Singlet Charge $2/3$ Quark hiding the Top: Tevatron and LEP Implications

Abstract

If $c$ and $t$ quarks are strongly mixed with a weak singlet charge $2/3$ quark, $BR(t\to \ell \nu +X)$ could be suppressed via the $t\to c{H}^0$ mode, thereby the top quark could still hide below $M_W$, whereas the heavy quark signal observed at the Tevatron is due to the dominantly singlet quark $Q$. This may occur without affecting the small $m_c$ value. Demanding $m_Q\simeq 175$ GeV and $m_t \ltap M_W$, we find that $BR(t\to \ell \nu +X)$ cannot be too suppressed. The heavy quark $Q$ decays via $W,H$, and $Z$ bosons. The latter can lead to $b$-tagged $Z+4$ jet events, while the strong $c$--$Q$ mixing is reflected in sizable $Q\to sW$ fraction. $Z\to t\bar{c}$ decay occurs at tree level and may be at the $10^{-3}$ order, leading to the signature of $Z\to \ell \nu b\bar{c}$, all isolated and with large $p_T$, at $10^{-5}$ order.

10 pages + 3 Figures (not included), ReVTeX, NTUTH-94-18