Abstract
Abstract 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. The measurement is based on 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 arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of $ \left( {6.5\pm 7.4\left( {\mathrm{stat}.} \right)_{-8.0}^{+8.3}\left( {\mathrm{sys}.} \right)} \right)\mathrm{ns} $ was measured corresponding to a relative difference of the muon neutrino velocity with respect to the speed of light $ {{{\left( {\upsilon -c} \right)}} \left/ {c} \right.}=\left( {2.7\pm 3.1\left( {\mathrm{stat}.} \right)_{-3.3}^{+3.4}\left( {\mathrm{sys}.} \right)} \right)\times {10^{-6 }} $ . The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5 μs long extractions, was confirmed by a test performed at the end of 2011 using a short bunch beam allowing to measure the neutrino time of flight at the single interaction level.
Highlights
The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in
By a full FLUKA-based simulation of the CNGS beam [24,25,26] it was shown that the time difference computed assuming a particle moving at the speed of light from the target down to LNGS, with respect to the value derived by taking into account the speed of the relativistic parent meson down to its decay point is less than 0.02 ns
In order to exclude possible systematic effects related to the use of the proton waveforms as probability density function (PDF) for the distributions of the neutrino arrival times within the two extractions and to their statistical treatment, a test was performed with a dedicated CNGS beam generated by a proton beam set up on purpose for the neutrino velocity measurement
Summary
The OPERA neutrino detector at LNGS is composed of two identical Super Modules, each consisting of an instrumented target section with a mass of about 625 tons followed by a magnetic muon spectrometre. The CNGS beam is produced by accelerating protons to 400 GeV/c with the CERN Super Proton Synchrotron (SPS) These protons are ejected with a kicker magnet towards a 2 m long graphite target in two extractions, each lasting 10.5 μs and separated by 50 ms. Secondary charged mesons are focused by a magnetic horn and reflector, each followed by a helium bag to minimise the interaction probability of the mesons. These decay in flight, mainly into neutrinos and muons, in a 1000 m long evacuated tunnel. The different components of the CNGS beam are shown in figure 2
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
