Search for a fourth generation b'-quark at LEP-II at $\sqrt{s}$ = 196-209 GeV

Authors: S. Andringa, N. Castro, M. Espírito-Santo, P. Gonçalves, O. Oliveira, S. M. Oliveira, A. Onofre, M. Pimenta, R. Santos, B. Tomé, F. Veloso

Ref.: DELPHI 2003-048 CONF 668 (2003)

Abstract: A search four pair production of fourth generation b'-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed datawere collectedat centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of about 420 pb$^{-1}$. No evidence for signal was found. Upper limits on BR$_{b' \rightarrow bz}$ and BR$_{b' \rightarrow c W}$ were obtained at 95 \% confidence level for m$_{b'}$ ranging from 96 to 103 GeV/c$^2$. These limits, together with the theoretical branching ratios predicted by a sequencial four generations model, were used to constraint the values of | V$_{c b'}$ / V$_{t b'}$ V$_{t b}$|, where V$_{c b'}$, V$_{t b'}$ and V$_{t b}$ are elements of the extended 4x4 CKM matrix.