It is shown that the existence of the long-lived neutral meson, and the absence of its decay into two pions, establishes that the gravitational masses of the and are equal to a few parts in of the inertial mass. This is of interest since the is the antiparticle of the , and is not identical with the . The gravitational mass of such a nonidentical antiparticle has never been directly measured.
Also, the has opposite strangeness to the . Thus the argument rules out any linear dependence of the gravitational mass on the strangeness quantum number, a point on which all previous experiments say nothing.
These observations are in accord with, and serve as a confirmation of, the equivalence principle of Einstein.
- Received 18 July 1960
- Published in the issue dated January 1961
© 1961 The American Physical Society