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 DAΦNE electron-positron collider of Laboratori Nazionali di Frascati. With a gaseous hydrogen target of density 15 ρ 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 α transition and 0.045 −0.012 +0.009 for K tot , the summation of all the emitted K -series transitions.