Measurements of the strong-interaction widths of the kaonic 3He and 4He 2p levels

The kaonic 3He and 4He X-rays emitted in the 3d→2p transitions were measured in the SIDDHARTA experiment. The widths of the kaonic 3He and 4He 2p states were determined to be Γ2p(He3)=6±6(stat.)±7 (syst.) eV, and Γ2p(He4)=14±8 (stat.)±5 (syst.) eV, respectively. Both results are consistent with the theoretical predictions. The width of kaonic 4He is much smaller than the value of 55±34eV determined by the experiments performed in the 70ʼs and 80ʼs, while the width of kaonic 3He was determined for the first time.