Dead-cone searches in heavy-ion collisions using the jet tree

We explore the possibility of using the dead cone of heavy quarks as a region of the Lund plane where medium-induced gluon radiation can be isolated and characterized. The filling of the dead cone by medium-induced gluons is expected to be the result of the interplay between the minimum angle of such radiation due to transverse momentum broadening and the dead-cone angle. Since the measurement of a fully corrected Lund plane in heavy-ion collisions is currently challenging, we propose to use jet grooming techniques to identify a particular splitting in the jet tree that is both perturbative and sensitive to the dead-cone effect. To that end, we propose a new jet substructure groomer, dubbed Late-<math display="inline"><msub><mi>k</mi><mi>t</mi></msub></math>, that selects the most collinear splitting in a QCD jet above a certain transverse momentum cutoff <math display="inline"><msub><mi>k</mi><mrow><mi>t</mi><mo>,</mo><mi>cut</mi></mrow></msub></math>. The role of <math display="inline"><msub><mi>k</mi><mrow><mi>t</mi><mo>,</mo><mi>cut</mi></mrow></msub></math> is to guarantee perturbative splittings, while selecting the most collinear splitting enhances the sensitivity to mass effects. As a proof of concept, we study the angular distribution of the splitting tagged by Late-<math display="inline"><msub><mi>k</mi><mi>t</mi></msub></math> both analytically and with Monte Carlo simulations. First, we derive the logarithmic resummation structure in vacuum and demonstrate its capability to distinguish between inclusive and heavy-flavored jets. Next, we extend the calculation for in-medium jets and show that medium-induced emissions lead to an enhancement of collinear emissions below the dead-cone angle. Numerically, we demonstrate an excellent resilience of Late-<math display="inline"><msub><mi>k</mi><mi>t</mi></msub></math> against uncorrelated thermal background, thus confirming this observable as a potential candidate to unveil medium dynamics around the dead-cone regime.