C. Grimani

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 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

Observations of cosmic ray electrons and positrons using an imaging calorimeter

A ballon-borne magnet spectrometer system was flown for 5.5 hr at an altitude of more than 117,00 feet from Prince Albert, Saskatchewan (Canada), on 1989 September 5, when the Newark neutron monitor rate was 2952. The instrument was a modified version of the one used to observe antiprotons in 1979. The most significant modification was the addition of an imaging calorimeter, 7.33 radiation lengths thick. Inclusion of the calorimeter has significantly improved the ability to distinguish electrons and positrons from the other constituents of the cosmic rays. The absolute electron flux has been determined in the energy interval 1.3-26 GeV. The electron spectrum at the top of the atmosphere was found to be J(sub e-) = 177E(exp -(3.15+/-0.13)) electrons/ sq m/(sr s GeV) in the energy range 4.0-26 GeV. Below 4 GeV, the spectrum showed flattening, which is consistent with the effect of solar modulation. The e(+)/(e(+)+e(-)) ratio was found to be (0.11 +/- 0.03) in the energy range 5.2-13 GeV.

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 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.

Balloon measurements of cosmic ray muon spectra in the atmosphere along with those of primary protons and helium nuclei over midlatitude

We report here the measurements of the energy spectra of atmospheric muons and of the cosmic ray primary proton and helium nuclei in a single experiment. These were carried out using the MASS superconducting spectrometer in a balloon flight experiment in 1991. The relevance of these results to the atmospheric neutrino anomaly is emphasized. In particular, this approach allows uncertainties caused by the level of solar modulation, the geomagnetic cut-off of the primaries and possible experimental systematics to be decoupled in the comparison of calculated fluxes of muons to measured muon fluxes. The muon observations cover the momentum and depth ranges of 0.3-40 GeV/c and 5-886 g/cmsquared, respectively. The proton and helium primary measurements cover the rigidity range from 3 to 100 GV, in which both the solar modulation and the geomagnetic cut-off affect the energy spectra at low energies.

Measurement of Cosmic-Ray Antiprotons from 3.7 to 19 GeV

The antiproton-to-proton ratio,p ¯/p, in cosmic rays has been measured in the energy range 3.7‐19 GeV. This measurement was carried out using a balloon-borne superconducting magnetic spectrometer along with a gas Cerenkov counter, an imaging calorimeter, and a time-of-flight scintillator system. The measuredp ¯/p ratio was

Absolute spectrum and charge ratio of cosmic ray muons in the energy region from 0.2 GeV to 100 GeV at 600 m above sea level

We have determined the momentum spectrum and charge ratio of muons in the region from 250 MeV/c to 100 GeV/c using a superconducting magnetic spectrometer. The absolute differential spectrum of muons obtained in this experiment at 600 m above sea level is in good agreement with the previous measurements at sea level. The differential spectrum can be represented by a power law with a varying index, which is consistent with zero below 450 MeV/c and steepens to a value of −2.7 ± 0.1 between 20 and 100 GeV/c. The integral flux of muons measured in this experiment span a very large range of momentum and is in excellent agreement with the earlier results. The positive to negative muon ratio appears to be constant in the entire momentum range covered in this experiment within the errors and the mean value is 1.220 ± 0.044. The absolute momentum spectrum and the charge ratio measured in this experiment are also consistent with the theoretical expectations. This is the only experiment which covers a wide range of nearly 3 decades in momentum from a very low momentum.

LISA Pathfinder: mission and status

LISA Pathfinder, the second of the European Space Agencys Small Missions for Advanced Research in Technology (SMART), is a dedicated technology demonstrator for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission. The technologies required for LISA are many and extremely challenging. This coupled with the fact that some flight hardware cannot be fully tested on ground due to Earth-induced noise led to the implementation of the LISA Pathfinder mission to test the critical LISA technologies in a flight environment. LISA Pathfinder essentially mimics one arm of the LISA constellation by shrinking the 5 million kilometre armlength down to a few tens of centimetres, giving up the sensitivity to gravitational waves, but keeping the measurement technology: the distance between the two test masses is measured using a laser interferometric technique similar to one aspect of the LISA interferometry system. The scientific objective of the LISA Pathfinder mission consists then of the first in-flight test of low frequency gravitational wave detection metrology. LISA Pathfinder is due to be launched in 2013 on-board a dedicated small launch vehicle (VEGA). After a series of apogee raising manoeuvres using an expendable propulsion module, LISA Pathfinder will enter a transfer orbit towards the first Sun?Earth Lagrange point (L1). After separation from the propulsion module, the LPF spacecraft will be stabilized using the micro-Newton thrusters, entering a 500?000 km by 800?000 km Lissajous orbit around L1. Science results will be available approximately 2 months after launch.

Measurement of the flux of atmospheric muons with the CAPRICE94 apparatus

A new measurement of the momentum spectra of both positive and negative muons as function of atmospheric depth was made by the balloon-borne experiment CAPRICE94. The data were collected during ground runs in Lynn Lake on the 19-20th of July 1994 and during the balloon flight on the 8-9th of August 1994. We present results that cover the momentum intervals 0.3-40 GeV/c for negative muons and 0.3-2 GeV/c for positive muons, for atmospheric depths from 3.3 to 1000 g/cm**2, respectively. Good agreement is found with previous measurements for high momenta, while at momenta below 1 GeV/c we find latitude dependent geomagnetic effects. These measurements are important cross-checks for the simulations carried out to calculate the atmospheric neutrino fluxes and to understand the observed atmospheric neutrino anomaly.