Springer : Disentangling Jet Modification in Jet Simulations and in Z+Jet Data

Brewer, Jasmine; Brodsky, Quinn; Rajagopal, Krishna

doi:10.1007/JHEP02(2022)175

Article
Report number	arXiv:2110.13159 ; CERN-TH-2021-163 ; MIT-CTP/5344
Title	Disentangling Jet Modification in Jet Simulations and in Z+Jet Data
Author(s)	Brewer, Jasmine (CERN) ; Brodsky, Quinn (MIT) ; Rajagopal, Krishna (MIT, Cambridge, CTP)
Publication	2022-02-21
Imprint	2021-10-25
Number of pages	21
In:	JHEP 2202 (2022) 175
DOI	10.1007/JHEP02(2022)175
Subject category	nucl-th ; Nuclear Physics - Theory ; hep-ph ; Particle Physics - Phenomenology
Abstract	We study the impact of selection biases on jet structure and substructure observables and separate these effects from effects caused by jet quenching. We use the angular separation $\Delta R$ of the hardest splitting in a jet as the primary example observable. We first conduct a simplified Monte Carlo study in which it is possible to identify the same jet after quenching in a heavy ion collision and as it would have been if it had formed in vacuum. We select a sample of jets by placing a cut on their quenched $p_T$ and, as is possible only in a Monte Carlo study, compare to the same jets unquenched, and see that the $\Delta R$ distribution seems to be unmodified. However, if we select a sample of jets formed in vacuum by placing a cut on their unquenched $p_T$ and compare to those same jets after quenching, we see a significant enhancement in the number of jets with large $\Delta R$, primarily due to the soft particles in the jet that originate from the wake in the droplet of quark-gluon plasma excited by the parton shower. We confirm that the jets contributing to this enhancement are those jets which lost the most energy, which were not included in the sample selected after quenching; jets selected after quenching are those which lose a small fraction of their energy. Next, we employ a method that is available to experimentalists: in a sample of jets with a recoiling $Z$ boson, we show that selecting jets based on the jet $p_T$ after quenching yields a $\Delta R$ distribution that appears unmodified while selecting a sample of jets produced in association with a $Z$ boson whose (unmodified) $p_T$ is above some cut yields a significant enhancement in the number of jets with large $\Delta R$. We again confirm that this is due to particles from the wake, and that the jets contributing to this enhancement are those which have lost a significant fraction of their energy.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2022-2024 The Author(s) (License: CC-BY-4.0), sponsored by SCOAP³

$Illustration exemplifying the Monte Carlo matching procedure. Left panel: $(\eta,\phi)$ distribution of hadrons in an unquenched jet, as reconstructed. Middle panel: the same jet, reconstructed after quenching but upon leaving out hadrons originating from the response of the medium, e.g. the wake the jet excites. Right panel: the same jet, reconstructed after quenching, with hadrons from the medium response included. Color indicates hadron $p_T$ as a fraction of the $p_T$ of this unquenched jet, which has $p_T^\text{unq.}=177$~GeV.$ $(a) $\Delta R$ distributions for a sample of jets selected on the basis of having quenched $p_T$ above $80$~GeV (solid and dashed blue) and the matching unquenched jets (dotted blue). Each quenched jet was matched to the unquenched jet that it would have been if it had formed in vacuum. (b) $\Delta R$ distributions for a sample of jets selected on the basis of having unquenched $p_T$ above $80$~GeV (dotted orange) and the matching quenched jets (solid and dashed orange). Dashed curves are for jets quenched as in a heavy ion collision with hadrons originating from medium response artificially excluded; solid curves are for quenched jets including those hadrons from medium response that are reconstructed as a part of the jets.$ $(a) $\Delta R$ distributions for a sample of jets selected on the basis of having quenched $p_T$ above $80$~GeV (solid and dashed blue) and the matching unquenched jets (dotted blue). Each quenched jet was matched to the unquenched jet that it would have been if it had formed in vacuum. (b) $\Delta R$ distributions for a sample of jets selected on the basis of having unquenched $p_T$ above $80$~GeV (dotted orange) and the matching quenched jets (solid and dashed orange). Dashed curves are for jets quenched as in a heavy ion collision with hadrons originating from medium response artificially excluded; solid curves are for quenched jets including those hadrons from medium response that are reconstructed as a part of the jets.$ Show more plots

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Zapis kreiran 2021-10-29, zadnja izmjena 2023-01-31

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