Flavor-Changing Non-Global Logarithms

Abstract

Non-global logarithms are low energy correlations between the substructure of a jet and the event in which it is immersed. We study the leading non-global logarithms that arise from soft quark--anti-quark emission and calculate their coefficient as a series in the jet radius, $R$, in arbitrary processes. We calculate the exact coefficient through quadratic order in $R$, and show that this truncation is within $5\%$ of the complete result for radii up to $R = 1$. These quark flavor-dependent non-global logarithms are also responsible for the infrared unsafety of a na\"ive definition of jet flavor that is simply the net sum of quark flavors in the jet of interest. We propose a small modification of this na\"ive jet flavor that we call subtractive jet flavor in which the problematic soft logarithms are explicitly subtracted. We further demonstrate how our analytic results can be interfaced with automated numerical fixed-order codes to extract subtractive jet flavor cross sections.