M. Imori

Cosmic-ray antiproton flux in the energy range from 200 to 600 MeV

We have studied the low-energy antiprotons in the cosmic rays by utilizing data obtained by the Balloon-borne Experiment with a Superconducting magnetic rigidity Spectrometer (BESS) flown in 1993 July from Lynn Lake, Manitoba, Canada. A detailed description of the event selection criteria and background corrections is given. Seven antiprotons are found that give an antiproton flux of 6.4 -->+ 5.5?3.5 ? 10-3(m2 sr s GeV)-1 and an antiproton/proton ratio of 5.2 -->+ 4.4?2.8 ? 10-6 in the 200-600 MeV energy range. These results are consistent with a secondary origin of low-energy cosmic-ray antiprotons within our uncertainties, but they still require the precise measurement of the spectrum shape below 500 MeV to clarify exactly the model of particle propagation and possible contributions from exotic sources.

Balloon-borne experiment with a superconducting solenoidal magnet spectrometer

Abstract A balloon-borne superconducting solenoidal magnet spectrometer, BESS, has been designed and developed to investigate cosmic-rays and particle-astrophysics. Search for primordial antimatter in cosmic-rays and observation of gamma-rays are primary objectives to study early history of the Universe. The cylindrical spectrometer configuration with a thin superconducting solenoid magnet is optimized to provide a large geometrical acceptance of 0.5–1.0 m 2 sr for these scientific objectives. The spectrometer system has been completed and is planned to be launched for the first scientific flight from Lynn Lake, Canada, in 1993. This report describes the progress of the spectrometer development and discuss about its capability to search for primordial antimatter in cosmic rays.

A NEW LIMIT ON THE FLUX OF COSMIC ANTIHELIUM

Abstract A very sensitive search for cosmic-ray antihelium was performed using data obtained from three scientific flights of the BESS magnetic rigidity spectrometer. We have not observed any antihelium; this places a model-independent upper limit (95% C.L.) on the antihelium flux of 6×10−4 m−2sr−1s−1 at the top of the atmosphere in the rigidity region 1 to 16 GV, after correcting for the estimated interaction loss of antihelium in the air and in the instrument. The corresponding upper limit on the He /He flux ratio is 3.1 ×10−6, 30 times more stringent than the limits obtained in similar rigidity regions with magnetic spectrometers previous to BESS.

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.

Real-time data processes in a balloon-borne apparatus

In a balloon-borne experiment, signals from detectors are processed in a balloon-borne apparatus so as to comply with data bandwidth of a storage device installed in the apparatus. The process begins at front-end processors receiving signals from detectors and proceeds under successive stages by dedicated processors. Event data are finally fed to a computer bank for post trigger selection where the events are further selected before being written into the storage device. The computer bank is made of transputer modules. The transputers are widely employed and some processors are implemented by the transputers. How the processors are integrated is described together with function and implementation of the individual processors.<<ETX>>

Measurement of cosmic ray H and HE isotopes in a balloon borne experiment with a superconducting solenoid spectrometer

Abstract The Balloon Borne Experiment with a Superconducting Solenoid Spectrometer (BESS) was flown annually in 1993, 1994, and 1995. In this report we present the energy spectra and isotopic composition of cosmic ray H and He measured from the 1993 flight. The low energy fluxes of H and He agree with the IMP-8 satellite data for a 26 day period (7/14/93 – 8/9/93) that overlapped the BESS flight. Both 2 H and 3 He were well separated from 1 H and 4 He. The measured spectra were corrected for the atmospheric overburden and compared with the interstellar/heliospheric propagation calculations.

A flash ADC system with fast data compression for a balloon-borne experiment

A multichannel flash ADC (analog to digital converter) system is developed for a balloon-borne experiment where flash ADCs installed in individual channels output samples of signals at the rate of 30 MHz. The system incorporates zero suppression and data compression. The samples from the converter are put to the zero suppression on a real-time basis and then submitted to the data compression. The data compression reduces the event data in a size further, so that the data of as many events as possible can be recorded on a storage device installed on the balloon-borne apparatus. A zero-suppression circuit is implemented in each channel. A data-compression module in the system begins to scan all the channels, performing compression, after the converter completes sampling. Special care is taken to keep the power consumption of the system within a moderate level.<<ETX>>

Status and result from BESS

Abstract A balloon-borne experiment using a superconducting solenoidal magnet spectrometer is being carried out with aims at making a precise measurement of low energy antiproton flux in cosmic rays and a highly sensitive search for primordial antimatter in the Universe. The spectrometer has a unique cylindrical configuration associated with a thin superconducting solenoidal magnet and is realizing a geometrical acceptance of 0.5 m 2 sr. The first scientific ballooning flight was successfully carried out in northern Canada, in summer, 1993, and the second flight is being prepared to be carried out in summer, 1994. Performance of the spectrometer in the first flight and progress of the experiment are described.

Intelligent CAMAC crate controller incorporating a transputer

Abstract A CAMAC crate controller module having a built-in transputer was developed, being named the “Intelligent CAMAC Crate Controller (ICCC)”. Due to the transputers architecture, multiple ICCCs can be networked by simple serial link connections. The control programs are developed in Occam or C language, which support conccurrent argorithms and their implementation in transputer networks. Each ICCC controls the front-end CAMAC modules in the crate, operates in parallel, and interpretes commands from the host computer. Data read from the modules is concurrently and autonomously processed, and then transmitted to the network where it is gathered into the host computer file system. The present paper describes the ICCCs hardware and software using a simple configuration network. Our particular device application for a balloon-borne experiment is also discussed, i.e., a data acquisition system networking twenty-seven transputers.

A remote console system for balloon borne experiments

A remote console system is developed to improve remote control over balloon-borne experimental apparatus. The remote console system, residing at a ground station for balloon-borne experiments, sends commands to the apparatus and receives transmissions from it. The system communicates by radio with microcomputers incorporated in the experimental apparatus borne on the balloon, where the microcomputers control the apparatus individually. Personal computers in the system emulate the remote console of the microcomputers. The apparatus is thereby remotely controlled through the personal computers placed at the ground station. The system includes plural personal computers which are interconnected so as to share the transmissions from the apparatus. The transactions between the ground station and the balloon-borne apparatus are supplied to work stations to be analyzed further. The authors describe the implementation of the system and the communication between the ground station and the balloon-borne apparatus. >