First operations of the FAMU experiment at RIKEN-RAL

The FAMU experiment (Fisica degli Atomi MUonici), led by INFN at the Rutherford Appleton Laboratory (UK), is designed to measure the hyperfine splitting of the muonic hydrogen ground state. This measurement, aiming to give an accurate insight of the proton’s electric and magnetic structure, plays a key role in verifying the most accurate QED calculations and tests the interaction between proton and muon. A 55 MeV/c pulsed negative muon beam is produced by the ISIS synchrotron at the RIKEN-RAL muon facility. The beam is directed against a gaseous hydrogen- oxygen target, where a pulsed Mid-InfraRed laser with a tunable wavelength around 6.8 μm is injected. The aim is to determine the laser wavelength stimulating the resonant spin-flip in μH atoms, which is related to on the proton Zemach radius. The experiment data talking started in 2023, and a new set of data is being taken in 2024 and 2025. In this presentation, the status of the FAMU experiment, its performance and its future development are presented.