Experimental limit for nucleon stability against charge-nonconserving decay

Abstract

The result of a search for a nucleon decay bound in a nucleus has been described in this work for the charge-nonconserving decay ⁸⁷Rb --> ^87mSr+neutrals. ^87mSr activities separated from 800 g of Rb₂CO₃ chemically were counted in a twin Si(Li) detector system using the K-conversion electron and K x-ray coincidence technique by looking at the 2.8-h isomeric decay of 388.4-keV M4 transition in ^87mSr. With modest shielding the background level has been reduced to 3×10^-4 keV^-1h^-1, yielding a lower limit of greater or equal 7.5×10¹⁹ yr on the mean life against the charge-nonconserving decay of a nucleon. This result sets an upper limit on the ratio of the charge-nonconserving to the normal weak-interaction decay width of a nucleon, Γ(n-->p+v_e+v^- _e)/Γ(n-->p+e^-+v_{- e})<=7.9×10^-21.