Large-angle scattering of multi-GeV muons on thin Lead targets

The probability of large-angle scattering for multi-GeV muons in thin ($t/X_0 \sim 10^{-1}$) lead targets is studied. The new estimates presented here are based both on simulation programs (GEANT4 libraries) and theoretical calculations. In order to validate the results provided by simulation, a comparison is drawn with experimental data from the literature. This study is particularly relevant when applied to muons originating from $\nu_\mu^{CC}$ interactions of CNGS beam neutrinos. In that circumstance the process under study represents the main background for the $\nu_\mu \to \nu_\tau$ search in the $\tau \to \mu$ channel for the OPERA experiment at LNGS. Finally, we also investigate, in the CNGS context, possible contributions from the muon photo-nuclear process which might in principle also produce a large-angle muon scattering signature in the detector.