Lecture on a Z' Coupled to Beauty and Truth

Abstract

By extending the standard gauge group to $SU(3)_c \times SU(2)_L \times U(1)_Y \times U(1)_X$ with $X$ charges carried only by the third family we accommodate the LEP measurement of $R_b$ and predict a potentially measurable discrepancy in $A_{FB}^{b}$ in $e^+e^-$ scattering and that $D^0 \bar D^0$ mixing may be near its experimental limit. The uniqueness of our model is that the Z' couplings are generation-dependent and hence explicitly violate the GIM mechanism, but can nevertheless be naturally consistent with FCNC constraints. Direct detection of this Z' is possible but challenging.

12 pages, latex including 3 Figures. Lecture at Ettore Majorana International School of Subnuclear Physics, Erice, Sicily, July 1996. This lecture is an updated version of hep-ph/9604260 by P.H.Frampton, M.B. Wise and B.D. Wright. Sections in italics, and the Figures, explain how this same model-building strategy (with different details) can accommodate different data on $R_b$ and $A^b$