Heavy leptons
Christopher Hubert Llewellyn Smith · Proceedings of the Royal Society of London A Mathematical and Physical Sciences · 1977
Abstract The exciting possibility that a new lepton may exist (Perl et al. 1975; Richter 1977) raises many immediate questions such as : is its electromagnetic coupling point-like (which is perhaps the definition of a lepton)? Does it have its own conserved lepton number or does it have Le = ± 1 or Lμ = ± 1? In the former case, what is the mass of the corresponding neutrino? If it has non-zero electron or muon number, are there also heavy neutral states E0 or M0 ? How does it decay ? With strength GF ? Does it couple to the usual weak current (W) or to some new current (W')? Is the coupling a vector-axial vector mixture, and if so in what proportion, or are there S, P or T couplings? To sharpen these questions and illustrate the available possibilities it is useful to begin by recalling theoretical arguments for the introduction of heavy leptons and some schemes which incorporate them. Next we discuss how hypothetical charged leptons might decay and how they might be produced, following which we briefly consider neutral heavy leptons. Finally we discuss the possibility of ‘hadro-leptons’ which enjoy more than just weak and electromagnetic interactions. A vast amount of work has been done on heavy leptons over the years and the discovery of events in which e+e¯→eμ +neutrals in the SLAC-LBL experiment at SPEAR last year has led to many new investigations. This report, which is based on a half-hour talk, does not pretend to be a complete review but much of the literature may be traced from the references.