The Matter – Anti-matter Asymmetry of the Universe: Why is there something, rather than nothing?
by
Prof.David Nygren(University of Texas at Arlington)
→
Portugal
Sala de Conferências (Departamento de Física)
Sala de Conferências
Departamento de Física
Universidade de Coimbra
Description
Our universe is filled with matter, but antimatter is an ephemera, seen only naturally in the debris of high-energy processes and cosmic rays. Yet the standard model of particle physics and cosmic implies that only about 1 proton or anti-proton in about 1020 should have escaped annihilation into photons or neutrinos. The measured ratio, however, of baryons–protons and neutrons–to the photons left over is about 6 x 10-10, ten orders of magnitude greater! At some very early moment, something broke that initial symmetry, yielding ultimately the universe we inhabit and explore today. The attractive theory of leptogenesis, with massive neutrinos that distinguish between matter and antimatter, predicts this ratio and imposes a Majorana nature on today’s neutrinos–neither matter nor antimatter. The only practical avenue for discovering a Majorana nature is the search for an almost unimaginably rare nuclear decay–neutrinoless double beta decay–possible in a few isotopes. If we convincingly observe this decay mode, we learn that that lepton number is not conserved and that the neutrino and anti-neutrino are identical. I focus on NEXT, a search based on high-pressure xenon gas that attempts to realize excellent energy resolution and high rejection of backgrounds through event topology. Strangely, a biochemistry technique might help us succeed. Perhaps an exciting discovery awaits, one that may indicate how the universe chose to keep about one part per billion of matter.