Underground Lab To Probe Ratio of Matter To Antimatter 82
Wired reports on the Enriched Xenon Observatory 200, a particle detector scientists hope will answer the question of why there is significantly more matter than antimatter in the universe. Quoting:
"The new detector will try to fill in the picture, determining basic features of [neutrinos], like their mass and whether or not they, unlike almost all other particles, are their own antiparticles. That quirk is why some scientists believe neutrinos could be the mechanism for the creation of our matter-filled universe. Almost all other particles have an antiparticle twin that, if it comes into contact with the particle, immediately annihilates it. But if neutrinos are their own antiparticles they could conceivably be knocked onto matter's 'team,' thereby causing the cascading win for matter over antimatter that we know occurred. As the Indian theoretical physicist G. Rajasekaran put it in a speech [PDF] earlier this year, neutrinos that are their own antiparticles would explain 'how, after [the] annihilation of most of the particles with antiparticles, a finite but small residue of particles was left to make up the present Universe.'"
Re:the neutrinos are everywhere (Score:3, Insightful)
Except most of them are not even sure what >90% of the universe is made of, so what makes them so sure that the rest of the universe is mostly straight?
Extension to the Standard Model (Score:5, Insightful)
The Standard Model assumes that all three neutrino species (electron, muon, and tau) are massless, and is essentially agnostic about whether neutrinos are their own antiparticles. If a neutrino is (is not) its own antiparticle, we call it a Majorana (Dirac) particle. Most any reaction which could tell the difference between Majorana and Dirac neutrinos can't occur in a Standard Model with massless neutrinos, so the difference is subtly and has no real experimental consequence.
We know the Standard Model is wrong, however. From neutrino oscillations, we know that neutrinos have tiny masses. This suddenly means that there ARE experimental consequences: neutrino-less double beta decay is possible for Majorana neutrinos but not Dirac neutrinos, for example. This is what EXO and many other experiments (GERDA, MAJORANA, CUORE, ...) are looking for. Existing results aren't quite sensitive enough to tell the difference, but new ones may be.
Just because something is not part of the Standard Model doesn't mean that it's unpopular - we need to change the Standard Model somehow, after all, since it's wrong about neutrino masses! My impression (as a particle physicist, but not in this sub-field) is that most particle theorists actually expect neutrinos to be Majorana particles. There are very interesting theories based upon a scheme called the "see-saw mechanism" which can simultaneously explain why neutrinos have such tiny masses and why the universe has so much more matter and antimatter. If neutrinos are just boring old Dirac particles, it will be back to the drawing board!