Energy-Energy Correlators in $Z$-Tagged Jets in $pp$ Collisions

Abstract

We present predictions for the collinear energy-energy correlator (EEC) measured inside $Z$-tagged jets in proton-proton collisions across the confinement transition. Our framework combines transverse-momentum-dependent factorization for back-to-back $Z+$jet production with an exclusive differential EEC jet function incorporating perturbative evolution and flavor-dependent non-perturbative fragmentation. The EEC jet function is evaluated at ${\mathrm{NLL}}^{\prime }$ accuracy, with separate quark and gluon non-perturbative scales constrained by existing $e^{+}{e}^{-}$ and inclusive-jet data. We provide predictions for forward $Z+$jet production at $\sqrt{s}=8\mathrm{TeV}$ and $13\mathrm{TeV}$ in the jet transverse-momentum intervals $(20,30)$, $(30,50)$ and $(50,100)\mathrm{GeV}$. The EEC distributions as functions of $z_{\chi }$ exhibit finite plateaus at small $z_{\chi }$, while the corresponding angular distributions display the characteristic turnover associated with the confinement transition. A flavor decomposition shows that this transition becomes increasingly dominated by quark-initiated jets as the jet transverse momentum increases. Forward $Z$-tagged jets therefore provide a clean probe of non-perturbative quark fragmentation and offer a direct test of whether the characteristic confinement scale extracted from $e^{+}{e}^{-}$ collisions remains universal in a hadronic environment.

Comments: 10 pages, 5 figures