Last week the T2K Collaboration in Japan announced the observation of electron neutrino appearance events using the neutrino beam from J-PARC to the Super Kamiokande detector (Read paper submitted to Physical Review Letters). The collaboration reported the observation of six events with an expected background of 1.5 ± 0.3 events. The probability that the background would fluctuate upward to give six events is less than 1 percent. Thus we now have strong evidence that muon neutrinos oscillate to electron neutrinos and that the last unknown neutrino mixing angle, called theta-13, which tells us about these oscillations is relatively large. That this parameter should be relatively large is important because it will enable a rich future program of neutrino oscillation experiments, in particular experiments that will be able to make statements about matter-antimatter asymmetry in the universe. This measurement is a great achievement for our colleagues at J-PARC and T2K.
The earthquake and tsunami stopped operations at T2K and J-PARC in March, but our Japanese colleagues expect to be back up and running by the end of this year. Once J-PARC is restored to working order, the number of protons on target will ramp up quickly and the results after a year of running will be considerably more precise. In the meantime the MINOS experiment will update its 2010 constraints on theta-13 and several reactor neutrino experiments could confirm the T2K results within a year or two. NOvA will be able to measure theta-13 accurately once it is up and running. This is also very good news for the Long Base Line Neutrino Experiment since the likely value of theta-13 is large enough for LBNE to achieve its full promised potential.
This week the working group established by Director of DOE’s Office of Science Bill Brinkman to develop options for the Homestake site where the far LBNE detector would be placed will present its report to HEPAP. This report will be used by the DOE to decide how to proceed. Later in the month a National Research Council committee chaired by Andy Lankford will report on the value of the science proposed for the Deep Underground Laboratory at the Homestake site. So all the pieces are gradually falling into place for the DOE to make a decision on Homestake and on LBNE.