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In this paper, we present the first tests performed after the full installation of the SIDDHARTA-2 experimental apparatus on the interaction region of the DA$\Phi$NE collider at the INFN National Laboratories of Frascati. Before starting the first measurement of the kaonic deuterium 2p $\rightarrow$ 1s transition, an accurate evaluation of the background rejection was required, mainly achieved with the kaon trigger system. This run, performed in the period 04–26/05/2022 with a $^{4}$He gaseous target, confirmed the 10$^{5}$ order of magnitude of the rejection factor obtained with the reduced version of the setup and different machine conditions in 2021. This important outcome motivated the filling of the target cell with deuterium and the start of the measurement campaign of the kaonic deuterium 2p $\rightarrow$ 1s transition.

The SIDDHARTA-2 experiment installed at the DA$\mathrmΦ$NE collider of INFN-LNF performed, for the first time, measurements of high-n transitions in intermediate mass kaonic atoms during the data taking campaigns of 2021 and 2022. Kaonic carbon, oxygen, nitrogen and aluminium transitions, which occur in the setup materials, were measured by using the kaons stopped in the gaseous helium target cell with aluminium frames and Kapton walls, and are reported in this paper. These new kaonic atoms measurements add valuable input to the kaonic atoms transitions data base, which is used as a reference for theories and models of the low-energy strong interaction between antikaon and nuclei. Moreover, these results pave the way for future dedicated kaonic atoms measurements through the whole periodic table and to a new era for the antikaon-nuclei studies at low energy., 8 pages, 7 figures

Kaonic atoms are a unique tool to explore quantum chromodynamics in the strangeness sector at low energy, with implications reaching neutron stars and dark matter. Precision X-ray spectroscopy can fully unlock the at-threshold isospin dependent antikaon-nucleon scattering lengths, via the atomic transitions to the fundamental level. While the SIDDHARTA experiment at the INFN-LNF DA$Φ$NE collider successfully measured kaonic hydrogen, its successor SIDDHARTA-2 is starting now its data taking campaign aiming to finally fully disentangle the isoscalar and isovector scattering lengths via the measurement of kaonic deuterium. An overview of the first experimental results from a preparatory run for the SIDDAHARTA-2 experiment is presented., 13 pages, 7 figures, to be sumbitted to Phys. Scr. - Focus on New Frontiers in Physics - Selected Papers from ICNFP 2021

The SIDDHARTA-2 experiment at the DA$\Phi$NE collider aims to perform precision measurements of kaonic atoms X-ray spectroscopy for the investigation of the antikaon-nucleon strong interaction. To achieve this goal, novel large-area Silicon Drift Detectors (SDDs) have been developed. These devices have special geometry, field configuration and readout electronics that ensure excellent performance in terms of linearity and stability. The paper presents preliminary results for the linearity determination and stability monitoring of the SDDs system during the measurement of kaonic deuterium carried out in the summer of 2022.