We propose a concept for a cryogenic source of atomic tritium at sub-Kelvin temperatures and energies suitable for magnetic trapping. The source is based on the dissociation of solid molecular T_{2} films below 1 K by electrons from a pulsed rf discharge, a technique recently demonstrated for atomic hydrogen, combined with buffer-gas cooling and magnetic confinement. We analyze the key processes limiting the source performance, adsorption, spin exchange, and recombination, and show that atomic tritium fluxes exceeding 10^{15} s^{−1} at temperature of ∼200 mK can be achieved. Such a source would enable Doppler-free two-photon 1S–2S spectroscopy in atomic tritium for high-precision measurements of the triton charge radius, providing a crucial benchmark for bound-state QED and improving the comparison between electronic, muonic, and scattering determinations of nuclear sizes in light systems. Beyond spectroscopy, using atomic tritium source avoids molecular final-state broadening in β decay and is therefore necessary for next-generation neutrino-mass measurements; combined with detector technologies such as sub-eV resolution quantum sensors or cyclotron radiation emission spectroscopy, it enables an order-of-magnitude improvement compared to the current best experimental limit. Additionally, the source can be used to generate a beam of low-field-seeking deuterium atoms for loading magnetic traps, an important benchmark before trapping tritium atoms, which is useful for precision spectroscopy.

We have performed hyperfine spectroscopy of two transitions in ground-state deuterium and searched for violations of CPT and Lorentz symmetry that would manifest as sidereal variations of the observed transition frequencies. Several nonrelativistic proton coefficients of the Standard-Model extension framework have been addressed. The spin-independent coefficients with momentum power k=2, 4 are constrained for the first time. Bounds on spin-dependent coefficients are improved by exploiting a sensitivity enhancement originating from the relative momenta of the nucleons in the deuteron. The best previous constraints by hydrogen maser measurements are surpassed by 4 and 14 orders of magnitude for coefficients with k=2 and 4, respectively.

The study of the strong interaction among hadrons at low energies remains one of the key challenges in fundamental physics because of its non-perturbative nature, which makes theoretical descriptions strongly dependent on experimental input. Although substantial progress has been made for systems involving up and down quarks, theoretical models in the strangeness sector continue to face limitations due to the lack of experimental data. Kaonic atoms provide a powerful tool to study the low-energy strong interaction with strangeness through the energy shifts and widths induced on their lowest atomic levels. In this context, kaonic deuterium X-ray spectroscopy has long represented one of the major open challenges in hadronic-atom physics because of its extremely low X-ray yield. This measurement is particularly important because it gives access to the experimentally inaccessible K^-n interaction at threshold energy. Here, we report the first observation of kaonic deuterium X-ray transitions, performed with the SIDDHARTA-2 experiment at the DAΦNE collider. We determine the strong-interaction shift and width of the 1s level to be ε_1s=-810.9±24.5 (stat)±2.1 (syst) eV and Γ_1s=812±97 (stat)±33 (syst) eV, respectively. This measurement constitutes the most precise experimental determination of the K^-d strong interaction at threshold and allows discrimination among competing theoretical models. Combined with the kaonic hydrogen measurement, this result provides the experimental input required to determine the isospin-dependent K^-N scattering lengths, with implications for the description of the nature of the first predicted hadronic molecular state, the Λ(1405), and neutron-rich matter.

A study of antiproton-nucleus annihilations at rest on a variety of thin solid targets using slow extracted antiprotons is being prepared. To detect the charged annihilation products, the experiment will employ seven Timepix4 ASICs coupled to 500 mu m thick silicon sensors. These will be arranged in a cuboid geometry that covers the majority of the full solid angle around the target, enabling precise tracking of outgoing particles using only one layer of detectors. With these novel chips, the annihilation will be studied by measuring the total multiplicity, energy, and angular distribution of various prongs produced in a number of targets. A 3D reconstruction algorithm for determining the annihilation vertex from particle tracks in the single-plane detectors has been developed using Monte Carlo simulations. This allows for event-by-event reconstruction, making it possible to distinguish antiproton annihilations on the target from those occurring elsewhere. The measurements will also enable a study of possible final state interactions triggered by the primary annihilation mesons, their evolution with the nuclear mass and their branching ratios.

A study of antiproton annihilations at rest on thin solid targets is underway at the ASACUSA facility, which now features a dedicated beam line for slow extraction at 250 eV. The experiment will employ new technologies, such as the Timepix4 ASICs coupled to silicon sensors, to measure the total multiplicity, energy, and angular distribution of various prongs produced in thin solid targets. A detection system consisting of seven Timepix4, covering most of the solid angle, is being constructed. A 3D annihilation vertex reconstruction algorithm from particle tracks in the single-plane detectors has been developed using Monte Carlo simulations. The measurements will enable a study of pbar-nucleus interactions, their dependence on nucleus mass and branching ratios. The results will be used to assess and potentially improve various simulation models.

We present a design and performance tests of an intense source of cold hydrogen atoms for loading large magnetic traps. Our source is based on a cryogenic dissociator of molecular hydrogen at 0.6 K followed by a series of thermal accommodators at 0.5, 0.2 and 0.13 K with inner surfaces covered by a superfluid helium film. All components are thermally anchored to corresponding stages of a dilution refrigerator. The source provides a continuous flux of 7× 10^13 H atoms/s in a temperature range of 130–200 mK. We have successfully used the source for loading a large Ioffe–Pritchard magnetic trap recently built in our laboratory (Ahokas et al. in Rev Sci Instrum 93(2):023201, 2022). Calorimetric measurements of the atomic recombination heat allow reliable determination of the atomic flux and H gas density in the trap. We have tested the performance of the source and loading of H atoms into the trap at various configurations of the trapping field, reducing the magnetic barrier height to 75 % and 50 % of the nominal value of 0.8 T (0.54 K) as well as at the open configuration of the trap at its lower end, when the atoms are in contact with the trapping cell walls covered by a superfluid helium film. In the latter case, raising the trapping cell temperature to 200–250 mK, the low-field seeking atoms at densities exceeding 10 ^11 cm^-3 can be stored for the time over 10 ^3 s, sufficiently long for experiments on precision spectroscopy of cold H gas.

We conducted measurements ofK-+3He ->pi YN+N ' reactions using a 1 GeV/cK--beam, with theobjective of understanding the broad decay width of KNN(approximately twice as broad as that ofETX(1405)considered to be the KNquasibound state). We successfully reproduced distributions of the pi YNinvariant massand momentum transfer for pi YNusing model-fitting functions for KNNformation and quasifree Kabsorption(QF K-abs) processes. The model can describe the experimental data quite well, and four KNN ->pi YNcrosssections were obtained. The results indicate that mesonic decay is the dominant decay branch of KNN.Theresults also suggest thatEOT pi ETXN approximate to EOT pi ENON, which indicates that theI KN=1 absorption channel, in addition to theNBSPI KN=0 absorption channel, substantially contributes to the KNNdecay, making the KNNstate approximatelytwice as unstable asETX(1405)

Abstract. We measured πE invariant mass spectra below and above the K¯N mass threshold in the K−d → NπE reaction in order to study the K¯N interaction and the Λ(1405) resonance. This reaction can be described by the two-step process: (i) K¯N1 → K¯N followed by (ii) K¯N2 → πΣ, where N1 and N2 are nucleons bound in the deuteron. We deduced the S -wave scattering amplitude of K¯N →K¯N in the framework of the K¯N πΣ coupled channel so as to reproduce the observed πΣ spectra in the I = 0 channel. We found a resonance pole at 1417.7-7.4+6.0 (fitting error)-1.0+1.1 (systematic error) - i[26.9-7.9+6.0 (fitting error)-2.0+1.7 (systematic error)]MeV/c2.

The Antiproton Decelerator (AD) at CERN provides antiproton bunches with a kinetic energy of 5.3 MeV. The Extra-Low ENergy Antiproton ring at CERN, commissioned at the AD in 2018, now supplies a bunch of electron-cooled antiprotons at a fixed energy of 100 keV. The MUSASHI antiproton trap was upgraded by replacing the radio-frequency quadrupole decelerator with a pulsed drift tube to re-accelerate antiprotons and optimize the injection energy into the degrader foils. By increasing the beam energy to 119 keV, a cooled antiproton accumulation efficiency of (26 +- 6)% was achieved.

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. The GRASIAN collaboration pursues the first observation of GQS of atoms, using a cryogenic hydrogen beam. This endeavor is motivated by the higher densities, which can be expected from hydrogen compared to neutrons, the easier access, the fact that GQS were never observed with atoms and the accessibility to hypothetical short-range interactions. In addition to enabling gravitational quantum spectroscopy, such a cryogenic hydrogen beam with very low vertical velocity components—a few cm s^-1 , can be used for precision optical and microwave spectroscopy. In this article, we report on our methods developed to reduce background and to detect atoms with a low horizontal velocity, which are needed for such an experiment. Our recent measurement results on the collimation of the hydrogen beam to 2 mm, the reduction of background and improvement of signal-to-noise and finally our first detection of atoms with velocities <72 ms^-1 are presented. Furthermore, we show calculations, estimating the feasibility of the planned experiment and simulations which confirm that we can select vertical velocity components in the order of cm s^-1 .

The mechanism of antiproton-nucleus annihilation at rest is not fully understood, despite substantial previous experimental and theoretical work. In this study we used slow extracted antiprotons from the ASACUSA apparatus at CERN to measure the charged particle multiplicities and their energy deposits from antiproton annihilations at rest on three different nuclei: carbon, molybdenum and gold. The results are compared with predictions from different models in the simulation tools Geant4 and FLUKA. A model that accounts for all the observed features is still missing, as well as measurements at low energies, to validate such models.

We present a Rabi-type measurement of two ground-state hydrogen hyperfine transitions performed in two opposite external magnetic field directions. This puts first constraints at the level of 2.3 10^-21 GeV on a set of coefficients of the Standard Model Extension, which were not measured by previous experiments. Moreover, we introduce a novel method, applicable to antihydrogen hyperfine spectroscopy in a beam, that determines the zero-field hyperfine transition frequency from the two transitions measured at the same magnetic field. Our value, nu_0 = 1.420 405 751 63(63) GHz, is in agreement with literature at a relative precision of 0.44 ppb. This is the highest precision achieved on hydrogen in a beam, improving over previous results by a factor of 6.

We conducted measurements of K^- + ^3 He→πY N + N' reactions using 1  GeV/c K^--beam, aiming to understand the broad decay width of K̅N N (≈ twice as broad as that of Λ(1405) considered to be the K̅N quasi-bound state). We successfully reproduced distributions of the π Y N invariant mass and momentum transfer of π Y N by employing model fitting functions for K̅ N N formation and quasi-free K̅ absorption (QF_K̅- abs) processes. The model can describe the experimental data quite well, and four K̅ N N →π Y N cross-sections were obtained. The result suggests that the mesonic decay is the dominant decay branch of K̅ N N. It was also suggested that Γ_πΛ N∼Γ_πΣ N, which indicates a significant contribution of the I_K̅ N=1 absorption channel to the K̅ N N decay as well as the I_K̅ N=0 makes the K̅ N N state ≈ twice as unstable as Λ(1405).

In the search for clues to the matter-antimatter puzzle, experiments with atoms or molecules play a particular role. These systems allow measurements with very high precision, as demonstrated by the unprecedented limits down to $10^{-30}$ e.cm on electron EDM using molecular ions, and relative measurements at the level of $10^{-12}$ in spectroscopy of antihydrogen atoms. Building on these impressive measurements, new experimental directions offer potentials for drastic improvements. We review here some of the new perspectives in those fields and their associated prospects for new physics searches.

The ASACUSA (atomic spectroscopy and collisions using slow antiprotons) Cusp experiment requires the production of dense positron plasmas with a high repetition rate to produce a beam of antihydrogen. In this work, details of the positron production apparatus used for the first observation of the antihydrogen beam, and subsequent measurements, are described in detail. This apparatus replaced the previous compact trap design resulting in an improvement in the positron accumulation rate by a factor of $52\pm 3$ .