New experimental limits to the time variations ofgp(me/mp) and α

A new experimental limit to the possible time variation of the proton gyromagnetic ratio times the electron-to-proton mass ratio has been obtained from the frequency comparison data between Cs and Mg atomic beam standards. The measurements, made over a period of one year, lead to an upper limit for the rate of change of [ital g][sub [ital p]]([ital m][sub [ital e]]/[ital m][sub [ital p]]) of 5.4[times]10[sup [minus]3]/yr. This result, based only on the validity of the quantum mechanical theory of the atomic spectra, together with astrophysical data regarding analogous products of atomic fundamental constants, leads also to a new limit for the time stability of the fine structure constant [alpha] (2.7[times]10[sup [minus]13]/yr).