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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Measurement of substructure-dependent suppression of large-radius jets with charged particles in Pb plus Pb collisions with ATLAS. Phys. Lett. B, 871, 139929–17pp.
Abstract: Measurements of jet substructure in Pb+Pb collisions provide key insights into the mechanism of jet quenching in the hot and dense QCD medium created in these collisions.This Letter presents a measurement of the suppression of large-radius jets with a radius parameter of R = 1.0 and its dependence on the jet substructure. The measurement uses 1.72 nb(-1) of Pb+Pb data and 255 pb(-1) of pp data, both at root s(NN) = 5.02 TeV, recorded with the ATLAS detector at the Large Hadron Collider. Large-radius jets are reconstructed by reclustering R = 0.2 calorimetric jets and are measured for transverse momentum above 200 GeV. Jet substructure is evaluated using charged-particle tracks, and the overall level of jet suppression is quantified using the jet nuclear modification factor (R-AA). The jet R-AA is measured as a function of jet p(T), the charged k(t) splitting scale (root d(12)), and the angular separation (Delta R-12) of two leading sub-jets. The jet R-AA gradually decreases with increasing root d(12), implying significantly stronger suppression of large-radius jets with larger k(t) splitting scale. The jet R-AA gradually decreases for Delta R-12 in the range 0.01-0.2 and then remains consistent with a constant for Delta R-12 greater than or similar to 0.2. The observed significant dependence of jet suppression on the jet substructure will provide new insights into its role in the quenching process.
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Horvat, S., Magas, V. K., Strottman, D. D., & Csernai, L. P. (2010). Entropy development in ideal relativistic fluid dynamics with the Bag Model equation of state. Phys. Lett. B, 692(4), 277–280.
Abstract: We consider an idealized situation where the Quark-Gluon Plasma (QGP) is described by a perfect, (3 + 1)-dimensional fluid dynamic model starting from an initial state and expanding until a final state where freeze-out and/or hadronization takes place. We study the entropy production with attention to effects of (i) numerical viscosity, (ii) late stages of flow where the Bag Constant and the partonic pressure are becoming similar, (iii) and the consequences of final freeze-out and constituent quark matter formation.
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