Neutrinos caught in evasive behavior

First proof of character shift documented at Japanese detector

Neutrinos have been caught switching identities. The indisputable detection is a first, physicists announced July 19 at the European Physical Society meeting in Stockholm.

Neutrinos, wispy neutral particles that barely interact with anything, come in three types, or flavors: tau, muon and electron. In recent years, scientists have fired beams of muon neutrinos and found that many of them disappear before they reach detectors hundreds of kilometers away. Physicists concluded that some of the muon neutrinos must have morphed into electron neutrinos, which are difficult to detect (SN Online 6/1/10).

Now physicists from the T2K experiment in Japan say they have pointed a beam of muon neutrinos at a detector nearly 300 kilometers away and measured the number of arriving electron neutrinos. Over three years they detected 28 electron neutrinos, proving that some of the muon neutrinos had changed flavors during their millisecond-long journeys.

The next step, says physicist Steve Brice of Fermilab in Batavia, Ill., is to compare the identity shifting of neutrinos with that of their antimatter counterparts. Neutrinos emerged right after the Big Bang and remain the most abundant particles that have mass (SN 1/26/13, p. 18), so their behavior could explain why the universe is rich in matter rather than antimatter.