  The FAMU experiment aims at an indirect measurement of the Zemach radius of
the proton. The measurement is carried out on muonic hydrogen atoms produced
through the low-momentum (50-60 MeV/c) muon beam a the RIKEN-RAL negative muon
facility. The particle flux plays an important role in this measurement, as it
is proportional to the number of muonic hydrogen 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.
