Evidence for leptonic colour?

Abstract

THE new Gargamelle data¹ on ν_μe scattering with 10 reported events of the type ν_μ + e⁻ → ν_μ + e⁻, where 1.7±0.2 would be expected on the basis of the SU(2)×U(1) model (with sin² θ_w = 1/4) taken at its face value, and ignoring problems connected with unconventional electron energy spectrum of the events, seem to suggest the existence of one (or more) new purely leptonic neutral currents, in addition to the familiar neutral current contained within SU(2)_L×U(1). To preserve² the excellent agreement of the standard SU(2)_L×U(1) model with the very accurate experimental data on semileptonic ν_μ + N → ν_μ + N and ν_μ + N → ν + N_μ + π, the new neutral current phenomena must exhibit the minimal possible interference with the old current phenomena. The situation is reminiscent of colour currents for quarks which have a minimal interference with the flavour (SU(2)×U(1)) currents. By analogy with the three quark colours it seems that the concept³ of a purely leptonic colour must be introduced, distinguishing between electronic (red) and muonic (yellow) varieties of leptons. The newly discovered leptons (τ⁰, τ⁻) may carry electronic or muonic colour or may define a third leptonic colour (blue). This colour quantum number is additional to leptonic flavour which distinguishes neutrinos from charged leptons.