First determination of the quark mixing matrix element Vtb independent of assumptions of unitarity

We present a new method for the determination of the Cabibbo-Kobayashi-Maskawa quark mixing matrix element $\mathrm{\mid }{V}_{tb}\mathrm{\mid }$ from electroweak loop corrections, in particular those affecting the process $Z\to b\bar{b}$. From a combined analysis of results from the LEP, SLC, Tevatron, and neutrino scattering experiments we determine $\mathrm{\mid }{V}_{tb}\mathrm{\mid }=0.77_{-0.24}^{+0.18}$. This is the first determination of $\mathrm{\mid }{V}_{tb}\mathrm{\mid }$ which is independent of unitarity assumptions.