Energy-energy correlations on tracks: factorization and resummation

To do experimentally clean measurements, one of the proposed strategies is to use track-based observables, which means working exclusively with final-state charged hadrons (tracks). The field-theoretic framework introduced to calculate track-based observables is the so-called track function formalism. Although the case of most experimental interest is track, this framework, based on the factorization and universality of collinear divergences, can be applied to measurements on any subset of final-state hadrons with a set of particular quantum numbers. While the track function formalism has existed for eleven years, it is just in the past few years that we have extended it beyond leading order, making it practical in higher-order calculations comparable to experimental data. We illustrate its power by probing into the kinematic singularities of energy correlators on tracks: we calculate the projected two- to six-point energy correlators on tracks in the collinear limit at next-to-leading logarithmic (NLL) accuracy; we give the factorization theorem for the track energy-energy correlation (EEC) observable in the back-to-back limit, and compute the track EEC at next-to-leading logarithm (NLL). This leads to the first full prediction of the track EEC in peturbation theory, making the track correlator a prime candidate for precision QCD studies.