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Register a new userLong-lived $2s$ state of muonic hydrogen: population and lifetime
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Ab initio study of the density-dependent population and lifetime of the long-lived $(mu p)_{2s}$ and the yield of $(mu p)_{1s}$ atoms with kinetic energy 0.9 keV have been performed for the first time. The direct Coulomb $2sto 1s$ deexcitation is proved to be the dominant quenching mechanism of the $2s$ state at kinetic energy below $2p$ threshold and explain the lifetime of the metastable $2s$ state and high-energy 0.9 keV component of $(mu p)_{1S}$ observed at low densities. The cross sections of the elastic, Stark and Coulomb deexcitation processes have been calculated in the close-coupling approach taking into account for the first time both the closed channels and the threshold effects due to vacuum polarization shifts of the $ns$ states. The cross sections are used as the input data in the detailed study of the atomic cascade kinetics. The theoretical predictions are compared with the known experimental data at low densities. The 40% yield of the 0.9 keV$(mu p)_{1s}$ atoms is predicted for liquid hydrogen density.
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Metastable ${2S}$ muonic-hydrogen atoms undergo collisional ${2S}$-quenching, with rates which depend strongly on whether the $mu p$ kinetic energy is above or below the ${2S}to {2P}$ energy threshold. Above threshold, collisional ${2S} to {2P}$ excitation followed by fast radiative ${2P} to {1S}$ deexcitation is allowed. The corresponding short-lived $mu p ({2S})$ component was measured at 0.6 hPa $mathrm{H}_2$ room temperature gas pressure, with lifetime $tau_{2S}^mathrm{short} = 165 ^{+38}_{-29}$ ns (i.e., $lambda_{2S}^mathrm{quench} = 7.9 ^{+1.8}_{-1.6} times 10^{12} mathrm{s}^{-1}$ at liquid-hydrogen density) and population $epsilon_{2S}^mathrm{short} = 1.70^{+0.80}_{-0.56}$ % (per $mu p$ atom). In addition, a value of the $mu p$ cascade time, $T_mathrm{cas}^{mu p} = (37pm5)$ ns, was found.
We determine the third Zemach moment of hydrogen (<r^3>_(2)) using only the world data on elastic electron-proton scattering. This moment dominates the O (Z alpha)^5 hadronic correction to the Lamb shift in muonic atoms. The resulting moment, <r^3 >_(2) = 2.71(13) fm^3, is somewhat larger than previously inferred values based on models. The contribution of that moment to the muonic hydrogen 2S level is -0.0247(12) meV.
The atomic cascade in $mu^- p$ and $pi^- p$ atoms has been studied with the improved version of the extended cascade model in which new quantum mechanical calculations of the differential and integral cross sections of the elastic scattering, Stark transitions and Coulomb de-excitation have been included for the principal quantum number values $nle 8$ and the relative energies $E ge 0.01$ eV. The $X$-ray yields and kinetic energy distributions are compared with the experimental data.
Studies of muonic hydrogen atoms and molecules have been performed traditionally in bulk targets of gas, liquid or solid. At TRIUMF, Canadas 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.
We report the microscopic origins of the anomalously suppressed beta decay of 14C to 14N using the ab initio no-core shell model (NCSM) with the Hamiltonian from chiral effective field theory (EFT) including three-nucleon force (3NF) terms. The 3NF induces unexpectedly large cancellations within the p-shell between contributions to beta decay, which reduce the traditionally large contributions from the NN interactions by an order of magnitude, leading to the long lifetime of 14C.
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