Search for new heavy quarks at Tristan

Study to search new heavy flavors has been considerably progressing at the TRISTAN e+e- collider as the beam energy has been pushed up. Three general purpose detectors, AMY, TOPAZ and VENUS have accumulated about 25pb-1 of luminosities at the beam energies from 25 GeV up to 30.4 GeV. R measurements, event shape analyses, isolated lepton and photon analyses were performed and new mass limits for top and b' quarks have been obtained. As for b', not only the charged current decay mode, but also the flavor changing neutral current decay were taken into account. Measured R values above √ bar s=56 GeV were slightly higher than the standard model prediction and this can be interpreted that the Z0 mass may be somewhat ligher than as was used