  The re-analysis of the archived data recorded at the ${\rm Z}^{0}$ resonance
by the ALEPH experiment at LEP during the years 1992-1995 shows an excess in
the opposite sign di-muon mass spectra at 30.40 $\pm$ 0.46 GeV in events
containing b quarks. The excess has a natural width of 1.78 $\pm$ 1.14 GeV.
  The di-muon excess has a local significance around $5\,\sigma$ ($Z_{\rm
asym}$), depending on the background model used. The significances for
background models based on a kernel density approximation stay close to
$3\,\sigma$ ($Z_{\rm freq,\,lee}$), when including a look elsewhere effect.
Another method to obtain a significance value results in at least $2.6\,\sigma$
($Z_{\rm Bi}$). A compatible, but smaller excess is visible in the opposite
di-electron mass spectrum as well.
  This paper uses the data collected by the ALEPH experiment in the years
1992-1995, which have been archived to allow their use for physics analyses
after the closure of the collaboration.
