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Updated: Jan 4, 2026

Cryogenic Liquid Jets for High Repetition Rate Discovery Science
Published on: May 9, 2020
Entropy of a Jet
Duff Neill1, Wouter J Waalewijn2,3
1Theoretical Division, MS B283, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Abstract:
Scattering processes often inevitably include the production of infrared states, which are highly correlated with the hard scattering event, and decohere the hard states. This can be described using the entropy of the hard reduced density matrix, which is obtained from tracing over infrared states. We determine this entropy for an asymptotically free gauge theory by separating the Hilbert space into hard and infrared states, and calculate it in a leading-logarithmic approximation for jets. We find that the entropy increases when the resolution scales defining the hard radiation are lowered, that this entropy is related to the subjet multiplicity, and explore connections to using jet images for machine learning, and the forward-scattering density matrix of partons in a nucleon probed in deep-inelastic scattering.
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