Morii, MasahiroHuth, JohnSpearman, WilliamSkottowe, HFranklin, MelissaCatastini, PMercurio, K2020-05-132018-08-28ATLAS Collaboration. 2017. Measurement of the Soft-Drop Jet Mass in Pp Collisions at S=13  TeV With the ATLAS Detector. Physical Review Letters 121: 092001.0031-90071079-7114http://nrs.harvard.edu/urn-3:HUL.InstRepos:42665476Calculations of jet substructure observables that are accurate beyond leading-logarithm ac- curacy have recently become available. Such observables are significant not only for probing the collinear regime of QCD that is largely unexplored at a hadron collider, but also for improving the understanding of jet substructure properties that are used in many studies at the Large Hadron Collider. This Letter documents a measurement of the first jet substructure quantity at a hadron collider to be calculated at next-to-next-to-leading-logarithm accuracy. to precise QCD calculations and leading-logarithm particle-level Monte Carlo simulations. The normalized, differential cross-section is measured as a function of log the ratio of the soft-drop mass to the ungroomed jet transverse momentum. This quantity is −1 √ measured in dijet events from 32.9 fb of ρ2, where ρ is s = 13 TeV proton–proton collisions recorded by the ATLAS detector. The data are unfolded to correct for detector effects and compareden-USJournal Article2018-07-1820172020-05-1310.1103/physrevlett.121.092001