PAMELA mission: preliminary results about nuclei analysis

The PAMELA (Payload for Antimatter Matter Exploration and Light nuclei Astrophysics) experiment is a satelliteborne apparatus that will make long duration measurements of the cosmic radiation over an extended energy range with a particular focus on antiparticles and light nuclei. Specifically, PAMELA will measure the cosmic-ray antiproton and positron spectra over the largest energy range ever achieved and will search for antinuclei with unprecedented sensitivity. Furthermore, it will measure the light nuclear component of cosmic rays and test cosmic-ray propagation models. PAMELA is housed on-board the Russian Resurs-DK1 satellite, which was launched from the Baikonur cosmodrome on June 15th 2006 in an elliptical (350-610 km of altitude) orbit with an inclination of 70 degrees. PAMELA consists of: a permanent magnet spectrometer which provide rigidity and charge sign information; a Time-of-Flight and trigger system for velocity and charge determination; an electromagnetic imaging calorimeter for lepton/hadron discrimination; a shower tail catcher scintillator and a neutron detector. An anticoincidence system is used offline to reject false triggers. This paper reviews the capability of the PAMELA subdetectors to identify light nuclei; preliminary results about nuclear abundance ratios will be presented. I. THE PAMELA INSTRUMENT The PAMELA experiment [1] is a space-borne apparatus devoted to the study of cosmic rays, with an emphasis on the measurement of the cosmic-ray antiproton and positron energy spectra. The instrument was launched by a Russian Soyuz-TM rocket on the 15th of June 2006 from the cosmodrome of Baykonur in Kazakhstan. It is carried as a ”piggy-back” on board of the Russian Resurs-DK1 satellite for Earth observation. The satellite flies on a quasi-polar (inclination 70◦), elliptical orbit (altitude 350-610 km), and the expected mission length is 3 years. The instrument measures the spectra of cosmic rays (protons, electrons, and corresponding antiparticles) over a wide energy range and with a statistics unreachable by balloonborne experiments. Additionally, PAMELA is searching for antimatter in the cosmic radiation and it is investigating phenomena connected with Solar and Earth physics and measuring the light nuclear component of Galactic cosmic rays in the interval 100 MeV/n 200 GeV/n. The apparatus is ∼ 1.3 m high, has a mass of 470 kg and an average power consumption of 355 W. 1INFN, Section of Rome Tor Vergata, Rome, Italy, laura.marcelli@roma2.infn.it Fig. 1. PAMELA apparatus with its reference system. The PAMELA apparatus is composed of the following subdetectors, arranged as shown in figure 1: • a Time of Flight system (ToF: S1, S2, S3); • a magnetic spectrometer; • an anticoincidence system (CARD, CAT, CAS); • an electromagnetic imaging calorimeter; • a shower tail catcher scintillator (S4); • a neutron detector. PAMELA is built around a 0.43 T permanent magnet spectrometer equipped with 6 planes of double-sided silicon detectors allowing the sign, absolute value of charge and momentum of traversing charged particles to be determined. The acceptance of the spectrometer (which also defines the overall acceptance of the PAMELA experiment) is 21.5 cms and the maximum detectable rigidity is ∼ 1 TV. Spillover effects limit the upper detectable antiparticle momentum to ∼ 190 GeV/c (∼ 270 GeV/c) for antiprotons (positrons). The spectrometer is surrounded by a plastic scintillator veto shield. An electromagnetic calorimeter, mounted below the spectrometer, measures the energy of incident electrons and allows topological discrimination between electromagnetic and hadronic showers (or non-interacting particles). Planes of