Measurement of R and search for new quark flavors decaying into multi-jet final states in e+e− collisions between 54.0 and 61.4 GeV CM energies

We accumulated e+e− annihilations into multi-hadrons at CM energies between 54.0 and 61.4 GeV with the VENUS detector at TRISTAN. Measured R-ratios are consistent with the standard model using the Z-boson mass; 91.1 GeV/c2. Using two new observables, we searched for a planar four-jet and other multi-jet events resulting from the decay of a charge — 13eb' quark. Having observed no positive signals, we excluded b' masses between 19.4 and 28.2 GeV/c2 with a 95% confidence level, regardless of branching into charged current and loop-induced flavor-changing neutral current decay, including a possible Higgs decay process. The charge +23e top quark was excluded below f30.2 GeV/c2.