Influence of magnetic fields on the response of a uranium scintillator electromagnetic calorimeter

The response of a uranium scintillator sampling calorimeter to incident electrons and to the uranium radioactivity was measured in transverse magnetic fields up to 1.4T. The signal from electrons rises by as much as 9% due to the expected increase in light output of plastic scintillators in magnetic fields. For fields below 0.3 T the response to the uranium radioactivity tracks the electron signal to within about 0.5%. At higher fields it drops sharply, reaching −1.5% at 1.4 T. The consequences for the calibration of the ZEUS uranium scintillator calorimeter are discussed. We found no evidence for a change in the electromagnetic sampling fraction for fields below 0.3 T