The Space Mission Pamela represents a state-of-the-art of the investigation of the cosmic radiation, addressing the most compelling issues facing astrophysics and cosmology: the nature of the dark matter that pervades the universe, the apparent absence of cosmological antimatter, the origin and evolution of matter in the galaxy. Pamela, a powerful particle identifier using a permanent magnet spectrometer with a variety of specialized detectors, is an instrument of extraordinary scientific potential that is measuring with unprecedented precision and sensitivity the abundance and energy spectra of cosmic rays electrons, positrons, antiprotons and light nuclei over a very large range of energy from 50 MeV to hundreds GeV, depending on the species. These measurements, together with the complementary electromagnetic radiation observation that will be carried out by AGILE and GLAST space missions, will help to unravel the mysteries of the most energetic processes known in the Universe.
The Pamela mission is devoted to the investigation of dark matter, the baryon asymmetry in the Universe, cosmic ray generation and propagation in our Galaxy and Solar System, and studies of solar modulation and the interaction of cosmic rays with the earth?s magnetosphere.
The primary scientific goal is the study of the antimatter component of the cosmic radiation, in order:
- To search for evidence of annihilations of dark matter particles (e.g. non-hadronic particles outside the Standard Model) by precisely measuring antiproton and positron energy spectra;
- To search for antinuclei, in particula antihelium;
- To test cosmic-ray propagation models through precise measurements of the antiparticle energy spectrum and precision studies of light nuclei and their isotopes.
Concomitant goals include:
- A study of solar physics and solar modulation during the 24th solar minimum by investigating low energy particles in the cosmic radiation;
- A study of Jovian electrons
- Reconstructing the cosmic ray electron energy spectrum up to several TeV thereby allowing a possible contribution from local sources to be studied.
By the late 1930s it was well established that matter in our everyday world essentially consists of electrons, protons and neutrons. However, the existence of antimatter, including positrons, antiprotons, antineutrons, antideuterons, antitritium and antihelium 3, had also been established in the laboratory. Scientists today are still puzzled about the apparent imbalance of matter and antimatter in the Universe. Why shouldn’t the Universe contain equal amounts of matter and antimatter? Big Bang theory for the origin of the Universe makes hypothesis that in the first instants of its existence matter and antimatter had to be present in equal amount.
Dark matter research
In recent years cosmological observations have provided increasingly convincing evidence that non-baryonic dark matter is the building block of all structures in the Universe. Galactic dark matter was suggested to solve the discrepancy between observed (luminous) matter in the Universe and that inferred by dynamical considerations. A matter density of about 30% of the critical density of the universe can be composed of dark matter.
The mystery of the dark matter in the universe remains unsolved. Among the most plausible candidates are weakly interacting massive particles (WIMP), of which the supersimmetric neutralino is a favourite candidate from the point of view of particle physics. The neutralino arises naturally in supersymmetric extension of the standard model, and has the attractive feature of giving a relic density which in large region of parameter space is adequate to explain cosmological dark matter.
Neutralino are Majorana fermions and will annihilate with each other in the halo, resulting in the symmetric production of particles and antiparticles, the latter providing an observable signature. With Pamela we look for annihilations that produce antiprotons and positrons.