ar X iv : h ep - e x / 99 05 01 8 v 1 1 3 M ay 1 99 9 HE . 3 . 2 . 13 Transition Radiation Detector in MACRO

The MACRO detector is located in the Gran Sasso Laboratory. MACRO's overburden varies from 3150 to 7000 hg/cm 2. A transition radiation detector (TRD) has been added to the MACRO detector in order to measure the residual energy of muons entering MACRO, i.e. the energy they have after passing through the Gran Sasso's rock overburden. The TRD consists of three identical modules with a total horizontal area of 36 m 2. The results presented here are referred to single and double events in MACRO with one muon crossing one of the TRD modules. Our data show that double muons are more energetic than single ones, as predicted by the interaction models of primary cosmic rays with the atmosphere.