Balloon-borne Experiment With A Superconducting Spectrometer Research Articles

The results from BESS-Polar experiment

The balloon-borne experiment with a superconducting spectrometer (BESS) instrument was developed as a high-resolution, high-geometric-acceptance magnetic-rigidity spectrometer for sensitive measurements of cosmic-ray antiparticles, searches for antinuclei, and precise measurements of the absolute fluxes of light GCR elements and isotopes. The original BESS experiment flew 8 times over Lynn Lake, Canada and once from Fort Sumner, USA during the period of 1993 through 2002, with continuous improvement in the instrument. Based on the instrument concept inherited from the BESS spectrometer, a very low instrumental energy cutoff for antiprotons was achieved with a new thin-walled superconducting magnet and removal of the outer pressure vessel for BESS-Polar project. The first and second scientific flights called BESS-Polar I/II were successfully performed, over Antarctica in 2004 December and 2007 December respectively. We report the scientific results, focusing on the long-duration flights of BESS-Polar I (2004) and BESS-Polar II (2007–2008).

Time variations of cosmic-ray helium isotopes with BESS-Polar I

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) is configured with a solenoidal superconducting magnet and a suite of precision particle detectors, including time-of-flight hodoscopes based on plastic scintillators, a silica-aerogel Cherenkov detector, and a high resolution tracking system with a central jet-type drift chamber. The charges of incident particles are determined from energy losses in the scintillators. Their magnetic rigidities (momentum/charge) are measured by reconstructing each particle trajectory in the magnetic field, and their velocities are obtained by using the time-of-flight system. Together, these measurements can accurately identify helium isotopes among the incoming cosmic-ray helium nuclei up to energies in the GeV per nucleon region. The BESS-Polar I instrument flew for 8.5days over Antarctica from December 13th to December 21st, 2004. Its long-duration flight and large geometric acceptance allow the time variations of isotopic fluxes to be studied for the first time. The time variations of helium isotope fluxes are presented here for rigidities from 1.2 to 2.5GV and results are compared to previously reported proton data and neutron monitor data.

Search for Primary Antiparticles and Cosmological Antimatter with BESS

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) has performed precise measurements of low-energy cosmic-ray antiproton spectra to investigate signatures of exotic origins such as dark matter candidates or primordial black holes, and has searched for antimatter in cosmic rays that might reach Earth from antimatter domains formed in the early Universe. BESS carried out its second Antarctic flight, BESS-Polar II, during the 2007–2008 Austral Summer, and obtained over 4.7 billion cosmic-ray events from 24.5 days of observation during a solar-minimum period, when the sensitivity of the low-energy antiproton measurements to a possible primary source would be greatest. Here, we report the scientific results.

Cosmic ray 2H/1H ratio measured from BESS in 2000 during solar maximum

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) was flown from Lynn Lake, Manitoba, Canada in August, 2000, during the maximum solar modulation period, with an average residual atmospheric overburden of 4.3g/cm2. Precise spectral measurements of cosmic ray hydrogen isotopes from 0.178GeV/n to 1.334GeV/n were made during the 28.7h of flight. This paper presents the measured energy spectra and their ratio, 2H/1H. The results are also compared with previous measurements and theoretical predictions.

Search for cosmic-ray antiproton origins and for cosmological antimatter with BESS

The balloon-borne experiment with a superconducting spectrometer (BESS) has performed cosmic-ray observations as a US–Japan cooperative space science program, and has provided fundamental data on cosmic rays to study elementary particle phenomena in the early Universe. The BESS experiment has measured the energy spectra of cosmic-ray antiprotons to investigate signatures of possible exotic origins such as dark matter candidates or primordial black holes, and searched for heavier antinuclei that might reach Earth from antimatter domains formed in the early Universe. The apex of the BESS program was reached with the Antarctic flight of BESS-Polar II, during the 2007–2008 Austral Summer, that obtained over 4.7billion cosmic-ray events from 24.5days of observation. The flight took place at the expected solar minimum, when the sensitivity of the low-energy antiproton measurements to a primary source is greatest. Here, we report the scientific results, focusing on the long-duration flights of BESS-Polar I (2004) and BESS-Polar II (2007–2008).

Search for primordial antiparticles with BESS

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 antihelium nuclei, and it made precise measurement of cosmic-ray 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.

The BESS Program

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.

Scientific ballooning in Japan – An over view of recent activities

Current status of scientific ballooning in Japan is reviewed. First, I describe successful application of balloon technologies to construct a vessel of transparent plastic film, to contain about 1000 tons of liquid scintillator in Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND). KamLAND is a project to study neutrino oscillation phenomena, by detecting anti-neutrinos produced in distant nuclear reactors. Next, I describe high altitude balloons developed by the ISAS balloon group. They developed balloons made from ultra-thin polyethylene film, producing a balloon of volume 60,000 m 3 which successfully reached an altitude of 53 km in 2002. This is a world record, the greatest altitude that a balloon has ever achieved. ISAS is applying further effort to develop balloons with even thinner films, to achieve a higher altitude than 53 km. Other recent activities by the ISAS balloon group are briefly described. I also review scientific ballooning projects now operating in Japan, particularly focusing on the Balloon-Borne Experiment with a Superconducting Spectrometer (BESS) program. This is a US–Japan collaborative program that has carried out very precise measurements of antiprotons, protons and other components in primary cosmic rays, as well as measuring the fluxes of atmospheric muons and other components. The results of these observations give us important information to improve our understanding of the production mechanism of antiprotons observed in the primary cosmic rays. The data are also important for analysis of atmospheric neutrino events observed by Super-Kamiokande and other ground-based neutrino detectors. Future prospects of BESS and other balloon-borne cosmic-ray research programs are also presented.

Sub-GeV galactic cosmic-ray antiprotons from primordial black holes in the Randall-Sundrum braneworld

We investigate cosmic-ray antiprotons emitted from the galactic primordial black holes (PBHs) in the Randall-Sundrum type-2 braneworld. The recent results of the Balloon-borne Experiment with a Superconducting Spectrometer (BESS) antiproton observation imply the existence of exotic primary sub-GeV antiprotons, one of whose most probable origin is PBHs in our Galaxy. We show that the magnitude of antiproton flux from PBHs in the Randall-Sundrum braneworld is proportional to negative power of the anti--de Sitter radius and immediately find that a large extra dimension can relax upper limits on the abundance of the galactic PBHs. If actually there are more PBHs than the known upper limit obtained in the pure 4D case, they set a lower bound on the size of the extra dimension above at least ${10}^{20}$ times 4D Planck length to avoid inconsistency. On completion of the numerical studies, we show that these constraints on the AdS radius are comparable to those obtained from the diffuse photon background by some of the authors in the previous paper. Moreover, in the low accretion rate case, only antiprotons can constrain the braneworld. We show that we will detect signatures of the braneworld as a difference between the flux of the antiprotons predicted in 4D and 5D by future observations in sub-GeV region with a few percent precision.

The BESS Program

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.

Precise measurements of the cosmic ray antiproton spectrum with BESS including the effects of solar modulation

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.

Progress of the BESS Superconducting Spectrometer

Balloon-borne Experiment with a Superconducting Spectrometer (BESS) is a balloon-borne spectrometer to study elementary particle phenomena in the early Universe as well as the origin and the propagation of cosmic radiation. The instrument has a unique feature of a thin superconducting solenoid which enables a large acceptance with a cylindrical configuration. Nine balloon flights have been successfully carried out since 1993. In 2002, the detector was upgraded as the BESS-TeV spectrometer to extend primary cosmic-ray spectra up to 1 TeV. For further studies of low-energy antiprotons, a new spectrometer, BESS-Polar, with a ultra-thin superconducting solenoid is being developed for long duration balloon flights in Antarctica.

Antihelium in Cosmic Rays: A New Upper Limit and Its Significance

We have searched for antihelium in the galactic cosmic rays using data obtained on the flight of the Balloon-borne Experiment with a Superconducting Spectrometer (BESS) launched from Lynn Lake, Manitoba, in northern Canada on 1995 July 25. The balloon reached an altitude of 36.5 km with a residual overburden of 5 g cm-2. The total observation time was 12.2 hr with a live-time fraction of 0.61. No antihelium was observed after selections based on dE/dx and event quality cuts at rigidities between 1.6 and 16 GV/c; we infer that 536,420 helium nuclei survived the same cuts. This result leads to an upper limit to the /He abundance ratio of 8.1 × 10-6 (95% confidence level), a factor of 2.7 over the lowest previous limit. Because this limit is for the first time at the level where predicted limits become astrophysically interesting (Ahlen et al.), we have reexamined the transport of cosmic rays in intergalactic space. We show that little can be learned about distant (>10 Mpc) domains of antimatter from a null result.