M. Bocciolini

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

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.

The Wizard/CAPRICE silicon-tungsten calorimeter

A silicon-tungsten calorimeter has been developed to be flown in the Wizard/CAPRICE balloon borne experiment to measure the flux of antiprotons, positrons and light nuclei in the cosmic radiation. The calorimeter is composed of 8 .r. .v silicon sampling planes [active area (48 X 48) cm’] interleaved with 7 tungsten absorbers (7 radiation lengths): it provides the topology of the interacting events together with an independent measurement of the deposited energy. Details of the front-end electronics and of the read-out system are given and the overall performances during pre-flight ground operations are described as well.

High-speed use of CCD area sensors as high energy particle detectors

A position sensitive detector for minimum ionizing particles is described. It is based on charge coupled devices (CCDs) area image sensors with single pixel sizes of 22 × 22 μm2. The operating frequency is 6.75 MHz and the total readout time for 2.3 × 105 pixels is about 40 ms. The devices are operated close to room temperature.

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.

WiZard SiW imaging calorimeter: a preliminary study on its particle identification capability during a balloon flight in 1993

Abstract The WiZard Collaboration is engaged in a program to study the antimatter components of the cosmic rays. A silicon-tungsten (WiW) imaging calorimeter has been developed as part of this program. We present its performance and preliminary results, obtained during a balloon flight on September 8, 1993. The flight was dedicated to the measurement of the positron spectrum in the energy range 4–50 GeV and took place from Ft. Sumner, New Mexico.

CAPRICE98: A balloon borne magnetic spectrometer to study cosmic ray antimatter and composition at different atmospheric depths

CAPRICE98 is a superconducting magnetic spectrometer built by the WiZard collaboration. It was launched from Ft. Summer, NM, USA on the 28th of May 1998. For the first time a gas RICH detector has been flown together with a silicon electromagnetic calorimeter. The instrument configuration included a time of flight detector and a drift chamber stack, which were placed in the region of a magnet field, for rigidity measurement. Science objectives for this experiment include the study of antimatter in cosmic rays and that of cosmic ray composition in the atmosphere with special focus on muons.

Ersicson's fluctuations in the photodisintegration of Si28

Abstract The cross section of the reactions Si 28 (γ, p) Al 27 and Si 28 (γ, α) Mg 24 as been measured in an energy range ΔE = 117 keV around 17.62 MeV gamma ray energy. Six different transitions (γ, p 0 ), (γ, p 1 ), (γ, p 2 ), (γ, p 4 ), (γ, α 0 ) and (γ, α 1 ) have been separately analysed; they show strong, uncorrelated fluctuations, the amplitude of which agrees with Ericsons predictions (pure statistical reaction and purely E1 gamma absorption being assumed). No free parameter, as the effective number of channels, is required for the comparison. Some contribution of direct effect (up to, say, 50%) is not excluded. The relative yield of (γ, α) to (γ, p) transitions is, on the average, lower (by a factor about 10) than the statistical model would predict, on the basis of transmission coefficients. This is probably an example of the isobaric spin selection rules, as applied to photodisintegration by Gell-Mann and Telegdi.

WiZard 2: a proposal to complement WiZard detector with two further modules of tracking calorimeter and an accurate spark counter t.o.f. system

Among the several existent proposals for the cosmic antimatter search, the Wi#x005A-0304;ard project for the U.S. Space Station Freedom shows the greatest interest. A possible upgrading of the Wi#x005A-0304;ard apparatus, called Wi#x005A-0304;ard 2, is presented in order to sensibly improve the capability of detecting antihelium nuclei in the cosmic radiation.SummaryAmong the several existent proposals for the cosmic antimatter search, the Wi#x005A-0304;ard project for the U.S. Space Station Freedom shows the greatest interest. A possible upgrading of the Wi#x005A-0304;ard apparatus, called Wi#x005A-0304;ard 2, is presented in order to sensibly improve the capability of detecting antihelium nuclei in the cosmic radiation.RiassuntoFra tutte le varie proposte esistenti nell’ambito della ricerca di antimateria cosmica, il progetto Wi#x005A-0304;ard per la Stazione Spaziale americana Freedom si dimostra del piú grande interesse. Si presenta un possibile ampliamento dell’apparato Wi#x005A-0304;ard allo scopo di migliorare sensibilmente la capacità di rivelare nuclei di antielio nella radiazione cosmica.Among the several existent proposals for the cosmic antimatter search, the Wi#x005A-0304;ard project for the U.S. Space Station Freedom shows the greatest interest. A possible upgrading of the Wi#x005A-0304;ard apparatus, called Wi#x005A-0304;ard 2, is presented in order to sensibly improve the capability of detecting antihelium nuclei in the cosmic radiation. Fra tutte le varie proposte esistenti nell’ambito della ricerca di antimateria cosmica, il progetto Wi#x005A-0304;ard per la Stazione Spaziale americana Freedom si dimostra del piu grande interesse. Si presenta un possibile ampliamento dell’apparato Wi#x005A-0304;ard allo scopo di migliorare sensibilmente la capacita di rivelare nuclei di antielio nella radiazione cosmica.

Identification of cosmic ray electrons and positrons by neural networks

Abstract A data analysis based on artificial neural network classifiers has been done to identify cosmic ray electrons and positrons detected with the balloon-borne NMSU/Wizard-TS93 experiment. The information is provided by two ancillary and independent particle detectors: a transition radiation detector and a silicon-tungsten imaging calorimeter. Electrons and positrons measured during the flight have been identified with background rejection factors of 80 ± 3 and 500 ± 37 at signal efficiencies of 72 ± 3% and 86 ± 2% for the transition radiation detector and silicon-tungsten imaging calorimeter, respectively. The ability of the artificial neural network classifiers to perform a careful multidimensional analysis surpasses the results achieved by conventional methods.