Energy-energy correlators in charm-tagged jets in proton-proton collisions at $\mathbf{\sqrt{s} = 13}$ TeV

In this letter, we present the first measurement of the energy-energy correlator (EEC) in charm-tagged jets from proton-proton (pp) collisions at $\sqrt{s} = 13$ TeV. EECs probe the structure of QCD radiation, providing a unique test of mass-dependent effects in parton showers involving a charm quark and offering a distinct view into non-perturbative phenomena, including the hadronization process. The EEC is measured for charm-tagged jets and flavor-untagged (inclusive) jets with transverse momenta of $10 <~ p_{\rm T} <~ 30$ GeV/$c$, where charm-quark mass effects are significant. We observe a significant suppression of the EEC amplitude in charm jets compared to inclusive ones, consistent with the expected suppression of radiation from massive quarks -- a fundamental prediction of QCD. Despite the significant amplitude difference, the observed peak positions of the charm and inclusive-jet EEC are similar, indicating a complex interplay between Casimir factor (differentiating quark and gluon jets), and quark-mass (dead-cone) effects in the QCD parton shower as well as subsequent hadronization effects. Comparisons with next-to-leading order calculations and various Monte Carlo event generators reveal the sensitivity of this observable to both mass effects in the parton shower and hadronization process. These results provide new constraints on theoretical models of heavy-quark jets and offer insights into the parton-to-hadron transition in QCD.

 

Submitted to: PRL
e-Print: arXiv:2504.03431 | PDF | inSPIRE
CERN-EP-2025-082
Figure group

Figure 1

\Dzero-tagged jet (red) EEC distribution compared to inclusive jets with no leading track \pt selection (blue) and inclusive jets with a 5 \GeVc leading-track \pt selection (green), to PYTHIA 8 simulations, and to pQCD predictions  in the \jetptrange{10}{15} (left) and \jetptrange{15}{30} (right) jet-\pt intervals. The middle panel shows the ratio of \Dzero-tagged jets to inclusive jets in the data. The bottom panel compares the ratio of \Dzero-tagged jets to inclusive jets with the ratio of \Dzero-tagged jets to light-quark jets in PYTHIA 8. The error bars show the statistical error, and the boxes represent the systematic error.

Figure 2

\Dzero-tagged jet (red) EEC distribution compared to inclusive jets without leading-track \pt selection (blue) in the \jetptrange{10}{15} (left) and \jetptrange{15}{30} (right) jet-\pt intervals. The data is shown in the solid points, and the different event generators (PYTHIA 8, Herwig, Sherpa Lund and Sherpa Ahadic) are shown in various line styles. The error bars show the statistical error, and the boxes represent the systematic error.