Study of the light produced in PMT / light guide region of Tile barrel Module 0

For the 1995 1m prototype data it was observed that particles escaping the calorimeter can produce light in the PMT/light guide region [1]. Using both test beam and laboratory data, evidence for this effect was found and the mechanism behind it identified as ionisation or Cherenkov light in the photocathode. For Module 0 this effect is expected to be smaller because of the use of smaller photomultipliers, light guides and fibre bundles. This note reports on a study done with Module 0 testbeam data from september 1996. For muons it is found that the effect is at least an order of magnitude smaller than what was found for the 1m prototypes. Moreover, it is also shown how pions which have longitudinal leakage also produce extra signals.