Revisiting the Bottom Quark Forward-Backward Asymmetry \(A_{\rm {FB}}\) in Electron-Positron Collisions

• Published in: arXiv.org
• Main Authors: Sheng-Quan, Wang, Rui-Qing Meng, Xing-Gang, Wu, Long, Chen, Jian-Ming Shen
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 28.07.2020
• Subjects: Asymmetry; Collisions; Physics - High Energy Physics - Experiment; Physics - High Energy Physics - Phenomenology; Quarks; Standard model (particle physics)
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2003.13941

The bottom quark forward-backward asymmetry \(A_{\rm{FB}}\) is a key observable in electron-positron collisions at the \(Z^{0}\) peak. In this paper, we employ the Principle of Maximum Conformality (PMC) to fix the \(\alpha_s\)-running behavior of the next-to-next-to-leading order QCD corrections to \(A_{\rm{FB}}\). The resulting PMC scale for this \(A_{\rm{FB}}\) is an order of magnitude smaller than the conventional choice \(\mu_r=M_Z\). This scale has the physically reasonable behavior and reflects the virtuality of its QCD dynamics, which is independent to the choice of renormalization scale. Our analyses show that the effective momentum flow for the bottom quark forward-backward asymmetry should be \(\mu_r\ll M_Z\) other than the conventionally suggested \(\mu_r=M_Z\). Moreover, the convergence of perturbative QCD series for \(A_{\rm{FB}}\) is greatly improved using the PMC. Our prediction for the bare bottom quark forward-backward asymmetry is refined to be \(A^{0,b}_{\rm FB}=0.1004\pm0.0016\), which diminishes the well known tension between the experimental determination for this (pseudo) observable and the respective Standard Model fit to \(2.1\sigma\).