Cern-Spsc-2004-029 Spsc-I-229 18.10.2004

this document we concentrate on charged kaons because the intensity of protons that can be delivered by the current SPS on the T10 target is not a limitation for this programme. We have performed a study for an experiment able to collect about 100 K ## events with a signal to background ratio of 10:1 in two years of data taking. Within the Collaboration we dubbed this initiative NA48/3 for short. The two undetectable neutrinos in the final state require the design of an experiment with redundant measurement of the event kinematics and hermetic vetoes to achieve the necessary background rejection. Particular care has to be taken to suppress the two body decays K and K # which have branching ratios up to 10 times larger than the expected signal. The reconstruction of the two body kinematics may su#er from reconstruction tails and backgrounds can originate if photons from K are not detected or if muons from K # are mis-identified as pions. To suppress backgrounds from the two body decays, kinematics and Particle Identification (PID) have to be used in conjunction. Backgrounds from K three-body decays need also to be addressed. For convenience we remind the reader of the most frequent K decay modes in Table 1, where they are reported together with the techniques intended to reject the backgrounds. The kinematics of the most frequent K decays are compared to that of K ## in Decay Mode Branching Ratio Background Rejection # 63% PID, Two-Body Kinematics 21% Photon Veto, Two-Body Kinematics # - 6% Charged Particle Veto, Kinematics 2% Photon Veto, Kinematics 3 ) Photon Veto, PID e3 ) Photon veto, E/p Table 1: The most frequest K decay mode