Study of Photonuclear Interaction of Muons in Rock with the MACRO Experiment

The inelastic muon-nucleus interaction was studied at accelerators, in the range of large Q transfer (Q ≥ 1GeV ) mainly to measure the nucleon structure functions (deep inelastic scattering experiments). However, the bulk of interactions are characterized by low Q (Q ≤ 0.1GeV ) and can be described with the exchange of a quasi-real photon between the muon and the nucleon and they are often referred to as photo-nuclear interaction of muons. Recently, it has been stressed that nuclear interactions of muons are an important source of background for many underground experiments. A comparison between experimental measurements about the hadrons production by muons and Monte Carlo (MC) simulations is mandatory to test the reliability of theoretical models. In fact, uncertainties do exist on the cross section calculation for the process, mainly due to the extrapolation of photonuclear cross section at high energies and in the simulation of the hadronic final state, because the smallness of the Q does not allow the use of perturbative QCD. The aim of the present work is to compare real data collected by the large area underground experiment MACRO [1], taking data at Gran Sasso laboratory, with GEANT 3.21 and with FLUKA97, the latter based on the cross section calculated by Bezrukov and Bugaev[3] and on DPM model[4] for the sampling of the final state.