Underground Lab To Probe Ratio of Matter To Antimatter

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.'"

How so?

[KasperMeerts]

Who says there is more matter than antimatter in the universe? Has anyone ever gone to the Andromeda galaxy? So how do we now it consists of normal matter? Doesn't matter react the same as antimatter in every possible way?

Questions for a physicist in this field

[kanweg]

Does antimatter attract matter or repulse it (could a double star, one of antimatter and one of matter, i.e. where the stars revolve around each other exist?).

Would it be a prerequisite that a big bang produces as much matter as antimatter?

Bert

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Re:To pick a nit

[The_Wilschon]

IIRC, standard model neutrinos are Dirac particles, which have well defined antiparticles. However, the hypothesis being tested is whether or not neutrinos are actually Majorana particles, which are invariant under charge conjugation (that is, they are precisely the same particle as their antiparticle.). It all comes down to representation theory and the Lorentz group (and friends). If we claim that charge conjugation is an interesting transformation to examine, then we must clearly describe exactly how each of our fields (particles) changes when we apply that transformation. Dirac and Majorana particles transform two different ways, and we don't know that our conjecture that all the fermions are Dirac particles is actually correct.

Re:To pick a nit

[rasputin465]

a neutrino isn't actually it's own anti-particle, strictly, it's that a neutrino doesn't actually have a known strictly defined antiparticle equivalent.

IAAPP. Neutrinos have very well-defined antiparticles, and we observe them all the time in nature. We can verify that they and neutrinos have quantum numbers that are opposite to one another. Normally, for charged particles, the antiparticles have the opposite charge and so there is no question that these are distinct. But for neutral particles, really the only non-zero quantum number available is the handedness (this is related to helicity, which describes if their spin is left-handed or right-handed with respect to their motion). We have only observed left-handed neutrinos and only right-handed antineutrinos. But the question arises, is that the ONLY difference? Because with the observation of neutrino oscillations, we have evidence that neutrinos have mass (which is not allowed in the standard model), and so their helicity is not fixed. If this is true, then whether a particle is a neutrino or antineutrino is simply a matter of reference frame, and hence neutrinos are their own antiparticles (similar to the way that photons are their own antiparticles).

Re:To pick a nit

[Anonymous Coward]

Why does the existence of neutrino oscillations mean that neutrinos must have mass?

Over simplifying (IANAPP): to oscillate, a thing much change. To change, a thing must experience time. Things traveling at the speed of light cannot experience time (a consequence of special relativity). A massless neutrino would travel at the speed of light.

Since neutrinos oscillate, they experience time, which means they cannot travel at the speed of light, which means they cannot be massless, which means they must have mass.