Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam

At the end of the 2011 run, the CERN CNGS neutrino beam has been briefly operated in lower intensity mode with ∼1012 p.o.t./pulse and with a proton beam structure made of four LHC-like extractions, each with a narrow width of ∼3 ns, separated by 524 ns. This very tightly bunched beam allowed a very accurate time-of-flight measurement of neutrinos from CERN to LNGS on an event-by-event basis. The ICARUS T600 detector (CNGS2) has collected 7 beam-associated events, consistent with the CNGS collected neutrino flux of 2.2×1016 p.o.t. and in agreement with the well-known characteristics of neutrino events in the LAr-TPC. The time of flight difference between the speed of light and the arriving neutrino LAr-TPC events has been analysed. The result δt=0.3±4.9(stat.)±9.0(syst.) ns is compatible with the simultaneous arrival of all events with speed equal to that of light. This is in a striking difference with the reported result of OPERA (OPERA Collaboration, 2011) [1] claiming that high energy neutrinos from CERN arrive at LNGS ∼60 ns earlier than expected from luminal speed.