Implications of LEP/SLD Data for New Physics in Zbb_bar Couplings

TL;DR

This paper investigates how LEP/SLD data suggests potential new physics in Zbb couplings, classifies possible operators, and discusses their effects on various collider processes, with current data constraining some of these operators.

Contribution

It introduces a classification of new physics operators affecting Zbb couplings based on Higgs field content and analyzes their collider implications.

Findings

LEP/SLD data indicates possible deviations in Zbb couplings.

Operators without Higgs fields can significantly affect collider processes.

Preliminary LEP II data disfavors operators without Higgs fields.

Abstract

The combined LEP/SLD data on the b\bar b forward-backward asymmetry from the Z-pole measurements may imply the presence of new physics in the $Zb\bar b$ couplings. In general, the effect of new physics can be parameterized by $SU_C(3)\times SU_L(2)\times U_Y(1)$ invariant higher dimensional operators. By fitting the recently announced LEP/SLD data on A_b and R_b, the size of the coupling strengths of these operators can be determined. We also found that the new physics operators can be divided into two types, depending on their Higgs field content. The ones involving the Higgs have very mild effects at higher energy colliders, while the other type which do not contain the Higgs field can show significantly large effects on $b\bar b$ production at LEP II, $t\bar t$ production at the NLC and single top production at the Tevatron. The preliminary data from the LEP II measurements disfavors the second type of operators.