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In March 2019, the HADES collaboration recorded 13:7 · 09 Ag(1.58A GeV)+Ag events as part of the FAIR Phase-0 program. The analysis steps necessary to extract the phase space information for K+, K− and ϕ(1020) are presented in this proceeding.

I will review recent developments in rare and radiative kaon decays from the theory side, with emphasis on those modes that are actively analyzed by the experimental collaborations.

Motivated by the future prospects of the NA62 and KOTO experiments, which aim to measure the rare kaon decays \\(K^+ ^+ \\) and \\(K_L ^0 \\), respectively, we discuss the present uncertainties of the Standard Model theory prediction. We also examine which calculations could further improve the theoretical accuracy of the charged and neutral decay modes.

The NA62 experiment at CERN reports results from a study of radiative kaon decay K+ → π0e+vγ, using a data sample recorded in the years 2017 and 2018. The sample comprises O(100k) candidates with sub-percent background contamination. Preliminary results of the most precise measurement of the corresponding branching ratio and with the measurement of the T-asymmetry parameter are presented.

NA61/SHINE is a large-acceptance fixed-target experiment conducted at the CERN SPS. The experiment has measured charged kaon production in 0-10% central Ar+Sc collisions at beam momenta of 13A, 19A, 30A, 40A, 75A, and 150A GeV/c. In this report, we present the measurements of K S 0 production and charged-to-neutral kaon ratio in 0-10% central Ar+Sc collisions at 75A GeV/c. The results are compared to the charged and neutral kaon production in other collision systems measured by NA61/SHINE, as well as to model predictions and data from other experiments.

Kaon photoproduction on the deuteron is investigated within the impulse approximation, with the reaction kinematics selected to minimize the effects of final-state interactions. The deuteron wave function is obtained from the Bonn OBEPQ potential and treated non-relativistically, while the elementary production operator is described using the KAON-MAID model. Off-shell effects are examined by varying the energy of the interacting nucleon, and the results indicate that these effects have a negligible influence on the photoproduction observables. To enhance the calculation, we propose employing a new elementary operator based on recent isobar models that reproduce all available experimental data. This new operator has been constructed and is ready for implementation in future investigations.

A bstract We present a comprehensive analysis of low-energy signals of hypothetical scalar leptoquark interactions in lepton and kaon transitions. We derive the most general effective four-fermion Lagrangian induced by tree-level scalar leptoquark exchange and identify the Wilson coefficients predicted by the five possible types of scalar leptoquarks. The current constraints on the leptoquark Yukawa couplings arising from lepton and kaon processes are worked out, including also loop-induced transitions with only leptons (or quarks) as external states. In the presence of scalar leptoquark interactions, we also derive the differential distributions for flavour-changing neutral-current transitions in semileptonic kaon modes, including all known effects within the Standard Model. Their interference with the new physics contributions could play a significant role in future improvements of those constraints that are currently hampered by poorly-determined non-perturbative parameters.

We review lattice results related to pion, kaon, D-meson, B-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More specifically, we report on the determination of the light-quark masses, the form factor f+(0) arising in the semileptonic K→π transition at zero momentum transfer, as well as the decay constant ratio fK/fπ and its consequences for the CKM matrix elements Vus and Vud. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of SU(2)L×SU(2)R and SU(3)L×SU(3)R Chiral Perturbation Theory. We review the determination of the BK parameter of neutral kaon mixing as well as the additional four B parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for mc and mb as well as those for D- and B-meson decay constants, form factors, and mixing parameters. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant αs. Finally, in this review we have added a new section reviewing results for nucleon matrix elements of the axial, scalar and tensor bilinears, both isovector and flavor diagonal.

The KLOE-2 Collaboration continues the KLOE long-standing tradition of flavour physics precision measurements in the kaon sector with a new KS → πeν branching fraction measurement with 1.63 fb−1 KLOE data acquired at the DAΦNE Frascati ϕ-factory. The strategy to achieve this new result has been presented together with the combination with our previous BR(KS → πeν) measurement, based on an independent data sample, which allows the total precision to be improved by almost a factor of two, and a new derivation of f+(0)|Vus|.

On the statistics of ∼ 8·109 positively charged kaons passing through a thin copper target a coherent production of the K+π0 - pair is studied. Contributions of Coulomb, strong interactions and their interference to the total cross section are determined in the region of K*(892). In the distribution over K+π0 invariant mass, an effect is seen, which can be explained by the interference of the chiral anomaly and the K* (892) amplitudes. From that, the ratio of the measured chiral anomaly amplitude and the theoretical one is obtained: Aexp/Ath = 0.9 ± 0.24 (stat.)±0.3 (syst.).