On the Velocity of Light Signals in the Deep Underwater Neutrino Experiments

TL;DR

This paper discusses the importance of using the correct group velocity of light signals in deep underwater neutrino telescopes for accurate track reconstruction, highlighting a previously overlooked delay of about 10 ns over 100 meters.

Contribution

It emphasizes the necessity of accounting for group velocity in light signal timing to improve the accuracy of deep underwater neutrino telescope measurements.

Findings

Group velocity causes a ~10 ns delay over 100 m

This delay was previously unmentioned in literature

Correct velocity usage is crucial for accurate track reconstruction

Abstract

During the last few years deep underwater neutrino telescopes of a new generation with dimensions close to 100 m or more were taken into operation. For the correct track reconstruction and for the interpretation of light pulses from calibration lasers one has to use the group velocity for light signals. The difference between group velocity leads to an additional delay of about 10 ns for a distance of 100 m between light source and photjmultiplier. From the time of the appearance of the first projects of deep underwater neutrino telescopes in the middle of 70th this fact was never mentioned in the literature.