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

TL;DR

This paper proposes a novel jet substructure technique called Late-$k_t$ to study the dead cone effect of heavy quarks in heavy-ion collisions, combining analytical and Monte Carlo methods to identify medium-induced gluon radiation.

Contribution

It introduces the Late-$k_t$ groomer for isolating perturbative, collinear splittings sensitive to the dead cone effect, and demonstrates its effectiveness through analytical and simulation studies.

Findings

Late-$k_t$ effectively distinguishes heavy-flavored jets from inclusive jets.

Medium-induced emissions enhance collinear splittings below the dead cone angle.

Late-$k_t$ shows resilience against thermal background noise.

Abstract

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 characterised. 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-$k_t$, that selects the most collinear splitting in a QCD jet above a certain transverse momentum cutoff $k_{t,\rm{cut}}$. The role of $k_{t,\rm{cut}}$ 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-$k_t$ 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-flavoured 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-$k_t$ against uncorrelated thermal background, thus confirming this observable as a potential candidate to unveil medium dynamics around the dead cone regime.