Related papers: Improved Study of the Antiprotonic Helium Hyperfin…
Experiments with low-energy antiprotons are currently performed at the Antiproton Decelerator of CERN. The main experiments deal with the spectroscopy of antiprotonic helium, an exotic three-body system, and the formation and spectroscopy…
A combination of the reduced $e^{\pm}p$ cross section, previously measured by H1 and ZEUS, has been performed and leads to well constrained QCD fits of the parton densities in the proton. These results, as well as the high-$Q^2$ neutral…
We investigate interactions between the proton spin, the deuteron spin, and the orbital angular momentum in the electronic ground state of the HD molecule. These interactions lead to hyperfine splittings of molecular energy levels. Our…
The upcoming operation of the Extra Low ENergy Antiprotons (ELENA) ring at CERN, the upgrade of the anti-proton decelerator (AD), and the installation in the AD hall of an intense slow positron beam with an expected flux of $10^{8}$ e$^+$/s…
Collisions of metastable antiprotonic helium atoms with atoms of the medium induce, among other processes, transitions between hyperfine structure (HFS) states, as well as shifts and broadening of microwave M1 spectral lines. In order to…
The longitudinal proton structure function (FL) has been measured at the HERA collider in positron-proton deep inelastic scattering collisions with the H1 and ZEUS detectors. This measurement is achieved by using multiple center-of-mass…
A few per cent fraction of antiprotons stopped in helium survives for an enormous time (up to tens of microseconds) in comparison with the usual lifetime ($10^{-12}s$) of these particles in matter. The explanation is that antiprotons are…
High precision radio-frequency, microwave and infrared spectroscopic measurements of the antihydrogen molecular ion $\bar{H}_{2}^{-}$ ($\bar{p}\bar{p}e^{+}$) compared with its normal matter counterpart provide direct tests of the CPT…
A new powerful longitudinal diagnostics is being developed for the two CERN's antiproton machines, the Antiproton Decelerator (AD) and the Extra Low ENergy ANtiproton (ELENA) ring. The longitudinal diagnostics receives data from the…
For decades, improved theory and experiment of the $n=2$ $^3$P fine structure of helium have allowed for increasingly-precise tests of quantum electrodynamics, determinations of the fine-structure constant $\alpha$, and limitations on…
Muonic helium atom hyperfine structure (HFS) measurements are a sensitive tool to test the three-body atomic system and bound-state quantum electrodynamics theory, and determine fundamental constants of the negative muon magnetic moment and…
A first measurement is reported of the longitudinal proton structure function F_L(x,Q^2) at the ep collider HERA. It is based on inclusive deep inelastic e^+p scattering cross section measurements with a positron beam energy of 27.5 GeV and…
The BASE collaboration at the Antiproton Decelerator facility of CERN compares the fundamental properties of protons and antiprotons using advanced Penning-trap systems. In previous measurement campaigns, we measured the magnetic moments of…
The usefulness of study of hyperfine splitting in the hydrogen atom is limited on a level of 10 ppm by our knowledge of the proton structure. One way to go beyond 10 ppm is to study a specific difference of the hyperfine structure intervals…
Transition frequencies and fine-structure splittings of the $2\,{}^3\!S_1 \rightarrow 2\,{}^3\!P_{\!J}$ transitions in helium-like $^{12}\mathrm{C}^{4+}$ were measured by collinear laser spectroscopy on a 1-ppb level. Accuracy is increased…
We present a detailed derivation of the QED effects of order $\alpha^7\,m$ to the hyperfine structure (hfs) of the $^3S$ states of helium-like ions and perform numerical calculations for $^6$Li$^+$ and $^7$Li$^+$. By comparing the…
Spectroscopy of antihydrogen has the potential to yield high-precision tests of the CPT theorem and shed light on the matter-antimatter imbalance in the Universe. The ALPHA antihydrogen trap at CERN's Antiproton Decelerator aims to prepare…
Positronium is an ideal system for the research of QED in the bound state. The hyperfine splitting of positronium (Ps-HFS: about 203 GHz) is a good tool to test QED and also sensitive to new physics beyond the Standard Model. Previous…
The unusually large hyperfine structure splittings in the 23P state of the 3He isotope is measured using electro-optic techniques with high precision laser spectroscopy. Originally designed to probe the fine structure of the 4He atom, this…
The spectroscopic hyperfine constants for all the alkali atoms are reported. For atoms from lithium to cesium, only the long lived atomic isotopes are examined. For francium, the measured data for nuclear ground states of all available…