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REVIEW 3 major objections 4 minor 10 references

Two-point jet correlator data already require both hydrodynamic wakes and quasi-particle scattering, and a new angular window can image the wake alone.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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2026-08-04 21:21 UTC pith:W65N3WDY

load-bearing objection Plausible and timely, but the two-ingredient claim rests on visual curve comparison, not a sensitivity study; the R_L > R proposal is the real gem. the 3 major comments →

arxiv 2509.08047 v1 pith:W65N3WDY submitted 2025-09-09 hep-ph nucl-exnucl-th

Imaging the Jet-Induced Medium Response with Energy Correlators

Hannah Bossi , Arjun Kudinoor , Ian Moult , Daniel Pablos , Ananya Rai , Krishna Rajagopal This is my paper
classification hep-ph nucl-exnucl-th PACS 25.75.-q12.38.Mh
keywords energy-energy correlatorsjet quenchingquark-gluon plasmaHybrid Modelelastic scatteringhydrodynamic wakejet substructureheavy-ion collisions
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper argues that the angular pattern of energy inside jets in heavy-ion collisions can tell apart two different faces of the quark-gluon plasma (QGP): a strongly coupled liquid that responds like a fluid when a jet dumps energy into it, and a gas of quark- and gluon-like quasi-particles that can knock jet constituents sideways. Using the Hybrid Model — a perturbative parton shower combined with holographic energy loss, Cooper-Frye hydrodynamic wakes, and 2-to-2 elastic scatterings — the authors compute two- and three-point energy-energy correlators (EECs) and compare the PbPb/pp ratio with CMS and ALICE data. Their central claim: the calculation that includes both the wakes and the elastic scatterings tracks the measured rise of the ratio toward larger angular separations most closely; turning off either ingredient degrades the fit. If this is right, the existing data already demand both liquid-like wake excitation and quasi-particle elastic scattering in the same plasma, with the wakes of the recoiling scattered partons — not just the original jet's wake — shaping the observable. The paper also proposes a new measurement, pushing EECs to angular separations beyond the jet radius, which should isolate the wake signal alone.

Core claim

The paper's central claim is that the CMS and ALICE two-point EEC data already discriminate between the competing ways a jet interacts with the quark-gluon plasma. The closest match comes from Hybrid Model calculations in which jet partons both lose energy to the medium — exciting hydrodynamic wakes — and scatter elastically off quasi-particles, with the deflected jet parton and the recoiling medium parton each subsequently exciting its own broad wake. This combination reproduces the observed rise of the PbPb/pp ratio toward large angular separation R_L, while removing either ingredient under-shoots the data. The three-point correlator then acts as a two-stage microscope: the overall scale R

What carries the argument

The carrying objects are the two-point and three-point energy-energy correlators (EEC/EEEC): the angular distribution of energy-weighted pairs, and of particle triplets, inside a jet, expressed as a PbPb/pp ratio to cancel the vacuum shower baseline. The physics input is the Hybrid Model — a perturbative DGLAP/PYTHIA8 parton shower; a holographic energy-loss formula that deposits the lost momentum into the plasma; the Cooper-Frye prescription applied to the linearized hydrodynamic stress-energy perturbation to generate the soft hadron wake spectrum; and 2-to-2 elastic (Molière) scatterings that deflect a jet parton and kick a medium quasi-particle into recoil, after which both partons lose e

Load-bearing premise

The load-bearing assumption is that the wake spectrum — the soft hadrons produced from the momentum a jet deposits in the plasma, computed with the Cooper-Frye prescription from a linearized hydrodynamic response — faithfully represents what the real medium emits; if the true wake were materially weaker, narrower, or differently normalized, the large-R_L enhancement attributed to wakes would shrink or shift and the data comparison would no longer single out the wake-plus-scat

What would settle it

Carry out the paper's proposed measurement: the PbPb/pp EEC ratio for 80 < pT < 100 GeV, R=0.2 charged-jets with a 150 MeV track-pT threshold, extended to angular separations up to 2R. If the ratio does not rise steeply above unity for R_L ≳ R — the region that only soft, peripheral hadrons can populate — the wake-dominated picture is falsified. A second check: measure the ratio at several track-pT thresholds; if the large-R_L enhancement does not grow as the threshold is lowered, the soft-hadron wake component is not the source of the rise.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

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If this is right

  • The measured rise of the PbPb/pp EEC ratio toward large R_L implies that the wakes of elastically scattered, recoiling partons — not only the wake of the original jet partons — carry the jet's deposited energy, and that this 'deflection memory' is visible in existing CMS and ALICE data.
  • The angular window 0.1 ≲ R_L ≲ 0.2 in the R=0.2 charged-jet EEC is where elastic scattering's deflection of hard, collinear constituents shows up, so data in that window constrain the presence of quasi-particle scatterings in the QGP.
  • Extending EEC measurements to R_L > R (beyond the jet radius) with a 150 MeV track-pT threshold — kinematically inaccessible to pairs with a hard core constituent — should reveal a marked PbPb/pp enhancement that isolates the wake of the jet.
  • In the three-point EEEC, an enhancement of equilateral triangles at large R_L diagnoses the angular structure of the wake, while a broad, uniform uplift at small R_L diagnoses elastic scattering — giving scale and shape information about jet-medium interactions.
  • Lowering the track-pT threshold generally increases the wake's leverage on the EEC, which is why the proposed low-threshold, extended-R_L variant is the sharpest test of the wake picture.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The argument implies a monotonic, testable trend: as the track-pT threshold is lowered from 1 GeV toward 150 MeV, the large-R_L enhancement of the PbPb/pp ratio should grow if soft wake hadrons are really its source; measuring the ratio at several thresholds would cross-check the wake hypothesis without relying on the model's details.
  • If quasi-particle scattering is genuinely required by the data, the same elastic kicks should leave imprints in other angularly sensitive jet observables — for instance, the distribution of the energy of the highest-pT sub-leading constituents, or large-angle jet-hadron correlations — offering independent confirmation outside EECs.
  • The shape decomposition could be pushed further than the paper does: the width and orientation of the equilateral enhancement at large R_L may be sensitive to the anisotropy of the wake (e.g., its response to collective flow), potentially making the EEEC a quantitative probe of the medium's transport properties.
  • The dominance of recoiling-parton wakes at R_L > 0.2 suggests that jets undergoing more hard scatterings should show larger medium-response signals; reselecting the jet sample by the number or momentum of its wide-angle constituents could test this correlation.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

3 major / 4 minor

Summary. The manuscript presents Hybrid Model calculations of two- and three-point energy-energy correlators (EECs) in Pb+Pb collisions and compares them to recent CMS and ALICE measurements. The central claim is that the PbPb/pp EEC ratio is best described when the model includes both elastic (Molière) scattering of jet partons off quasi-particles and hydrodynamic wakes generated by the energy lost by all partons, including the elastically scattered recoil partons. The paper further proposes a new EEC measurement extending to angular scales beyond the jet radius and presents three-point EEEC shape projections as a two-stage microscope for separating wake and elastic-scattering contributions.

Significance. If the central claim is correct, the comparison would be an important external benchmark: the EEC data would already discriminate among mechanisms of jet–medium interaction, supporting the presence of quasi-particle-like scatterings alongside strongly-coupled wake response. The paper is strongest in its concrete falsifiable predictions: the R_L>R region in Fig. 2 is a clean, model-driven target for experiment, and the EEEC shape projections in Fig. 3 make qualitative distinctions between wake and elastic effects. The comparison in Figs. 1–3 is not a fit to the same data — the model parameters were fixed in earlier R_AA-style studies — so the agreement is a genuine prediction rather than a circular fit. However, the manuscript's main evidence is qualitative; the absence of model uncertainties and parameter sensitivity prevents the reader from assessing how strongly the data actually discriminate between the variants.

major comments (3)
  1. [Sec. 2, Fig. 1] The statement that the 'both' curve 'tracks the observed rise ... most closely' is supported only by visual inspection. No goodness-of-fit statistic, no chi-square per point, and no statistical uncertainty band on the model curves is given. Since the central conclusion is a comparative ranking of four model variants, please provide a quantitative measure of agreement over the plotted R_L range and show Monte Carlo or bootstrap uncertainties on the model curves.
  2. [Sec. 1, Sec. 2] The wake contribution is generated by Cooper–Frye from a linearized hydrodynamic response following Refs. [2–4]. Its normalization and spectral shape are model inputs that are not varied. If the wake normalization were moderately increased, the 'wake-only' curve in Fig. 1 could plausibly match the data; if the elastic scattering rate were reduced, the 'both' curve might no longer be closest. A sensitivity scan over the wake normalization/freeze-out temperature and the elastic scattering rate is needed to support the claim that both ingredients are required by the data.
  3. [Sec. 2, Fig. 1] The abstract and Sec. 2 state that data are best described 'when the elastically scattered recoil-partons produce their own wakes,' but the four curves shown do not isolate wakes of recoil partons from wakes of the deflected parent partons or from the elastic deflection of the hard shower. The difference between 'elastic + wake' and 'wake-only' includes both the elastic shower modification and all additional wakes. To make the recoil-wake attribution rigorous, show a variant with elastic scatterings enabled but only original-parton wakes included, or otherwise quantify the separate contribution of recoil-parton wakes.
minor comments (4)
  1. [Acknowledgements] Duplicate 'the' in the Ramón y Cajal funding sentence.
  2. [Ref. [7]] Reference [7] is an ALICE conference talk; if a journal version exists or becomes available, it should be cited instead of the talk.
  3. [Sec. 3] The text says the shape-dependent EEEC is a function of three angles, but Figs. 3 and the preceding paragraph present projections onto x and y separately. Please clarify that the full correlator is a function of (R_L, x, y) and that projections are shown.
  4. [Fig. 1 caption] The track-pT cut 'p_ch^T > 1 GeV' and jet pT ranges should be typeset consistently with the text, and it would be helpful to define R_L in the caption for readers unfamiliar with the EEC variable.

Circularity Check

0 steps flagged

No significant circularity: the EEC ratios are computed from a previously built model and compared to independent CMS/ALICE data; no parameter is fitted to the predicted observable.

full rationale

The paper's central claim is that Hybrid Model calculations including both wakes and elastic scatterings best track the measured PbPb/pp EEC ratios. This is a model-to-data comparison, not a derivation that reduces to its own inputs. The wake and elastic-scattering implementations are taken from earlier papers by overlapping authors (Refs. [1–5]), but those components were not tuned to the EEC data shown here; they are physical ingredients (holographic energy loss, Cooper–Frye wakes, 2→2 Molière scattering) whose consequences are then computed and confronted with CMS and ALICE measurements. No equation in the paper defines the predicted EEC ratio in terms of the measured EEC ratio, and no fitted parameter is renamed as a prediction. The EEEC shape-variable construction following Ref. [2] is a coordinate/parametrization choice, not a result that presupposes the conclusions. Concerns about unquantified wake normalization or lack of a sensitivity scan are legitimate evidence-quality critiques, but they are not circularity: the model could in principle be ruled out or supported by the external data. The self-citations are load-bearing in the sense that the model is built in prior work, but they are not invoked as an external uniqueness theorem or as a substitute for the comparison performed here. Therefore the derivation chain is self-contained with respect to the EEC predictions, and no circular step can be exhibited.

Axiom & Free-Parameter Ledger

3 free parameters · 4 axioms · 0 invented entities

The central claim inherits the Hybrid Model's calibrated parameters (energy-loss rate, elastic scattering rate, wake freeze-out), all set in the authors' prior work; this paper adds no new fitted numbers but the EEC predictions are sensitive to these choices.

free parameters (3)
  • Energy-loss rate parameter (kappa) in the holographic formula = set in refs [1-3] to reproduce jet R_AA
    Controls how much energy each parton deposits in the medium; directly sets the magnitude of the wake and thus the EEC enhancement at large R_L.
  • Elastic scattering coupling / cross-section normalization = set in ref [5]
    Controls the rate of 2->2 Moliere scatterings that deflect jet partons and generate recoil-parton wakes; drives the enhancement at 0.1 < R_L < 0.2.
  • Wake freeze-out temperature (T_f) and speed of sound (c_s) = standard choices (e.g. T_f near T_c, c_s^2 = 1/3) from refs [2-4]
    Shape of the Cooper-Frye spectrum of wake hadrons determines the soft-hadron distribution at large angles; changing them changes the model-data comparison.
axioms (4)
  • domain assumption DGLAP parton showers as implemented in PYTHIA8 reproduce the vacuum jet structure
    Used in Sec. 1 for the jet shower evolution; standard but model-dependent choice.
  • domain assumption The holographic energy loss formula derived in N=4 super-Yang-Mills applies to QGP
    Central to the Hybrid Model; sets the energy deposited in the medium and hence wake strength.
  • domain assumption The medium response is a linearized hydrodynamic wake with Cooper-Frye freeze-out
    Determines the soft-hadron spectrum from the wake; the paper defers all assumptions to refs [2-4].
  • ad hoc to paper Recoiling medium partons from elastic scatterings also lose energy and excite wakes in the same way as the original jet partons
    This modeling choice is central to the new comparison (Sec. 2, 'Crucially, both the deflected jet parton and the recoiling medium parton subsequently lose energy and each excites its own broad wake') and is implemented in the authors' prior ref [5].

pith-pipeline@v1.3.0-alltime-deepseek · 3850 in / 12556 out tokens · 135398 ms · 2026-08-04T21:21:47.619448+00:00 · methodology

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Cite this review

Pith. "Pith review of Imaging the Jet-Induced Medium Response with Energy Correlators." pith.science (2026). https://pith.science/paper/W65N3WDY

@misc{pith2026250908047,
  author       = {Pith},
  title        = {Pith review of: Imaging the Jet-Induced Medium Response with Energy Correlators},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/W65N3WDY}},
  note         = {Machine review of arXiv:2509.08047}
}
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read the original abstract

Quark-gluon plasma (QGP), when viewed at length scales of order the inverse of its temperature, behaves as a strongly-coupled liquid. However, when it is probed with sufficiently high momentum transfer, asymptotic freedom mandates the presence of quark- and gluon-like quasi-particles. High energy partons within jets can trigger these high-momentum exchanges, making jets valuable probes for revealing the presence of such quasi-particles. Such elastic scatterings are implemented in the Hybrid Model, where a jet parton that scatters is deflected, kicking a medium parton, which recoils. Before and after a scattering, as one and then both partons propagate through the medium, they lose energy and momentum, exciting wakes in the QGP droplet. We use two-point and three-point energy-energy correlators (EECs) to reveal the relevant angular regions at which (modified) parton showers and wakes in the QGP each dominate, offering a new way with which to visualize and constrain the corresponding dynamics. We compare our calculations to recent CMS and ALICE measurements of two-point EECs of charged-particle tracks in jets produced in PbPb collisions. We show that our calculations are closest to the experimental measurements when elastic scattering is included and when the elastically scattered recoil-partons produce their own wakes. We also propose a new variant of the measurement that is especially sensitive to jet wakes.

Figures

Figures reproduced from arXiv: 2509.08047 by Ananya Rai, Arjun Kudinoor, Daniel Pablos, Hannah Bossi, Ian Moult, Krishna Rajagopal.

Figure 1
Figure 1. Figure 1: PbPb/pp ratio of EECs calculated using charged-particle tracks with p ch T > 1 GeV within a sample of inclusive jets with 120 < pT < 140 GeV R = 0.4 (left) and 80 < p ch T < 100 GeV R = 0.2 charged-jets (right). We plot colored Hybrid Model curves, with/without elastic scattering, and with/without hadrons from the wakes of jets. CMS (left) and ALICE (right) experimental measurements from Refs. [6, 7] are d… view at source ↗
Figure 2
Figure 2. Figure 2: PbPb/pp ratio of charged-particle EECs calculated using a sample of 80 < p ch T < 100 GeV R = 0.2 charged-jets and a particle track-pT cut of 150 MeV. Hybrid Model curves are shown with/without elastic scattering and hadrons from the wakes of jets. The horizontal RL-axis extends up to twice the jet radius. Our results motivate extending the EEC measurement in this way. wake or elastic scatterings degrades … view at source ↗
Figure 3
Figure 3. Figure 3: PbPb/pp ratio of EEECs of anti-kt R = 0.8 jets with 140 < pT < 240 GeV, projected onto the x-coordinate (left) and the y-coordinate (right) for 0.2 < RL < 0.3 (top) and 0.6 < RL < 0.7 (bottom). Hybrid Model curves are shown with/without elastic scattering and hadrons from the wakes of jets. near x ≃ 0 or 1. In this representation, the shape-dependent EEEC is a function of three angles — RL, x, and y — and … view at source ↗

discussion (0)

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Reference graph

Works this paper leans on

10 extracted references · 4 canonical work pages · 1 internal anchor

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