NA48 results on neutral kaon rare decays and

Introduction The main goal of the NA48 experiment has been the measurement of =") and it has been shown that direct CP violation in neutral kaon decays exists [1][2]. The data taken for this measurement has been used also for a series of studies of rare decays of K L , K S and hyperons. 2. Data taking in 1997-2000 Starting from 1997 to 2000, NA48 has collected millions of K L , K S decays for Re(" =") measurement. The available bandwidth in the data acquisition system allowed to con gure the trigger such that it selected also speci c rare decays, like K L ! or decays. During each year of run, special runs were also taken, in which a negative pion beam was transported in the path of K L beam to a pair of 2 cm polyethylene targets, located inside the ducial volume of K L ,K S decays. These pions generated and , whose decays in two and six gammas were used to study the performances and the stability of the response of the liquid krypton calorimeter. Pres