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We investigate an excess observed in hadronic events in the archived LEP2ALEPH data. This excess was observed at preselection level during data-MCcomparisons of four-jet events when no search was being performed. The eventsare clustered into four jets and paired such that the mass difference betweenthe two dijet systems is minimized. The excess occurs in the region$M_1+M_2\sim 110\mbox{ GeV}$; about half of the excess is concentrated in theregion $M_1\sim 80\mbox{ GeV}$, $M_2\sim 25\mbox{ GeV}$, with a localsignificance between $4.7\sigma$ and $5.5\sigma$, depending on assumptionsabout hadronization uncertainties. The other half of the events are in a broadexcess near $M_1\sim M_2\sim 55\mbox{ GeV}$; these display a local significanceof $4.1-4.5\sigma$. We investigate the effects of changing the SM QCD MonteCarlo sample, the jet-clustering algorithm, and the jet rescaling method. Wefind that the excess is remarkably robust under these changes, and we find nosource of systematic uncertainty that can explain the excess. No analogue ofthe excess is seen at LEP1.

Localized $4\sigma$ and $5\sigma$ Dijet Mass Excesses in ALEPH LEP2 Four-Jet Events