Balloon-borne Magnet Research Articles

Energy spectra of atmospheric muons measured with the CAPRICE98 balloon experiment

The measurement of the atmospheric muon spectrum is currently of great interest because of the study of atmospheric neutrinos and the claim of neutrino oscillations made in 1998 by the Super-Kamiokande Collaboration. A measurement of the muon flux is an indirect measure of the neutrino flux. Therefore, it can be used to improve the calculation of the atmospheric neutrino flux, which in turn can be compared with the observed neutrino rates in underground detectors. This article reports a new measurement of the m 1 and m 2 spectra at several atmospheric depths in the momentum ranges 0.3‐20 GeV/c and 0.3‐40 GeV/c, respectively. The data were collected by the balloon-borne experiment CAPRICE98 during the ascent of the payload on 28 May 1998 from Fort Sumner, N. M. The experiment used the NMSU-WIZARD/CAPRICE 98 balloon-borne magnet spectrometer equipped with a gas ring imaging Cherenkov detector and a silicon-tungsten calorimeter.

Peter Meyer

Peter Meyer

Measurements of the absolute energy spectra of cosmic-ray positrons and electrons above 7 GeV

A measurement of the energy spectra of cosmic-ray positrons and electrons was made with a balloon-borne magnet- spectrometer, which was flown at a mean geomagnetic cut-o of 4.5 GV/c. The observed positron flux in the energy range 7-16 GeV is approximately an order of magnitude lower than that of electrons, as measured in other experiments at various energies. The power law spectral index of the observed dierential energy spectrum of electrons is 2:89 0:10 in the energy interval 7.5-47 GeV. For positrons the overall fit of the available data above 7 GeV has been considered. The spectral index is found to be 3:37 0:26 and the fraction of positrons, e + /(e + + e ), has a mean value of 0:064 0:003. The world data on e + /(e + + e ) from 0.1 to 30 GeV indicate that a plerion type electron spectrum is preferred over the other types. The trend of the presently existing high energy data also suggests a possible contribution of positrons produced at the pulsar polar cap. High resolution experiments capable of identifying positrons at least up to 100 GeV with high statistics are required to pinpoint the origin of both electrons and positrons in the cosmic radiation.

Measurement of the cosmic-ray antiproton-to-proton abundance ratio between 4 and 50 GeV.

We present a new measurement of the antiproton-to-proton abundance ratio, pbar/p, in the cosmic radiation. The HEAT-pbar instrument, a balloon borne magnet spectrometer with precise rigidity and multiple energy loss measurement capability, was flown successfully in Spring 2000, at an average atmospheric depth of 7.2 g/cm(2). A total of 71 antiprotons were identified above the vertical geomagnetic cutoff rigidity of 4.2 GV. The highest measured proton energy was 81 GeV. We find that the pbar/p abundance ratio agrees with that expected from a purely secondary origin of antiprotons produced by primary protons with a standard soft energy spectrum.

The Cosmic‐Ray Antiproton Flux between 3 and 49 GeV

We report on a new measurement of the cosmic ray antiproton spectrum. The data were collected by the balloon-borne experiment CAPRICE98 which was flown on 28-29 May 1998 from Fort Sumner, New Mexico, USA. The experiment used the NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas Ring Imaging Cherenkov (RICH) detector, a time-of-flight system, a tracking device consisting of drift chambers and a superconducting magnet and a silicon-tungsten calorimeter. The RICH detector was the first ever flown capable of mass-resolving charge-one particles at energies above 5 GeV. A total of 31 antiprotons with rigidities between 4 and 50 GV at the spectrometer were identified with small backgrounds from other particles. The absolute antiproton energy spectrum was determined in the kinetic energy region at the top of the atmosphere between 3.2 and 49.1 GeV. We found that the observed antiproton spectrum and the antiproton-to-proton ratio are consistent with a pure secondary origin. However, a primary component may not be excluded.

First Mass-resolved Measurement of High-Energy Cosmic-Ray Antiprotons

We report new results for the cosmic-ray antiproton-to-proton ratio from 3 to 50 GeV at the top of the atmosphere. These results represent the first measurements, on an event-by-event basis, of mass-resolved antiprotons above 18 GeV. The results were obtained with the NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas-RICH (Ring-Imaging Cerenkov) counter and a silicon-tungsten imaging calorimeter. The RICH detector was the first ever flown that is capable of identifying charge-one particles at energies above 5 GeV. The spectrometer was flown on 1998 May 28-29 from Fort Sumner, New Mexico. The measured p&d1;/p ratio is in agreement with a pure secondary interstellar production.

The Cosmic‐Ray Electron and Positron Spectra Measured at 1 AU during Solar Minimum Activity

We report on a new measurement of the cosmic-ray electron and positron spectra. The data were collected by the balloon-borne experiment CAPRICE94, which was —own from Lynn Lake, Canada, on 1994 August 8¨9 at an altitude corresponding to 3.9 g cm~2 of average residual atmosphere. The experi- ment used the NMSU-WIZARD/CAPRICE94 balloon-borne magnet spectrometer equipped with a solid radiator Ring Imaging Cerenkov (RICH) detector, a time-of-—ight system, a tracking device consisting of drift chambers and multiwire proportional chambers, and a silicon-tungsten calorimeter. This was the —rst time a RICH detector was used together with an imaging calorimeter in a balloon-borne experi- ment. A total of 3211 electrons, with a rigidity at the spectrometer between 0.3 and 30 GV, and 734 positrons, between 0.3 and 10 GV, were identi—ed with small backgrounds from other particles. The absolute energy spectra were determined in the energy region at the top of the atmosphere between 0.46 and 43.6 GeV for electrons and between 0.46 and 14.6 GeV for positrons. We found that the observed positron spectrum and the positron fraction are consistent with a pure secondary origin. A comparison of the theoretically predicted interstellar spectrum of electrons shows that the injection spectrum of primary electrons is steeper than that of the nucleonic components of cosmic rays. Furthermore, the observed electron and positron spectra can be reproduced from the interstellar spectra by a spherically symmetric model for solar modulation; hence, the modulation is independent of the sign of the particle charge. Subject headings: balloonscosmic rayselementary particlesSun: activity

The Cosmic‐Ray Proton and Helium Spectra between 0.4 and 200 GV

We report on the hydrogen nuclei (protons and deuterons) spectrum from 0.15 to 200 GeV and on the helium nuclei spectrum over the energy range from 0.2 to 100 GeV nucleon~1 at the top of the atmo- sphere measured by the balloon-borne experiment Cosmic Antiparticle Ring-Imaging Cerenkov Experi- ment (CAPRICE), which was —own from Lynn Lake, Manitoba, Canada, on 1994 August 8¨9. We also report on the proton spectrum over the energy range from 0.15 to 4.2 GeV. The experiment used the NMSU-WiZard/CAPRICE balloon-borne magnet spectrometer equipped with a solid radiator Ring- Imaging Cerenkov (RICH) detector and a silicon-tungsten calorimeter for particle identi—cation. This was the —rst time a RICH was used together with an imaging calorimeter in a balloon-borne experiment. These detectors allowed for clear particle identi—cation, as well as excellent control of the detector effi- ciencies. The data were collected during 18 hr at a residual mean atmospheric depth of 3.9 g cm~2. With this apparatus 516,463 hydrogen and 32,457 helium nuclei were identi—ed in the rigidity range 0.4 to 200 GV and 1.2 to 200 GV, respectively. The observed energy spectrum at the top of the atmosphere can be represented by (1.1 ^ 0.1) ) 104 E~2.73B0.06 particles (m2 GeV sr s)~1 for hydrogen (E in GeV) between 20 and 200 GeV and (4.3 ^ 0.9) ) 102 E~2.65B0.07 particles (m2 GeV nucleon~1 sr s)~1 for helium nuclei (E in GeV nucleon~1) between 10 and 100 GeV nucleon~1. These spectra are in good agreement with other recent measurements above 10 GeV. The observed spectra —atten below 10 GeV due to solar modulation and are consistent with earlier measurements when solar modulation is taken into account. Between 5 and 200 GV the hydrogen to helium ratio as a function of rigidity was found to be approx- imately constant at 6.1 ^ 0.1. Subject headings: cosmic rayselementary particles

The Cosmic‐Ray Antiproton Flux between 0.62 and 3.19 GeV Measured Near Solar Minimum Activity

We report on the absolute antiproton Nux and the antiproton to proton ratio in the energy range 0.62E3.19 GeV at the top of the atmosphere, measured by the balloon-borne experiment CAPRICE Nown from Lynn Lake, Manitoba, Canada, on 1994 August 8E9. The experiment used the New Mexico State University WiZard/CAPRICE balloon-borne magnet spectrometer equipped with a solid radiator Ring Imaging Cherenkov (RICH) detector and a silicon-tungsten calorimeter for particle identi-cation. This is the -rst time a RICH is used together with an imaging calorimeter in a balloon experiment, and it allows antiprotons to be clearly identi-ed over the rigidity range 1.2E4 GV. Nine antiprotons were identi-ed in the energy range 0.62E3.19 GeV at the top of the atmosphere. The data were collected over 18 hr at a mean residual atmosphere of 3.9 g cm~2. The absolute antiproton Nux is consistent with a pure secondary production of antiprotons during the propagation of cosmic rays in the Galaxy. Subject headings: balloons E cosmic rays E elementary particles E Sun: activity

Search for Antihelium in the Cosmic Rays

On 1987 August 22 a balloon flight was conducted using the Goddard Space Flight Center Low-Energy Antiproton configuration of the New Mexico State University balloon-borne magnet spectrometer. The launch site was Prince Albert, Saskatchewan, Canada. The balloon flew at an average atmospheric depth of 4.7 g cm-2 for more than 22 hr. During this period a sample of 4.2 × 104 helium nuclei was gathered. No antihelium candidates were found in this sample. The resultant upper limit for the ratio of antihelium to helium in cosmic rays over the rigidity interval from 1 to 25 GV/c is 9 × 10-5 at 95% confidence. This limit is below the predicted level, assuming equal matter and antimatter in the extragalactic cosmic rays.

Performance of the CAPRICE RICH detector during the 1994 balloon flight

A RICH detector capable of detecting unit charged particles, e.g. antiprotons and positrons, has been used successfully for the first time in a balloon-borne magnet spectrometer. The thin and compact CAPRICE RICH detector uses a NaF solid radiator, TMAE vapour as photo converter and cathode pad readout in the photosensitive MWPC operated at low gain. 15 photoelectrons are detected per ring for β = 1, perpendicular incidence particles giving a resolution on the Cherenkov angle of 8 mrad, increasing to 14 mrad at 20°C incidence angle. Besides particle identification on an event-by-event basis it efficiently rejects multiparticle events and albedo particles.

Measurement of the Positron to Electron Ratio in the Cosmic Rays above 5 GeV

As part of a series of experiments to search for antimatter in cosmic rays, the New Mexico State University balloon-borne magnet spectrometer was configured for a flight to study positrons. Two completely new instruments, a transition radiation detector and a silicon-tungsten imaging calorimeter, were added to the magnet spectrometer. These two detectors provided a proton rejection factor better than 3 × 104. This instrument was flown from Fort Sumner, New Mexico, at an average depth of 4.5 g cm-2 of residual atmosphere for a period of 25 hr. We report here the measured fraction of positrons e+/(e+ + e-) from ~5 to 60 GeV at the top of the atmosphere. Our measurements do not show any compelling evidence for an increase in this ratio with energy, and our results are consistent with a constant fraction of 0.078 ± 0.016 over the entire energy region.

A neural network for positron identification by transition radiation detector

A neural network algorithm has been applied in order to distinguish positrons from protons by a transition radiation detector (TRD). New variables are introduced, that simultaneously take into account spatial and energy TRD information. This method is found to be better than the one based on classical analysis: the results improve the detector performance in particle identification for efficiency higher than 90%. The high accuracy achieved with this method is used to identify positrons versus protons with 3 × 10 −3 contamination, as required by TRAMP-SI cosmic ray space experiment on the NASA Balloon-Borne Magnet Facility.

A RICH counter for identifying antimatter and light isotopes in the cosmic radiation

A ring imaging Cherenkov (RICH) counter using a solid radiator of NaF is described. It will be an important part of a balloon borne magnet spectrometer to measure the flux of antiprotons and light nuclei in cosmic radiation. For /spl beta/=1 particles of unit charge (normal incidence), 20 photoelectrons per event are detected resulting in a resolution of the reconstructed Cherenkov angle of 5 mrad (r.m.s.). For /sup 14/N nuclei more than 1000 photoelectrons are detected per event (/spl beta/=0.86, normal incidence). Together with a time-of-flight system and an electromagnetic calorimeter it is capable of identifying, in the energy region 0.3-5 GeV, antiprotons and positrons in the presence of a large background. To a good accuracy it measures both the charge and the velocity of the cosmic rays, and can be used to identify different isotopes with Z:1-10 in the energy range of 0.3-3 GeV/nucleon. This detector is planned to fly for 24 hours in the New Mexico State University Balloon Borne Magnet Facility in July 1994 from Lynn Lake in Canada.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A RICH counter for identifying antiprotons and light isotopes in the cosmic radiation

A RICH counter using a solid radiator of NaF is described. It will be an important part of a balloon borne magnet spectrometer to measure the flux of antiprotons and light nuclei in the cosmic radiation. The photosensitive MWPC is operated with a TMAE and ethane mixture at atmospheric pressure and has a cathode pad plane to give an unambiguous image of the Cherenkov light. The induced signals in the pad plane are read out using the AMPLEX chip and DRAMS. For β = 1 particles of unit charge (normal incidence), 25 photoelectrons per event are detected resulting in a resolution of the reconstructed Cherenkov angle of 5 mrad (rms). For 14N nuclei more than 1000 photoelectrons are detected per event ( β = 0.86, normal incidence). By measuring the amount of Cherenkov light produced, the charge of a particle is determined with a 5 standard deviation precision ( Z = 1–10). Combining the information about the charge and the Cherenkov angle with the measured rigidity in the magnetic field, isotope separation is possible for Z = 1–4 in the energy interval 0.8–3 GeV/nucleon and for Z = 5–10 in a more limited energy region.

A measurement of the cosmic-ray H-2 and He-3 spectra and H-2/He-4 and He-3/He-4 ratios in 1989

The energy spectra of H-2 and H-3 nuclei up to energies of 450 and 800 MeV nucleon, respectively, were measured during a balloon flight of the NASA/NMSU Balloon Borne Magnet Facility on September 5, 1989. These isotopes were cleanly resolved from the more abundant H-1 and He-4 using a measurement of rigidity versus velocity as measured in a high-resolution scintillation counter. After correction for atmospheric secondaries the measured H-2/He-4 and He-3/He-4 ratios are both consistent with the production expected if H-1 and He-4 have the same path length in the galaxy as heavier cosmic-ray nuclei such as C and Fe, to within about 20 percent. Solar modulation effects play an important role in this uncertainty. This result favors a generally similar propagation history, along with similar types of sources for H-1 and He-4 and the heavier cosmic-ray nuclei.

Performance of a balloon-borne magnet spectrometer for cosmic ray studies

Abstract This paper summarizes the performance characteristics of the balloon-borne magnet spectrometer operated by New Mexico State University's Particle Astrophysics Laboratory. Particular emphasis has been placed on the rigidity resolution, including both random and systematic errors of the magnetic spectrometer system. Measurement of the performance characteristics has been greatly enhanced through the use of an imaging calorimeter as an independent aid in the identification of cosmic rays.

PBAR: A superconducting magnet spectrometer for cosmic ray antiproton studies

We describe the PBAR balloon-borne magnet spectrometer flown on August 13–14, 1987 to measure the abundance of cosmic ray antiprotons in the energy interval 100–1580 MeV at the top of the atmosphere. The limits first reported [S.P. Ahlen et al., Phys. Rev. Lett. 61 (1988) 145] have been improved [M.H. Salamon et al., Astrophys. J. 349 (1990) 78] to an overall limit p / p<2.0×10 − 5 (85% CL). We summarize the overall design and performance of the PBAR spectrometer, which had the unique ability to establish the mass of each singly charged cosmic ray, as well as to reject spurious antimatter candidates caused by hard scatterings within the instrument.