2020/11/01 by D. d’Enterria, d'Enterria, David, Cynthia Yan +1 · 1 citation
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2011.00530
openalex publication_date 2020/11/01 · openalex created_date 2020/11/09 · openalex updated_date 2026/07/28
The forward-backward (FB) asymmetry of b quarks in e+e- collisions at the Z pole measured at LEP, AFB0,b = 0.0992±0.0016, remains today one of the electroweak precision observables with the largest disagreement (2.4σ) with respect to the Standard Model prediction, (AFB0,b)th = 0.1030 ± 0.0002. Beyond the dominant statistical uncertainties, QCD effects, such as b-quark showering and hadronization, are the leading sources of AFB0,b systematic uncertainty, and have not been revised in the last twenty years. We reassess the QCD uncertainties of the eight original AFB0,b LEP measurements, using modern parton shower PYTHIA 8 and VINCIA simulations with nine different implementations of soft and collinear radiation as well as of parton fragmentation. Our analysis, combined with NNLO massive b-quark corrections independently computed, indicates total propagated QCD uncertainties of ∼0.7% and ∼0.3% for the lepton- and jet-charge analyses, respectively, that are about a factor of two smaller than those of the original LEP results. Accounting for such updated QCD effects leads to a new AFB0,b = 0.0995±0.0016 average, with a data-theory tension slightly reduced from 2.4σ to 2.2σ. Confirmation or resolution of this long-term discrepancy requires a new high-luminosity e+e- collider collecting orders-of-magnitude more data at the Z pole to significantly reduce the dominant AFB0,b statistical uncertainties, and to improve our understanding of b-quark showering and hadronization.