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 DA phi NE collider of INFN-LNF, with gaseous He-4 targets at densities of 1.90g/l and 0.82g/l, corresponding to 1.5% and 0.66%, respectively, of the liquid helium-4 density. The absolute yields for the L-alpha are determined to be 0.15 +/- 0.03and 0.12 +/- 0.03, for the two target densities. The yields for the L-ss and L(gamma)transitions are presented relatively to that of the Latransition. 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.