Nuclear modification factors for jet fragmentation
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Springer
Received: June 4, Revised: September 16, Accepted: September 24, Published: October 30,
2020 2020 2020 2020
P. Caucal,a E. Iancu,a A.H. Muellerb and G. Soyeza a
Institut de Physique Th´eorique, Universit´e Paris-Saclay, CNRS, CEA, F-91191, Gif-sur-Yvette, France b Department of Physics, Columbia University, New York, NY 10027, U.S.A.
E-mail: [email protected], [email protected], [email protected], [email protected] Abstract: Using a recently-developed perturbative-QCD approach for jet evolution in a dense quark-gluon plasma, we study the nuclear modification factor for the jet fragmentation function. The qualitative behaviour that we find is in agreement with the respective experimental observations in Pb+Pb collisions at the LHC: a pronounced nuclear enhancement at both ends of the spectrum. Our Monte Carlo simulations are supplemented with analytic estimates which clarify the physical interpretation of the results. The main source of theoretical uncertainty is the sensitivity of our calculations to a low-momentum cutoff which mimics confinement. To reduce this sensitivity, we propose a new observable, which describes the jet fragmentation into subjets and is infrared-and-collinear safe by construction. We present Monte Carlo predictions for the associated nuclear modification factor together with their physical interpretation. Keywords: Heavy Ion Phenomenology, Jets ArXiv ePrint: 2005.05852
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP10(2020)204
JHEP10(2020)204
Nuclear modification factors for jet fragmentation
Contents 1 Introduction
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2 General picture and its Monte Carlo implementation
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4 Analytic insight for x close to one 4.1 Brief summary of the vacuum results 4.2 Nuclear effects on the fragmentation function near x = 1 4.2.1 Effect of the vetoed region 4.2.2 Effect of medium-induced emissions 4.2.3 Energy loss at large angles 4.2.4 Energy redistribution via a hard MIE 4.3 Bias introduced by the steeply falling jet spectrum
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5 Small-x enhancement: colour decoherence and medium-induced radiation 23 5.1 Analytic estimates 23 5.2 Beyond DLA: Monte-Carlo results 27 6 Jet 6.1 6.2 6.3
fragmentation into subjets Definition and leading-order estimate in the vacuum Nuclear modification for Dsub (z): Monte-Carlo results Analytic studies of the nuclear effects
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7 Conclusions
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A Expressions with running coupling
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B Large x jet fragmentation to NLL accuracy
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C Saddle-point method for in-medium intra-jet multiplicity at DLA
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3 Monte Carlo results for the in-medium fragmentation function 3.1 Definitions and general set-up 3.2 Monte Carlo results and physical interpretation 3.2.1 Variability with respect to the unphysical cutoffs 3.2.2 Variability with respect to the (physical) medium parameters 3.3 Behaviour at large x 3.4 Behaviour at small x 3.5 Dependence on the jet pT
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Introduction
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JHEP10(2020)204
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