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Dark matter search Print
checked.gif Link to PAMELA Results Antiprotons
checked.gif Link to PAMELA Results Positrons


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 24% of the critical density of the universe should 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 that annihilate with each other in the halo, resulting in the symmetric production of particles and antiparticles, that can provide an observable signature. Pamela is looking for annihilations that produce antiprotons  and positrons as final states, both through primary annihilation channels or directly.

Dark Matter annihilation
Dark Matter annihilation


Some models predict that the antiproton flux at energies of tens of GeV resulting from annihilation of high-mass neutralinos (e.g. Higgsinos) could be more than an order of magnitude above the flux of secondary antiprotons, and thus could be unambiguously observed. The most interesting energy range of this search should be above ~ 10 GeV , where the excellent performances of Pamela are combined with the smallness of the solar modulation effects.

Pre-PAMELA data - Antiproton
Pre-PAMELA data - Antiproton
Pre-PAMELA data - Positron
Pre-PAMELA data - Positron


WIMPs could contribuite to the positron flux by direct annihilation in e+e- , and to continuum positrons from the other annihilation channels. This could be seen as an excess or bump beginning at a few GeV and extending upward in energy to a point depending on the WIMP mass.

 

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Edited by Vincenzo Buttaro