First Direct Observation of the Dead-Cone Effect

Abstract

We report the first direct measurement of the dead-cone effect at colliders, using iterative jet declustering techniques in pp collisions at $\sqrt{s} = 13$ TeV. The procedure exposes the splittings of $\rm{D^{0}}$ mesons in the jet shower, by iteratively declustering the angular ordered C/A tree. The splitting history of the $\rm{D^{0}}$ meson initiated jet is mapped onto the Lund Plane, where appropriate cuts can be made to suppress hadronisation effects. The reported variable is the splitting angle with respect to the $\rm{D^{0}}$ meson axis, which is updated after each splitting. Track-based jet finding, along with the low transverse momentum reach for charged tracks of the ALICE detector, allow for an accurate reconstruction of the splitting angle in the phase-space where the dead-cone effect is expected to be largest. The results are compared to those of inclusive jets, where the dead-cone effect is expected to be negligible.