November 19, 2011

Measurement of the neutrino velocity with the OPERA detector in the CNGS beam

Arxiv (32 pages)- The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km with much higher accuracy than previous studies conducted with accelerator neutrinos. The measurement is based on high-statistics data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An early arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum was measured. This anomaly corresponds to a relative difference of the muon neutrino velocity with respect to the speed of light. The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5 {\mu}s long extractions, was confirmed by a test performed using a beam with a short-bunch time-structure allowing to measure the neutrino time of flight at the single interaction level.