On the theory of heavy electrons and nuclear forces

The view has been expressed by several authors, including Neddermeyer and Anderson (1937), and Street and Stevenson (1937a, b ), that the penetrating component of cosmic radiation consists largely of new particles of electronic charge and mass intermediate between those of the electron and proton, and I have shown in a recent paper (Bhabha 1938a ) that the shape of experimentally well-established facts, also necessitate such a particle and are not compatible with a breakdown of the theory for electrons of very high energy. It has further been shown in the same paper that it does not seem to be sufficient just to postulate another particle behaving exactly like an electron of larger mass, but that the experimental evidence demands further that under certain circumstances a single heavy electron must be able to change its rest mass in the absence or presence of particles constituting ordinary matter. Indeed, the energy loss measurements of Blackett and Wilson indicate that most particles below about 2 X 108 e-volts are electrons, whereas most particles above this energy there must be a large probability of a heavy electron changing or losing its identity. Now since one may assume that charge is always conserved, it follows that there are essentially only two ways in which a single heavy electron may disappear. If, for example it has a negative charge, it may collide with a proton and communicate its charge to it, the proton changing into a neutron, or it may turn an ordinary electron by changing its rest mass. In either of these two processes, a certain amount of energy is liberated and the spin and statistics to be attributed to the heavy electron depend on whether the liberation of this energy is accompained by the simultaneous liberation of some particle having a half internal spin and obeying Fermi statistics or not. Unfortunately, so far there is no experimental evidence upon this point.