arXiv subjects
Publications and source records attributed to K. S. Gadedjisso-Tossou.
The article gives the motivations for the measurement of the hyperfine splitting (hfs) in the ground state of muonic hydrogen to explore the properties of the proton at low momentum transfer. It summarizes these proposed measurement methods and finally describes the FAMU experiment in more detail.
The FAMU experiment at RIKEN-RAL is a muonic atom experiment with the aim to determine the Zemach radius of the proton by measuring the 1s hyperfine splitting in muonic hydrogen. The activity of the FAMU Collaboration in the years 2015-2023 enabled the final optimisation of the detector-target setup as well as the gas working condition in terms of temperature, pressure and gas mixture composition. The experiment has started its data taking in July 2023. The status of the detector setup for the 2023 experimental runs, for the beam characterisation and muonic X-ray detection in the 100-200 keV energy range, is presented and discussed.
The first measurement of the temperature dependence of the muon transfer rate from muonic hydrogen to oxygen was performed by the FAMU collaboration in 2016. The results provide evidence that the transfer rate rises with the temperature in the range 104-300 K. This paper presents the results of the experiment done in 2018 to extend the measurements towards lower (70 K) and higher (336 K) temperatures. The 2018 results confirm the temperature dependence of the muon transfer rate observed in 2016 and sets firm ground for comparison with the theoretical predictions.
We report the first measurement of the temperature dependence of muon transfer rate from $μ$p atoms to oxygen between 100 and 300 K. Data were obtained from the X-ray spectra of delayed events in gaseous target H$_2$/O$_2$ exposed to a muon beam. Based on the data, we determined the muon transfer energy dependence up to 0.1 eV, showing an 8-fold increase in contrast with the predictions of constant rate in the low energy limit. This work set constraints on theoretical models of muon transfer, and is of fundamental importance for the measurement of the hyperfine splitting of $μ$p by the FAMU collaboration.
The FAMU (Fisica degli Atomi Muonici) experiment at the RIKEN RAL pulsed muon facility will measure the proton Zemach radius with high precision, thus contributing to the solution of the so-called proton radius puzzle. The situation is now confused and new measurements will help reduce the discrepancy as measured with electrons or muons. To this aim, FAMU will make use of a high-intensity pulsed muon beam at RIKEN-RAL impinging on a cryogenic hydrogen target and a tunable Mid-infrared (MIR) laser emitting at around 6.78 um, to measure the hyperfine (HFS) splitting of the 1S state of muonic hydrogen. The injection of light into the cryogenic target and its monitoring via dedicated MIR sensors is an asset for the experiment. A possible solution is via specialty MIR fibres based on hollow core waveguides or polycrystalline fibres. Two dedicated setups based on pulsed QCL lasers, from Alpes Laser, emitting around 6.78 um have been used to study the fibre attenuation while the high energy laser developed at Elettra Sincrotrone in Trieste has been used to study the damage threshold at high energies. The alignment of MIR laser radiation into an optical cavity presents criticalities due to geometrical constraints. Its control requires the use of small and sensitive detectors. The results obtained with a quantum IR sensor with an integrated circuit for signal processing are reported.
The main goal of the FAMU experiment is the measurement of the hyperfine splitting (hfs) in the 1S state of muonic hydrogen $ΔE_{hfs}(μ^-p)1S$. The physical process behind this experiment is the following: $μp$ are formed in a mixture of hydrogen and a higher-Z gas. When absorbing a photon at resonance-energy $ΔE_{hfs}\approx0.182$~eV, in subsequent collisions with the surrounding $H_2$ molecules, the $μp$ is quickly de-excited and accelerated by $\sim2/3$ of the excitation energy. The observable is the time distribution of the K-lines X-rays emitted from the $μZ$ formed by muon transfer $(μp) +Z \rightarrow (μZ)^*+p$, a reaction whose rate depends on the $μp$ kinetic energy. The maximal response, to the tuned laser wavelength, of the time distribution of X-ray from K-lines of the $(μZ)^*$ cascade indicate the resonance. During the preparatory phase of the FAMU experiment, several measurements have been performed both to validate the methodology and to prepare the best configuration of target and detectors for the spectroscopic measurement. We present here the crucial study of the energy dependence of the transfer rate from muonic hydrogen to oxygen ($Λ_{μp \rightarrow μO}$), precisely measured for the first time.