Recently the OPERA collaboration measured the velocity of neutrinos by measuring the time difference between the creation of a burst of neutrinos at CERN and the annihilation of one of these neutrinos at the OPERA detector. The method relies on the assumption, that each of the neutrinos created at CERN has the same probability to be detected at OPERA. If this assumption is wrong, then the determination of the neutrino velocity as performed by OPERA is biased.
