002789024 001__ 2789024
002789024 005__ 20230131120020.0
002789024 0248_ $$aoai:cds.cern.ch:2789024$$pcerncds:FULLTEXT$$pcerncds:CERN:FULLTEXT$$pcerncds:CERN
002789024 0247_ $$2DOI$$9Springer$$a10.1007/JHEP02(2022)175
002789024 037__ $$9arXiv$$aarXiv:2110.13159$$chep-ph
002789024 037__ $$9arXiv:reportnumber$$aCERN-TH-2021-163
002789024 037__ $$9arXiv:reportnumber$$aMIT-CTP/5344
002789024 035__ $$9arXiv$$aoai:arXiv.org:2110.13159
002789024 035__ $$9Inspire$$aoai:inspirehep.net:1952275$$d2023-01-30T12:29:13Z$$h2023-01-31T03:03:46Z$$mmarcxml$$ttrue$$uhttps://inspirehep.net/api/oai2d
002789024 035__ $$9Inspire$$a1952275
002789024 041__ $$aeng
002789024 100__ $$aBrewer, [email protected]$$tGRID:grid.9132.9$$uCERN$$vTheoretical Physics Department, CERN, CH-1211 Genève 23, Switzerland
002789024 245__ $$9Springer$$aDisentangling Jet Modification in Jet Simulations and in Z+Jet Data
002789024 269__ $$c2021-10-25
002789024 260__ $$c2022-02-21
002789024 300__ $$a21 p
002789024 520__ $$9Springer$$aThe selection of jets in heavy-ion collisions based on their p$_{T}$ after jet quenching is known to bias towards jets that lost little energy in the quark-gluon plasma. In this work, we study and quantify the impact of this selection bias on jet substructure observables so as to isolate effects caused by the modification of the substructure of jets by quenching. We do so at first in a simplified Monte Carlo study in which it is possible to identify the same jet before and after quenching. We show explicitly that jets selected based on their quenched (i.e. observable) p$_{T}$ have substantially smaller fractional energy loss than those selected based on the p$_{T}$ that they would have had in the absence of any quenching. This selection bias has a large impact on jet structure and substructure observables. As an example, we consider the angular separation ∆R of the hardest splitting in each jet, and find that the ∆R distribution of the (biased) sample of jets selected based upon their quenched p$_{T}$ is almost unmodified by quenching. In contrast, quenching causes dramatic modifications to the ∆R distribution of a sample of jets selected based upon their unquenched p$_{T}$, with a significant enhancement at larger ∆R coming from the soft particles originating from the wake of the jet in the quark-gluon plasma. The jets which contribute to this enhancement are those which have lost the most energy and which were, therefore, left out of the sample selected after quenching. In a more realistic study, we then show that the same qualitative effects can all be observed in Z+jet events. Selecting jets in such events based on either the jet p$_{T}$ or the Z-boson p$_{T}$ provides an experimentally accessible way to quantify the effects of selection biases in jet observables and separate them from the modification of jet substructure caused by quenching. Selecting Z+jet events based upon the jet p$_{T}$ yields a ∆R distribution that appears almost unmodified whereas selecting Z+jet events based upon the Z-boson p$_{T}$ reveals a significant modification to the ∆R-distribution caused by quenching, once again arising from the wakes of those jets that lose more energy.
002789024 520__ $$9arXiv$$aWe study the impact of selection biases on jet structure and substructure observables and separate these effects from effects caused by jet quenching. We use the angular separation $\Delta R$ of the hardest splitting in a jet as the primary example observable. We first conduct a simplified Monte Carlo study in which it is possible to identify the same jet after quenching in a heavy ion collision and as it would have been if it had formed in vacuum. We select a sample of jets by placing a cut on their quenched $p_T$ and, as is possible only in a Monte Carlo study, compare to the same jets unquenched, and see that the $\Delta R$ distribution seems to be unmodified. However, if we select a sample of jets formed in vacuum by placing a cut on their unquenched $p_T$ and compare to those same jets after quenching, we see a significant enhancement in the number of jets with large $\Delta R$, primarily due to the soft particles in the jet that originate from the wake in the droplet of quark-gluon plasma excited by the parton shower. We confirm that the jets contributing to this enhancement are those jets which lost the most energy, which were not included in the sample selected after quenching; jets selected after quenching are those which lose a small fraction of their energy. Next, we employ a method that is available to experimentalists: in a sample of jets with a recoiling $Z$ boson, we show that selecting jets based on the jet $p_T$ after quenching yields a $\Delta R$ distribution that appears unmodified while selecting a sample of jets produced in association with a $Z$ boson whose (unmodified) $p_T$ is above some cut yields a significant enhancement in the number of jets with large $\Delta R$. We again confirm that this is due to particles from the wake, and that the jets contributing to this enhancement are those which have lost a significant fraction of their energy.
002789024 540__ $$3preprint$$aarXiv nonexclusive-distrib 1.0$$uhttp://arxiv.org/licenses/nonexclusive-distrib/1.0/
002789024 540__ $$3publication$$aCC-BY-4.0$$bSpringer$$fSCOAP3$$uhttp://creativecommons.org/licenses/by/4.0/
002789024 542__ $$3publication$$dThe Author(s)$$g2022
002789024 595__ $$aCERN-TH
002789024 595_D $$a3$$d2021-11-03$$sabs
002789024 595_D $$a3$$d2021-11-08$$sprinted
002789024 65017 $$2arXiv$$anucl-th
002789024 65017 $$2SzGeCERN$$aNuclear Physics - Theory
002789024 65017 $$2arXiv$$ahep-ph
002789024 65017 $$2SzGeCERN$$aParticle Physics - Phenomenology
002789024 690C_ $$aCERN
002789024 690C_ $$aARTICLE
002789024 700__ $$aBrodsky, Quinn$$tGRID:grid.116068.8$$uMIT$$vMassachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA
002789024 700__ $$aRajagopal, Krishna$$tGRID:grid.116068.8$$uMIT, Cambridge, CTP$$vCenter for Theoretical Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA
002789024 773__ $$c175$$pJHEP$$v2202$$y2022
002789024 8564_ $$82330901$$s34859$$uhttps://cds.cern.ch/record/2789024/files/fig5a.png$$y00008 $\Delta R$ distributions, (a, blue curves) for jets with $p_T$ above $80$~GeV in $Z$+jet events and (b, orange curves) for jets in events containing a $Z$ boson with $p_T$ above $80$~GeV. We show these distributions for $Z$+jet events in vacuum (dotted), in heavy ion collisions with hadrons coming from the wake that the jet deposits in the droplet of quark-gluon plasma artificially excluded (dashed), and in heavy ion collisions including hadrons coming from the response of the medium that are reconstructed as a part of the jets (solid).
002789024 8564_ $$82330902$$s32626$$uhttps://cds.cern.ch/record/2789024/files/fig5b.png$$y00009 $\Delta R$ distributions, (a, blue curves) for jets with $p_T$ above $80$~GeV in $Z$+jet events and (b, orange curves) for jets in events containing a $Z$ boson with $p_T$ above $80$~GeV. We show these distributions for $Z$+jet events in vacuum (dotted), in heavy ion collisions with hadrons coming from the wake that the jet deposits in the droplet of quark-gluon plasma artificially excluded (dashed), and in heavy ion collisions including hadrons coming from the response of the medium that are reconstructed as a part of the jets (solid).
002789024 8564_ $$82330903$$s32474$$uhttps://cds.cern.ch/record/2789024/files/fig7a.png$$y00013 \C distributions, (a) for jets with $p_T$ above $80$~GeV and (b) for jets recoiling against a $Z$ boson with $p_T$ above $80$~GeV, in vacuum (dotted), in heavy ion collisions without medium response (dashed), and in heavy ion collisions with medium response (solid).
002789024 8564_ $$82330904$$s30625$$uhttps://cds.cern.ch/record/2789024/files/fig4b.png$$y00007 \C distributions for jets with quenched $p_T$ above $80$~GeV (a) and unquenched $p_T$ above $80$~GeV (b), in vacuum (dotted), in heavy ion collisions without medium response (dashed), and in heavy ion collisions with medium response (solid).
002789024 8564_ $$82330905$$s32999$$uhttps://cds.cern.ch/record/2789024/files/fig4a.png$$y00006 \C distributions for jets with quenched $p_T$ above $80$~GeV (a) and unquenched $p_T$ above $80$~GeV (b), in vacuum (dotted), in heavy ion collisions without medium response (dashed), and in heavy ion collisions with medium response (solid).
002789024 8564_ $$82330906$$s28378$$uhttps://cds.cern.ch/record/2789024/files/fig8b.png$$y00016 $\Delta R$ distributions with and without medium response for $z_{\text{cut}}=0.1,0.3$, $\beta=0$ (a) and $z_{\text{cut}}=0.1,0.3$, $\beta=1$ (b), for jets recoiling against a $Z$ boson with $p_T$ above $80$~GeV (namely, jets selected as in the orange curves of \Fig{fig:fig5b}). All curves are for quenched jets as in PbPb collisions. Dashed curves indicate in-medium jets where hadrons originating from the wake in the medium have been artificially excluded, whereas solid curves indicate those where particles from the response of the medium are included.
002789024 8564_ $$82330907$$s27954$$uhttps://cds.cern.ch/record/2789024/files/fig8a.png$$y00015 $\Delta R$ distributions with and without medium response for $z_{\text{cut}}=0.1,0.3$, $\beta=0$ (a) and $z_{\text{cut}}=0.1,0.3$, $\beta=1$ (b), for jets recoiling against a $Z$ boson with $p_T$ above $80$~GeV (namely, jets selected as in the orange curves of \Fig{fig:fig5b}). All curves are for quenched jets as in PbPb collisions. Dashed curves indicate in-medium jets where hadrons originating from the wake in the medium have been artificially excluded, whereas solid curves indicate those where particles from the response of the medium are included.
002789024 8564_ $$82330908$$s34162$$uhttps://cds.cern.ch/record/2789024/files/fig2b.png$$y00002 (a) $\Delta R$ distributions for a sample of jets selected on the basis of having quenched $p_T$ above $80$~GeV (solid and dashed blue) and the matching unquenched jets (dotted blue). Each quenched jet was matched to the unquenched jet that it would have been if it had formed in vacuum. (b) $\Delta R$ distributions for a sample of jets selected on the basis of having unquenched $p_T$ above $80$~GeV (dotted orange) and the matching quenched jets (solid and dashed orange). Dashed curves are for jets quenched as in a heavy ion collision with hadrons originating from medium response artificially excluded; solid curves are for quenched jets including those hadrons from medium response that are reconstructed as a part of the jets.
002789024 8564_ $$82330909$$s30122$$uhttps://cds.cern.ch/record/2789024/files/fig7b.png$$y00014 \C distributions, (a) for jets with $p_T$ above $80$~GeV and (b) for jets recoiling against a $Z$ boson with $p_T$ above $80$~GeV, in vacuum (dotted), in heavy ion collisions without medium response (dashed), and in heavy ion collisions with medium response (solid).
002789024 8564_ $$82330910$$s36179$$uhttps://cds.cern.ch/record/2789024/files/fig6a.png$$y00010 (a) Fractional $p_T$ asymmetry between a $Z$ boson and its recoiling jet, for jets with jet $p_T$ above $80$~GeV (blue) and $Z$ $p_T$ above $80$~GeV (orange) in vacuum (dotted), and in heavy ion collisions with hadrons originating from medium response artificially excluded from (dashed) or included in (solid) the reconstructed jets. Panels (b) and (c) show the same distributions for those jets with $\Delta R \leq 0.2$ and $\Delta R > 0.2$, respectively.
002789024 8564_ $$82330911$$s32601$$uhttps://cds.cern.ch/record/2789024/files/fig3b.png$$y00004 (a) Fractional energy loss for matched jets with quenched $p_T$ above $80$~GeV (blue) and unquenched $p_T$ above $80$~GeV (orange) in heavy ion collisions without (dashed) and with (solid) medium response. Blue and orange samples are as in \Fig{fig:fig2}, as is the meaning of dashed versus solid. Panels (b) and (c) show the same distributions for those jets with $\Delta R \leq 0.2$ and $\Delta R > 0.2$, respectively.
002789024 8564_ $$82330912$$s34036$$uhttps://cds.cern.ch/record/2789024/files/fig3c.png$$y00005 (a) Fractional energy loss for matched jets with quenched $p_T$ above $80$~GeV (blue) and unquenched $p_T$ above $80$~GeV (orange) in heavy ion collisions without (dashed) and with (solid) medium response. Blue and orange samples are as in \Fig{fig:fig2}, as is the meaning of dashed versus solid. Panels (b) and (c) show the same distributions for those jets with $\Delta R \leq 0.2$ and $\Delta R > 0.2$, respectively.
002789024 8564_ $$82330913$$s31716$$uhttps://cds.cern.ch/record/2789024/files/fig3a.png$$y00003 (a) Fractional energy loss for matched jets with quenched $p_T$ above $80$~GeV (blue) and unquenched $p_T$ above $80$~GeV (orange) in heavy ion collisions without (dashed) and with (solid) medium response. Blue and orange samples are as in \Fig{fig:fig2}, as is the meaning of dashed versus solid. Panels (b) and (c) show the same distributions for those jets with $\Delta R \leq 0.2$ and $\Delta R > 0.2$, respectively.
002789024 8564_ $$82330914$$s32210$$uhttps://cds.cern.ch/record/2789024/files/fig1.png$$y00000 Illustration exemplifying the Monte Carlo matching procedure. Left panel: $(\eta,\phi)$ distribution of hadrons in an unquenched jet, as reconstructed. Middle panel: the same jet, reconstructed after quenching but upon leaving out hadrons originating from the response of the medium, e.g. the wake the jet excites. Right panel: the same jet, reconstructed after quenching, with hadrons from the medium response included. Color indicates hadron $p_T$ as a fraction of the $p_T$ of this unquenched jet, which has $p_T^\text{unq.}=177$~GeV.
002789024 8564_ $$82330915$$s35592$$uhttps://cds.cern.ch/record/2789024/files/fig2a.png$$y00001 (a) $\Delta R$ distributions for a sample of jets selected on the basis of having quenched $p_T$ above $80$~GeV (solid and dashed blue) and the matching unquenched jets (dotted blue). Each quenched jet was matched to the unquenched jet that it would have been if it had formed in vacuum. (b) $\Delta R$ distributions for a sample of jets selected on the basis of having unquenched $p_T$ above $80$~GeV (dotted orange) and the matching quenched jets (solid and dashed orange). Dashed curves are for jets quenched as in a heavy ion collision with hadrons originating from medium response artificially excluded; solid curves are for quenched jets including those hadrons from medium response that are reconstructed as a part of the jets.
002789024 8564_ $$82330916$$s38986$$uhttps://cds.cern.ch/record/2789024/files/fig6c.png$$y00012 (a) Fractional $p_T$ asymmetry between a $Z$ boson and its recoiling jet, for jets with jet $p_T$ above $80$~GeV (blue) and $Z$ $p_T$ above $80$~GeV (orange) in vacuum (dotted), and in heavy ion collisions with hadrons originating from medium response artificially excluded from (dashed) or included in (solid) the reconstructed jets. Panels (b) and (c) show the same distributions for those jets with $\Delta R \leq 0.2$ and $\Delta R > 0.2$, respectively.
002789024 8564_ $$82330917$$s37677$$uhttps://cds.cern.ch/record/2789024/files/fig6b.png$$y00011 (a) Fractional $p_T$ asymmetry between a $Z$ boson and its recoiling jet, for jets with jet $p_T$ above $80$~GeV (blue) and $Z$ $p_T$ above $80$~GeV (orange) in vacuum (dotted), and in heavy ion collisions with hadrons originating from medium response artificially excluded from (dashed) or included in (solid) the reconstructed jets. Panels (b) and (c) show the same distributions for those jets with $\Delta R \leq 0.2$ and $\Delta R > 0.2$, respectively.
002789024 8564_ $$82330918$$s1025921$$uhttps://cds.cern.ch/record/2789024/files/2110.13159.pdf$$yFulltext
002789024 8564_ $$82352127$$s1737873$$uhttps://cds.cern.ch/record/2789024/files/document.pdf$$yFulltext
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