J. Z. Wang

Precise Measurement of Cosmic-Ray Proton and Helium Spectra with the BESS Spectrometer

We report cosmic-ray proton and helium spectra in energy ranges of 1-120 GeV nucleon-1 and 1-54 GeV nucleon-1, respectively, measured by a flight of the Balloon-borne Experiment with Superconducting Spectrometer (BESS) in 1998. The magnetic rigidity of the cosmic ray was reliably determined by highly precise measurement of the circular track in a uniform solenoidal magnetic field of 1 T. Those spectra were determined within overall uncertainties of ±5% for protons and ±10% for helium nuclei including statistical and systematic errors.

Successive measurements of cosmic-ray antiproton spectrum in a positive phase of the solar cycle

Abstract The energy spectrum of cosmic-ray antiprotons ( p s) has been measured by BESS successively in 1993, 1995, 1997 and 1998. In total, 848 p s were clearly identified in energy range 0.18–4.20 GeV. From these successive measurements of the p spectrum at various solar activity, we discuss about the effect of the solar modulation and the origin of cosmic-ray p s. The p / p ratios showed no distinctive year-to-year variation during the positive Suns polarity phase.

Measurement of Cosmic-Ray Hydrogen and Helium and Their Isotopic Composition with the BESS Experiment

The cosmic-ray hydrogen and helium spectra have been measured by the Balloon Borne Experiment with a Superconducting Solenoid Spectrometer (BESS), which has been flown from Lynn Lake, Manitoba, Canada, annually since 1993. The BESS experiment provides excellent rigidity measurement and precise particle identification with a large geometric acceptance. We present here the hydrogen and helium nuclei energy spectra from 0.2 to 10 GeV nucleon-1 and their isotopic composition from 0.2 to about 1 GeV nucleon-1 for the first BESS flight. This provides the first simultaneous measurements of the cosmic-ray secondaries, deuterons, and 3He, with their primaries, protons, and 4He over this energy range in a period of solar minimum. In this paper, we have achieved significant improvements in data analysis in the following aspects. First, the latest available cross-section data and their parameterizations were utilized in the simulation code developed for this study. Second, a complete simulation was performed for both protons and heavy ions: the δ-ray effect was properly simulated and showed a large influence on the measurement of heavy ions at high energies. Third, the secondary particle correction, which dominates the systematic uncertainty at low energies for singly charged particles, protons and deuterons, was calculated iteratively with the simultaneously measured primary cosmic-ray spectra. In general, the results of this experiment are consistent with other recent measurements using balloon-borne or satellite experiments, but with better precision. The measured spectra of protons, deuterons, 3He, and 4He and their corresponding ratios are compared with different interstellar/heliospheric propagation calculations, which were derived to fit observations of heavy nuclei. The overall good agreement indicates that the propagation history for light cosmic-ray elements, protons, deuterons, and helium nuclei is similar to that of the heavy nuclei. The 2H/1H ratio is sensitive to the propagation models, and our results show a tendency of better agreement with the reacceleration model than the standard leaky-box model.

Precise measurements of atmospheric muon fluxes with the BESS spectrometer

The vertical absolute fluxes of atmospheric muons and muon charge ratio have been measured precisely at different geomagnetic locations by using the BESS spectrometer. The observations had been performed at sea level (30 m above sea level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada. The vertical cutoff rigidities in Tsukuba (36.2°N, 140.1°E) and in Lynn Lake (56.5°N, 101.0°W) are 11.4 and 0.4 GV, respectively. We have obtained vertical fluxes of positive and negative muons in a momentum range from 0.6 to 20 GeV/c with systematic errors <3% in both measurements. By comparing the data collected at two different geomagnetic latitudes, we have seen an effect of cutoff rigidity. The dependence on the atmospheric pressure and temperature, and the solar modulation effect have been also clearly observed. We also clearly observed the decrease of charge ratio of muons at low momentum side with at higher cutoff rigidity region.

Bess and its future prospect for polar long duration flights

Abstract The Balloon-borne Experiment with a Superconducting Spectrometer, BESS, aims to study elementary particle/antiparticle phenomena in the early history of the Universe. The instrument has a unique feature of a thin superconducting solenoid magnet enabling a large geometrical acceptance with a horizontally cylindrical configuration. Seven balloon flights have been successfully carried out since 1993. More than 10 3 comic-ray antiproton have been unambiguously detected, and the energy spectrum has been measured with the characteristic peak at 2 GeV. The search for cosmic-ray antihelium brought the upper-limit of the antihelium/helium ratio down to −6 . To extend the highly sensitive measurements, we are planning polar long duration flights in Antarctica focusing on the very low energy antiproton spectrum towards the solar-minimum in the next decade.

Cosmic-ray energetics and mass (CREAM) balloon experiment

Abstract The Cosmic Ray Energetics And Mass (CREAM) Ultra Long Duration Balloon (ULDB) mission will investigate ultra high energy (1012 to > 5 × 1014 eV) cosmic rays over the elemental range from protons to iron. The measurements will be made with an instrument that consists of a sampling tungsten/scintillator calorimeter preceded by a graphite target with scintillator layers for trigger and track-reconstruction purposes, a transition radiation detector (TRD) for observing heavy nuclei, and a segmented timing-based particle-charge detector. A key feature of the instrument is its ability to obtain simultaneous measurements of the energy and charge of a subset of nuclei by the complementary calorimeter and TRD techniques, thereby allowing in-flight inter-calibration of their energy scales. The energy extent will depend on a series of ULDB flights of identical instruments: three flights will reach 5 × 1014 eV. The different flights can be carried out at essentially any latitude, including the polar regions of either hemisphere. CREAM will be ready for flight one year after the TIGER (Trans-Iron Galactic Element Recorder) ULDB demonstration flight, which is currently scheduled for launch in December 2001.

Advanced Thin Ionization Calorimeter (ATIC) balloon experiment: expected performance

An advanced thin ionization calorimeter (ATIC) will be used to investigate the charge composition and energy spectra of ultrahigh energy primary cosmic rays in a series of long- duration balloon flights. While obtaining new high priority scientific results, this balloon payload can also serve as a proof of concept for a BGO calorimeter-based instrument on the International Space Station. The ATIC technical details are presented in a companion paper at this conference. Here we discuss the expected performance of the instrument based on a GEANT code developed for simulating nuclear- electromagnetic cascades initiated by protons. For simulations of helium and heavy nuclei, a nucleus-nucleus interaction event generator LUCIAE was linked to the GEANT based program. Using these models, the design of the ATIC detector system has been optimized by simulating the instrument response to particles of different charges over the energy range to be covered. Results of these simulations are presented and discussed.

Progress in Search for Antihelium with BESS

We have searched for antihelium nuclei in cosmic rays using the data obtained from balloon flights of the BESS magnetic spectrometer. The search was mainly based on track-quality selection, followed by rigidity analysis, and on the time-of-flight and dE/dx measurements by the scintillation counter hodoscope. We analysed all the data collected during 1993–2000 with a common analysis procedure. No antihelium nuclei events were found in the energy range from 1 to 14 GV. In order to determine a new upper limit, we have simulated the loss in the air and in the instrument of He (He) using the GEANT/GHEISHA code. Combined with the data collected in 1993 through 2000, a new 95 % confidence upper limit for the ratio of He/He at the top of the atmosphere of 6.8 × 10−7 has been obtained to be after correcting for the interactions in the air and in the instruments.

Advanced thin ionization calorimeter to measure ultrahigh energy cosmic rays

Abstract An Advanced Thin Ionization Calorimeter (ATIC) will be used to investigate the charge composition and energy spectra of primary cosmic rays over the energy range from about 10 10 to >10 14 eV in a series of long-duration balloon flights. The totally active BGO calorimeter, 22 radiation length thick, will measure the electromagnetic energy ensuing from nuclear interactions in a one interaction length thick carbon target. Trajectory information will be obtained from the location of the cascade axis in the BGO calorimeter and in the segmented scintillator layers of the upstream carbon target. The highly segmented charge module comprised of scintillator strips, a silicon matrix, and a Cherenkov array will minimize the effect of backscattered particles on primary charge measurements. While obtaining new high priority scientific results, the ATIC balloon payload can also serve as a proof of concept, or engineering model, for a BGO calorimeter-based instrument on the International Space Station. We examine the added advantage of locating such an experiment for long durations on a platform such as the Space Station.

Spectra of H and HE measured in a series of annual flights

Abstract We have obtained the absolute spectra of H and He by analyzing data collected by a series of annual flights of the Balloon borne Experiment with a Superconducting solenoid Spectrometer payload. This instrument is configured with a cylindrical magnet, a Time-of-Flight system, a set of cylindrical multiwire drift chambers inside and outside the magnet, and a central tracking device Jet chamber. The analysis involves Monte Carlo simulations of the effective geometry factor, studies of various efficiencies, and corrections for the ionization energy loss, attenuation and atmospheric secondaries. Variations of the H and He fluxes at different levels of solar modulation are presented.