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

## TL;DR

This study searched for fourth-generation b'-quarks at LEP-II energies, setting upper limits on their production and decay probabilities, and constraining related CKM matrix elements, with no evidence of such particles found.

## Contribution

First search for b'-quarks at LEP-II energies, providing upper limits on their production and decay, and constraining CKM matrix element ratios within a four-generation model.

## Key findings

- No evidence for b'-quark production was observed.
- Upper limits on branching ratios were established for b' decays.
- Constraints on CKM matrix element ratios were derived.

## Abstract

A search for the pair production of fourth generation b'-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb^{-1}. No evidence for a signal was found. Upper limits on BR(b' -> bZ) and BR(b' -> cW) were obtained for b' masses ranging from 96 to 103 GeV/c^2. These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of R_{CKM}=|V_{cb'}/V_{tb'}V_{tb}|, where V_{cb'}, V_{tb'} and V_{tb} are elements of the extended CKM matrix.