Abstract

The FAMU experiment aims to measure for the first time the hyperfine splitting of the muonic hydrogen ground state. From this measurement the proton Zemach radius can be derived and this will shed light on the determination of the proton charge radius. In this paper, we describe the scientific goal, the method and the detailed preparatory work. This includes the outcome of preliminary measurements, subsequent refined simulations and the evaluation of the expected results. The experimental setup being built for the measurement of the hyperfine splitting to be performed at the RAL laboratory muon facility is also described.

Highlights

  • Muonic hydrogen allows high-precision spectroscopy studies of the fundamental interactions of the proton and its structure

  • The FAMU experiment aims to measure for the first time the hyperfine splitting of the muonic hydrogen ground state

  • The typical binding energies and distances in the muonic hydrogen atom are rescaled by the ratio of their reduced masses f = m pμ/m pe = 185.83

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Summary

Introduction

Muonic hydrogen allows high-precision spectroscopy studies of the fundamental interactions of the proton and its structure. To measure the hyperfine splitting (hfs) in the ground state of muonic hydrogen ΔEhfs(μ− p)1S with a relative accuracy better than 10−5, an intense, pulsed, low-energy, negative muon beam and an appropriate mid-infrared laser source are required [5,6,7]. – the exceptional precision of 10−12 of the experimental value of ΔEhfs in hydrogen [9] makes it sensitive, in addition to QED corrections, to the contribution from the proton finite size and proton polarizability. They cannot be extracted at the same time from a single experiment.

The muon transfer method
Preparatory work
Feasibility of the transfer method for oxygen
Monte Carlo simulation of the physical processes
The FAMU experimental setup
Muon beam
Narrowband mid-infrared pulsed laser
Target system
Cryogenic system
The pressurized gas target system
Monte Carlo simulations of the target
Multipass optical cavity
Detectors system
Beam profile monitor
X-ray detectors
Rate evaluation from recent data
Number of measurements
Conclusion
Findings
Methods
Full Text
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