Neutrinos in the News

A little more tab clearance, here, this time a few recent stories dealing with those elusive little buggers, neutrinos. In roughly chronological order:< /p>

• The Daya Bay experiment in China has measured a key parameter for neutrino oscillation (arxiv paper), the phenomenon where neutrinos of one of the three observed types slowly evolve into one of the others. Mathematically, this is described as each of the three types we observe being an admixture of three more fundamental types. This mixing is described in terms of the sine of some “mixing angle,” because physicists love geometry, and two of the three mixing angles had already been measured. The Daya Bay experiment measured the third– or, more precisely, they found that the square of the sine of the third mixing angle is 0.092 +/- 0.016 +/- 0.005, where the two uncertainty values are for statistical and systematic uncertainties. This is somewhat larger than expected, which is probably a good thing, because it may imply more of a difference between matter and antimatter than you get from the simplest models, which in turn would help explain why everything we see in the universe is matter and not antimatter.
• A group at Fermilab has sent a message via neutrinos (press release), encoding a simple signal in on-off pulses of neutrinos generated at Fermilab and detected by a giant underground detector a kilometer away. This is not particularly useful for anything, because they need a big particle accelerator to make the pulses and a detector with a mass on the order of tons to detect them, but it’s kind of cute.
• Finally, a second group at the Gran Sasso laboratory in Italy has used the same neutrino beam used by the OPERA collaboration to check the time of flight of the neutrinos passing from CERN to Italy, and find that it agrees perfectly with what you expect for neutrinos moving at light speed, not the tiny bit faster that OPERA saw. As usual with particle physics stuff, Matt Strassler has a good and balanced round-up. These results from the ICARUS experiment (I’m not even going to try to figure out what linguistic crimes they committed to get that acronym) are fairly conclusive evidence that OPERA’s result was in error, though given the complexity of both measurements, it’s still worth repeating the experiment as planned in May.

And that’s the news regarding the elusive neutrino.