Search

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 − 2 s − 1 sr − 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. [ABSTRACT FROM AUTHOR]

Abstract: The General Antiparticle Spectrometer (GAPS) is a new approach to the indirect detection of dark matter. It relies on searching for primary antideuterons produced in the annihilation of dark matter in the galactic halo. Low energy antideuterons produced through Standard Model processes, such as collisions of cosmic-rays with interstellar baryons, are greatly suppressed compared to primary antideuterons. Thus a low energy antideuteron search provides a clean signature of dark matter. In GAPS antiparticles are slowed down and captured in target atoms. The resultant exotic atom deexcites with the emission of X-rays and annihilation pions, protons and other particles. A tracking geometry allows for the detection of the X-rays and particles, providing a unique signature to identify the mass of the antiparticle. A prototype detector was successfully tested at the KEK accelerator in 2005, and a prototype GAPS balloon flight is scheduled for 2011. This will be followed by a full scale experiment on a long duration balloon from Antarctica in 2014. We discuss the status and future plans for GAPS. [Copyright &y& Elsevier]

We present spectral analysis from XMM-Newton observations of the Vela pulsar. We analyzed thermal emission from the pulsar dominating below ∼1 keV since extracted spectra are heavily contaminated by nebular emission at higher energy. Featureless high-resolution spectra of the reflection grating spectrometer aboard XMM-Newton suggest the presence of a hydrogen atmosphere, as previously indicated by Chandra results. Both the temperature and radius are consistent with those values deduced from Chandra. The derived Chandra and XMM-Newton temperature of T∞≃(6.4–7.1)×105 K at its age of ∼104 years is below the standard cooling curve. [Copyright &y& Elsevier]

Abstract: The General AntiParticle Spectrometer (GAPS) is a novel approach for indirect dark matter searches that exploits cosmic antideuterons. The GAPS detection method involves capturing antiparticles into a target material with the subsequent formation of an excited exotic atom. The exotic atom decays with the emission of atomic X-rays and charged particles from nuclear annihilation, which uniquely identifies the captured antiparticle. We are currently developing the lithium-drifted silicon (Si(Li)) detector for the GAPS flight experiment. In this paper, we describe the diagnostic tests conducted on three prototype Si(Li) detectors and the noise model to characterize each detector. The GAPS prototype flight, preparatory for a long duration balloon flight from Antarctica in 2016–2017, is scheduled for launch from Japan in summer 2012. [Copyright &y& Elsevier]

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. 21 GeV/ 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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 ( 0.25GeV) 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. [Copyright &y& Elsevier]

Abstract: The General Anti-Particle Spectrometer (GAPS) project is being carried out to search for primary cosmic-ray antiparticles especially for antideuterons produced by cold dark matter. GAPS plans to realize the science observation by Antarctic long duration balloon flights in the late 2010s. In preparation for the Antarctic science flights, an engineering balloon flight using a prototype of the GAPS instrument, “pGAPS”, was successfully carried out in June 2012 in Japan to verify the basic performance of each GAPS subsystem. The outline of the pGAPS flight campaign is briefly reported. [Copyright &y& Elsevier]

Abstract: The General AntiParticle Spectrometer experiment (GAPS) is foreseen to carry out a dark matter search using low-energy cosmic ray antideuterons at stratospheric altitudes with a novel detection approach. A prototype flight from Taiki, Japan was carried out in June 2012 to prove the performance of the GAPS instrument subsystems (Lithium-drifted Silicon tracker and time-of-flight) and the thermal cooling concept as well as to measure background levels. The flight was a success and the stable flight operation of the GAPS detector concept was proven. During the flight about charged particle triggers were recorded, extensive X-ray calibrations of the individual tracker modules were performed by using an onboard X-ray tube, and the background level of atmospheric and cosmic X-rays was measured. The behavior of the tracker performance as a function of temperature was investigated. The tracks of charged particle events were reconstructed and used to study the tracking resolution, the detection efficiency of the tracker, and coherent X-ray backgrounds. A timing calibration of the time-of-flight subsystem was performed to measure the particle velocity. The flux as a function of flight altitude and as a function of velocity was extracted taking into account systematic instrumental effects. The developed analysis techniques will form the basis for future flights. [Copyright &y& Elsevier]

Abstract: The General Antiparticle Spectrometer (GAPS) experiment is a novel approach for the detection of cosmic ray antiparticles. A prototype GAPS (pGAPS) experiment was successfully flown on a high-altitude balloon in June of 2012. The goals of the pGAPS experiment were: to test the operation of lithium drifted silicon (Si(Li)) detectors at balloon altitudes, to validate the thermal model and cooling concept needed for engineering of a full-size GAPS instrument, and to characterize cosmic ray and X-ray backgrounds. The instrument was launched from the Japan Aerospace Exploration Agency's (JAXA) Taiki Aerospace Research Field in Hokkaido, Japan. The flight lasted a total of 6h, with over 3h at float altitude . Over one million cosmic ray triggers were recorded and all flight goals were met or exceeded. [Copyright &y& Elsevier]

Abstract: The General AntiParticle Spectrometer (GAPS) is a novel approach for the indirect dark matter search that exploits cosmic antideuterons. GAPS utilizes a distinctive detection method using atomic X-rays and charged particles from the exotic atom as well as the timing, stopping range and dE/dX energy deposit of the incoming particle, which provides excellent antideuteron identification. In anticipation of a future balloon experiment, an accelerator test was conducted in 2004 and 2005 at KEK, Japan, in order to prove the concept and to precisely measure the X-ray yields of antiprotonic exotic atoms formed with different target materials [1]. The X-ray yields of the exotic atoms with Al and S targets were obtained as 75%, which are higher than were previously assumed in [2]. A simple, but comprehensive cascade model has been developed not only to evaluate the measurement results but also to predict the X-ray yields of the exotic atoms formed with any materials in the GAPS instrument. The cascade model is extendable to any kind of exotic atom (any negatively charged cascading particles with any target materials), and it was compared and validated with other experimental data and cascade models for muonic and antiprotonic exotic atoms. The X-ray yields of the antideuteronic exotic atoms are predicted with a simple cascade model and the sensitivity for the GAPS antideuteron search was estimated for the proposed long duration balloon program [3], which suggests that GAPS has a strong potential to detect antideuterons as a dark matter signature. A GAPS prototype flight (pGAPS) was launched successfully from the JAXA/ISAS balloon facility in Hokkaido, Japan in summer 2012 [4,5] and a proposed GAPS science flight is to fly from Antarctica in the austral summer of 2017–2018. [Copyright &y& Elsevier]

Abstract: The General AntiParticle Spectrometer (GAPS) is a novel approach for indirect dark matter searches that exploits cosmic antideuterons. GAPS complements existing and planned direct dark matter searches as well as other indirect techniques, probing a different and unique region of parameter space in a variety of proposed dark matter models. The GAPS method involves capturing antiparticles into a target material with the subsequent formation of an excited exotic atom. The exotic atom decays with the emission of atomic X-rays and pions from the nuclear annihilation, which uniquely identifies the captured antiparticle. This technique has been verified through the accelerator testing at KEK in 2004 and 2005. The prototype flight is scheduled from Hokkaido, Japan in 2011, preparatory for a long duration balloon flight from the Antarctic in 2014. [ABSTRACT FROM AUTHOR]

Abstract: We discuss current progress and future plans for the general antiparticle spectrometer experiment (GAPS). GAPS detects antideuterons through the X-rays and pions emitted during the deexcitation of exotic atoms formed when the antideuterons are slowed down and stopped in targets. GAPS provides an exceptionally sensitive means to detect cosmic-ray antideuterons. Cosmic-ray antideuterons can provide indirect evidence for the existence of dark matter in such form as neutralinos or Kaluza–Klein particles. We describe results of accelerator testing of GAPS prototypes, tentative design concepts for a flight GAPS detector, and near-term plans for flying a GAPS prototype on a balloon. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 ≳ 2. 2 mm (≳ 90 %) sensitive thickness. An energy resolution ≲ 4 keV full-width at half-maximum (FWHM) for 20 − 100 keV X-rays is required at the operating temperature ∼ − 40 ° C , 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 ≳ 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 %. [ABSTRACT FROM AUTHOR]