New tests conducted at the Gran Sasso National Laboratory of INFN by the OPERA Collaboration, with a specially set up neutrino beam from CERN, confirm so far the previous results on the measurement of the neutrino velocity. The new tests seem to exclude part of potential systematic effects that could have affected the original measurement.
"A measurement so delicate and carrying a profound implication on physics requires an extraordinary level of scrutiny - said Fernando Ferroni, president of Italian Institute for Nuclear Physics (INFN) - The experiment OPERA, thanks to a specially adapted CERN beam, has made an important test of consistency of its result. The positive outcome of the test makes us more confident in the result, although a final word can only be said by analogous measurements performed elsewhere in the world".
"One of the eventual systematic errors is now out of the way, but the search is not over. They are more checks of systematics currently under discussion, one of them could be a synchronisation of the time reference at CERN and Gran Sasso independently from the GPS, using possibly a fiber" said Jacques Martino, Director of National Institute of Nuclear and Particle Physics of French CNRS.
On November 17 the OPERA Collaboration has submitted the paper on the neutrino velocity measurement for publication on JHEP, and in parallel to the ArXiv. The paper is online today November 18. The time passed from the public seminar at CERN on September 23 was used to make the preprint more readable, to take into account valuable suggestions from the community, to further check the main issues of the data analysis, and mainly to conduct a new test with the specially set up neutrino beam from CERN.
This beam was characterized by a better time definition of the proton extraction time, by having about 3 nanoseconds long bunches spaced by as much as 524 nanoseconds. In this way, compared to the previous measurement, the neutrinos bunches are narrower and more spaced from each other. This permits to make a more accurate measure of their velocity at the price of a much lower beam intensity: only 20 clean events have been collected by OPERA in this phase. Additional events could be eventually collected in the next year run.
This achievement was possible thanks to the strong collaboration with the CERN accelerator team. The Collaboration will continue taking data next year also employing a new muon detector at CERN placed behind the hadron absorber to perform additional independent studies.