Weighing the antiproton by parts-per-billion-scale laser spectroscopy of antiprotonic helium

A femtosecond optical frequency comb and continuous-wave pulse-amplified laser were used to measure 12 transition frequencies of antiprotonic helium (metastable three-body system consisting of an antiproton, an electron, and a helium nucleus) to fractional precisions of (9–16) × 10–9. One of these is between two states having microsecond-scale lifetimes hitherto unaccessible to our precision laser spectroscopy method. Comparisons with three-body QED calculations yielded an antiproton-to-electron mass ratio of [Formula: see text] = 1836.152 674(5).PACS Nos.: 36.10.–k, 14.20.Dh, 32.70.Jz

New evaluation of proton structure corrections to hydrogen hyperfine splitting

We consider the proton structure corrections to the hydrogen ground-state hyperfine structure, focusing on a state-of-the-art evaluation of the inelastic nucleon corrections — the polarizability corrections — using analytic fits to the most recent data. We find a value for the fractional correction Δpol of 1.3 ± 0.3 ppm. This is 1–2 ppm smaller than the value of Δpol one would deduce using hyperfine-splitting data and elastic proton structure corrections obtained from modern form factor fits. In addition, we discuss the derivations of the relevant formulas, paying attention to lepton mass effects and to questions surrounding the use of unsubtracted dispersion relations. PACS Nos.: 31.30.Gs, 32.10.Fn, 14.20.Dh, 13.40.Gp

Nucleon form factor measurements in Mainz: past and future

The form factors of protons and neutrons provide a natural and direct insight into their internal structure. They were a main research goal in the nuclear physics program of the Universitat Mainz, which led to some of the most precise measurements to date. This article gives an overview, starting from the very first experiments at the now obsolete linear accelerator and ending at the exhaustive experiments currently underway at the MAMI facilities. PACS Nos.: 14.20.Dh, –13.40.Gp, –25.30.Bf

Precise proton radii from electron scattering

We summarize various analyses of the world data on elastic electron scattering for the determination of the most precise charge rms-radius of the proton. We also present the Zemach moments needed for the interpretation of atomic HFS structure and μ-X-ray experiments.PACS Nos.: 13.40.Gp, 13.40.Em, 14.20.Dh