吉田 哲也

The energy spectrum of cosmic-ray antiprotons ((p) over bar 's) from 0.17 to 3.5 GeV has been measured using 7886 (p) over bar 's detected by BESS-Polar II during a long-duration flight over Antarctica near solar minimum in December 2007 and January 2008. This shows good consistency with secondary (p) over bar calculations. Cosmologically primary (p) over bar 's have been investigated by comparing measured and calculated (p) over bar spectra. BESS-Polar II data show no evidence of primary (p) over bar 's from the evaporation of primordial black holes.

LiteBIRD [Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection] is a small satellite to map the polarization of the cosmic microwave background (CMB) radiation over the full sky at large angular scales with unprecedented precision. Cosmological inflation, which is the leading hypothesis to resolve the problems in the Big Bang theory, predicts that primordial gravitational waves were created during the inflationary era. Measurements of polarization of the CMB radiation are known as the best probe to detect the primordial gravitational waves. The LiteBIRD working group is authorized by the Japanese Steering Committee for Space Science (SCSS) and is supported by JAXA. It has more than 50 members from Japan, USA and Canada. The scientific objective of LiteBIRD is to test all the representative inflation models that satisfy single-field slow-roll conditions and lie in the large-field regime. To this end, the requirement on the precision of the tensor-to-scalar ratio, r, at LiteBIRD is equal to or less than 0.001. Our baseline design adopts an array of multi-chroic superconducting polarimeters that are read out with high multiplexing factors in the frequency domain for a compact focal plane. The required sensitivity of 1.8 mu Karcmin is achieved with 2000 TES bolometers at 100mK. The cryogenic system is based on the Stirling/JT technology developed for SPICA, and the continuous ADR system shares the design with future X-ray satellites.

科学観測用に使用されているゼロプレッシャー気球には,日没後に浮揚ガスの温度が低下するため夜間に浮遊高度が低下するという根本的な問題がある.排気口がなく体積変化がほとんどないスーパープレッシャー気球が開発されれば,浮遊時間を大きく延ばすことが可能となる.我々は,lobed-pumpkinにlobed-cylinder構造を付け加え,幅広い容積に対して1つの設計が適応可能な新しいスーパープレッシャー気球形状を提案した.この新しい形状の定式化と利点について述べ,その妥当性と製造方法を検証するために実施した地上膨張試験および飛翔試験の結果について述べる.この方法により気球の空気抵抗を大きく減らすことができ,将来,パワードバルーンシステムを実現することが可能になる.

Although cosmic-ray antideuterons can be produced in primary cosmic-ray interactions with the interstellar medium in the same way as cosmic-ray antiprotons, the probability is much smaller, especially at low energies, because of the very low production cross-section and strict kinematic requirement compared to secondary antiproton production. The lack of significant astrophysical background indicates that a search for low-energy antideuterons could be a good probe for a novel production mechanisms such as pair-annihilation of neutralino dark matter or evaporation of primordial black holes. The BESS-Polar program has accumulated cosmic-ray data in near solar minimum conditions with more than ten times the statistics of those obtained by BESS flights during the previous solar minimum period. Based on these data, we perform a new antideuteron search with unprecedented sensitivity.

The first flight of the Balloon-Borne Experiment with a Superconducting Spectrometer (BESS-Polar I) in Antarctica collected about 900 million cosmic ray events during 8.5 days in 2004. Particle charge was determined from energy loss in the scintillators, rigidity by reconstructing each particle trajectory in the magnetic field, and velocity by utilizing time of flights counters. These measurements can clearly identify hydrogen and helium isotopes among the incoming particles. These isotopes are generally believed to result from nuclear interactions of primaries with the interstellar medium. Measurement of their flux is expected to provide important information on cosmic ray sources and particle propagation in interstellar space. The presentation will focus on determination of the helium isotope flux in the kinetic energy per nucleon range 0.1 GeV/n to about 1.5 GeV/n. After quickly introducing the BESS-Polar I detector, the dedicated analysis to differentiate isotopes will be described. Finally, the energy spectra will be presented and compared to previous measurements.

We have searched for antihelium in cosmic-rays since 1993 using a series of nine conventional BESS northern latitude balloon flights and two long-duration BESS-Polar Antarctic balloon flights. The BESS-Polar spectrometer is an evolutionary development of the previous BESS instruments, adapted to long duration flight. No antihelium candidate was found in the rigidity ranges of 0.6-20 GV among 8 × 106 helium nuclei events for BESS-Polar I and in the rigidity range of 0.6-14 GV among 4 × 107 events for BESS-Polar II, respectively. A resultant upper limit of 6.9 × 10 -8 for the abundance ratio of antihelium/helium at the top of the atmosphere in the rigidity range of 1-14 GV was set by combining all the BESS and BESS-Polar flight data. This is the most stringent limit obtained to date.

The energy spectrum of cosmic-ray antiprotons (p's) has been measured in the range 0.17 to 3.5 GeV, based on 7886 p's collected by the BESS-Polar II instrument during a long duration flight over Antarctica in a Solar minimum period of December 2007 through January 2008. The p spectrum measured by BESS-Polar II shows good consistency with the secondary p calculations. Given this background of secondary p's, cosmologically primary p's have been searched for using the observed p spectrum. BESS-Polar II result shows no evidence of primary p's that originated from the evaporation of PBH.

BESS (Balloon-borne Experiment with a Superconducting Spectrometer) had its first circumpolar flight from Williams Field near McMurdo Station, Antarctica from Dec. 13 to 21, 2004. Our sub-1% precision reveals BESS-Polar I proton fluxes exhibit transient variations at the few1% level. The time progression of proton flux has three main features a rising flux at the beginning of the flight, a transition region around Dec. 17, followed by quasi-periodic variation. Neutron monitor data show that the BESS-Polar I flight occurred during the recovery phase of a small Forbush decrease. The solar wind plasma and particle data show that this flight took place during the tail end of a high-energy, multiple-eruption solar energetic particle (SEP) event. A high speed solar wind stream arrived near the Earth around Dec. 17, 2004. We present the flux progression as a function of energy between 0.1 - 100.0 GeV and suggest possible physical interpretations.

The super-pressure balloon (SPB) has been expected to be a flight vehicle that can provide a long flight duration to science. Since 1997, we have developed the SPB. Now we are at the phase of developing an SPB of a practical size. In 2009, we carried out a test flight of a pumpkin-shaped SPB with a 60,000 m(3) volume. The undesirable result of this flight aroused us to resolve the deployment instability of the pumpkin-shaped SPB, which has been known as one of the most challenging issues confronting SPB development. To explore this deployment issue, in 2010, we carried out a series of ground tests. From results of these tests, we found that an SPB design modified from pumpkin, named "tawara", can be a good candidate to greatly improve the deployment stability of the lobed SPB. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

現在,大気球実験室では,標準的に用いているテレメータ・コマンドシステムに代わる新しいテレメータ・コマンドシステムの開発を進めており,2012 年度の移行を目指している.これに先立ち,新システムへの移行の第一段階として,気球尾部に搭載し,気球切り離しと切り離し後の気球追尾を行うことを主な目的とした新しい気球管制システム(ゴンドラに搭載するメインシステムに対し,これを冗長系システムと呼ぶ)の開発を行い,2010 年度以降の実用化の目処をつけた.本報告書では,開発中の新システムの概要について述べるとともに,冗長系システムの概要と,飛翔実証試験について報告する.

The Japanese balloon base was moved from the Sanriku Balloon Center (SBC) to the Taiki Aerospace Research Field (TARF). The SBC was closed in September 2007, and the new base at the TARF became operational in May 2008. In 2008, the first series of balloon flights at the TARF was carried out. By the success of these flights, we verified that the whole system of the new balloon base is well established. From FY 2009, regular balloon operations with science payloads started at the TARF. In May/June 2009, flight operations of three science experiments were carried out successfully. Five more science flights are planned at the TARF in August/September 2009.

Since 1971, numerous balloons have been launched from the Japanese balloon base, the Sanriku Balloon Center (SBC). Through these years, balloon technologies have been developed continuously and many scientific achievements have resulted. Recently, however, because of the limited area of the launching pad of the SBC, we have been faced with the difficulty of safely launching large balloons. To solve this issue, we decided to move the balloon base from the SBC to the Taiki Aerospace Research Field (TARF) in northern Japan. The TARF had an existing huge hanger and a paved launch pad capable of being utilised for balloon operations. To evolve the TARF into a new balloon base, new balloon facilities have been constructed at the TARF and equipment was transferred from the SBC to the TARF during July 2007 and March 2008. The SBC was closed in September 2007, and the new base became operational in May 2008. The new base at the TARF is designed to launch larger balloons with greater safety and to perform balloon operations more effectively than ever before. In the summer of 2008, we carried out the first series of the balloon campaign at the TARF, and succeeded in two engineering flights of stratospheric balloons. By the success of these flights, we have verified that the whole system of the new balloon base is well established. (C) 2009 COSPAR. Published by Elsevier Ltd. All rights reserved.

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. Published by Elsevier Ltd. on behalf of COSPAR.

A zero-pressure balloon used for scientific observation in the stratosphere has an unmanageable limitation that its floating altitude decreases during a nighttime because of temperature drop of the lifting gas. Since a super-pressure balloon may not change its volume, the lifetime can extend very long. We had introduced so called the 'lobed-pumpkin' type of super-pressure balloon that can realize a full-scale long-duration balloon and it will be in practical use in the very near future. As for larger super-pressure balloons, however, we still have some potential difficulties to be resolved. We here propose a new design suitable for a larger super-pressure balloon, which is roughly 'lobed pumpkin with lobed cylinder' and can adapt a single design for balloons of a wide range of volumes. Indoor inflation tests were successfully carried out with balloons designed and made by the method. It has been shown that the limit of the resisting pressure differential for a new designed balloon is same as that of a normal lobed-pumpkin balloon.

Recently, long duration balloon flights are strongly desired by the communities of Astronomy, Astrophysics and Cosmic-ray physics, in order to carry out very precise measurements with high statistics and/or to search for rare phenomena in huge background. Circumnavigation flights over Antarctica give us excellent flight opportunity, but the number of flights in a year is very limited, and the logistics is very hard. Once long duration balloon flights in mid-latitude more than several days can be realized much frequently, scientific ballooning will become much useful for space science experiments. Technical developments for long duration flights in Japan are introduced and the provision for the possible international collaboration will be discussed.

We report on recent work on the General Antiparticle Spectrometer Experiment (GAPS). GAPS is a balloon-based search for antideuterons generated in the annihilation of weakly interacting massive particles. Antideuterons provide an extremely clean signature of dark matter. It is difficult to produce backgrounds that mimic the annihilation antideuterons. GAPS consists of a time-of-flight system combined with a multi-layer particle tracker composed of pixellated Si(Li) detectors. When an antideuteron enters the telescope it slows down and is captured in a silicon atom. The resultant exotic atom deexcites with the emission of multiple atomic X-rays, and a shower of subatomic particles when the antideuteron enters the nucleus from the atomic ground state. The atomic Xrays, TOF, depth sensing and charged particle multiplicity provide an extremely stringent particle identification capability. GAPS can improve the current BESS experiment antideuteron limits by more than three orders of magnitude and access a large part of beyond standard model physics parameter spaces.

To collect stratospheric air samples for greenhouse gas measurements, a compact cryogenic air sampler has been developed using a cooling device called the Joule-Thomson (J-T) minicooler. The J-T minicooler can produce liquefied neon within 5 s from high pressure neon gas precooled by liquid nitrogen. The sampler employs liquid neon as a refrigerant to solidify or liquefy sampled atmospheric constituents. Laboratory experiments showed that the sampler is capable of collecting about 3 and more than 7 L STP of air at 25 and 120 hPa, respectively, which corresponds to about 25 and 15 km above ground within 240 s, respectively. The new balloon-borne sampling system, which was set up for Antarctic experiments, consists of the compact sampler, a 2-L high pressure neon gas cylinder, pneumatic and solenoid valves, a controller with a GPS receiver, a telemetry transmitter, and batteries. The size of the sampling system is 300 mm width X 300 mm depth X 950 mm height and it weighs about 22 kg (including liquid nitrogen). Two of these compact sampling systems (configured for sampling at altitudes 18 and 25 km) were launched from Syowa Station (69.0 degrees S, 39.5 degrees E) Antarctica, in January 2008 using 1000 or 2000 m(3) plastic balloons. They were launched successfully and recovered without any problem on sea ice on the same day as their launch. The collected stratospheric air samples showed reasonable concentrations of the stratospheric greenhouse gases over the Antarctic region.

The Scientific Balloon Center of ISAS/JAXA has managed balloon-borne experiments in Japan. Since 1971 domestic balloon campaigns have been carried out at Sanriku Balloon Center. In 2007 ten scientific experiments were conducted by seven balloon flights at Sanriku. We have also developed next generation super-pressure balloons and ultra-thin balloons. In order to meet recent user requirements, i.e., stable flights of heavier payloads at the highest possible altitude, Japanese scientific balloons will be operated at Taiki, Hokkaido from 2008. This new balloon facility was constructed to launch the first balloon in May 2008. Standardization of balloons and the balloon system is also in progress, in order to maximize the reliability for our operation of larger balloons with heavier payloads. In this paper, we introduce the new balloon facility in Taiki and discuss the strategy of the Japanese scientific balloon activities. The status of the development of new balloon technologies and international collaborations will also be discussed. © 2009 The Physical Society of Japan.

The aims of the BESS-Polar experiment are precise measurements of the low-energy antiproton spectrum and search for cosmologically significant antimatter. After its first flight (BESS-Polar I), we had developed a new spectrometer based on the feedback from the results. Most of the detector components had been redesigned and upgraded to improve their performance and to increase the data taking period and capacity. The second flight (BESS-Polar II) was successfully carried out in December 2007- January 2008. We performed 24.5 days scientific observation just at the solar minimum. In this paper, BESS-Polar II instrument and flight summary will be presented. © 2009 The Physical Society of Japan.

The General Antiparticle Spectrometer (GAPS) exploits low energy antideuterons produced in neutralino-neutralino annihilations as an indirect dark matter (DM) signature that is effectively free from background. When an antiparticle is captured by a target material, it forms an exotic atom in an excited state which quickly decays by emitting X-rays of precisely defined energy and a correlated pion signature from nuclear annihilation. We have successfully demonstrated the GAPS method in an accelerator environment and are currently planning a prototype flight from Japan for 2009. This will lead to a long duration balloon (LDB) mission that will complement existing and planned direct DM searches as well as other indirect techniques, probing a different, and often unique, region of parameter space in a variety of proposed DM models. Planes of coarsely pixellated Si(Li) detectors form the heart of the GAPS flight detector, providing both high X-ray energy resolution and good particle tracking. We will describe the proto-flight mission that will verify the performance of our Si(Li) detectors and cooling system in a flight-like configuration. We also will outline the LDB science payload design.

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. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

The first scientific flight of the BESS-Polar balloon-borne experiment was successfully carried out in December 2004 from Antarctica with the primary scientific objectives of searching for primordial antiparticles from the universe and making precision measurements of primary cosmic-ray fluxes. During the 8.5 day flight, the newly developed BESS-Polar spectrometer worked well and gathered data from 9 x 10(8) cosmic-ray events, showing its capability for making long-duration science observations. We have already started hardware development for the second experiment, which is expected to be a flight of more than 20 days during the next solar minimum period with the upgraded spectrometer. In this manuscript, progress on and prospects for the BESS-Polar experiment are described. (C) 2008 Published by Elsevier Ltd on behalf of COSPAR.

The BESS-Polar spectrometer had its first successful balloon flight over Antarctica in December 2004. During the 8.5-day long-duration flight, almost 0.9 billion events were recorded and 1,520 antiprotons were detected in the energy range 0.1-4.2 GeV. In this Letter, we report the antiproton spectrum obtained, discuss the origin of cosmic-ray antiprotons, and use antiproton data to probe the effect of charge-sign-dependent drift in the solar modulation. (C) 2008 Elsevier B.V. All rights reserved.

The Scientific Balloon Center of ISAS/JAXA has carried out two balloon campaigns at Sanriku, Iwate, Japan every year. Ten to twelve balloon vehicles are launched annually for scientific and engineering experiments. Since 2005, a Brazilian balloon campaign has also been conducted in cooperation with INPE. In the 2006 Brazilian campaign, large and heavy payloads up to 1500 kg for astronomy will be launched. New generation balloons, such as super-pressure balloons and high-altitude balloons with ultra-thin films, are being developed. The current status and prospect of the Japanese scientific ballooning are discussed. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

In this paper, we report searches for antilielium in cosmic rays using two recently flown magnetic rigidity spectrometers. BESS-TeV had extended rigidity with all MDR of 1.4 TV and had a flight duration of one day. BESS-Polar was optimized for collecting power. It was flown for 8.5 days and had an MDR of 240 GV. Tile former flight allows us to explore a previously unexplored rigidity band and the latter flight yields a factor of three improvement in the overall BESS limit. No antilielium candidate was found in the rigidity ranges of 1-500 GV, and 0.6-20 GV, among 7 x 10(4) events taken with BESS-TeV, and 8 X 10(6) events taken with BESS-Polar, respectively. (c) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) has been carried out to search for primordial antiparticles in cosmic rays. In ten flights from 1993 to 2004, it measured the cosmic-ray.antiproton spectrum in the energy range 0.1-4.2 GeV at various solar activity conditions. It also searched for antideuterons and antilielium nuclei, and it made precise measurement of cosmicray particle spectra. The BESS program has been extended to long duration balloon (LDB) flights in Antarctica (BESS-Polar) with the goal of achieving unprecedented sensitivity in the search for primordial antiparticles. This report describes recent results from BESS and progress of the BESS-Polar program. (c) 2008 Published by Elsevier Ltd on behalf of COSPAR.

Historically, there are been many searches for fractionally charged particles in the cosmic radiation. However, few searches have been performed near the top of the atmosphere. We performed a search for relativistic 2/3e charged particles in cosmic rays using data collected during four BESS balloon flights from 1997 to 2000 carried out in northern Canada. The data were analyzed by examining energy deposition in the time-of-flight scintillator hodoscopes. No candidate was found. We derive an upper limit of 4.5 x 10(-7) (cm(2) s sr)(-1) for the flux of 2,e charged particles, at the 90% confidence level. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

We measured low energy cosmic-ray proton and helium spectra in the kinetic energy range 0.215-21.5 GeV/n at different solar activities during a period from 1997 to 2002. The observations were carried out with the BESS spectrometer launched on a balloon at Lynn Lake, Canada. A calculation for the correction of secondary particle backgrounds from the overlying atmosphere was improved by using the measured spectra at small atmospheric depths ranging from 5 through 37 g/cm(2). The uncertainties including statistical and systematic errors of the obtained spectra at the top of atmosphere are 5-7% for protons and 6-9% for helium nuclei in the energy range 0.5-5 GeV/n. (C) 2007 Elsevier B.V. All rights reserved.

The Balloon-Born Experiment with a Superconducting Spectrometer (BESS) has measured cosmic-ray spectra blow 1 TeV and searched for antiparticle of novel cosmic origin. The BESS program is extended to long duration balloon (LDB) flights in Antarctica (BESS-Polar) aiming at unprecedented sensitivity to search for primordial antiparticles. This report describes recent results from BESS and the progress in the BESS-Polar program.

An ultra-thin superconducting solenoid has been developed to provide a magnetic field of 0.8 T in a balloon-borne spectrometer for cosmic ray research, which is named BESS-Polar. The coil with a diameter of 0.9 m, a length of 1.4 m and a thickness of 3.5 mm was fabricated by using a mechanically strengthened aluminum stabilized superconductor. The coil winding is strong enough to eliminate the outer support cylinder which is necessary in the former thin solenoid type coils. Consequently 2 the coil weight and material thickness are 40 kg, and 2.52 g/cm, respectively. The BESS-Polar was launched near the US McMurdo Station in Antarctica on December 13th 2004, floated at an altitude of 37000 m around the South Pole for nine days. The solenoid was charged up on the ground and kept the field in a persistent current mode during launch and floating. This report describe the flight performance of the solenoid.

We measured atmospheric antiproton spectra in the energy range 0.2 to 3.4 GeV, at sea level and at balloon altitude in the atmospheric depth range 4.5 to 26 g/cm(2). The observed energy spectra, including our previous measurements at mountain altitude, were compared with estimated spectra calculated on various assumptions regarding the energy distribution of antiprotons that interacted with air nuclei. (c) 2005 Elsevier B.V. All rights reserved.

The BESS experiment has measured cosmic-rays at low geomagnetic cutoff for more than a decade and has found suggestive and important results. To study these phenomena further, we planned a long duration flight in Antarctica to accumulate statistics with an instrument built specifically for that purpose. To adapt to the particular requirements of the Antarctica flight, we developed low-power Front-End-Electronics (FEE) using techniques originally developed for space instruments at Goddard Space Flight Center. A Digital Signal Processor (DSP) was resident on each FEE board and controlled each board independently to maximize the data throughput rate. The power consumption of the time-to-digital converter was about 0.5 W per channel and data processing time of one event was less than 30 microseconds. The data obtained by the FEE were sent to an event-builder subsystem board which converted the data format to be handled by a USB 2.0 controller chip. A Compact PCI embedded computing system gathered these data through USB 2.0 ports and built the complete event data including the tracking information. The event data were recorded on an array of hard disk drives (HDD) with total capacity of 3.6 terabytes. This system was flown nearly 9 days over Antarctica successfully recording cosmic-ray events.

The isotopic composition measurements of cosmic-ray hydrogen and helium were made during the most recent period of solar maximum using the Balloon-borne Experiment with a Superconducting Spectrometer (BESS). The data selection procedure and the mass histograms for proton, helium and their isotopes of BESS-2000 are presented in this paper.

We report a cosmic-ray antiproton spectrum measured with the BESS balloon experiment performed in 2002, which was in an intermediate period between the solar maximum in 2000 and the coming solar minimum. The observed antiproton spectrum and the antiproton to proton ratio are crucial for further development of the drift model of the solar modulation effect which has been generally supported by the previous measurements.

The first scientific flight of the BESS-Polar experiment was carried out in December 2004, aiming at elementary particle phenomena in the early Universe through observation of low energy antiprotons and search for antimatter in the cosmic radiation. The BESS-Polar payload was launched on December 13 from Williams Field near the US McMurdo Station in Antarctica, and circulated around the South Pole for 8 days and 17 hours. During the flight, the superconducting spectrometer including the solar-cell power supply system worked well, and two terabytes scientific data were recorded on the onboard hard disk drives. The flight was terminated on December 21, and the payload landed on the Ross Ice Shelf. The recovery operation continued for a week, and the spectrometer was recovered safely.

A flatter spectrum of low-energy cosmic ray antiprotons below 1 GeV measured by the BESS experiment in the last solar minimum period suggests the existence of possible novel and exotic sources of cosmic-ray antiprotons, such as evaporation of primordial black holes and annihilation of supersymmetric dark matter. In order to investigate these antiproton sources and to search for antimatter in the cosmic radiation, the BESS-Polar experiment was carried out with a NASA long duration balloon flight over Antarctica in December 2004. During this 8.5-day flight, the BESS-Polar superconducting spectrometer gathered 900 million cosmic-ray events. The data show that the newly developed particle detector system functioned well enough to observe the low energy antiprotons during the entire flight. Thus' we can expect to derive a precise energy spectrum of the low-energy antiprotons with several-times higher statistics than that from the flight of the previous solar minimum period.

The BESS-Polar balloon payload had its first flight on December 13th-21st, 2004 (UTC) from McMurdo Station, Antarctica. The flight duration was over eight days and more than 9 x 108 cosmic-ray events were recorded. An overview of the BESS-Polar flight, the status of the antiproton analysis, and a discussion of the low-power readout electronics and data acquisition system can be found elsewhere in these proceedings. In this paper we discuss the design, testing, and flight performance of the BESS-Polar Cherenkov counter, which operated in ambient conditions outside a pressure vessel. The silica-aerogel Cherenkov radiator had a nominal index-of-refraction, n = 1.02, yielding an lower limit for the most likely photoelectron (PE) number of 7 in the center of the counter and 9 near the photomultiplier tubes.

The Balloon-borne Experiment with a Super-solenoidal Spectrometer (BESS) instrument has been flown annually from Lynn Lake Manitoba since 1993. The instrument has been upgraded several times to improve its performance. The instalment flown in 1998 was able to detect 2H clearly between 0.13 and 1.78 GeV/n as a result of improvements made on the time-of-flight (TOF) system. The BESS 98 data were analyzed to obtain the ratio and absolute fluxes of 1H and 2H over this energy range. The results were compared with different cosmic ray propagation models and their implications regarding their propagation history are discussed in this paper. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

The Balloon Borne Experiment with a Superconducting Spectrometer (BESS) has measured the energy spectrum of cosmic-ray antiprotons between 0.18 and 4.20 GeV in eight flights between 1993 and 2002. Above about 1 GeV, models in which antiprotons are secondary products of the interactions of primary cosmic rays with the interstellar gas agree with the BESS antiproton spectrum. Below 1 GeV, the data show a possible excess antiproton flux compared to secondary model predictions, suggesting the presence of an additional source of antiprotons. The antiproton/proton ratios measured between 1993 and 1999, during the Sun's positive-polarity phase, are consistent with simple models of solar modulation. However, results from the 2000 flight, following the solar magnetic field reversal, show a sudden increase in the antiproton/proton ratio and tend to favor a charge-sign-dependent drift model. To extend BESS measurements to lower energies, an evolutionary instrument, BESS-Polar, is under construction for polar flight in 2004. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

In nine flights between 1993 and 2002, the Balloon Borne Experiment with a Superconducting Spectrometer (BESS) has measured the energy spectrum of cosmic-ray antiprotons between 0.18 and 4.20 GeV, and the spectra of protons and helium to several hundred GeV. BESS has also placed stringent upper limits on the existence of antihelium and antiduterons. Above about 1 GeV, models in which antiprotons are secondary products of the interactions of primary cosmic rays with the ISM agree with the BESS spectrum. Below 1 GeV, BESS data suggest the presence of an additional source of antiprotons. The antiproton/proton ratios measured between 1993 and 1999, during the Sun's positive-polarity phase, are consistent with simple models of solar modulation. Results from the 2000 flight, following the solar magnetic field reversal, show a sudden increase in the antiproton/proton ratio and tend to favor a charge-sign-dependent drift model. To extend BESS measurements to lower energies, a new instrument, BESS-Polar, is under construction for a flight from Antarctica in 2004. © 2004 Elsevier B.V. All rights reserved.