Development of the FAMU experimental apparatus for the proton radius measurement

The proton, the nucleus of the hydrogen atom, is the building block of the universe and its fascinating internal structure is defined by Quantum Chromo-Dynamics. Our experiment will measure the hyperfine splitting of the muonic hydrogen atom (μp) to study the proton’s internal magnetic structure by laser exciting from singlet μp to the triplet state with an original technique that we have proposed and tested in recent years. Have had the chance to enter the FAMU (Fisica degli Atomi MUonici) experiment in its final realization phase and I could take part in the development of all aspects of the experiment from the preliminary data taking and the subsequent analysis to the definition of the layout and the development of the laser. In particular, I took part in the preliminary data collection at ISIS accelerator facility at Rutherford Appleton Laboratory (RAL) in UK. I contributed to the analysis of the data collected by the detectors based on Ce:LaBr3 scintillation crystals with an innovative readout based on SiPM (Silicon Photo-Multiplier), finding useful improvements to perfection the resolution of these detectors. I also analyzed the data collected in the 2016 FAMU data acquisition, improving the knowledge on the argon transfer rate dependence on the temperature and X-rays de-excitation energy spectra. I designed the trigger system and realized the laser data acquisition system. The major work in which I was involved was on FAMU laser system, which will excite the hyperfine splitting transition, the most crucial part of the experiment. I participated, taking also the responsibility of the laser safety officer a RAL, to the development and characterization of the oscillator and amplifier for the 1.26 μm laser source, which we developed on purpose for our experiment. The test and qualification of all the non-linear crystals were additional aspects of my work for our laser source, for which I developed the whole laser control program. This program allows to control remotely and in real time every aspect of the laser: from the wavelength to the energy production and the control of the stabilization of the beams through a feedback system developed on purpose. Hit by the consequences of the COVID-19 pandemic, while continuously improving the laser and experiment layout, we were forced to postpone the data acquisition of the experiment at RAL in September 2022, after the one-year-long maintenance shutdown of the accelerator.