Bottom-Quark Forward-Backward and Charge Asymmetries at Hadron Colliders

TL;DR

This paper predicts bottom-quark asymmetries at hadron colliders within the Standard Model, compares them with experimental data, and evaluates implications for new physics scenarios, especially regarding Zbar{b} couplings.

Contribution

It provides detailed SM predictions for bottom-quark asymmetries, including electroweak and mixed corrections, and assesses their consistency with experimental results and beyond Standard Model theories.

Findings

SM predictions align with experimental data from CDF, D0, and LHCb.

Certain BSM models like a 100 GeV axigluon are disfavored.

Modified Zbar{b} couplings can explain LEP1 asymmetry discrepancies.

Abstract

Predictions are made for the forward-backward and charge asymmetries in bottom-quark pair production at hadron colliders. Tree-level exchanges of electroweak (EW) gauge bosons dominate the Standard Model (SM) contribution to the asymmetry near the $Z$-pole. The mixed EW-QCD corrections are computed in an approximate way, and are found to be small in magnitude. These SM predictions are consistent with experimental results from CDF, D0, and LHCb. In particular, CDF and LHCb find that the asymmetry in the invariant mass bin containing the $Z$-pole is larger than in the adjacent bins, as predicted. Several beyond the Standard Model scenarios proposed for the top-quark forward-backward asymmetry, including a 100 GeV axigluon, are disfavored by this combination of SM predictions and measurements. On the other hand, modified $Zb\bar{b}$ couplings can explain the 2$\sigma$ discrepancy in the bottom-quark forward-backward asymmetry at LEP1, while being consistent with the results of CDF and LHCb. It is also shown that $t$-channel $W$ exchange makes a non-negligible contribution to the charm-quark charge asymmetry.