The yield of kaonic hydrogen X-rays in the SIDDHARTA experiment

We measured K-series kaonic hydrogen X-rays in the SIDDHARTA experiment performed at the DA Phi NE electron-positron collider of Laboratori Nazionali di Frascati. With a gaseous hydrogen target of density 15 rho(STP), preliminary values of the absolute yields, defined as the number of atomic X-rays emitted per kaon stopped inside the target, were determined to be 0.012(-0.004)(+0.003) for K alpha transition and 0.045(-0.012)(+0.009) for K-tot, the summation of all the emitted K-series transitions.