Description
The FAMU experiment targets a high-precision measurement of the ground-state hyperfine splitting (1S-hfs) in muonic hydrogen, aiming for an accuracy of $10^{-5}$. This will enable extraction of the proton Zemach radius with <1% uncertainty, offering key insights into proton structure and testing QED contributions.
Being carried out the ISIS RIKEN Port1 beamline at the Rutherford Appleton Laboratory (UK), the experiment uses a 55 MeV/c pulsed negative muon beam injected into an 8-bar hydrogen gas target. After thermalisation, muonic hydrogen atoms are irradiated with tunable mid-infrared laser light (~6788 pm) to induce the 1S-hfs transition.
If the transition happens, the atom is left with a residual kinetic energy, which enhances the probability of ceasing the muon to another atom. For this reason, the gaseous target contains also 1.5% oxygen, and the observable is the laser-enhanced number of muonic oxygen X-rays. This variable is measured as a function of the laser wavelength, looking for a resonance.
The X-ray detector system is based on a set of 34 custom LaBr$_3$:Ce scintillators, optimized for timing and energy resolution. Six of them are read-out by fast PMTs, whereas the remaining 28 have a SiPM readout. A dedicated muon beam monitor ensures accurate beam diagnostics and data normalization. Initial results, systematics, and detector performance are presented, demonstrating the experiment’s potential for advancing precision muon physics.
| Secondary track | T05 - QCD and Hadronic Physics |
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