Are some forms of antimatter more massive than regular matter?

Matter and antimatter should be of equal weight, but the results from a new experiment suggest that they aren't.

Neutrinos are tough things to study. They are a little like electrons, if electrons didn't have any charge. Charge is the main reason that electrons interact with the outside world. Neutrinos only interact with other atoms through the subatomic weak force or when they get so close to other atoms that they are affected by gravity. This happens pretty rarely. So rarely that neutrinos can pass through the earth without interacting with anything. It's like they were never there.

So any experiments made to study neutrinos involves very large scale experiments looking for very small scale objects. MINOS – Main Injector Neutrino Oscillation Search – is one of those experiments. It involves two facilities; one made to generate a stream of neutrinos, and pass them through a detector, and the other 750 miles away, measuring the stream after it has passed through solid earth.

Are some forms of antimatter more massive than regular matter?

MINOS, as the name suggests, is specifically looking for neutrino oscillation. Neutrino oscillation is when neutrinos change from one kind of neutrino to another. These different kinds of neutrinos have different masses, and that difference is what's being measured. The MINOS team detects any difference in mass between the stream measured at the Fermilab, outside of Chicago, and the stream measured hundreds of miles away in a mine in Minnesota.

The MINOS team performed experiments in which they measured the change in mass between muon and tau neutrinos. They then measured the change in mass between muon and tau antineutrinos. To everyone's surprise, the experiments indicated that the antineutrinos dropped more mass than the regular neutrinos. It's possible, given the results of the experiments, that antineutrinos are forty percent larger than neutrinos.

That shouldn't be. Antimatter particles are supposed to have the same mass as their regular matter equivalents. Only the charge is supposed to be different. If the mass of antimatter, even only certain particles of antimatter, has a significantly different mass than matter, that could point to the reason why we are living in a matter, rather than an anti-matter, universe. Although this initial finding will need further confirmation, it could lead to a whole new understanding of particle physics and of the origins of the universe.

Via Scientfic American, MINOS for the Public, Physics.org, and Physics World.