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Eberhard Widmann (Austrian Academy of Sciences (AT))18/05/2026, 09:00
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Edmund Myers (Florida State University)18/05/2026, 09:10Invited Talk
We present measurements of the cyclotron frequency ratios $^{4}$He$^{+}$/D$_{2}^{+}$, $^{4}$He$^{+}$/H$_{2}$D$^{+}$, and $^{4}$He$^{+}$/$^{12}$C$^{3+}$ using a cryogenic Penning ion trap [1,2]. Our results clearly differentiate between an earlier measurement of the mass of $^{4}$He by the University of Washington [3] and a more recent measurement by the LIONTRAP collaboration [4] in favor of...
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Jonathan Morgner (CERN)18/05/2026, 09:50Invited Talk
The pronounced imbalance between matter and antimatter in the universe motivates high precision comparisons of fundamental properties of matter–antimatter conjugates. At CERN’s Antiproton Decelerator, the BASE collaboration performs such tests using cryogenic Penning traps. We have achieved the most precise proton–antiproton charge to mass ratio comparison to date, with a fractional...
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Gregory Adkins18/05/2026, 11:00Talk
Muonium and positronium, the $e^-\mu^+$ and $e^-e^+$ bound systems, are described almost completely within quantum electrodynamics. Their energy levels can be calculated to high precision, and these systems are also subject to high precision measurements. Recent developments include intense experimental work on muonium by the MuSEUM collaboration at J-PARC and the MuMASS collaboration at...
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Edward Thorpe-Woods (ETH Zurich (CH))18/05/2026, 11:30Talk
Positronium and muonium, as purely leptonic atoms without internal structure, provide ideal systems for precision tests of quantum electrodynamics (QED) and searches for new physics [1].
We report a new measurement of the positronium $1^3S_1 \to 2^3S_1$ transition frequency using two-photon continuous-wave laser spectroscopy, $\nu = 1233607224.1(6.0)\ \mathrm{MHz}$ [2].
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Our result agrees... -
Shoichiro Nishimura (KEK IMSS)18/05/2026, 12:00Talk
Muonium is a bound state of a positive muon and an electron. Precise measurements of the muonium hyperfine structure (HFS) provide a stringent test of quantum electrodynamics (QED), whose theoretical predictions are calculated with extremely high precision [1]. In the field of precision muon physics, there is ongoing discussion regarding the hadronic vacuum polarization contribution to the...
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Ivo Schulthess (ETH Zurich)18/05/2026, 12:20Talk
True muonium (µ⁺µ⁻), the purely leptonic bound state of a muon and an antimuon, is a unique atomic system that has not yet been observed experimentally. Together with positronium (e⁺e⁻) and muonium (µ⁺e⁻), it provides a clean laboratory for tests of bound-state quantum electrodynamics, while uniquely probing a regime characterized by a large reduced mass, extreme compactness, and short...
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Thorsten Schumm (T)18/05/2026, 14:10Invited Talk
Among the >3000 isotopes, Thorium-229 provides the lowest-energy nuclear first excited state, a so-called isomer state. This isomer state at 8.4 eV is the only nuclear state accessible to laser manipulation and spectroscopy. It’s long >10 minutes lifetimes with a connected narrow transition linewidth, combined with the intrinsic robustness of nuclear transitions, makes it an exciting candidate...
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M. V. Okhapkin (Physikalisch-Technische Bundesanstalt, Braunschweig, Germany)18/05/2026, 14:50Talk
The first low-energy nuclear excited state of thorium-229 has gained an increasing interest since direct laser excitation have been demonstrated [1] and quickly confirmed in various solid-state experiments. This unique transition of the thorium isotope offers many applications, including a highly accurate nuclear clock, and a new testbed for physics beyond the standard model
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Still, one... -
Dr Carsten Brandau (GSI-Helmholtzzentrum für Schwerionenforschung mbH)18/05/2026, 15:10Talk
Since at least the first laser excitations of the $^{229}$Th nucleus in 2024, $^{229}$Th nuclear clocks is the talk of the town [1-3]. In the HiThor project an alternative scenario for $^{229}$Th studies is pursued that is based on $^{229}$Th$^{q+}$ ions in their highest charge states (q»1). Key to the HiThor programm is H-like $^{229}$Th$^{89+}$ that exhibits an effect termed nuclear...
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Bastian Sikora18/05/2026, 16:10Talk
The bound-electron $𝑔$-factor in heavy highly charged ions can be measured with high precision. However, due to uncalculated two-loop QED binding corrections, the theoretical uncertainty in this regime is orders of magnitude larger than the experimental uncertainty. This was also highlighted in a recent collaborative project, where the comparison of bound-electron $𝑔$-factors in hydrogenlike...
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Brajesh Kumar Mani (Indian Institute of Technology Delhi)18/05/2026, 16:40Talk
Atomic systems offer a plethora of fundamental and functional properties and therefore are of importance to several key implications. Some examples where atoms and ions can serve as important probes include, atomic clocks [1], parity and time-reversal violations [2, 3], and the search for the variations in the fundamental constants [4]. Atomic systems, however, form a many-body complex system...
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Dr Zoltan Harman (Max Planck Institute for Nuclear Physics)18/05/2026, 17:00Talk
Precision measurements in simple atomic systems offer powerful probes for physics beyond the Standard Model. One promising approach is based on high-precision measurements of the bound-electron g factor in hydrogen-like ions. The exchange of a hypothetical scalar boson would produce a small additional contribution to the ground-state g factor. By calculating this effect and comparing it...
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Anton Gramberg (Max Planck Institute for Nuclear Physics (DE))18/05/2026, 17:20Talk
The $g$ factor of the bound electron in few-electron highly charged ions is a highly sensitive probe for new physics and its measurement allows to test the predictions of quantum electrodynamics (QED) in the extremely strong electric field of the nucleus. Studying these simple atomic systems allows to examine bound-state QED and even nuclear effects to high accuracy. ALPHATRAP [1] is a...
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Felix Schneider (TU Wien)18/05/2026, 17:40Poster
The lowest-energy Thorium-229 isomeric state at 148.3 nm can be used to build a worlds-first nuclear clock. The transition is also sensitive to variations of the fine-structure constant and may be used to search for dark matter.
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This poster presents the ongoing experimental progress towards building and optimizing a continuous-wave laser system at 148.38 nm and its use in high-precision... -
Iren Ignatov (Technion - Israel Institute of Technology)18/05/2026, 17:41Poster
Muonium is an exotic atom consisting of a positive muon and an electron. As it comprises two leptons, it lacks contributions from hadronic interactions or corrections due to the finite size of the nucleus, while still resembling hydrogen in its theoretical simplicity. Therefore, comparing measured and calculated energy levels in muonium provides a clean test of QED. Here, I report a new...
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Patrick Schaile (Max-Planck-Institut für Quantenoptik)18/05/2026, 17:42Poster
Precision spectroscopy of atomic hydrogen provides a uniquely clean test of bound-state quantum electrodynamics due to its simple electronic structure. While spectroscopy of trapped atomic samples can significantly enhance precision, trapping hydrogen in optical potentials has not been realized yet. Existing approaches rely on magnetic trapping, which introduce substantial Zeeman shifts and...
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Dr Ádám Margócsy (ELTE, Eötvös Loránd University)18/05/2026, 17:47Poster
Spectroscopists have been interested in the low-lying electronically excited states of $\text{He}_2$ (the lowest being $^3\Sigma_\text{u}^+$, denoted as "a") and their cation (ground state $^2\Sigma_\text{u}^+$, denoted as "X") for decades. These excited states are strongly bound compared to the $^1\Sigma_\text{g}^+$ ground state and, therefore, have much richer rovibrational spectra. The...
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Mr Mathis Panet (Laboratoire Kastler Brossel - Sorbonne Universite)18/05/2026, 17:48Poster
In the last decade, the experimental determination of the transition frequencies of Molecular Hydrogen Ions (MHIs) has improved significantly, reaching a level of precision that surpasses theoretical predictions. These advances play a crucial role in the determination of fundamental constants (e.g., $m_p/m_e$) and the testing of the Standard Model [1]. However, they also highlight the need for...
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Fabian Raab18/05/2026, 17:49Poster
LSym is a new cryogenic Penning trap experiment that intends to test the
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symmetry of matter and antimatter in the lepton sector. By measuring the coherent difference of their spin precession, the experiment will test for differences in mass, charge and g-factor of the positron and electron to achieve the most precise test for a hypothetical CPT violation for leptons so far. In the experiment... -
Prof. Michael Eides (University of Kentucky)18/05/2026, 17:50Poster
Uncertainty of the quantum electrodynamics theoretical prediction for the hyperfine splitting in the ground state of muonium is considered. It is compared with the respective discussion in the two most recent CODATA adjustments of the fundamental physical constants.
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Vadim Lensky (JGU Mainz)18/05/2026, 17:51Poster
We evaluate the hadronic vacuum polarization corrections to the Lamb shift and hyperfine splitting of $1S$ and $2S$ energy levels in ordinary and muonic hydrogen as well as ${}^3\mathrm{He}^+$ ions. Despite the smallness of these corrections, their precise knowledge is very important in view of the high experimental precision achieved in measurements of the spectra of both ordinary and muonic...
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95. Wichmann-Kroll vacuum polarization correction to lithium-like systems \\ in a Gaussian basis setHaisum Hayat (University of Melbourne)18/05/2026, 17:52Poster
Recent developments have seen the application of finite Gaussian basis sets to the $\alpha(Z\alpha)^{n\geq3}$ vacuum polarization. The energy shift for $s$ and $p$ electron states have been tabulated and their convergence investigated. In this work, we extend this problem to the multi-electron case. Hartee-Fock potentials obtained self-consistently are used to treat the vacuum polarization for...
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Joanna Peszka (GSI Helmholtz Centre for Heavy Ion Research)18/05/2026, 17:53Poster
Low-energy beams of positive muons, at tens of keV and below, allow for experiments in the field of fundamental particle physics, such as the search for the muon electric dipole moment [1], exotic atoms physics with muonium spectroscopy and gravitational experiments [2] and numerous material science applications thanks to muon-spin resonance (muSR) technique [3]. Current sources of muons...
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Katharina Schreiner (Laboratoire Kastler Brossel / Marietta Blau Institute)18/05/2026, 17:54Poster
If a sufficiently slow beam of particles is incident upon a curved surface with a small grazing angle, so called whispering gallery states (WGS) will form. The WGS are quasi-stable quantum states, arising from the effect of the centrifugal force and mirror surface potentials experienced by the particles. Interference patterns generated by WGS have already been measured with cold neutrons at...
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Martin Simon (Austrian Academy of Sciences (AT))18/05/2026, 17:55Poster
Hyperfine structure measurements on antihydrogen can provide sensitive tests of CPT invariance. The ASACUSA collaboration proposed such experiments on a beam of antihydrogen at the antiproton decelerator of CERN. We benchmark spectroscopy methods and equipment in supporting matter experiments. Beyond the relevance for antihydrogen these measurements can put new as well as improved constraints...
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Tymon Kilich (University of Warsaw)18/05/2026, 17:56Poster
The hydrogen anion H$^-$ is the lightest stable anion and its bound states and resonances are well studied, but magnetic shielding has not been computed to comparable precision. Due to the planned comparison of the bare antiproton to H$^-$ in a Penning trap, we study the magnetic shielding of H$^-$ using nonrelativistic quantum electrodynamics theory (NRQED). We compute the nonrelativistic...
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Péter Jeszenszki (MTA–ELTE Lendület ‘Momentum’ Molecular Quantum electro-Dynamics Research Group, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, Budapest, H-1117, Hungary)18/05/2026, 17:57Poster
The simplest, algebraic quantum-electrodynamical corrections due to the double-negative energy subspace and instantaneous interactions are computed to the no-pair energy of two-spin-1/2-fermion systems$^1$. Numerical results are reported for two-electron atoms with a clamped nucleus and positronium-like genuine two-particle systems. The Bethe-Salpeter equation provides the theoretical...
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Quentin Senetaire (Laboratoire Kastler Brossel (FR))18/05/2026, 17:58Poster
Precision measurements to study strong-field Bound-State Quantum Electrodynamics (BSQED) involve systems that remain largely unexplored, and thus requires the use of new detection techniques. One paradigm lies in the spectroscopy of transitions between Rydberg states of exotic atoms [1].
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The antiProtonic Atom X-ray spectroscopy (PAX) experiment aims to study such transitions in mid to high-Z... -
Balázs Rácsai (MTA–ELTE Lendület ‘Momentum’ Molecular Quantum electro-Dynamics Research Group, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, Budapest, H-1117, Hungary)18/05/2026, 17:59Poster
Relativistic, quantum electrodynamics, as well as non-adiabatic corrections and couplings, are computed for the $\text{b}\ ^3\Pi_\text{g}$ and $\text{c}\ ^3\Sigma_\text{g}^+$ electronic states of the helium dimer. The underlying Born-Oppenheimer potential energy curves are converged to 1 ppm ($1:10^6$) relative precision using a variational explicitly correlated Gaussian approach. The quantum...
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Dimitar Bakalov (INRNE)18/05/2026, 18:00Poster
We determine from the available experimental data the cross section of muon transfer to molecular oxygen at low energies with account of the oxygen molecule structure. Building on an earlier work, the results highlight the role of the molecular structure effects and significantly improve the agreement with theoretical calculations of the muon transfer rate. An efficient computational model of...
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Maria Beatriz Gomes Goncalves (Swansea University (GB))18/05/2026, 18:01Poster
Antihydrogen, the bound state of a positron and an antiproton, is a uniquely powerful system for precision tests of fundamental symmetries between matter and antimatter. The ALPHA collaboration synthesises antihydrogen by merging cold positron and antiproton plasmas. The positron temperature limits the number of trapped antihydrogen atoms, thereby constraining the data-taking rate and...
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Xiao-Qiu Qi (Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China)18/05/2026, 18:02Poster
We report recent progress in precision spectroscopy of helium isotopes ($^{3,4}$He) and lithium ions ($^{6,7}$Li$^+$), focusing on extracting nuclear structure information from high-accuracy atomic transitions. For helium, we consider the off-diagonal hyperfine mixing effects to resolve the discrepancy in the squared charge-radius difference between $^3$He and $^4$He, leading to a new squared...
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Goncalo Garces Sobreira Rodrigues Baptista (Laboratoire Kastler Brossel (FR))18/05/2026, 18:03Poster
The PAX experiment is a new effort to improve the study of x ray transitions in antiprotonic atoms for testing Bound State QED (BSQED) [1,2]. By selecting transitions between circular Rydberg states, where the bound antiproton resides orders of magnitude closer to the nucleus than an electron, whilst avoiding any nuclear overlap with its wavefunction, the dominant uncertainties that limit the...
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Vitaly Wirthl (MPQ)18/05/2026, 18:04Poster
Our recent measurement of the 2S–6P transition frequency in atomic hydrogen [1] achieves a precision of 0.7 parts per trillion, enabling a Standard Model (SM) test at a level comparable to the electron anomalous magnetic moment (g−2) [2] and representing the most precise test to date of bound-state quantum electrodynamics (QED) to 0.5 parts per million. This poster presents our ongoing efforts...
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Lei Cong (Helmholtz Institute Mainz)18/05/2026, 18:05Poster
Precision atomic spectroscopy provides a sensitive probe of physics beyond the Standard Model. A recently reported theory-experiment discrepancy in the ionization energy of metastable helium has motivated the hypothesis of a new boson mediating exotic electron-electron interactions. Using a model-independent sign-consistency analysis of the induced energy shifts, we show that the sign...
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Daniel Mayer (Acceleron Fusion, Inc.)18/05/2026, 18:06Poster
In hydrogen isotopic mixtures, stopped muons form tightly bound exotic molecules in which nuclear fusion proceeds rapidly, as the muon’s large mass enhances Coulomb barrier penetration between the nuclei. Following fusion, the muon is typically released and can repeat the process until it decays or becomes stuck to a final-state helium nucleus, with over 100 fusions per muon having been...
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Ayodeji Awobode (Department of Physics, University of Massachusetts, Boston, Massachusetts, USA)18/05/2026, 18:07Poster
Deviations from the exact value 1, of the electron orbital g-factor g_L, are determined from the measured g_J ratios of some states of the noble gas atoms He, Ne and Ar. The calculated values are compared with those previously found from the ratio of the Lande g-factors measured on the atoms of In, Ga and Na. The anomalies obtained from some of the rare gas atoms are, at least, one order of...
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Ben Ohayon (Technion IIT)19/05/2026, 09:00Invited Talk
Compact exotic atoms involve replacing one or more electrons with negative exotic particles, such as muons or antiprotons. Contact-full transitions, i.e., those that involve an "s" state, are useful for measuring nuclear radii and QCD contact terms. On the other hand, contact-free transitions allow for comparisons of experiment and theory largely free from difficult-to-calculate nuclear...
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Natalia S. Oreshkina (MPIK (Heidelberg))19/05/2026, 09:40Talk
Nuclear root-mean-square are fundamental benchmarks bridging various fields of physics. They serves as indispensable input parameters for nuclear-, atomic-, and molecular-physics calculations. Reliable rms radii are crucial for precision tests of quantum electrodynamics, for the determination of fundamental constants, and for many searches for physics beyond the Standard Model. There are two...
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Prof. Michael Eides (University of Kentucky)19/05/2026, 10:10Talk
Energy levels of QED bound states, which depend on a number of independent mass parameters, can be calculated as matrix elements of the QED energy-momentum trace. As an example of such system we consider muonic hydrogen. The leading one-loop corrections to its energy levels depend on the electron and muon masses. These corrections are calculated as matrix elements of the energy-momentum trace....
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Kjeld S.E. Eikema (Vrije Universiteit Amsterdam)19/05/2026, 11:00Invited Talk
Precision spectroscopy measurements on calculable systems are widely used to perform tests of theory, but also for determinations of fundamental constants, nuclear charge radii, and as a probe of physics beyond the standard model. We will present spectroscopy in ultracold $^3$He and $^4$He, on the 2 $^3$S$_1$ – 2 $^1$S$_0$ transition at 1557 nm.
Our latest measurement have been performed...
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Dr Jinlu Wen (Institute of Advanced Light Source Facilities, Shenzhen)19/05/2026, 11:40Talk
Precision spectroscopy of few-electron systems, such as hydrogen and helium, has significantly advanced modern physics. By comparing high-precision spectroscopy measurements in these simple atomic systems with theoretical calculations, we can test quantum electrodynamics (QED), determine fundamental physical constants, and impose constraints on physics beyond the Standard Model. Over the past...
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Gordon Drake (University of Windsor)19/05/2026, 12:00Talk
High-precision measurements of transition frequencies to the $P$-states of helium [1] for principal quantum number $n$ as high as 102 have confirmed a 9$\sigma$ disagreement between theory and experiment for the ionization energy of the $1s2s\;^3S_1$ state. However, traditional theoretical methods of calculation fail in this range of high $n$ for comparison. This paper presents high precision...
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Claudio Lenz Cesar (Federal University of Rio de Janeiro (BR))19/05/2026, 14:00Talk
We discuss, on behalf of the ALPHA collaboration, studies of some systematic effects on the 1S-2S spectroscopy on trapped and laser-cooled antihydrogen atoms through the use of a quasi-analytical lineshape [1]. This work is part of the preparation of a manuscript soon to be submitted by the ALPHA collaboration that should significantly improve the measurement of this transition frequency over...
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Abbygale Grace Swadling (University of Calgary (CA))19/05/2026, 14:30Talk
The imbalance of observed antimatter in the Universe remains an open problem in modern physics. Simple anti-atomic systems provide unique platforms to test the fundamental symmetries that predict equal amounts of matter and antimatter. Antihydrogen is an attractive candidate owing to its simple composition and the extensive study of its matter counterpart. The ALPHA (Antihydrogen Laser PHysics...
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Ross Edward Sheldon (Austrian Academy of Sciences (AT))19/05/2026, 14:50Talk
Comparisons of hydrogen to antihydrogen provide an excellent test of CPT symmetry, particularly in identifying any symmetry breaking between matter and antimatter. The energy levels of atomic hydrogen are some of the most precisely characterised quantities in nature, the challenge therefore lies in measuring the properties of antihydrogen to the same level of precision to make a meaningful...
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Ivana Belosevic (Université Paris-Saclay (FR))19/05/2026, 15:20Talk
The origin of matter-antimatter asymmetry is one of the big unanswered questions in modern physics. Various experiments look for an explanation of this asymmetry by searching for CPT symmetry violations and by testing the Weak Equivalence Principle with antimatter. The GBAR (Gravitational Behaviour of Antihydrogen at Rest) experiment at CERN seeks to measure the gravitational acceleration of...
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Patrick Strasser (KEK)19/05/2026, 16:10Talk
Muonic helium is an exotic, hydrogen-like atom formed when a negative muon replaces one of the two electrons in an ordinary helium atom. Its ground-state hyperfine structure (HFS), arising from the interaction between the magnetic moments of the negative muon and the remaining electron, is very similar to muonium HFS but inverted. The same microwave magnetic resonance technique used to measure...
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Takayuki Yamazaki19/05/2026, 16:30Talk
At the J-PARC muon facility (MUSE), we have launched a new project to precisely measure muon properties, such as magnetic moment, mass, and lifetime, by confining muons in a Penning trap.
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In our experiment, high-intensity pulsed muons are slowed down before entering a Penning trap. Ultra-slow positive muons can be generated efficiently by laser ionization of thermal muonium. In a Penning... -
Robert Potvliege (Durham University)19/05/2026, 16:50Talk
The importance of accurately taking into account the energy level shifts due to the blackbody radiation (BBR) in high precision spectroscopy is well known. The work in this area tends to focus on the BBR shift of the ground state and low excited states in view of the needs of current and forthcoming experiments. An early and notable exception is Farley and Wing's calculation of the BBR shift...
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Alina Weiser (Austrian Academy of Sciences (AT))19/05/2026, 17:10Talk
Although theoretical studies predict the existence of more than thirty positronium compounds [1], experimental observation remains limited to the simplest systems, positronium hydride (PsH) [2] and deuteride (PsD) [3]. Ps compounds are relevant in multiple fields, including many-body quantum calculations [1], materials studies [3], and antihydrogen ion formation [4], but the lack of...
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Sergey Vasiliev (University of Turku)19/05/2026, 17:40Poster
We present experimental results on loading a large Ioffe-Pritchard trap with atomic hydrogen gas at temperatures around 100 mK. Dissociation of molecular hydrogen is performed in a cryogenic RF dissociator operating below 1 K. We demostrate that atomic fluxes close to atoms/s are obtained with the average RF power in the dissociator of several mW. We propose modifications of this source for...
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Andrzej Maroń (University of Warsaw)19/05/2026, 17:41Poster
Precision spectroscopy of simple atomic systems requires increasingly accurate theoretical predictions to match the growing precision of experimental measurements. In this work, a significantly improved theory of the muonic hydrogen hyperfine splitting (HFS) is presented in anticipation of upcoming high-precision measurements. The main achievement is the rigorous calculation of some finite...
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27. Updates towards a high precision Ortho-Positronium lifetime measurement with a PET-like detectorValentin Schmidt (ETH IPA)19/05/2026, 17:42Poster
Positronium, as a purely leptonic bound state, provides a unique laboratory for precision tests of bound-state QED. Among its measurable observables, the ortho-positronium decay rate plays a central role. Second-order corrections have been calculated, leading to a theoretical prediction at the 1 ppm level [1]. In contrast, the most precise experimental results remain two orders of magnitude...
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Wenting Gan (Innovation Academy for Precision Measurement Science and Technology, CAS)19/05/2026, 17:43Poster
Among nuclear isomers spanning keV to MeV energies, ^{229m}Th is exceptional: its excitation energy of 8.4 eV and radiative lifetime of ~10^3 s make it the lowest-known nuclear excited state. This unique system offers an intrinsic narrow transition with high insensitivity to external electromagnetic fields, establishing ^{229m}Th as the premier candidate for a nuclear optical clock. Such a...
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Ms Akiho Tanaka (Department of Applied Physics, School of Engineering, The University of Tokyo, Japan)19/05/2026, 17:44Poster
Positronium (Ps), the bound state of an electron and its antiparticle, the positron, is one of the simplest atomic systems suitable for rigorous tests of fundamental physics. Specifically, more precise experimental measurements and theoretical calculations of the 1S–2S interval of ortho-Ps hold the potential to discover indications of new physics beyond the Standard Model. Currently, a...
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Palki Gakkhar (Indian Institute of Technology Delhi)19/05/2026, 17:45Poster
Optical atomic clocks represent the state of the art in time and frequency metrology, achieving unprecedented levels of precision and stability by exploiting ultra-narrow optical transitions in atoms [1]. With demonstrated fractional uncertainties approaching the $10^{-18}$ level and beyond, optical clocks now surpass microwave standards and play an essential role in the redefinition of the SI...
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Florian Egli (Max-Planck-Institut für Quantenoptik)19/05/2026, 17:46Poster
The precise measurement of the 1s–2s transition in hydrogen serves as a cornerstone for testing quantum electrodynamics (QED) in simple atomic systems [1]. Extending such measurements to other hydrogen-like systems, such as He$^+$, probes higher-order QED corrections scaling with the atomic number $Z$ and reveals nuclear structure contributions beyond hydrogen. Despite its scientific interest,...
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Siegfried Werlen (ETH Zürich)19/05/2026, 17:47Poster
The LEMING experiment aims to measure the free fall of muonium (Mu) atoms to learn about the gravitational interaction of second generation leptonic antimatter. This measurement can only be carried out by a precise atomic beam interferometer. A novel Mu source based on superfluid helium allows us to produce a horizontal beam of the required quality. We are developing a prototype to demonstrate...
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Marcus Mähring (ETH Zürich)19/05/2026, 17:48Poster
Muonium, a purely leptonic system of an anti-muon and an electron, is a promising candidate to probe physics beyond the standard model and bound-state QED. The Mu-MASS collaboration has a broad spectroscopy program, including a rich microwave program, and long-term aims to measure the 1S-2S transition in the muonium atom to several orders of magnitude beyond the current state of the art....
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Viktoria Kraxberger (Austrian Academy of Sciences (AT))19/05/2026, 17:49Poster
Antiproton–nucleus annihilation at rest is a complex process that is not yet fully described by existing models, particularly due to the scarcity of experimental data on production of heavy nuclear fragments, which has led to a limited understanding of final state interactions (FSI). New measurements are therefore essential to validate models of the annihilation dynamics and to clarify how the...
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Eugenio Fasci (1) Dipartimento di Matematica e Fisica, Università degli Studi della Campania “Luigi Vanvitelli”, Caserta, Italy / Istituto Nazionale di Fisica Nucleare – Sezione di Napoli, Napoli, Italy)19/05/2026, 17:50Poster
The ground-state hyperfine splitting in muonic hydrogen provides direct sensitivity to the proton Zemach radius, reflecting the combined effects of its spatial charge and magnetic moment distributions. Despite its fundamental importance, the hyperfine spin-flip transition has not yet been observed, owing to its extremely small excitation probability and the weak de-excitation energy underlying...
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Vincent Weis (Max Planck Institute of Quantum Optics)19/05/2026, 17:51Poster
Due to its simple structure, the Hydrogen atom is a powerful platform for precision tests of fundamental physics, more explicitly quantum electrodynamics (QED). The energy levels in atomic Hydrogen can be calculated up to a high degree of precision and can be written as:...
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Ádám Nonn (MTA–ELTE Lendület ‘Momentum’ Molecular Quantum electro-Dynamics Research Group, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, Budapest, H-1117, Hungary)19/05/2026, 17:52Poster
The equal-time Bethe–Salpeter (Salpeter–Sucher) relativistic QED wave equation is used to describe two-spin-1/2-fermion systems, e.g., positronium-like systems or two-electron atoms and molecules. The equation containing only the instantaneous part of the interaction is the with-pair Dirac–Coulomb(–Breit) equation (wpDC(B)), which includes the double-pair correction to the no-pair DC(B)...
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Evans Javary (ETH Zurich)19/05/2026, 17:53Poster
As purely leptonic atoms lacking internal structure, positronium constitutes an ideal system for high-precision tests of bound state quantum electrodynamics (QED) and search for new physics [1]. We report our results on the $\text{1}^\text{3}\text{S}_\text{1} \to \text{2}^\text{3}\text{S}_\text{1}$ interval in positronium, measured via two-photon optical spectroscopy using a continuous-wave...
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Surabhi Deshpande (Max Planck Institute of Quantum Optics)19/05/2026, 17:55Poster
The hydrogen atom has emerged as an ideal candidate for precision measurements of fundamental constants, since its energy levels can be calculated with high accuracy owing to its simple structure. Spectroscopy of two transitions of hydrogen provides a means to determine the precise values of the Rydberg constant $R_{\infty}$ and the proton charge radius $r_p$, and further comparison with other...
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Peter Hollosy (MTA–ELTE Lendület ‘Momentum’ Molecular Quantum electro-Dynamics Research Group, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, Budapest, H-1117, Hungary), Péter Jeszenszki (MTA–ELTE Lendület ‘Momentum’ Molecular Quantum electro-Dynamics Research Group, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, Budapest, H-1117, Hungary)19/05/2026, 17:56Poster
This work collects the spin-dependent leading-order relativistic and quantum-electrodynamical corrections for the electronic structure of atoms and molecules within the non-relativistic quantum electrodynamics.$^1$ We report the computation of perturbative corrections using an explicitly correlated Gaussian basis set, which allows high-precision computations for few-electron systems. In...
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Elio Bera19/05/2026, 17:57Poster
This work is part of the international GRASIAN collaboration (https://grasian.ue). One goal of this collaboration is to demonstrate the existence of Gravitational Quantum States (GQSs) of Hydrogen atoms, using a cryogenic Hydrogen beam and an atomic mirror and absorber setup, located at Marietta Blau Institute. GQSs settle when particles are trapped in a triangular potential well made, on the...
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Tesse Tiemens (Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Stadionallee 2, A-1020 Vienna, Austria)19/05/2026, 17:58Poster
In recent years, molecules have emerged as valuable precision metrology platforms for probing symmetry violations in fundamental physics. Heavy dipolar molecular species such as barium monofluoride (BaF) are particularly attractive, as their sensitivity to potential new physics is greatly enhanced, while remaining relatively simple to control due to their favorable molecular structure. Owing...
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Peter Hollosy (MTA–ELTE Lendület ‘Momentum’ Molecular Quantum electro-Dynamics Research Group, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, Budapest, H-1117, Hungary)19/05/2026, 17:59Poster
This work is concerned with two(many)-spin-1/2-fermion relativistic quantum mechanics and it is about the construction of one-particle projectors and potentially, one-particle propagators, necessary for quantum-electrodynamics (QED) corrections, using an inherently two(many)-particle, `explicitly correlated' basis representation, necessary for good numerical convergence of the results.
It...
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Caroline Rodenbeck (IAP-TLK)19/05/2026, 18:00Poster
From the observation of oscillations, neutrinos are known to have a mass.
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However, it remains an open question as to how large that mass is. One
way of determining the neutrino mass is the investigation of weak decay
kinematics. Especially suited is the beta decay of tritium, mainly due to its simple structure, high activity, and comparatively low endpoint value.
KATRIN, the Karlsruhe... -
Kees Steinebach (VU Amsterdam)19/05/2026, 18:01Poster
Precision measurements on calculable systems are widely used for tests of QED and probes for physics beyond the standard model. In our experiment we perform high precision spectroscopy on the $2\,^3S_1 – 2\,^1S_0$ transition at 1557 nm in ultracold $^3$He and $^4$He.
On this transition we recently performed the most accurate frequency measurement (48 Hz) in helium, using a Bose-Einstein...
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Foivos Vouzinas (ETH Zurich)19/05/2026, 18:02Poster
$H_2^+$ is the simplest stable molecule, and its structure can be calculated ab initio with high precision using quantum electrodynamics. By comparing the calculations with experimental data, fundamental constants can be determined, and the validity of the theory itself can be tested. However, challenging properties such as high reactivity, low mass, and the absence of rovibrational dipole...
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Randolf Pohl20/05/2026, 09:00Talk
In muonic atoms, a single muon replaces all of the atomic electrons, resulting in a 2-body system whose hydrogen-like theory is very well understood. The large muon mass of 200 times the electron mass results in a 200^3 = 10 million fold improved sensitivity of muonic-atom energy levels to nuclear structure.
Using laser spectroscopy, we have investigated the charge radii of Z=1 and 2 (H to...
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Vojtěch Patkóš (Charles University)20/05/2026, 09:30Talk
Light two-body systems such as hydrogen, muonic hydrogen, or muonium are the most viable candidates for tests of the Standard Model of fundamental interactions at low energies. It is because these simple systems allow for highly accurate theoretical predictions. Therefore, from the comparison of theory with precise experimental data we are able to search for new physics and to determine values...
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Michael Roosa (Laboratoire Kastler Brossel)20/05/2026, 10:00Talk
From dark matter and dark energy, to neutrino oscillations and the lack of antimatter in the universe, there is growing evidence that the Standard Model is incomplete. Tests of Quantum Electrodynamics (QED) with few-electron systems offer a promising avenue for looking for new physics, as QED is the best understood quantum field theory and extremely precise predictions can be obtained for...
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Carina Killian (Stefan Meyer Institute for Subatomic Physics, Austrian Academy of Sciences, Kegelgasse 27, Vienna, 1030, Austria)20/05/2026, 11:00Talk
A low energy particle confined by a horizontal reflective surface and gravity settles in gravitationally bound quantum states. These gravitational quantum states (GQS) were so far only observed with neutrons. However, the existence of GQS is predicted also for atoms.
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The GRASIAN collaboration pursues the first observation of GQS of atoms, using a cryogenic hydrogen (H) beam. This endeavor is... -
Prof. Valery Nesvizhevsky (Institut Max von Laue - Paul Langevin)20/05/2026, 11:30Talk
We discuss small shifts in the interference patterns of gravitational and whispering gallery quantum states that can be observed with neutrons, atoms, antiatoms, muonium, positronium, and other
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particles. A gravitational shift of interference patterns of neutron gravitational and whispering-gallery states can be easily observed with cold, very cold, or ultracold neutrons. The developed... -
Francesco Lancellotti (ETH Zurich)20/05/2026, 12:00Talk
The LEMING experiment aims to measure the gravitational interaction of muonium (Mu = μ⁺ + e⁻) and to perform next-generation laser spectroscopy. A high-intensity, subthermal vacuum muonium beam is produced via muon conversion in a thin layer of superfluid helium. This novel source enables sub-nanometer-sensitive measurements of muonium displacement due to gravitational acceleration and,...
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Wim Ubachs (VU University Amsterdam)20/05/2026, 14:00Talk
The hydrogen molecule (H$_2$), as the smallest molecule, is the benchmark system for testing quantum electrodynamics calculations in molecular systems. In particular the values of the dissociation and ionization energies, linked to each other via a thermodynamic cycle, have been a target to compare theory with the most advanced experiments. Since the advent of quantum mechanics many orders of...
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Mr Dariusz Kierski (Nicolaus Copernicus University in Torun, Poland)20/05/2026, 14:30Talk
We demonstrate the first cavity-enhanced spectrometer fully operating in a deep cryogenic regime down to 4 K. Not only the sample but the entire cavity, including the mirrors and cavity length actuator [1], is uniformly cooled down ensuring the thermodynamic equilibrium of the gas sample. The setup is designed in a way that efficiently attenuates both external vibrations and those originating...
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Piotr Wcislo (Nicolaus Copernicus University in Torun)20/05/2026, 15:00Talk
Due to its simplicity, H$_2$ constitutes a perfect tool for testing fundamental physics: testing quantum electrodynamics, determining fundamental constants, or searching for new physics beyond the Standard Model. H$_2$ has a huge advantage over the other simple calculable systems of having a set of a few hundred ultralong living rovibrational states, which implies the ultimate limit for...
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Trond Saue (Laboratoire de Chimie et Physique Quantiques, UMR 5626 CNRS/Université de Toulouse)20/05/2026, 15:20Talk
The [HAMP-vQED][1] project, funded by an ERC advanced grant, aims to set new standards for highly accurate calculations of molecular properties. This includes exploring the possible role of QED-effects on properties that explore the electronic density in the vicinity of nuclei, such as the parameters of NMR and Mössbauer spectroscopies. A first line of attack has been the inclusion of...
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Samuel Gaudout (Laboratoire Kastler Brossel)20/05/2026, 16:10Talk
The fine-structure constant $\alpha$ can be determined with high precision through measurements of the ratio $h/m$ between the Planck constant and the atomic mass using atom interferometry. Our latest determination of $\alpha$ has achieved a relative uncertainty of $8.1\times 10^{-11}$, establishing recoil measurements as a cornerstone of precision metrology and tests of the Standard Model....
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Sergiy Bubin (Nazarbayev University, Astana, Kazakhstan)20/05/2026, 16:40Talk
Accurate energy intervals in light open-shell atoms remain a stringent test for both precision spectroscopy and ab initio electronic-structure theory. One of the most persistent benchmarks is neutral boron: the separation between the ground $^2P^o$ state and the lowest $^4P^e$ quartet, together with the quartet fine structure, has resisted definitive theoretical--experimental reconciliation...
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Francesco Clozza (INFN-LNF & Università degli Studi di Roma "Tor Vergata")20/05/2026, 17:00Talk
Exotic atoms constitute a unique platform to explore fundamental interactions and symmetries. In particular, kaonic atoms are a great tool to investigate quantum electrodynamics in extreme electromagnetic fields. While conventionally exploited to investigate low-energy QCD through hadronic shifts and widths, kaonic atoms also offer a unique opportunity to probe bound-state QED (BSQED) in a...
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21/05/2026, 09:00
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Prof. Stephan Schiller (Heinrich-Heine-Universität Düsseldorf)21/05/2026, 09:10Invited Talk
Molecular hydrogen ions (MHIs) represent a class of bound quantum systems with significant potential for advancing our knowledge in multiple scientific domains, including the determination of fundamental constants, test of quantum physics, and the search for new interparticle forces. Furthermore, the comparison of transitions in MHIs and their antimatter counterparts provides an opportunity...
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Fabian Schmid (ETH Zurich)21/05/2026, 09:50Invited Talk
The hydrogen molecular ion H$_2^+$ is the simplest stable molecule, and its structure can be calculated ab initio with high precision using quantum electrodynamics. By comparing the calculations with experimental data, fundamental constants can be determined, and the validity of the theory itself can be tested. However, challenging properties such as high reactivity, low mass, and the absence...
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Ashley Béguin (CNRS-LTE)21/05/2026, 11:00Talk
Since 1967, time has been defined through atomic transition frequencies, establishing atomic clocks as fundamental tools for science and technology. More recently, optical atomic clocks have surpassed historical atomic microwave clocks, reaching uncertainties close to 10⁻¹⁸ and enabling both applied and fundamental investigations. At this level of performance, atomic clocks serve as sensitive...
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Jorge Moreno (Max Planck Institute of Quantum Optics)21/05/2026, 11:30Talk
The precise measurement of the 1s–2s transition in hydrogen serves as a cornerstone for testing quantum electrodynamics (QED) in simple atomic systems [1]. Extending such measurements to other hydrogen-like systems such as He$^+$ probes higher-order QED corrections scaling with the atomic number $Z$ and reveals nuclear structure contributions beyond hydrogen. Despite its scientific interest,...
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Ayush Agrawal (University of Oxford)21/05/2026, 12:00Talk
Over the past few decades, advancements in optical atomic clocks have enabled measurements of time and frequency with unprecedented stability and systematic uncertainty [1,2]. Precision frequency comparisons between macroscopically separated clocks have applications in geodesy [3], probing variations in fundamental constants, and in dark matter searches [4]. Frequency comparisons between...
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Prof. Krzysztof Pachucki (University of Warsaw)21/05/2026, 14:00Talk
The finite nuclear mass $(Z\,\alpha)^2\,m/M\,E_F$ correction to the hyperfine splitting in hydrogenic systems are calculated using
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a combined relativistic heavy particle and nonrelativistic quantum electrodynamics. Obtained results are in disagreement with previous calculations
by Bodwin and Yennie [Phys. Rev. D {\bf 37}, 498 (1988)].
The comparison of improved theoretical predictions... -
Franziska Hagelstein (JGU Mainz & PSI)21/05/2026, 14:30Talk
I reexamine theory predictions of the ground-state hyperfine splitting in muonic hydrogen. A particular focus will be on proton finite-size and polarizability contributions. The common $(Z \alpha)^5$ finite-size contributions are extended up to and including $(Z \alpha)^6$. Their reanalysis based on electron-proton scattering data is presented, discussing limitations
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of the scattering data... -
Dr Vladimir Pascalutsa (University of Mainz)21/05/2026, 15:00Talk
In view of ongoing hyperfine-structure measurements by FAMU and CREMA, we investigate relativistic recoil corrections in muonic hydrogen. We particularly emphasize on relativistic contributions involving vacuum polarization and finite-size effects (see e.g., Ref. [1]), refining the theoretical description to align with the precision of current experiments.
[1]. A.Antognini, F.Hagelstein...
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Siddharth Rajamohanan (ETH Zürich)21/05/2026, 15:20Talk
Muonic hydrogen ($\mu p$) consists of a negatively charged muon bound to a proton. The large mass of the muon makes the energy levels of this atomic system sensitive to the finite size effects of the proton. The CREMA collaboration aims to measure the 1S hyperfine splitting in muonic hydrogen to $1\,$ppm relative uncertainity. This measurement can be used to determine the proton structure...
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Matthew Bohman (Max-Planck-Institut für Kernphysik)21/05/2026, 16:10Talk
Diatomic molecular hydrogen ions (MHI) such as H$_2^+$ and HD$^{+}$ are simple, single-electron systems with properties that can be calculated to high precision by ab initio theory. Comparison to precision experiments then enables stringent tests of the Standard Model and high-precision determinations of fundamental constants. Laser spectrosocopy of rovibrational transitions has now been...
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Dr Jean-Philippe Karr (Laboratoire Kastler Brossel)21/05/2026, 16:40Talk
In the last few years, spectroscopy of molecular hydrogen ions (MHI) contributed for the first time in the adjustment of fundamental constants and in establishing bounds on beyond-standard-model interactions. Ongoing improvements and diversification of experimental methods require advancing further the theoretical description of MHIs. One way in which this may be achieved consists in combining...
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David Ferenc (CNRS)21/05/2026, 17:00Talk
The largest source of uncertainty in the theory of spin-averaged rovibrational transitions in hydrogen molecular ions arises from uncalculated higher-order ($m\alpha^{8+}$) corrections to the one-loop self-energy [1]. These terms are extremely challenging to evaluate via the standard $Z\alpha$ expansion, therefore—similarly to the case of the hydrogen atom [2]—a numerical all-order approach is...
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Meng-yi Yu (University of Science and Technology of China)21/05/2026, 17:20Talk
Cold molecules exhibit significant potential in many applications, including precision measurement, quantum metrology, and fundamental physics. Although a few specific types of molecules have been successfully laser-cooled by selecting electronic transitions with appropriate Franck-Condon factors, laser deceleration of general molecules still poses significant challenges. In order to explore...
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Dvir Yaari (The Hebrew University of Jerusalem)22/05/2026, 09:00Talk
The MUon Scattering Experiment (MUSE) at the Paul Scherrer Institute (PSI) is designed to address the "proton radius puzzle" through high-precision measurements of elastic lepton-proton scattering. By utilizing a mixed secondary beam in the $\pi$M1 channel, MUSE performs simultaneous measurements of electron-proton ($e^{\pm}p$), muon-proton ($\mu^{\pm}p$), and pion-proton ($\pi^{\pm}p$)...
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Vladimir Yerokhin (Max Planck Institute for Nuclear Physics)22/05/2026, 09:30Talk
I report on recent advances in ab initio QED theory of the 2pj-2s transition energies in Li-like ions and present the most accurate calculations to date for the Li isoelectronic sequence with Z >= 10 [1]. Improved convergence of the calculations was achieved by employing the extended Furry picture, which includes the screening potential nonperturbatively, in addition to the nuclear binding...
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Prof. Ulrich Jentschura (Missouri S&T University)22/05/2026, 10:00
The bound system of a deuteron and its antiparticle (deuteronium) appears to be an almost ideal candidate for the study of higher-order corrections to the electromagnetic interactions of spin-1 particles. As shown in the preprints arXiv:2506.15974 and arXiv:2602.04743 (accepted for publication in Physical Review Research and Physical Review D), the fine and hyperfine structure of deuteronium...
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Vitaly Wirthl22/05/2026, 11:00Talk
Quantum electrodynamics (QED) forms the basis for all other quantum field theories, upon which the Standard Model (SM) of particle physics is constructed. Because of the hydrogen atom's simplicity, its energy levels can be precisely calculated from bound-state QED and compared with experiment. Such a comparison between theory and experiment is linked to the determination of fundamental...
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Stephan Fritzsche (Helmholtz-Institute Jena + GSI Darmstadt)22/05/2026, 11:30Talk
The hyperfine interaction between the nuclear moments and electronic charge and current distributions occurs naturally for all atoms and ions with non-zero nuclear spin, $I\neq 0$. While the hyperfine splitting of most ionic levels usually remain (very) small, this coupling of the nuclear and electronic degrees of freedom can significantly modify the lifetime of isomeric and electronic states....
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Dr Anna Viatkina (TU Braunschweig, PTB Braunschweig)22/05/2026, 11:50Talk
We calculate parity-violation-induced E1 amplitudes for the $1s\rightarrow 2s$ and $1s^2 2s\rightarrow 1s^2 3s$ transitions in H- and Li-like ions of $^{40}$Ca, $^{48}$Ca, and $^{208}$Pb; neutron skin effects and nuclear uncertainties are included for each nucleus. We consider spin-independent weak-interaction contribution of the $Z^0$ boson described by standard model, as well as the effects...
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Dr Wencui Peng22/05/2026, 12:10Talk
Beryllium ions (9Be+) serve as a four-body system with a closed electronic shell and a single valence electron, offering advantages for both theoretical and experimental research. Theoretically, their energy level structure can be accurately calculated using high-precision quantum electrodynamics (QED) methods. Experimentally, laser cooling enables the preparation of ultracold Coulomb...
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