L-series X-ray yields of kaonic 3He and 4He atoms in gaseous targets

The SIDDHARTA experiment measured X-rays from kaonic helium atoms using, for the first time, gaseous 3He and 4He targets. Clear patterns of the L-series X-rays of kaonic 3He and 4He atoms were observed. By using accurate Monte Carlo simulations, the absolute yields of these X-ray transitions were determined to be Y(3d → 2p) = 25.0 −5.8 +6.7 % for 3He (0.96 g/l), Y(3d → 2p) = 23.1 −4.2 +6.0 % for 4He (1.65 g/l), and Y(3d → 2p) = 17.2 −9.5 +2.6 % for 4He (2.15g/l). In addition, the yields Y (nd → 2p), with n > 3 were also determined. The measured yields provide valuable information for understanding the cascade processes of kaonic helium atoms as a function of the target density.