A determination of #Delta#(m) from tagged neutral kaons.
The CPLEAR experiment is a high precision experiment aiming to measure several
CP violating parameters in the neutral kaon system.
In order to decouple the errors on the phase angles of these parameters with the
error on the KL- Ks mass difference (~m), the experiment will also make a measurement
of ~m from semileptonic neutral kaon decays. This thesis describes a preliminary
determination of ~m from a time dependent asymmetry in the semileptonic decays
of tagged KOs and KOs.
In order to select a sample of semileptonic decays it was necessary to develop a
method of separating electron and pion tracks. The electromagnetic calorimeter can
only separate electrons and pions at momenta above 200 MeVIc. In this thesis the
development of a method of separating the two types of particle at momenta below
250 MeV[c is also described.
From data collected between September 1990 and October 1991, a sample of 45000
semileptonic decays has been isolated and a value of the mass difference determined
~mhs = 0.477 ± 0.016(stat.) +-00..000014 } (syst.)