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Register a new userNuclear structure corrections to the Lamb shift in $mu^3$He$^+$ and $mu^3$H
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Measuring the 2S-2P Lamb shift in a hydrogen-like muonic atom allows one to extract its nuclear charge radius with a high precision that is limited by the uncertainty in the nuclear structure corrections. The charge radius of the proton thus extracted was found to be 7-sigma away from the CODATA value, in what has become the yet unsolved proton radius puzzle. Further experiments currently aim at the isotopes of hydrogen and helium: the precise extraction of their radii may provide a hint at the solution of the puzzle. We present the first ab initio calculation of nuclear structure corrections, including the nuclear polarization correction, to the 2S-2P transition in $mu^3$He$^+$ and $mu^3$H, and assess solid theoretical error bars. Our predictions reduce the uncertainty in the nuclear structure corrections to the level of a few percents and will be instrumental to the on-going $mu^3$He$^+$ experiment. We also support the mirror $mu,^3$H system as a candidate for further probing of the nucleon polarizabilities and shedding more light on the puzzle.
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In view of the future plans to measure the Lamb shift in muonic Lithium atoms we address the microscopic theory of the $mu$-$^6$Li$^{2+}$ and $mu$-$^7$Li$^{2+}$ systems. The goal of the CREMA collaboration is to measure the Lamb shift to extract the charge radius with high precision and compare it to electron scattering data or atomic spectroscopy to see if interesting puzzles, such as the proton and deuteron radius puzzles, arise. For this experiment to be successful, theoretical information on the nuclear structure corrections to the Lamb shift is needed. For $mu$-$^6$Li$^{2+}$ and $mu$-$^7$Li$^{2+}$ there exist only estimates of nuclear structure corrections based on experimental data that suffer from very large uncertainties. We present the first steps towards an ab initio computation of these quantities using few-body techniques.
QED radiative corrections to the cross-section of muon-antimuon annihilation into Higgs boson and photon are calculated within the 1-loop approximation. We write down the expression for cross-section in the form of Drell-Yan process, taking into account higher order leading logs. The non-singlet structure functions of fermions are shown to obey here evolution equations of twist-3 operators. Numerical estimation shows an importance of the correction in the region close to the threshold of Higgs production.
Four light-mass nuclei are considered by an effective two-body clusterisation method; $^6$Li as $^2$H$+^4$He, $^7$Li as $^3$H$+^4$He, $^7$Be as $^3$He$+^4$He, and $^8$Be as $^4$He$+^4$He. The low-energy spectrum of each is determined from single-channel Lippmann-Schwinger equations, as are low-energy elastic scattering cross sections for the $^2$H$+^4$He system. These are presented at many angles and energies for which there are data. While some of these systems may be more fully described by many-body theories, this work establishes that a large amount of data may be explained by these two-body clusterisations.
We report the first measurement of the $(e,ep)$ reaction cross-section ratios for Helium-3 ($^3$He), Tritium ($^3$H), and Deuterium ($d$). The measurement covered a missing momentum range of $40 le p_{miss} le 550$ MeV$/c$, at large momentum transfer ($langle Q^2 rangle approx 1.9$ (GeV$/c$)$^2$) and $x_B>1$, which minimized contributions from non quasi-elastic (QE) reaction mechanisms. The data is compared with plane-wave impulse approximation (PWIA) calculations using realistic spectral functions and momentum distributions. The measured and PWIA-calculated cross-section ratios for $^3$He$/d$ and $^3$H$/d$ extend to just above the typical nucleon Fermi-momentum ($k_F approx 250$ MeV$/c$) and differ from each other by $sim 20%$, while for $^3$He/$^3$H they agree within the measurement accuracy of about 3%. At momenta above $k_F$, the measured $^3$He/$^3$H ratios differ from the calculation by $20% - 50%$. Final state interaction (FSI) calculations using the generalized Eikonal Approximation indicate that FSI should change the $^3$He/$^3$H cross-section ratio for this measurement by less than 5%. If these calculations are correct, then the differences at large missing momenta between the $^3$He/$^3$H experimental and calculated ratios could be due to the underlying $NN$ interaction, and thus could provide new constraints on the previously loosely-constrained short-distance parts of the $NN$ interaction.
We propose a practical folding model to describe $^{3}$He elastic scattering. In the model, $^{3}$He optical potentials are constructed by making the folding procedure twice. First the nucleon-target potential is evaluated by folding the Melbourne $g$-matrix with the target density and localizing the nonlocal folding potential with the Brieva--Rook method, and second the resulting local nucleon-target potential is folded with the $^{3}$He density. This double single-folding model well describes $^{3}$He elastic scattering from $^{58}$Ni and $^{208}$Pb targets in a wide incident-energy range from 30 MeV/nucleon to 150 MeV/nucleon with no adjustable parameter. Spin-orbit force effects on differential cross sections are found to be appreciable only at higher incident energies such as 150 MeV/nucleon. Three-nucleon breakup effects of $^{3}$He are investigated with the continuum discretized coupled-channels method and are found to be appreciable only at lower incident energies around 40 MeV/nucleon. Effects of knock-on exchange processes are also analyzed.
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