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The fragmentation properties of colour charges in QCD exhibit strong flavour dependence. For heavy-flavour quarks, a significant component of this flavour dependence is driven by their large masses. The mechanism responsible for generating these mass-dependent properties in QCD is the dead-cone effect, which sets a cone surrounding each emitter within which emissions are suppressed. The opening angle of this cone is proportional to the mass of the emitter and is inversely proportional to its energy, meaning that the effect is largest for low energy heavy-flavour quarks. The ALICE collaboration presents the first direct observation of the QCD dead cone in the gluon radiation pattern from charm quarks generated in proton-proton collisions at $\sqrt{s}$ = 13 TeV, using novel iter- ative declustering techniques to reconstruct the charm shower. Charm-initiated track-based jets are reconstructed in the low transverse momentum interval of $5\leq p_{\rm T,jet} \leq 50$ GeV/c, where significant mass effects are expected, and are tagged via the presence of a fully reconstructed $D^0$ meson amongst their constituents. The techniques are further extended to enact a program to quantify the properties of charm emissions, with measurements mapping the c→cg splitting function also presented.
Michelangelo Mangano, Monica Pepe-Altarelli and Pedro Silva