Remarks Concerning BOB0 Mixing and Single Quark Decays in Toponium*

We discuss the possibility of measuring particle-antiparticle mixing using toponium bound states where the top quark t (or Z) decays weakly. It is suggested to detect B” Do mixing via events having three leptons of the same charge in the final state. Such a signature could lead to samples with a very low background. Estimations are given for an e+eexperiment of 200 pb-l assuming that the toponium has a mass in the 70 110 GeV/c2 range. Submitted to Physical Review D * Work supported by the Department of Energy, contract DE AC03 76SF00515. + Permanent address: DPHPE, Centre d’Etudes Nucle’aires de Saclay, 91191 Gif sur Yvette, France 1 Introduction Here we will discuss the possibilities of studying particle-antiparticle mixing by means of toponium where one of the bound quarks decays weakly (the so called single quark decay or SQD). W e consider the case of toponium formed as an S-channel resonance in e+einteractions and where mixing is measured by means of like sign leptons in the final state (e or ~1, denoted throughout by I). In conventional approaches the To To system is not expected to manifest a large mixing1 which could therefore be hardly detectable in the decay of toponium as well (See below). However we will see that the single quark decay phenomenon in toponium might be very suitable for the study of the B” B” mixing because of its clean signature accompanied with a low background. The mass of the top quark mt (and hence the mass M of the toponium) is not known yet. However the experimental facts accumulated so far indicate that a top quark should have a large mass. The e+eexperiments carried out at PETRA, for instance, give a lower limit for the toponium mass of about 45 GeV/c2 (Ref. 2). For large quark masses it has long being realized that weak decays of constituent quarks will become important3-7 as the decay width is proportionnal to rn: (when mt is smaller than the W mass). On the other hand if the mass of the toponium (M 2mt) is close to the 2’ mass, interference phenomena8yg may complicate the investigation of toponium features. The single quark decay mechanism, however, does not interfer with other processes314. The -energy dependence of the corresponding cross section can then by characterized in the vicinity of the toponium mass by a Breit-Wigner type of function. At the resonance the cross section will then be given bylo where BSQD N 2I’f/I’t is the branching ratio for the weak t --+ f (or f + f7 decay having a width of I?f and M is the assumed toponium mass. Here Ice is the leptonic width of the toponium (in which there is a contribution due the Z”