Implications of LEP and SLD data for new physics inZbb¯couplings

Abstract

The combined LEP/SLD data on the bb forward-backward asymmetry from the Z-pole measurements may imply the presence of new physics in the Zbb couplings. In general, the effect of new physics can be parameterized byBy 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 bb production at LEP II, tt 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.

Limits on scalar leptoquark interactions and consequences for GUTs

“…Calculational details along with functions f 1 and f 2 are given in the Appendix A. Taking into account higher order SM corrections, the relative shift in R b due to such NP contributions can be written as [60]…”

“…On the other hand, the forward-backward asymmetry in b b production as measured at LEP exhibits a 2.7 σ tension with the SM EW fit. Since ∆ contributions only affect the right-handed effective Zb b coupling (δg R ) they cannot fully reconcile this tension [60] and we do not include this observable in the fit.…”