小財 正義

The General Antiparticle Spectrometer (GAPS) is a balloon-borne experiment that aims to measure low-energy cosmicray antiparticles. GAPS has developed a new antiparticle identification technique based on exotic atom formation caused by incident particles, which is achieved by ten layers of Si(Li) detector tracker in GAPS. The conventional analysis uses the physical quantities of the reconstructed incident and secondary particles. In parallel with this, we have developed a complementary approach based on deep neural networks. This paper presents a new convolutional neural network (CNN) technique. A three-dimensional CNN takes energy depositions as three-dimensional inputs and learns to identify their positional/energy correlations. The combination of the physical quantities and the CNN technique is also investigated. The findings show that the new technique outperforms existing machine learning-based methods in particle identification.

This study developed a novel thermal control system to cool detectors of the General AntiParticle Spectrometer (GAPS) before its flights. GAPS is a balloon-borne cosmic-ray observation experiment. In its payload, GAPS contains over 1000 silicon detectors that must be cooled below −40℃. All detectors are thermally coupled to a unique heat-pipe system (HPS) that transfers heat from the detectors to a radiator. The radiator is designed to be cooled below −50℃ during the flight by exposure to space. The pre-flight state of the detectors is checked on the ground at 1 atm and ambient room temperature, but the radiator cannot be similarly cooled. The authors have developed a ground cooling system (GCS) to chill the detectors for ground testing. The GCS consists of a cold plate, a chiller, and insulating foam. The cold plate is designed to be attached to the radiator and cooled by a coolant pumped by the chiller. The payload configuration, including the HPS, can be the same as that of the flight. The GCS design was validated by thermal tests using a scale model. The GCS design is simple and provides a practical guideline, including a simple estimation of appropriate thermal insulation thickness, which can be easily adapted to other applications.

Solar modulation of galactic cosmic rays around the solar minimum in 2019–2020 looks different in the secondary neutrons and muons observed at the ground. To compare the solar modulation of primary cosmic rays in detail, we must remove the possible seasonal variations caused by the atmosphere and surrounding environment. As such surrounding environment effects, we evaluate the snow cover effect on neutron count rate and the atmospheric temperature effect on muon count rate, both simultaneously observed at Syowa Station in the Antarctic (69.01° S, 39.59° E). A machine learning technique, Echo State Network (ESN), is applied to estimate both effects hidden in the observed time series of the count rate. We show that the ESN with the input of GDAS data (temperature time series at 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, and 20 hPa) at the local position can be useful for both the temperature correction for muons and snow cover correction for neutrons. The corrected muon count rate starts decreasing in late 2019, preceding the corrected neutron count rate which starts decreasing in early 2020, possibly indicating the rigidity-dependent solar modulation in the heliosphere.

Low-energy cosmic ray antideuterons (< 0.25 GeV/n) are a compelling, mostly uncharted channel of many viable dark matter models and benefit from highly suppressed astrophysical background. The General Antiparticle Spectrometer (GAPS) is a first-of-its-kind exotic-atom-based Antarctic balloon-borne experiment specialized for detection of low-energy antiprotons, antideuterons, and antihelium with a targeted launch in 2022. The results of novel technology development and a summary of current construction status are the focus of this contribution. GAPS exploits a novel antiparticle identification technique based on exotic atom formation and decay, allowing more active target material for a larger overall acceptance since no magnet is required. The GAPS instrument consists of a large-area (∼ 50 m2) scintillator time-of-flight, ten planes of custom silicon detectors with dedicated ASIC readout, and a novel oscillating heat pipe cooling approach. This contribution will briefly introduce the exotic atom detection technique. Following this, the instrument design will be discussed and detailed description of experimental hardware and expected performance will be presented. I will conclude with recent construction and testing progress while also highlighting developments of a scaled, integrated prototype.

At low energies, cosmic antideuterons and antihelium provide an ultra-low background signature of dark matter annihilation, decay, and other beyond the Standard Model phenomena. The General Antiparticle Spectrometer (GAPS) is an Antarctic balloon experiment designed to search for low-energy (0.1−0.3 GeV/n) antinuclei, and is planned to launch in the austral summer of 2022. While optimized for an antideuteron search, GAPS also has unprecedented capabilites for the detection of low-energy antihelium nuclei, utilizing a novel detection technique based on the formation, decay, and annihilation of exotic atoms. The AMS-02 collaboration has recently reported several antihelium nuclei candidate events, which sets GAPS in a unique position to set constraints on the cosmic antihelium flux in an energy region which is essentially free of astrophysical background. In this contribution, we illustrate the capabilities of GAPS to search for cosmic antihelium-3 utilizing complete instrument simulations, event reconstruction, and the inclusion of atmospheric effects. We show that GAPS is capable of setting unprecedented limits on the cosmic antihelium flux, opening a new window on exotic cosmic physics.

The General Antiparticle Spectrometer (GAPS) experiment is a balloon payload designed to measure low-energy cosmic antinuclei during at least three ∼35-day Antarctic flights, with the first flight planned for December, 2022. With its large geometric acceptance and novel exotic atom-based particle identification method, GAPS will detect ∼1000 antiprotons per flight, producing a precision cosmic antiproton spectrum in the kinetic energy range of 0.03 − 0.23 GeV/n at float altitude (corresponding to 0.085 − 0.30 GeV/n at the top of the atmosphere). With these high statistics in a measurement extending to lower energy than any previous experiment, and with orthogonal sources of systematic uncertainty compared to measurements made using traditional magnetic spectrometer techniques, the GAPS antiproton measurement will be sensitive to physics including dark matter annihilation, primordial black hole evaporation, and cosmic ray propagation. The antiproton measurement will also validate the GAPS exotic atom technique for the antideuteron and antihelium rare-event searches and provide insight into models of cosmic particle attenuation and production in the atmosphere. This contribution demonstrates the GAPS sensitivity to antiprotons using a full instrument simulation, event reconstruction, and solar and atmospheric effects.

The General Antiparticle Spectrometer (GAPS) is the first experiment optimized to identify low-energy (.0.25 GeV/n) cosmic antinuclei, in particular antideuterons from dark matter annihilation or decay. The GAPS program will deliver unprecedented sensitivity to cosmic antideuterons, an essentially background-free signature of various dark matter models, as well as a high-statistics antiproton spectrum in the unexplored low-energy range, and leading sensitivity to cosmic antihelium. GAPS is currently under construction. The first Antarctic balloon flight of GAPS is planned for late 2022, and two additional flights are planned for the coming years. Based on measurements of our custom-developed instrument technology, including large-area lithium-drifted silicon (Si(Li)) detectors and a large-acceptance time-of-flight system, as well as detailed instrument simulation and reconstruction studies, we present here the anticipated impact of the GAPS program on dark matter searches. This contribution discusses the current status of cosmic antinuclei studies while focusing on the science potential of GAPS.

The General Antiparticle Spectrometer (GAPS) experiment is designed to detect low-energy (< 0.25 GeV/n) cosmic-ray antinuclei as indirect signatures of dark matter. Several beyond-the-standard-model scenarios predict a large antideuteron flux due to dark matter decay or annihilation compared to the astrophysical background. The GAPS experiment will perform such measurements using long-duration balloon flights over Antarctica, beginning in the 2022/23 austral summer. The experimental apparatus consists of ten planes of Si(Li) detectors surrounded by a time-of-flight system made of plastic scintillators. The detection of the primary antinucleus relies on the reconstruction of the annihilation products: the low-energy antinucleus is captured by an atom of the detector material, forming an exotic atom that de-excites by emitting characteristics X-rays. Finally, the antinucleus undergoes nuclear annihilation, producing a “star” of pions and protons emitted from the annihilation vertex. Several algorithms were developed to determine the annihilation vertex position and to reconstruct the topology of the primary and secondary particles. An overview of the event reconstruction techniques and their performances, based on detailed Monte Carlo simulation studies, will be presented in this contribution.

The General Antiparticle Spectrometer (GAPS) is a balloon-borne experiment, scheduled for a first flight in the austral summer 2022. It is designed to measure low energy (< 0.25 GeV/n) cosmic antinuclei. A particular focus is on antideuterons, which are predicted to have an ultra-low astrophysical background as compared to signals from dark matter annihilation or decay in the Galactic halo. GAPS uses a novel technique for particle identification based on the formation and decay of exotic atoms. To achieve sufficient rejection power for particle identification, an accurate determination of several fundamental quantities is needed. The precise reconstruction of the energy deposition pattern on the primary track is a particularly intricate problem and we developed a strategy devised to solve this using modern machine learning techniques. In the future, this approach can also be used for particle identification. Here, we present preliminary results of these efforts obtained from simulations.

We report observations of gamma-ray emissions with energies in the 100-TeV energy region from the Cygnus region in our Galaxy. Two sources are significantly detected in the directions of the Cygnus OB1 and OB2 associations. Based on their positional coincidences, we associate one with a pulsar PSR and the other mainly with a pulsar wind nebula PWN , with the pulsar moving away from its original birthplace situated around the centroid of the observed gamma-ray emission. This work would stimulate further studies of particle acceleration mechanisms at these gamma-ray sources.

In the TeV energy region, the anisotropy of cosmic ray intensity was observed by some air shower experiments, like Tibet ASgamma, ARGO, HAWC, and so on. But, our previous results are contaminated with the gamma rays and electrons/positrons, and it is difficult to discriminate them with only the plastic scintillation air shower detector. Tibet ASgamma has installed underground muon detector(MD) in 2014. With MD, Tibet ASgamma became capable of discriminating two type primaries in shower events, gamma ray like (due to primary gamma rays, electrons and positron) and cosmic ray like, and to observe the anisotropies of cosmic rays and gamma rays/electrons/positrons, separately. In this work, we will report the result of the anisotropies observed by the Tibet air shower array and muon detector array.

© 2019 IEEE. Large-area lithium-drifted silicon (Si(Li)) detectors, operable 150°C above liquid nitrogen temperature, have been developed for the General Antiparticle Spectrometer (GAPS) balloon mission and will form the first such system to operate in space. These 10 cm-diameter, 2.5 mm-thick multi-strip detectors have been verified in the lab to provide < 4 keV FWHM energy resolution for X-rays as well as tracking capability for charged particles, while operating in conditions (~-40C and ~1 Pa) achievable on a long-duration balloon mission with a large detector payload. These characteristics enable the GAPS silicon tracker system to identify cosmic antinuclei via a novel technique based on exotic atom formation, de-excitation, and annihilation. Production and large-scale calibration of ~1000 detectors has begun for the first GAPS flight, scheduled for late 2021. The detectors developed for GAPS may also have other applications, for example in heavy nuclei identification.

© owned by the author(s) under the terms of the Creative Commons The large-scale sidereal anisotropy of cosmic rays is observed by Tibet air shower array in the northern hemisphere. Energy dependence of the cosmic-ray anisotropy from 300 TeV to 1 PeV is analysed. We find that the anisotropy maps above 300 TeV are distinct from that at the multi-TeV energy band. The spatial distribution of the GCR intensity of an excess and a deficit is observed in the 1 PeV anisotropy map. All these results may further our understanding of the origin and propagation of GCRs.

© Copyright owned by the author(s) under the terms of the Creative Commons The Tibet air shower (AS) array and underground water-Cherenkov-type muon detector (MD) array have been successfully operated since 2014, at an altitude of 4,300 m in Tibet, China. we observed 24 gamma-ray events with energy greater than 100 TeV against 5.5 background events, which corresponds to 5.6s statistical significance [1]. The highest energy of the detected gamma rays is estimated to be 450 TeV. This is the first detection of gamma rays beyond 100 TeV from an astrophysical source, and a pioneering work opening a new higher energy window in the astronomy and astrophysics.

Experiments aiming to directly detect dark matter (DM) particles have yet to make robust detections, thus underscoring the need for complementary approaches such as searches for new particles at colliders, and indirect DM searches in cosmic-ray spectra. Low energy (&lt; 0.25 GeV/n) cosmic-ray antiparticles such as antideuterons are strong candidates for probing DM models, as the yield of these particles from DM processes can exceed the astrophysical background by more than two orders of magnitude. The General Antiparticle Spectrometer (GAPS), a balloon borne cosmic-ray detector, will perform an ultra-low background measurement of the cosmic antideuteron flux in the regime &lt; 0.25 GeV/n, which will constrain a wide range of DM models. GAPS will also detect approximately 1000 antiprotons in an unexplored energy range throughout one long duration balloon (LDB) flight, which will constrain &lt; 10 GeV DM models and validate the GAPS detection technique. Unlike magnetic spectrometers, GAPS relies on the formation of an exotic atom within the tracker in order to identify antiparticles. The GAPS tracker consists of ten layers of lithium-drifted silicon detectors which record dE/dx deposits from primary and nuclear annihilation product tracks, as well as measure the energy of the exotic atom deexcitation X-rays. A two-layer, plastic scintillator time of flight (TOF) system surrounds the tracker and measures the particle velocity, dE/dx deposits, and provides a fast trigger to the tracker. The nuclear annihilation product multiplicity, deexcitation X-ray energies, TOF, and stopping depth are all used together to discern between antiparticle species. This presentation provided an overview of the GAPS experiment, an update on the construction of the tracker and TOF systems, and a summary of the expected performance of GAPS in light of the upcoming LDB flight from McMurdo Station, Antarctica in 2020....

The General Antiparticle Spectrometer (GAPS) is designed to carry out indirect dark matter search by measuring low-energy cosmic-ray antiparticles. Below a few GeVs the flux of antiparticles produced by cosmic-ray collisions with the interstellar medium is expected to be very low and several well-motivated beyond-standard models predict a sizable contribution to the antideuteron flux. GAPS is planned to fly on a long-duration balloon over Antarctica in the austral summer of 2020. The primary detector is a 1m3 central volume containing planes of Si(Li) detectors. This volume is surrounded by a time-of-flight system to both trigger the Si(Li) detector and reconstruct the particle tracks. The detection principle of the experiment relies on the identification of the antiparticle annihilation pattern. Low energy antiparticles slow down in the apparatus and they are captured in the medium to form exotic excited atoms, which de-excite by emitting characteristic X-rays. Afterwards they undergo nuclear annihilation, resulting in a star of pions and protons. The simultaneous measurement of the stopping depth and the dE/dx loss of the primary antiparticle, of the X-ray energies and of the star particle-multiplicity provides very high rejection power, that is critical in rare-event search. GAPS will be able to perform a precise measurement of the cosmic antiproton flux below 250 MeV, as well as a sensitive search for antideuterons....

The General AntiParticle Spectrometer (GAPS) is a balloon-borne instrument designed to detect cosmic-ray antimatter using the novel exotic atom technique, obviating the strong magnetic fields required by experiments like AMS, PAMELA, or BESS. It will be sensitive to primary antideuterons with kinetic energies of $\approx0.05-0.2$ GeV/nucleon, providing some overlap with the previously mentioned experiments at the highest energies. For $3\times35$ day balloon flights, and standard classes of primary antideuteron propagation models, GAPS will be sensitive to $m_{\mathrm{DM } }\approx10-100$ GeV c$^{-2}$ WIMPs with a dark-matter flux to astrophysical flux ratio approaching 100. This clean primary channel is a key feature of GAPS and is crucial for a rare event search. Additionally, the antiproton spectrum will be extended with high statistics measurements to cover the $0.07 \leq E \leq 0.25 $ GeV domain. For $E&gt;0.2$ GeV GAPS data will be complementary to existing experiments, while $E&lt;0.2$ GeV explores a new regime. The first flight is scheduled for late 2020 in Antarctica. These proceedings will describe the astrophysical processes and backgrounds relevant to the dark matter search, a brief discussion of detector operation, and construction progress made to date....

We analyze the Sun's shadow observed with the Tibet-III air shower array and find that the shadow's center deviates northward (southward) from the optical solar disk center in the "away" ("toward") interplanetary magnetic field (IMF) sector. By comparing with numerical simulations based on the solar magnetic field model, we find that the average IMF strength in the away (toward) sector is 1.54±0.21stat±0.20syst (1.62±0.15stat±0.22syst) times larger than the model prediction. These demonstrate that the observed Sun's shadow is a useful tool for the quantitative evaluation of the average solar magnetic field.

The SciBar Cosmic Ray Telescope (SciCRT) is a massive scintillator tracker to observe cosmic rays at a very high-altitude environment in Mexico. The fully active tracker is based on the Scintillator Bar (SciBar) detector developed as a near detector for the KEK-to-Kamioka long-baseline neutrino oscillation experiment,(K2K) in Japan. Since the data acquisition (DAQ) system was developed for the accelerator experiment, we determined to develop a new robust DAQ system to optimize it to our cosmic-ray experiment needs at the top of Mt. Sierra Negra (4600 m). One of our special requirements is to achieve a 10 times faster readout rate. We started to develop a new fast readout back-end board (BEB) based on 100 Mbps SiTCP, a hardware network processor developed for DAQ systems for high energy physics experiments. Then we developed the new BEB which has a potential of 20 times faster than the current one in the case of observing neutrons. Finally we installed the new DAQ system including the new BEBs to a part of the SciCRT in July 2015. The system has been operating since then. In this paper, we describe the development, the basic performance of the new BEB, the status after the installation in the SciCRT, and the future performance.

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). We continuously observed the Sun's shadow in 3 TeV cosmic-ray intensity with the Tibet-III air shower array since 2000. We find a clear solar-cycle variation of the deficit intensity in the Sun's shadow during the periods between 2000 and 2009. The MC simulation of the Sun's shadow based on the coronal magnetic field model does not well reproduce the observed deficit intensity around the solar maximum. However, when we exclude the transit periods during ICMEs towards to the Earth, the MC simulation shows better reproducibility. In the present paper, we report on the MC simulation and the analysis method of the Sun's shadow observed by the Tibet-III array.

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). We have started a new hybrid air shower experiment at Yangbajing (4300 m a.s.l.) in Tibet in February 2014. This new hybrid experiment consists of the YAC-II comprised of 124 core detectors placed in the form of a square grid of 1.9 m spacing covering about 500 m2, the Tibet-III air shower array with the total area of about 50, 000 m2 and the underground MD array consisting of 80 cells, with the total area of about 4, 200 m2. This hybrid-array system is used to observe air showers of high energy celestial gamma-ray origin and those of nuclear-component origin. In this paper, a short review of the experiment will be followed by an overview on the current results on energy spectrum and chemical composition of CRs and test of hadronic interaction models.

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). The angular displacement of the center of the observed Sun's shadow from the center of the optical solar disc tells us the information of average solar magnetic field strength in the space between the Sun and the Earth. We analyze the displacement of the Sun's shadow observed in 5 ∼ 240 TeV cosmic-ray intensity with the Tibet-III air shower array during 10 years between 2000 and 2009, and compare with the MC simulations based on the coronal magnetic field model and Parker's spiral interplanetary magnetic field model. We find that the observed North-South displacement is significantly larger than the prediction of simulations. This result uniquely suggests the underestimation of the average field strength between the Sun and the Earth in our model. In this work, we will report the actual solar magnetic field strength evaluated from the observed Sun's shadow.

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). We built a large (approximately 4,000 m2) water Cherenkov-type muon detector array under the existing Tibet air shower array at 4,300 m above sea level, to observe 10-1000 TeV gamma rays from cosmic-ray accelerators in our Galaxy with wide field of view at very low background level. A gamma-ray induced air shower has significantly less muons compared with a cosmic-ray induced one. Therefore, we can effectively discriminate between primary gamma rays and cosmic-ray background events by means of counting number of muons in an air shower event by the muon detector array. We make a status report on the experiment.

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). The GAPS experiment is designed to carry out a sensitive dark matter search by measuring low-energy cosmic ray antideuterons and antiprotons. GAPS will provide a new avenue to access a wide range of dark matter models and masses that is complementary to direct detection techniques, collider experiments and other indirect detection techniques. Well-motivated theories beyond the Standard Model contain viable dark matter candidates which could lead to a detectable signal of antideuterons resulting from the annihilation or decay of dark matter particles. The dark matter contribution to the antideuteron flux is believed to be especially large at low energies (E < 1 GeV), where the predicted flux from conventional astrophysical sources (i.e. from secondary interactions of cosmic rays) is very low. The GAPS low-energy antiproton search will provide stringent constraints on less than 10 GeV dark matter, will provide the best limits on primordial black hole evaporation on Galactic length scales, and will explore new discovery space in cosmic ray physics. Unlike other antimatter search experiments such as BESS and AMS that use magnetic spectrometers, GAPS detects antideuterons and antiprotons using an exotic atom technique. This technique, and its unique event topology, will give GAPS a nearly background-free detection capability that is critical in a rare-event search. GAPS is designed to carry out its science program using long-duration balloon flights in Antarctica. A prototype instrument was successfully flown from Taiki, Japan in 2012. GAPS has now been approved by NASA to proceed towards the full science instrument, with the possibility of a first long-duration balloon flight in late 2020. This presentation will motivate low-energy cosmic ray antimatter searches and it will discuss the current status of the GAPS experiment and the design of the payload.

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). Interplanetary shocks are caused both by interplanetary counterparts of coronal mass ejections (ICMEs) and by co-rotating interaction regions (CIRs) propagating in the interplanetary medium. CIRs are formed by the interaction between high-speed and slow solar wind streams. When the interplanetary disturbance propagates faster than the magnetosonic wave speed, in the solar wind frame, a shock wave is formed. Shocks frequently produce decreases of cosmic rays observed both by neutron monitors and muon detectors located at the Earth's surface. In this work, we analyze this kind of modulation of high-energy cosmic rays (≧ 50 GeV) observed by the Global Muon Detector Network (GMDN). After correcting both the atmospheric temperature and pressure effects, we calculated the isotropic intensity and the anisotropy vector. From a list of 38 interplanetary shocks identified in 2015 using interplanetary magnetic field and plasma parameters, we performed a superposed epoch analysis grouping the events by type and orientation of shocks. We found that the cosmic ray isotropic intensity is higher when it is associated to fast forward shocks when compared to fast reverse shocks. We also identified some differences in the anisotropy vector when comparing different types of shocks or shocks that are quasi-perpendicular with the remaining ones.

Copyright © International Astronomical Union 2018Â. The Global Muon Detector Network (GMDN) is composed by four ground cosmic ray detectors distributed around the Earth: Nagoya (Japan), Hobart (Australia), Sao Martinho da Serra (Brazil) and Kuwait City (Kuwait). The network has operated since March 2006. It has been upgraded a few times, increasing its detection area. Each detector is sensitive to muons produced by the interactions of ~50 GeV Galactic Cosmic Rays (GCR) with the Earth′s atmosphere. At these energies, GCR are known to be affected by interplanetary disturbances in the vicinity of the earth. Of special interest are the interplanetary counterparts of coronal mass ejections (ICMEs) and their driven shocks because they are known to be the main origins of geomagnetic storms. It has been observed that these ICMEs produce changes in the cosmic ray gradient, which can be measured by GMDN observations. In terms of applications for space weather, some attempts have been made to use GMDN for forecasting ICME arrival at the earth with lead times of the order of few hours. Scientific space weather studies benefit the most from the GMDN network. As an example, studies have been able to determine ICME orientation at the earth using cosmic ray gradient. Such determinations are of crucial importance for southward interplanetary magnetic field estimates, as well as ICME rotation.