Si(Li) detectors mass-produced for the GAPS experiment

The lithium-drifted silicon (Si(Li)) detector developed for the General Antiparticle Spectrometer (GAPS) experiment features a thick (∼2.2 mm) sensitive layer, large (10 cm) diameter, and excellent energy resolution (∼4 keV for 20–100 keV X-rays) at a relatively high operating temperature (approximately −40 °C). Mass production of GAPS Si(Li) detectors has been performed to construct a large-volume silicon tracker for GAPS. We achieved the first success of the mass production of large-area Si(Li) detectors with a high (∼90%) yield rate. Valuable datasets related to detector fabrication, such as detector performance and manufacturing parameters, were recorded and collected during the mass production. This study analyzes the datasets using statistical methods with the aim of comprehensively examining the mass production and to gain valuable insight into the fabrication method. Sufficient uniformities of the performance parameters (leakage current and capacitance) between detectors and strips are found, demonstrating high-quality and stable mass production. We also search for correlations between detector performance and manufacturing parameters by using data-mining techniques. Conventional multivariate analysis (multiple regression analysis) and machine-learning techniques (regression tree analysis) are complementarily used, and it is found that the Li-drift process makes a significant contribution to the performance parameters of the finished detectors. Detailed investigation of the drift process is performed using environmental data, and physical interpretations are presented. Our results provide valuable insight into the fabrication methods for this kind of large-area Si(Li) detector, and encourages future projects that require large-volume silicon trackers.

Low-Noise Analog Channel for the Readout of the Si(Li) Detector of the GAPS Experiment

This work is focused on the design and the experimental characterization of an analog channel developed for the readout of lithium-drifted silicon detectors of the General AntiParticle Spectrometer (GAPS) experiment aimed at the search for dark matter. The instrument is designed for the identification of antideuteron particles from cosmic rays during an Antarctic balloon mission scheduled for late 2022. A low-noise analog front-end, featuring a dynamic signal compression to comply with the wide input range, has been designed in commercial 180-nm CMOS technology. The channel was fabricated in 2018 and is the first building block toward the development of a multichannel readout ASIC. The article will provide a description of the design criteria, the architecture of the channel, and a summary of the results of the experimental characterization.

The antinucleus annihilation reconstruction algorithm of the GAPS experiment

The General AntiParticle Spectrometer (GAPS) is an Antarctic balloon-borne detector designed to measure low-energy cosmic antinuclei (<0.25GeV/n), with a specific focus on antideuterons, as a distinctive signal from dark matter annihilation or decay in the Galactic halo. The instrument consists of a tracker, made up of ten planes of lithium-drifted Silicon Si(Li) detectors, surrounded by a plastic scintillator Time-of-Flight system. GAPS uses a novel particle identification method based on exotic atom capture and decay with the emission of pions, protons, and atomic X-rays from a common annihilation vertex.An important ingredient for the antinuclei identification is the reconstruction of the “annihilation star” topology. A custom antinucleus annihilation reconstruction algorithm, called the “star-finding” algorithm, was developed to reconstruct the annihilation star fully, determining the annihilation vertex position and reconstructing the tracks of the primary and secondary charged particles. The reconstruction algorithm and its performances were studied on simulated data obtained with the Geant4-based GAPS simulation software, which fully reproduced the detector geometry. This custom algorithm was found to have better performance in the vertex resolution and reconstruction efficiency compared with a standard Hough-3D algorithm.

Cosmic antihelium-3 nuclei sensitivity of the GAPS experiment

The General Antiparticle Spectrometer (GAPS) is an Antarctic balloon experiment designed for low-energy (0.1–0.3 GeV/n) cosmic antinuclei as signatures of dark matter annihilation or decay. GAPS is optimized to detect low-energy antideuterons, as well as to provide unprecedented sensitivity to low-energy antiprotons and antihelium nuclei. The novel GAPS antiparticle detection technique, based on the formation, decay, and annihilation of exotic atoms, provides greater identification power for these low-energy antinuclei than previous magnetic spectrometer experiments. This work reports the sensitivity of GAPS to detect antihelium-3 nuclei, based on full instrument simulation, event reconstruction, and realistic atmospheric influence simulations. The report of antihelium nuclei candidate events by AMS-02 has generated considerable interest in antihelium nuclei as probes of dark matter and other beyond the Standard Model theories. GAPS is in a unique position to detect or set upper limits on the cosmic antihelium nuclei flux in an energy range that is essentially free of astrophysical background. In three 35-day long-duration balloon flights, GAPS will be sensitive to an antihelium flux on the level of 1.3−1.2+4.5·10−6 m-2sr-1s-1(GeV/n)-1 (95% confidence level) in the energy range of 0.11–0.3 GeV/n, opening a new window on rare cosmic physics.

Passivation of Si(Li) detectors operated above cryogenic temperatures for space-based applications

This work evaluates the viability of polyimide and parylene-C for passivation of lithium-drifted silicon (Si(Li)) detectors. The passivated Si(Li) detectors will form the particle tracker and X-ray detector of the General Antiparticle Spectrometer (GAPS) experiment, a balloon-borne experiment optimized to detect cosmic antideuterons produced in dark matter annihilations or decays. Successful passivation coatings were achieved by thermally curing polyimides, and the optimized coatings form an excellent barrier against humidity and organic contamination. The passivated Si(Li) detectors deliver ≲ 4 keV energy resolution (FWHM) for 20−100 keV X-rays while operating at temperatures of −35 to −45 °C. This is the first reported successful passivation of Si(Li)-based X-ray detectors operated above cryogenic temperatures.

The GAPS experiment – a search for cosmic-ray antinuclei from dark matter

The General Antiparticle Spectrometer (GAPS) is a balloon-borne experiment that aims to study low-energy cosmic-ray antinuclei. A novel detection concept that utilizes the physics of exotic atoms allows GAPS to realize a large sensitive area, a low energy threshold, and a high identification capability for antinuclei. The primary goal is to search for antideuterons in the energy region <0.25 GeV/n, where they are predicted to be backgroundfree probes for dark matter-annihilation or decay in the Galactic halo. GAPS will also measure precise low-energy antiproton spectra, which provide crucial information about the source and propagation of cosmic rays. Three flights on long-duration balloons from Antarctica are planned; the first flight of GAPS is scheduled for late 2021. This paper presents the scientific motivation, detection concept, development status, and plans for GAPS.

Large-area Si(Li) detectors for X-ray spectrometry and particle tracking in the GAPS experiment

The first lithium-drifted silicon (Si(Li)) detectors to satisfy the unique geometric, performance, and cost requirements of the General Antiparticle Spectrometer (GAPS) experiment have been produced by Shimadzu Corporation. The GAPS Si(Li) detectors will form the first large-area, relatively high-temperature Si(Li) detector system with sensitivity to X-rays to operate at high altitude. These 10 cm-diameter, 2.5 mm-thick, 4- or 8-strip detectors provide the active area, X-ray absorption efficiency, energy resolution, and particle tracking capability necessary for the GAPS exotic-atom particle identification technique. In this paper, the detector performance is validated on the bases of X-ray energy resolution and reconstruction of cosmic minimum ionizing particle (MIP) signals. We use the established noise model for semiconductor detectors to distinguish sources of noise due to the detector from those due to signal processing electronics. We demonstrate that detectors with either 4 strips or 8 strips can provide the required ≲4 keV (FWHM) X-ray energy resolution at flight temperatures of −35 to −45̂C, given the proper choice of signal processing electronics. Approximately 1000 8-strip detectors will be used for the first GAPS Antarctic balloon flight, scheduled for late 2021.

Developing a mass-production model of large-area Si(Li) detectors with high operating temperatures

This study presents a fabrication process for lithium-drifted silicon (Si(Li)) detectors that, compared to previous methods, allows for mass production at a higher yield, while providing a large sensitive area and low leakage currents at relatively high temperatures. This design, developed for the unique requirements of the General Antiparticle Spectrometer (GAPS) experiment, has an overall diameter of 10 cm, with ~9 cm of active area segmented into 8 readout strips, and an overall thickness of 2.5 mm, with $\gtrsim$2.2 mm ($\gtrsim$90%) sensitive thickness. An energy resolution $\lesssim$4 keV full-width at half-maximum (FWHM) for 20-100 keV X-rays is required at the operating temperature ~-40C, which is far above the liquid nitrogen temperatures conventionally used to achieve fine energy resolution. High-yield production is also required for GAPS, which consists of $\gtrsim$1000 detectors. Our specially-developed Si crystal and custom methods of Li evaporation, diffusion and drifting allow for a thick, large-area and uniform sensitive layer. We find that retaining a thin undrifted layer on the p-side of the detector drastically reduces the leakage current, which is a dominant component of the energy resolution at these temperatures. A guard-ring structure and optimal etching of the detector surface are also confirmed to suppress the leakage current. We report on the mass production of these detectors that is ongoing now, and demonstrate it is capable of delivering a high yield of ~90%.

Dual MeV gamma-ray and dark matter observatory - GRAMS Project

GRAMS (Gamma-Ray and AntiMatter Survey) is a novel project that can simultaneously target both astrophysical observations with MeV gamma rays and an indirect dark matter search with antimatter. The GRAMS instrument is designed with a cost-effective, large-scale LArTPC (Liquid Argon Time Projection Chamber) detector surrounded by plastic scintillators. The astrophysical observations at MeV energies have not yet been well-explored (the so-called “MeV-gap”) and GRAMS can improve the sensitivity by more than an order of magnitude compared to previous experiments. While primarily focusing on MeV gamma-ray observations, GRAMS is also optimized for cosmic ray antimatter surveys to indirectly search for dark matter. In particular, low-energy antideuterons will provide an essentially background-free dark matter signature. GRAMS will be a next generation experiment beyond the current GAPS (General AntiParticle Spectrometer) project for antimatter survey.

GAPS: A balloon-borne cosmic-ray antimatter experiment

Theories beyond the Standard Model predict dark matter candidates that could provide a significant enhancement of the antideuteron and antiproton flux, in particular at low energies. The General Antiparticle Spectrometer (GAPS) experiment is the first antimatter search experiment designed specifically for low-energy cosmic ray antideuterons and antiprotons. GAPS identifies antideuterons and antiprotons using a technique based on exotic atoms. This novel detection technique allows GAPS to have unprecedented sensitivity in the low energy range (< 0.25 GeV/n) for antiprotons and antideuterons. The apparatus consists of 10 planes of lithium-drifted Si (Si(Li)) detectors, surrounded on all sides by a plastic scintillator time-of-flight. GAPS is designed to carry out its science program using long-duration balloon flights in Antarctica and is currently scheduled by NASA for its first flight in late 2020. This presentation will describe the design, status, and discovery potential of the GAPS scientific program.

Fabrication of low-cost, large-area prototype Si(Li) detectors for the GAPS experiment

A Si(Li) detector fabrication procedure has been developed with the aim of satisfying the unique requirements of the GAPS (General Antiparticle Spectrometer) experiment. Si(Li) detectors are particularly well-suited to the GAPS detection scheme, in which several planes of detectors act as the target to slow and capture an incoming antiparticle into an exotic atom, as well as the spectrometer and tracker to measure the resulting decay X-rays and annihilation products. These detectors must provide the absorption depth, energy resolution, tracking efficiency, and active area necessary for this technique, all within the significant temperature, power, and cost constraints of an Antarctic long-duration balloon flight. We report here on the fabrication and performance of prototype 2′′-diameter, 1–1.25mm-thick, single-strip Si(Li) detectors that provide the necessary X-ray energy resolution of ∼4 keV for a cost per unit area that is far below that of previously-acquired commercial detectors. This fabrication procedure is currently being optimized for the 4′′-diameter, 2.5mm-thick, multi-strip geometry that will be used for the GAPS flight detectors.

Balloon Flight Demonstration of an Oscillating Heat Pipe

The oscillating heat pipe (OHP) is a novel heat-transfer technique used in thermal engineering. Although the OHP offers many technical advantages, it has not yet been actually used in the sky. Motivated by the need to develop a cooling system for use in the balloon-borne General Anti-Particle Spectrometer (GAPS) project, we are developing OHP technologies. To demonstrate the thermal performances of an OHP in real balloon flight conditions, a scaled-down OHP model was launched by a stratospheric balloon in Japan. In this study, we report the results of the flight demonstration.

Antideuteron sensitivity for the GAPS experiment

The General Antiparticle Spectrometer (GAPS) is a novel approach for indirect dark matter searches that exploits cosmic antiparticles, especially antideuterons. The GAPS antideuteron measurement utilizes distinctive detection methods using atomic X-rays and charged particles from the decay of exotic atoms as well as the timing and stopping range of the incoming particle, which together provide excellent antideuteron identification. Prior to the future balloon experiment, an accelerator test and a prototype flight were successfully conducted in 2005 and 2012 respectively, in order to verify the GAPS detection concept. This paper describes how the sensitivity of GAPS to antideuterons was estimated using a Monte Carlo simulation along with the atomic cascade model and the Intra-Nuclear Cascade model. The sensitivity for the GAPS antideuteron search obtained using this method is 2.0 ×10−6[m−2s−1sr−1(GeV/n)−1] for the proposed long duration balloon program (LDB, 35 days × 3 flights), indicating that GAPS has a strong potential to probe a wide variety of dark matter annihilation and decay models through antideuteron measurements. GAPS is proposed to fly from Antarctica in the austral summer of 2019–2020.

より戻しモータのみを用いた気球ゴンドラ方向制御とGAPS実験への適用

In this paper, direction control of balloon gondola with only untwisting motor is proposed. Typically a reaction wheel and another actuator for unloading the reaction wheel are in use to control the attitude (or direction) of the gondola. Although this method can get high accuracy control performance, two actuators spend many resources of the gondola. The proposed method uses only untwisting motor installed above the gondola to rotate. This method can not realize such high accuracy control performance but realize direction control with the most simple configuration. The proposed method is applied to prototype GAPS (General Anti-Particle Spectrometer) balloon experiment in 2012. This paper shows control design for this experiment and the results of the proposed method.

Development of Meter-Scale U-Shaped and O-Shaped Oscillating Heat Pipes for GAPS

A meter-scale Oscillating Heat Pipe (OHP) has been developed for the General Anti-Particle Spectrometer (GAPS) project. Two types of OHP routing, U-shaped and O-shaped, have been investigated. For the operation at low temperature, R410A was used as the working fluid. As the result of the investigation, we verified for the first time that both the meter-scale U-shaped and O-shaped OHPs can transfer heat under gravity in a wide temperature range between 20°C and -60°C. Generally, the O-shaped OHP showed better performance than the U-shaped OHP. Both OHP models showed good thermal conductance and a good amount of heat transport under the particular sets of conditions which meet the design requirements. In order to clarify the drive force to operate OHP to further improve the OHP design, the performance difference between the U-shaped and the O-shaped models has been interpreted in terms of the gravity effect and the pressure loss.

Potential for precision measurement of low-energy antiprotons with GAPS for dark matter and primordial black hole physics

The general antiparticle spectrometer (GAPS) experiment is a proposed indirect dark matter search focusing on antiparticles produced by WIMP (weakly interacting massive particle) annihilation and decay in the Galactic halo. In addition to the very powerful search channel provided by antideuterons (Donato et al., 2000, 2008) [1,2], (Vittino et al.) [3], (Fornengo, 2013) [4], GAPS has a strong capability to measure low-energy antiprotons (0.07⩽E⩽0.25GeV) as dark matter signatures. This is an especially effective means for probing light dark matter, whose existence has been hinted at in the direct dark matter searches, including the recent result from the CDMS-II experiment (Agnese, 2013) [5]. While severely constrained by LUX and other direct dark matter searches (Akerib et al.) [6], light dark matter candidates are still viable in an isospin-violating dark matter scenario and halo-independent analysis (Del Nobile et al.) [7,8]. Along with the excellent antideuteron sensitivity, GAPS will be able to detect an order of magnitude more low-energy antiprotons, compared to BESS (Abe et al., 2012) [9], (Orito et al., 2000) [10], PAMELA (Adriani et al., 2010) [11] and AMS-02 (Casaus, 2009) [12], providing a precision measurement of low-energy antiproton flux and a unique channel for probing light dark matter models. Additionally, dark matter signatures from gravitinos and Kaluza–Klein right-handed neutrinos as well as evidence of primordial black hole evaporation can be observed through low-energy antiproton search.