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Jet Energy-Energy Correlator in Cold QCD Matter

Yu Fu, Berndt Müller, Chathuranga Sirimanna

TL;DR

This work analyzes how cold nuclear matter (CNM) modifies the jet Energy-Energy Correlator (EEC) using a higher-twist framework. In e+A DIS, the authors derive a factorized, energy-weighted cross section with LT and NLT contributions, showing that CNM-induced medium effects amplify large-angle EEC components while initial-state nuclear PDFs suppress small-angle regions. Extending to p+Pb, they incorporate comover contributions and compare predictions to ALICE data, finding qualitative agreement after a simple rescaling and highlighting the sensitivity to path length and comover density. Overall, the study demonstrates that the jet EEC is a powerful observable for probing nuclear PDFs and the transport properties of CNM, with potential applications at the EIC and LHC.

Abstract

We present a study of medium-induced modifications to the energy-energy correlator (EEC) for jets in cold nuclear matter. For electron-nucleus collisions, at leading order in the QCD coupling and in the jet-medium interaction, we derive an analytic expression for the EEC modification as a function of the opening angle and show that the modification is strongest at large angles within the jet cone. The dependence on jet energy, the transport properties of cold nuclear matter, and the in-medium path length is made explicit. We further extend the analysis to gluon jets in proton-nucleus collisions and compare with preliminary proton-lead data from the LHC. Possible effects of comovers on the EEC in proton-nucleus collisions are also discussed.

Jet Energy-Energy Correlator in Cold QCD Matter

TL;DR

This work analyzes how cold nuclear matter (CNM) modifies the jet Energy-Energy Correlator (EEC) using a higher-twist framework. In e+A DIS, the authors derive a factorized, energy-weighted cross section with LT and NLT contributions, showing that CNM-induced medium effects amplify large-angle EEC components while initial-state nuclear PDFs suppress small-angle regions. Extending to p+Pb, they incorporate comover contributions and compare predictions to ALICE data, finding qualitative agreement after a simple rescaling and highlighting the sensitivity to path length and comover density. Overall, the study demonstrates that the jet EEC is a powerful observable for probing nuclear PDFs and the transport properties of CNM, with potential applications at the EIC and LHC.

Abstract

We present a study of medium-induced modifications to the energy-energy correlator (EEC) for jets in cold nuclear matter. For electron-nucleus collisions, at leading order in the QCD coupling and in the jet-medium interaction, we derive an analytic expression for the EEC modification as a function of the opening angle and show that the modification is strongest at large angles within the jet cone. The dependence on jet energy, the transport properties of cold nuclear matter, and the in-medium path length is made explicit. We further extend the analysis to gluon jets in proton-nucleus collisions and compare with preliminary proton-lead data from the LHC. Possible effects of comovers on the EEC in proton-nucleus collisions are also discussed.

Paper Structure

This paper contains 6 sections, 2 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Formalism
  3. Jet EECs in DIS
  4. Jet EECs in p+Pb collisions
  5. Results
  6. Summary

Figures (2)

  • Figure 1: Ratio of the EEC in e+Pb to e+p as a function of the splitting angle $\theta$, obtained by varying each of the four parameters $x_B$, $Q^2$, $\hat{q}$, and $L$ while keeping the others fixed.
  • Figure 2: Ratio of the EEC for a $30~\mathrm{GeV}$ jet at mid-rapidity in p+Pb to p+p as a function of $\theta$, compared with the ALICE data fit. In the panels (a,b), results are shown for variations of the path length $L$ (a) and $\hat{q}_{\mathrm{co}}$ (b). The panels (c,d) show the corresponding results with an overall multiplicative factor of $0.9$.