Neutrino mixing angles from T2K and MINOS
By Hamish Johnston
Less than a fortnight ago we brought you news that the T2K experiment in Japan has caught the first glimpse of muon neutrinos changing (or oscillating) into electron neutrinos as they travel 300 km under Japan.
Now researchers at the MINOS experiment in the US have seen the same neutrino oscillation. The MINOS physicists sent a beam of neutrinos more than 700 km underground from Fermilab in Chicago to the Soudan Underground Laboratory in Minnesota. At Soudan, the team detected a total of 62 electron neutrinos, which is 13 more than they should have seen if some muon neutrinos had not changed to electron neutrinos.
Neutrinos exist in three “flavours” – muon, electron and tau – that change or “oscillate” from one to another as they travel in space. The oscillation strength between different types of neutrino is characterized by three “mixing angles” – known as theta-12, theta-23 and theta-13. Theta-12 and theta-23 have already been measured but theta-13 requires the observation of the muon-electron neutrino oscillation.
More data are required before theta-13 can be nailed down – you can see the uncertainties in the T2K and MINOS results in the diagram. Then physicists will try to measure the same quantity for anti-muon and anti-electron neutrinos. Comparing the two angles could help physicists understand why there is much more matter than antimatter in the universe.
You can read Fermilab’s announcement here.