arXiv subjects

A. Adamczak

Publications and source records attributed to A. Adamczak.

At least 19 recordsLinked to original sources

arXiv2026

Molecular effects in low-energy muon transfer from muonic hydrogen to oxygen

In the present study we determine from the available experimental data the cross section of muon transfer to molecular oxygen at low energies with account of the oxygen molecule structure. Building on an earlier work, the results highlight the role of the molecular structure effects and signifcantly improve the agreement with theoretical calculations of the muon transfer rate. An effcient computational model of the kinetics of processes involving muonic hydrogen atoms in gaseous mixture of H2 and O2 is developed and analyzed. The model is applied in the description of the FAMU experiment for the measurement of the hyperfine splitting in muonic hydrogen and the Zemach radius of the proton.

physics.atom-ph↗

arXiv2025

First operation of the FAMU experiment at the RIKEN-RAL high intensity muon beam facility

The FAMU experiment, supported and funded by the Italian Institute of Nuclear Physics (INFN) and by the Science and Technology Facilities Council (STFC), aims to perform the first measurement of the ground-state hyperfine splitting (1S-hfs) of muonic hydrogen ($μH$). This quantity is highly sensitive to the proton's Zemach radius $R_Z$. An experimental determination of $R_Z$ provides significant constraints on the parametrization of the proton form factors as well as on theoretical models describing the proton's electromagnetic structure. Following years of technological and methodological development, the FAMU experiment began operations in 2023 at Port 1 of the RIKEN-RAL muon beam line at the ISIS Neutron and Muon Source facility (Didcot, UK). In this paper, we first describe the unique detection technique employed by FAMU to determine the 1S-hfs of muonic hydrogen, followed by a detailed presentation of the final experimental layout. Finally, we report the first outcome from the 2023 commissioning run and from the initial physics runs performed in 2023 and 2024.

physics.atom-ph↗

arXiv2024

Investigating the Proton Structure: The FAMU experiment

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.

physics.atom-ph↗

arXiv2023

Status of the detector setup for the FAMU experiment at RIKEN-RAL for a precision measurement of the Zemach radius of the proton in muonic hydrogen

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.

physics.atom-ph↗

arXiv2023

Muonic atom spectroscopy with microgram target material

Muonic atom spectroscopy -- the measurement of the x rays emitted during the formation process of a muonic atom -- has a long standing history in probing the shape and size of nuclei. In fact, almost all stable elements have been subject to muonic atom spectroscopy measurements and the absolute charge radii extracted from these measurements typically offer the highest accuracy available. However, so far only targets of at least a few hundred milligram could be used as it required to stop a muon beam directly in the target to form the muonic atom. We have developed a new method relying on repeated transfer reactions taking place inside a 100-bar hydrogen gas cell with an admixture of 0.25% deuterium that allows us to drastically reduce the amount of target material needed while still offering an adequate efficiency. Detailed simulations of the transfer reactions match the measured data, suggesting good understanding of the processes taking place inside the gas mixture. As a proof of principle we demonstrate the method with a measurement of the 2p-1s muonic x rays from a 5-μg gold target.

nucl-ex↗

arXiv2023

Diffusion of muonic hydrogen in hydrogen gas and the measurement of the 1$s$ hyperfine splitting of muonic hydrogen

The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen ($μ$p) with 1 ppm accuracy by means of pulsed laser spectroscopy. In the proposed experiment, the $μ$p atom is excited by a laser pulse from the singlet to the triplet hyperfine sub-levels, and is quenched back to the singlet state by an inelastic collision with a H$_2$ molecule. The resulting increase of kinetic energy after this cycle modifies the $μ$p atom diffusion in the hydrogen gas and the arrival time of the $μ$p atoms at the target walls. This laser-induced modification of the arrival times is used to expose the atomic transition. In this paper we present the simulation of the $μ$p diffusion in the H$_2$ gas which is at the core of the experimental scheme. These simulations have been implemented with the Geant4 framework by introducing various low-energy processes including the motion of the H$_2$ molecules, i.e. the effects related with the hydrogen target temperature. The simulations have been used to optimize the hydrogen target parameters (pressure, temperatures and thickness) and to estimate signal and background rates. These rates allow to estimate the maximum time needed to find the resonance and the statistical accuracy of the spectroscopy experiment.

physics.atom-ph↗

arXiv2023

Experimental determination of the energy dependence of the rate of the muon transfer reaction from muonic hydrogen to oxygen for collision energies up to 0.1 eV

We report the first experimental determination of the collision-energy dependence of the muon transfer rate from the ground state of muonic hydrogen to oxygen at near-thermal energies. A sharp increase by nearly an order of magnitude in the energy range 0 - 70 meV was found that is not observed in other gases. The results set a reliable reference for quantum-mechanical calculations of low-energy processes with exotic atoms, and provide firm ground for the measurement of the hyperfine splitting in muonic hydrogen and the determination of the Zemach radius of the proton by the FAMU collaboration.

physics.atom-ph↗

arXiv2022

Laser excitation of the 1s-hyperfine transition in muonic hydrogen

The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen ($μ$p) with 1 ppm accuracy by means of pulsed laser spectroscopy to determine the two-photon-exchange contribution with $2\times10^{-4}$ relative accuracy. In the proposed experiment, the $μ$p atom undergoes a laser excitation from the singlet hyperfine state to the triplet hyperfine state, {then} is quenched back to the singlet state by an inelastic collision with a H$_2$ molecule. The resulting increase of kinetic energy after the collisional deexcitation is used as a signature of a successful laser transition between hyperfine states. In this paper, we calculate the combined probability that a $μ$p atom initially in the singlet hyperfine state undergoes a laser excitation to the triplet state followed by a collisional-induced deexcitation back to the singlet state. This combined probability has been computed using the optical Bloch equations including the inelastic and elastic collisions. Omitting the decoherence effects caused by {the laser bandwidth and }collisions would overestimate the transition probability by more than a factor of two in the experimental conditions. Moreover, we also account for Doppler effects and provide the matrix element, the saturation fluence, the elastic and inelastic collision rates for the singlet and triplet states, and the resonance linewidth. This calculation thus quantifies one of the key unknowns of the HFS experiment, leading to a precise definition of the requirements for the laser system and to an optimization of the hydrogen gas target where $μ$p is formed and the laser spectroscopy will occur.

physics.atom-ph↗

arXiv2021

Measurement of the muon transfer rate from muonic hydrogen to oxygen in the range 70-336 K

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.

physics.atom-ph↗

arXiv2020

First measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen

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.

nucl-ex↗

arXiv2019

FAMU: study of the energy dependent transfer rate $Λ_{μp \rightarrow μO}$

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.

nucl-ex↗

arXiv2018

The next generation of laser spectroscopy experiments using light muonic atoms

Precision spectroscopy of light muonic atoms provides unique information about the atomic and nuclear structure of these systems and thus represents a way to access fundamental interactions, properties and constants. One application comprises the determination of absolute nuclear charge radii with unprecedented accuracy from measurements of the 2S$\,$-$\,$2P Lamb shift. Here, we review recent results of nuclear charge radii extracted from muonic hydrogen and helium spectroscopy and present experiment proposals to access light muonic atoms with $Z \geq 3$. In addition, our approaches towards a precise measurement of the Zemach radii in muonic hydrogen ($μ$p) and helium ($μ$$^{3}$He$^{+}$) are discussed. These results will provide new tests of bound-state quantum-electrodynamics in hydrogen-like systems and can be used as benchmarks for nuclear structure theories.

physics.atom-ph↗

arXiv2016

Steps towards the hyperfine splitting measurement of the muonic hydrogen ground state: pulsed muon beam and detection system characterization

The high precision measurement of the hyperfine splitting of the muonic-hydrogen atom ground state with pulsed and intense muon beam requires careful technological choices both in the construction of a gas target and of the detectors. In June 2014, the pressurized gas target of the FAMU experiment was exposed to the low energy pulsed muon beam at the RIKEN RAL muon facility. The objectives of the test were the characterization of the target, the hodoscope and the X-ray detectors. The apparatus consisted of a beam hodoscope and X-rays detectors made with high purity Germanium and Lanthanum Bromide crystals. In this paper the experimental setup is described and the results of the detector characterization are presented.

physics.ins-det↗

arXiv2003

Scattering of p$μ$ muonic atoms in solid hydrogen

We present the results of experimental and theoretical study of the scattering of low energy p$μ$ atoms in solid hydrogen cooled to 3 K. The resulting emission of low energy p$μ$ atoms from the hydrogen layer into the adjacent vacuum was much higher than that predicted by calculations which ignored the solid nature of the hydrogen. New differential scattering cross sections have been calculated for the collisions of p$μ$ atoms on solid hydrogen to acount for its quantum crystalline nature. Analysis of the experimental data performed using such cross sections shows the important role of the coherent scattering in p$μ$ atom diffusion. For p$μ$ energies lower than the Bragg cutoff limit (2 meV) the elastic Bragg scattering vanishes which makes the total scattering cross section fall by several orders of magnitude, and thus the hydrogen target becomes transparent allowing the emission of cold p$μ$ atoms to occur.

nucl-ex↗

arXiv2001

Resonant Scattering of Muonic Hydrogen Atoms and Dynamics of Muonic Molecular Complex

Resonant scattering of muonic hydrogen atoms via back decay of molecular complex, a key process in the understanding of epithermal muonic molecular formation, is analyzed. The limitations of the effective rate approximation are discussed and the importance of the explicit treatment of the back decay is stressed. An expression of the energy distribution for the back-decayed atoms is given.

nucl-ex↗

arXiv2001

Measurement of the Resonant $dμt$ Molecular Formation Rate in Solid HD

Measurements of muon-catalyzed dt fusion ($dμt \to ^4He+n+μ^-$) in solid HD have been performed. The theory describing the energy dependent resonant molecular formation rate for the reaction $μt$ + HD $\to [(dμt)pee]^*$ is compared to experimental results in a pure solid HD target. Constraints on the rates are inferred through the use of a Monte Carlo model developed specifically for the experiment. From the time-of- flight analysis of fusion events in 16 and 37 $μg\cdot cm^{-2}$ targets, an average formation rate consistent with 0.897$\pm$(0.046)$_{stat}\pm$ (0.166)$_{syst}$ times the theoretical prediction was obtained.

physics.atom-ph↗

arXiv2001

Resonant $ddμ$ Formation in Condensed Deuterium

The rate of $ddμ$ muonic molecule resonant formation in $dμ$ atom collision with a condensed deuterium target is expressed in terms of a single-particle response function. In particular, $ddμ$ formation in solid deuterium at low pressures is considered. Numerical calculations of the rate in the case of fcc polycrystalline deuterium at 3 K have been performed using the isotropic Debye model of solid. It is shown that the energy-dependent $ddμ$ formation rates in the solid differ strongly from those obtained for D$_2$ gaseous targets, even at high $dμ$ kinetic energies. Monte Carlo neutron spectra from $dd$ fusion in $ddμ$ molecules have been obtained for solid targets with different concentrations of ortho-D$_2$ and para-D$_2$. The neutron time spectra calculated for pure ortho-D$_2$ and para-D$_2$ targets are very similar.

physics.atom-ph↗

arXiv2001

Time-of-Flight Spectroscopy of Muonic Hydrogen Atoms and Molecules

Studies of muonic hydrogen atoms and molecules have been performed traditionally in bulk targets of gas, liquid or solid. At TRIUMF, Canada's meson facility, we have developed a new type of target system using multilayer thin films of solid hydrogen, which provides a beam of muonic hydrogen atoms in vacuum. Using the time-of-flight of the muonic atoms, the energy-dependent information of muonic reactions are obtained in direct manner. We discuss some unique measurements enabled by the new technique, with emphasis on processes relevant to muon catalyzed fusion.

nucl-ex↗