Abstract
Whether quark- and gluon-initiated jets are modified differently by the quark-gluon plasma produced in heavy-ion collisions is a long-standing question that has thus far eluded a definitive experimental answer. A crucial complication for quark-gluon discrimination in both proton-proton and heavy-ion collisions is that all measurements necessarily average over the (unknown) quark-gluon composition of a jet sample. In the heavy-ion context, the simultaneous modification of both the fractions and substructure of quark and gluon jets by the quark-gluon plasma further obscures the interpretation. Here, we demonstrate a fully data-driven method for separating quark and gluon contributions to jet observables using a statistical technique called topic modeling. Assuming that jet distributions are a mixture of underlying "quark-like" and "gluon-like" distributions, we show how to extract quark and gluon jet fractions and constituent multiplicity distributions as a function of the jet transverse momentum. This proof-of-concept study is based on proton-proton and heavy-ion collision events from the Monte Carlo event generator Jewel with statistics accessible in Run 4 of the Large Hadron Collider. These results suggest the potential for an experimental determination of quark and gluon jet modifications.
Highlights
High-energy collisions between large nuclei at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) are a critical laboratory for studying the deconfined phase of QCD matter, the quark-gluon plasma, created in these collisions
Our method is based on a statistical technique called topic
We present a proof of concept that an extension of that technique can be used to extract differences in the modification of quark and gluon jets in heavy-ion collisions with the statistics anticipated in Run 4 of the LHC
Summary
[8], which defines the quark and gluon categories as the mutually irreducible (i.e., maximally separable) distributions underlying a pair of jet samples. Since the base distributions extracted from a jet observable x using DEMIX are mutually irreducible, they can only agree with the MC quark- and gluon-jet distributions of x if those are mutually irreducible [8], is to define κto be the ratio of histograms in the bin for which the ratio plus its uncertainty is minimized This method turns out to be insufficient to deal with the much more limited statistics we aim to utilize in this work, because κis typically extracted at the low-statistics end points of the distributions.
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