Verification of the CNGS timing system using fast diamond detectors

A new fast diagnostic tool was installed in the CNGS facility in 2011 following the neutrino time-of-flight results published by OPERA in September 2011. Among others, four polycrystalline CVD (pCVD) diamond detectors were placed in the secondary beam line about 1200 m downstream of the CNGS target in order to measure the beam structure of the muons which are produced together with the muon neutrinos. Upstream of the CNGS target, a fast beam current transformer measures the proton beam structure. The sub-nanosecond single-pulse time resolution of pCVD diamond for a minimum ionising particle in combination with a GPS system allows the measurement of the GPS timing of individual secondary particle bunches crossing these detectors with a precision of < 1 ns. The complicated structure of the CNGS muon beam in 2011 necessitates the combination of adjacent bunches in order to compare the proton beam structure with the muon beam structure. An analysis of the detector signals was carried out, which provides an independent timing measurement at CERN with a precision of 1.2 ns. Uncertainties from other sources as cable lengths add up to 3.4 ns, resulting in an overall precision of 3.6 ns. The distance between the beam current transformer and the diamond detectors has been measured to (1859.95±0.02) cm. The nominal time-of-flight of (6205.3±1.7) ns for a 17 GeV/c muon, as present in the CNGS muons beam, falls within the uncertainties of the measured time-of-flight of (6205.2±3.6) ns. Hence, the GPS timing measurements performed at CERN are consistent.