Matthew Schwartz

Measuring αs from jet mass

Abstract:

One of the key parameters in the Standard Model is the strong coupling constant αs. It has been extracted from data in numerous ways, from lattice QCD to top quark cross sections, with remarkable consistency. There is, however, some small tension between low-energy extractions using lattice QCD or decay rates and high-energy extractions using colliders. On the high-energy side, one powerful observable at colliders for measuring αs is the mass of jets. Progress has been made on precision predictions of the jet mass and both e+e- colliders and hadron colliders. At e+e- colliders, jet mass is often measured through the heavy jet mass, which has some unusual properties contrasting it with other event shapes like thrust. In particular, it manifests a left Sudakov shoulder which must be understood before αs can be extracted. At hadron colliders, jet mass suffers from contamination due to underlying events and pileups. A remedy is to use the soft-drop jet mass. This talk will overview recent progress on the Sudakov shoulder effect and computations of the soft drop jet mass, and discuss prospects for improving the high-energy measurements of αs.