Jet splitting measurements in Pb--Pb and pp collisions at ${\sqrt{s}}_{\mathrm{NN}}=$ 5.02 TeV with ALICE

Abstract

Recent ALICE measurements of jet splittings in Pb--Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV are reported. These measurements scan the phase space of jet emissions in search of medium-induced signals which are expected to emerge at different scales. These include effects such as multiple soft-radiation, single hard emissions, and color coherence. The Lund plane diagram is shown, including projections onto distributions of the splitting scale $k_{\mathrm{T}}$ in intervals of the splitting angle $R_{\mathrm{g}}$. Soft Drop grooming is applied to access hard splittings within the jet, enabling measurements of groomed substructure variables. These include the shared momentum fraction $z_{\mathrm{g}}$ between the two hardest subjets and the number of Soft Drop splittings $n_{\mathrm{SD}}$. The results in Pb--Pb collisions are compared to PYTHIA events embedded into a Pb--Pb background to separate out background from in-medium effects. Measurements of $z_{\mathrm{g}}$ and the normalized splitting angle ${\theta }_{\mathrm{g}}$ will also be shown in pp collisions at $\sqrt{s}$ = 5.02 TeV for different grooming settings.

4 pages, 4 figures, Proceedings of Quark Matter 2019