Dimitar Bakalov

Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen

While measurements of the hyperfine structure of hydrogen-like atoms are traditionally regarded as test of bound-state QED, we assume that theoretical QED predictions are accurate and discuss the information about the electromagnetic structure of protons that could be extracted from the experimental values of the ground state hyperfine splitting in hydrogen and muonic hydrogen.Using recent theoretical results on the proton polarizability effects and the experimentalhydrogen hyperfine splitting we obtain for the Zemach radius of the proton the value 1.040(16) fm. We compare it to the various theoretical estimatesthe uncertainty of which is shown to be larger that 0.016 fm.This point of view gives quite convincing arguments in support of projects to measure the hyperfine splitting of muonic hydrogen.

Magnetic field effects in the transitions of the HD + molecular ion and precision spectroscopy

We analyse the effects of an external magnetic field on the ro-vibrational, rotational and radiofrequency transitions of the HD+ molecular ion—an important systematic effect in precision spectroscopy of HD+, which is of interest for metrology of the fundamental constants. The effects of an external magnetic field on the ro-vibrational, rotational and radiofrequency (hyperfine) transitions of the HD+ molecular ion are considered, for one-photon and, where relevant, two-photon transitions. The hyperfine structure of the spectrum lines is taken into account. Particular attention has been devoted to those transitions which are most insensitive to the magnetic field and its orientation with respect to the polarization of the radiation field. We identify experimentally accessible two-photon transitions that exhibit no Zeeman shift, one-photon and two-photon transitions that provide symmetrically split doublets, and one-photon transitions that show only a very weak quadratic Zeeman shift. The importance of the spin-stretched states is emphasized. The results can be used to determine the most suitable transitions given the experimental conditions.

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.

Quantum Vacuum Friction in highly magnetized neutron stars

In this letter we calculate the energy loss of a highly magnetized neutron star due to Quantum Vacuum Friction (QVF). Taking into account one-loop corrections in the effective Heisenberg-Euler Lagrangian of the light-light interaction, we derive an analytic expression for QVF allowing us to take into account a magnetic field at the surface of the star as high as 1011 T. In the case of magnetars, with magnetic fields above the QED critical field, we show that the QVF is the dominating energy loss process. This has important consequences, in particular for the inferred value of the magnetic field. This also indicates the need for independent measurements of magnetic field, energy loss rate, and the braking index in order to fully characterize magnetars.

Measuring the size of the proton

The size of an atom’s nucleus is roughly five orders of magnitude smaller than the size of the atom. Consequently, the nuclear corrections to atomic energy levels are very tiny. However, these corrections have become important in recent highprecision measurements of transitions in the hydrogen atom, which are being performed to test quantum electrodynamics (QED) and to determine related fundamental constants. Today, the interpretation of this data is only limited by the uncertainties in the size of the nucleus, which in the case of hydrogen is a single proton. The charge radius rp of the proton is a physical parameter that characterizes important aspects of the effective size of the proton. Its value is used together with the Rydberg constant in the calculations of bound-state QED involving hydrogen atoms as well as muonic hydrogen atoms that have a muon orbiting the nucleus rather than the electron. (Muons are like electrons but 200 times heavier.) A recent spectroscopic study of muonic hydrogen resulted in a new measurement of the proton root mean square (rms) charge radius.1 The reported value, rp D 0:84184.67/fm, differs by 5 standard deviations from (and is a factor of 10 more precise than) previous determinations. These earlier values come from three very different methods that are based mostly on electronic hydrogen data. Specifically, a compilation of physical constants (CODATA) gives rp D 0:8768.69/fm,2 the Lamb shift of electronic hydrogen results in rp D 0:883.14/fm,3, 4 and electron scattering from hydrogen yields rp D 0:895.18/fm.5 It is noteworthy that QED considerations show6 that the electron scattering experiments and the atomic hydrogen spectroscopy determine the same Figure 1. Block diagram of the layout of the first approach to a dedicated nonlinear laser source.

Static and dynamic polarizability and the Stark and blackbody-radiation frequency shifts of the molecular hydrogen ionsH2+,HD+, andD2+

We calculate the DC Stark effect for three molecular hydrogen ions in the non-relativistic approximation. The effect is calculated both in dependence on the rovibrational state and in dependence on the hyperfine state. We discuss special cases and approximations. We also calculate the AC polarisabilities for several rovibrational levels, and therefrom evaluate accurately the black-body radiation shift, including the effects of excited electronic states. The results enable the detailed evaluation of certain systematic shifts of the transitions frequencies for the purpose of ultra-high-precision optical, microwave or radio-frequency spectroscopy in ion traps.

Precision Spectroscopy of Molecular Hydrogen Ions: Towards Frequency Metrology of Particle Masses

We describe the current status of high-precision ab initio calculations of the spectra of molecular hydrogen ions (H2 + and HD+) and of two experiments for vibrational spectroscopy. The perspectives for a comparison between theory and experiment at a level of 1 part in 109 are considered.

Theoretical and computational study of the energy dependence of the muon transfer rate from hydrogen to higher- Z gases

Abstract The recent PSI Lamb shift experiment and the controversy about proton size revived the interest in measuring the hyperfine splitting in muonic hydrogen as an alternative possibility for comparing ordinary and muonic hydrogen spectroscopy data on proton electromagnetic structure. This measurement critically depends on the energy dependence of the muon transfer rate to heavier gases in the epithermal range. The available data provide only qualitative information, and the theoretical predictions have not been verified. We propose a new method by measurements of the transfer rate in thermalized target at different temperatures, estimate its accuracy and investigate the optimal experimental conditions.

Shift and broadening of resonance lines of antiprotonic helium atoms in solid helium

We have estimated the shift and broadening of the resonance lines in the spectrum of antiprotonic helium atoms

Collisional shift and broadening of the transition lines in pionic helium

\overline{p}{\mathrm{He}}^{+}