 |
INFN Sezione di Roma 2 |  |
| Universita' di Roma Tor Vergata" |
| |
INFN Sezione di Roma 2 | |
| Universita' di Roma Tor Vergata" |
The Cosmic AntiParticle Ring Imaging Cherenkov
Experiment (CAPRICE) flew for the first time in a balloon at 38
km altitude
for 27 hours in August 1994 (CAPRICE94). It collected data
about more than 6 million cosmic ray particles and the analysis
to
measure the amount of antimatter in the cosmic radiation is well
under
way [see the web site for references and publications]. The main
aim
of the experiment is to measure the flux of antiparticles
(antiprotons and positrons) in the cosmic radiation. The result will
give valuable information on the production and transport of
cosmic rays in our galaxy. In addition one might find exotic sources
of antimatter, others than the expected secondary
production from cosmic ray nucleon interaction with the
interstellar gas. Any excess of antimatter can come from annihilation
of dark matter particles, extragalactic origin, evaporation of
primordial black holes etc. We also continue the search for
heavier antinuclei (antihelium, anticarbon etc.) which would be a
direct evidence for the
existence of anti-stars. The flux of all light isotopes in the
cosmic
radiation gives valuable information about the production and
transportation mechanisms of cosmic rays in our galaxy. Besides the
RICH detector the spectrometer includes a super conducting magnet with
a tracking detector system of drift chamber and multiproportional
chambers, a time-of-flight system and an Si-W imaging
calorimeter. The CAPRICE97 experiment was successfully launched
on the morning of 24 May1997. All instruments worked well and muon data
were recorded during the three hour long ascent to a float altitude of
36 km. The flight had to be terminated after four hours due to
pressure problems.
CAPRICE98 was launched by balloon from Fort
Sumner, New Mexico, on 1998 May 2. It floated at an atmospheric depth
of about
5.5 g cm-2 for a period of 21 hr at a mean vertical cutoff
rigidity of about 4.5 GV. More than 5 million triggers were collected
at float altitude. A total of 31 antiprotons with a rigidity at the
spectrometer between 4 and 50 GV were identified with small backgrounds
from other particles. The absolute antiproton energy spectrum was
determined in the 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 cannot be excluded.This experiment
has reported the first mass-resolved high-energy antiprotons ever
detected.
CAPRICE is one of the flights performed by the WiZard
collaboration with members from France, Germany, Italy, Sweden and USA.
Schematic view of the CAPRICE98 apparatus.