Experimental Observation of a Heavy Particle<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>J</mml:mi></mml:math>

Abstract

We report the observation of a heavy particle $J$, with mass $m=3.1$ GeV and width approximately zero. The observation was made from the reaction $p+\mathrm{Be}\ensuremath{\rightarrow}{e}^{+}+{e}^{\ensuremath{-}}+x$ by measuring the ${e}^{+}{e}^{\ensuremath{-}}$ mass spectrum with a precise pair spectrometer at the Brookhaven National Laboratory's 30-GeV alternating-gradient synchrotron.