Low energy kaon-nuclei interaction at DAΦNE: The SIDDHARTA-2 experiment

Light kaonic atoms spectroscopy is a unique tool for the investigation of the low-energy quantum chromodynamics (QCD) in the strangeness sector. The precise measurements of the X-ray emission from light kaonic atoms provide information on the kaon-nucleus interaction at threshold without the need of an extrapolation as in the case of scattering experiments. In 2009, the SIDDHARTA Collaboration performed the most precise measurement of kaonic hydrogen (K-H) X-ray transition to the fundamental level. Nowadays, the SIDDHARTA-2 Collaboration is ready to perform the more challenging measurement of kaonic deuterium (K-d) 2p → 1s transition. To achieve this unprecedented result, which is fundamental to extract the isospin-dependent antikaon-nucleon scattering lengths, an upgraded experimental apparatus with respect to the SIDDHARTA one was realized. This paper presents an overview on the SIDDHARTA-2 setup installed on the DAΦNE collider of LNF-INFN and the first results obtained during the machine optimization phase, in preparation for the kaonic deuterium data taking campaign planned in 2021–2022.