Neutrinos herald possible new physics in Japan

There’s an embarrassment of choice for my message this week. Firstly, it was great to see a press release from the Japanese T2K (Tokai to Kamioka) experiment on 15 June, signalling not only potentially great physics, but also that the Japanese physics community is getting back on its feet after the earthquake and tsunami. Back home, the LHC is running beautifully... 

Crossing the inverse femtobarn threshold so early into this years run is wonderful achievement, and augurs well for the summer conferences. We’ve now reached the stage where a single LHC fill is delivering as much data as the entire 2010 run. And finally, when Council met this week, I was pleased to announce that CERN has received formal confirmation from all five applicants for membership, opening the way to CERN welcoming new members soon. A busy two weeks, then, but what I’d like to focus on is the new result from Japan.

Simply stated, the T2K result shows the first indication of the appearance of electron neutrinos in a muon neutrino beam – further evidence that these most elusive of particles can change, chameleon like, into other forms. This so-called neutrino oscillation is nothing new. Its effects were first observed in the 1970s by a pioneering experiment hosted in the Homestake gold mine in the USA that studied neutrinos coming from the Sun. Neutrino oscillation was then observed directly early this century by experiments in Canada and Japan. Since then, many measurements have been made, including those at the Gran Sasso lab using a neutrino beam from CERN. The Gran Sasso results show indications for the appearance of tau neutrinos in a muon neutrino beam.

So why are the indications from T2K important? Firstly, although almost massless, neutrinos are an incredibly abundant component of our universe. That alone makes their detailed study worthwhile. To fully understand the neutrino family of particles requires measuring each oscillation pattern in detail, and different facilities in Asia, Europe and North America coordinate their efforts to do so.

What makes the appearance of electron neutrinos in a muon neutrino beam particularly significant, however, is that an accurate knowledge of this particular process is a vital pre-condition to designing experiments to use neutrinos to probe nature’s matter-antimatter imbalance. From a physics point of view, it’s an intriguing result and I’m looking forward to more to come from T2K once the beam is back and more data can be accumulated. More importantly, however, it’s a very welcome sign that Japan is getting back to normal.

Rolf Heuer