The purpose of this work is to report the measurement of a time-shift in the
OPERA set-up in a totally independent way from Time Of Flight (TOF)
measurements of CNGS neutrino events. The LVD and OPERA experiments are both
installed in the same laboratory: LNGS. The relative position of the two
detectors, separated by an average distance of ~ 160 m, allows the use of very
high energy horizontal muons to cross-calibrate the timing systems of the two
detectors, using a TOF technique which is totally independent from TOF of CNGS
neutrino events. Indeed, the OPERA-LVD direction lies along the so-called
"Teramo anomaly", a region in the Gran Sasso massif where LVD has established,
many years ago, the existence of an anomaly in the mountain structure, which
exhibits a low m. w. e. thickness for horizontal directions. The "abundant"
high-energy horizontal muons (nearly 100 per year) going through LVD and OPERA
exist because of this anomaly in the mountain orography. The total live time of
the data in coincidence correspond to 1200 days from mid 2007 until March 2012.
The time coincidence study of LVD and OPERA detectors is based on 306 cosmic
horizontal muon events and shows the existence of a negative time shift in the
OPERA set-up of the order of deltaT(AB) = - (73 \pm 9) ns when two calendar
periods, A and B, are compared. This result shows a systematic effect in the
OPERA timing system from August 2008 until December 2011. The size of the
effect is comparable with the neutrino velocity excess recently measured by
OPERA. It is probably interesting not to forget that with the MRPC technology
developed by the ALICE Bologna group the TOF world record accuracy of 20 ps was
reached. That technology can be implemented at LNGS for a high precision
determination of TOF with the CNGS neutrino beams of an order of magnitude
smaller than the value of the OPERA systematic effect