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arXiv · 2608.01764

Jet-by-jet energy correlators as stochastic probes of the parton-to-hadron transition

Jingyu Zhang
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Abstract

Energy-energy correlators are usually reported as ensemble averages and therefore do not specify how different angular regions fluctuate together from jet to jet. We retain the binned two-point correlator for each jet and study the distribution and covariance of its angular-shell weights. In a high-statistics Pythia sample, the shell variables are sparse and strongly non-Gaussian, and their covariance contains nonzero cross-shell structure spread over many modes. Regressing each shell on five jet-level summaries leaves 84-92% of the covariance trace, while shell-wise permutation and constituent-angle shuffling do not reproduce the observed off-diagonal correlations. We then compare separately generated parton- and hadron-level samples in Pythia and Herwig. Across 24 generator-radius-momentum configurations, the hadron-level covariance trace is smaller and the average neighboring-shell correlation over 0.30 <= r/R < 1 is larger. The size and angular dependence of the change differ between the generators, and a characteristic-position analysis does not identify a common scale. Jet-by-jet EEC covariance thus provides information on the parton-to-hadron transition that is absent from the mean spectrum.

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Jingyu Zhang. 2026-08-03. Jet-by-jet energy correlators as stochastic probes of the parton-to-hadron transition. https://arxiv.org/abs/2608.01764

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