Characterisation of a low-momentum high-rate muon beam monitor for the FAMU experiment at the CNAO-XPR beam facility

The FAMU experiment aims at an indirect measurement of the Zemach radius of the proton. The measurement is carried out on muonic hydrogen atoms (mu H) produced through the low -momentum (50-60 MeV/c) muon beam a the RIKEN-RAL mu- facility. The particle flux plays an important role in this measurement, as it is proportional to the number of mu H atoms produced, which is the target of the FAMU experimental method. The beam monitor calibration technique and results, presented here, are meant to extract a reliable estimation of the muon flux during the FAMU data taking. These measurements were carried out at the CNAO synchrotron in Pavia, Italy, using proton beams and supported by Monte Carlo simulation of the detector in Geant4.