Evidence for the dead-cone effect in bottom quark initiated jets produced in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

The suppression of collinear gluon emissions from a massive quark, or the ``dead-cone effect,'' is the primary manifestation of quark mass effects in parton showers. A proton-proton collision data set recorded by the CMS experiment at $\sqrt{s}$ = 13 TeV with an integrated luminosity of 59.8 fb$^{-1}$ is analyzed. A differential measurement is presented of the emission density of bottom quark jets, studied as a function of the angular separation between iteratively declustered subjets. The measurement is performed in bottom quark initiated jets with transverse momenta between 40 and 200 GeV originating from top quark pair production. Compared to data, a parton shower Monte Carlo model that includes the dead-cone effect is favored, while a model without the dead-cone effect is disfavored with a significance of 4.3 standard deviations.