Speaker
Description
We explore systematic effects of renormalon cancellation schemes and perturbative scale choices on extractions of the strong coupling constant $\alpha_s(m_Z)$ and the leading non-perturbative shift parameter $\Omega_1$ from resummed predictions of hadronic event shapes in electron-positron collisions. Our analysis is based on thrust distributions to N$^3$LL$'$ accuracy in resummed perturbation theory using Soft Collinear Effective Theory, both matched to the most accurate available fixed-order predictions in QCD. We test the phenomenological impact sourced from varying amongst different renormalon cancellation schemes and sets of perturbative scale profile choices. We then perform a global fit to available data spanning center-of-mass energies between 35--207 GeV. Our results are consistent with prior SCET-based extractions of $\alpha_s(m_Z)$, but we are also led to a number of novel observations. Notably, we find that the combined effect of altering the renormalon cancellation scheme and profile parameters can lead to increased uncertainties on the extracted values in the $\alpha_s-\Omega_1$ plane. We also observe that fits performed over windows dominated by dijet events are typically of a higher quality than those that extend into the far tails of the distributions, motivating future fits focused more heavily in this region. We conclude with the potential of new strategies to mitigate these systematic effects and improve the precision of event-shape-based determinations of $\alpha_s(m_Z)$ and $\Omega_1$.
