Search for narrow resonances below the $\Upsilon$ mesons

The authors have investigated the invariant mass spectrum of dimuons collected by the CDF experiment during the 1992-1995 run of the Fermilab Tevatron collider to improve the limit on the existence of narrow resonances set by the experiments at the SPEAR e{sup +}e{sup -} collider. In the mass range 6.3-9.0 GeV/c{sup 2} they derive an average 90% upper credible limit of 8 eV to the leptonic width of possible resonances. This limit is much worse at the mass of 7.2 GeV/c{sup 2} due to an excess of 250 {+-} 61 events with a width consistent with the detector resolution.