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Measuring energy correlators inside jets – CERN Courier

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Quarks and gluons are the only known elementary particles that cannot be seen in isolation. Once produced, they immediately start a cascade of radiation (the parton shower), followed by confinement, when the partons bind into (colour-neutral) hadrons. These hadrons form the jets that we observe in detectors. The different phases of jet formation can help physicists understand various aspects of quantum chromodynamics (QCD), from parton interactions to hadron interactions – including the confinement transition leading to hadron formation, which is particularly difficult to model. However, jet formation cannot be directly observed. Recently, theorists proposed that the footprints of jet formation are encoded in the energy and angular correlations of the final particles, which can be probed through a set of observables called energy correlators. These observables record the largest angular distance between N particles within a jet (xL), weighted by the product of their energy fractions. T

A report from the CMS experiment. Fig. 1. Top: the unfolded distribution of E2C, after subtracting backgrounds and removing detector effects, in four different jet pT regions. Bottom: the E3C over E2C ratio as measured by CMS (red points) and as computed by theory (grey bars); the lower panels show the data over theory ratios. Source: CMS-PAS-SMP-22-015 Quarks and gluons are the only known elementary particles that cannot be seen in isolation. Once produced, they immediately start a cascade of radiation (the parton shower), followed by confinement, when the partons bind into…

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