Preliminary study of kaonic deuterium X-rays by the SIDDHARTA experiment at DAΦNE

The study of the (K) over bar N system at very low energies plays a key role for the understanding of the strong interaction between hadrons in the strangeness sector. At the DA Phi NE electron-positron collider of Laboratori Nazionali di Frascati we studied kaonic atoms with Z = 1 and Z = 2, taking advantage of the low-energy charged kaons from Phi-mesons decaying nearly at rest. The SIDDHARTA experiment used X-ray spectroscopy of the kaonic atoms to determine the transition yields and the strong interaction induced shift and width of the lowest experimentally accessible level (1s for H and D and 2p for He). Shift and width are connected to the real and imaginary part of the scattering length. To disentangle the isospin dependent scattering lengths of the antikaon-nucleon interaction, measurements of K- p and of K- d are needed. We report here on an exploratory deuterium measurement, from which a limit for the yield of the K-series transitions was derived: Y(K-tot) < 0.0143 and Y (K-alpha) < 0.0039 (CL 90%). Also, the upcoming SIDDHARTA-2 kaonic deuterium experiment is introduced.