New measurements of kaonic helium-4 L-series X-rays yields in gas with the SIDDHARTINO setup

The L-series X-rays transitions of the kaonic helium-4 exotic atom were measured by SIDDHARTINO, the reduced configuration of the SIDDHARTA-2 experiment, at the DAΦNE collider of INFN-LNF, with gaseous 4He targets at densities of 1.90 g/l and 0.82 g/l, corresponding to 1.5% and 0.66%, respectively, of the liquid helium-4 density. The absolute yields for the Lα transition are determined to be 0.15 ±0.03 and 0.12 ±0.03, for the two target densities. The yields for the Lβ and Lγ transitions are presented relatively to that of the Lα transition. These results are compatible with the yields measured by the SIDDHARTA experiment at the densities of 1.65 g/l and 2.15 g/l and contribute to refine the cascade models describing the de-excitation of kaonic atoms as function of density.