First Tests of the Full SIDDHARTA-2 Experimental Apparatus with a 4 He Gaseous Target

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 -> 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 He-4 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 -> 1s transition.