Report of the LEP Working Group on four-jet production in $e^{+}e^{-}$ collisions at centre-of-mass energies of 130 - 172 GeV

The four-jet topology is studied, using data collected by ALEPH, DELPHI, L3 and OPAL at centre-of-mass energies of 130-136 GeV in 1995 and of 161 GeV and 172 GeV in 1996. ALEPH has reported an excess in the sum of the dijet masses around 105 GeV/c2. No excess is observed by the other three experiments which are consistent with Standard Model expectations. The analyses of the four experiments are compared; all four experiments select and reconstruct four jet events with similar efficiencies and mass resolutions. In the hypothesis of pair-production of a new particle the excess around 105 GeV/c2 in the ALEPH data would correspond to an average cross section of 2.3+-0.6 pb. From the combined mass distribution of DELPHI, L3 and OPAL a 95% C.L. upper limit cross section of 0.6 pb is derived. Probabilities for different hypotheses are estimated. This study is based on preliminary results from the four LEP experiments.