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arxiv: 2606.20028 · v1 · pith:3E6TRTPRnew · submitted 2026-06-18 · ⚛️ nucl-ex · nucl-th

Probing flavor effects in the QCD parton shower using mathbf{{rm D}⁰}-tagged jet angularities in proton-proton collisions at mathbf{ sqrt{s} = 5.02} TeV

ALICE Collaboration This is my paper

Pith reviewed 2026-06-26 15:14 UTC · model grok-4.3

classification ⚛️ nucl-ex nucl-th
keywords D0-tagged jetsjet angularitydead-cone effectcharm quark massproton-proton collisionsjet substructureflavor-dependent fragmentation
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The pith

D0-tagged jets exhibit smaller angularity values than inclusive jets at low angular weights, indicating charm-quark radiation suppression.

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

The paper measures angularities of D0-tagged jets and compares them to inclusive jets in proton-proton collisions at 5.02 TeV. At low values of the angular weighting parameter, which emphasize collinear radiation, the D0-tagged jets show smaller angularity than the inclusive sample. This difference is presented as direct evidence that the finite mass of the charm quark suppresses radiation near the jet axis. The difference shrinks as the weight increases and wider angles are emphasized. PYTHIA 8 reproduces the tagged-jet distributions more closely than the inclusive ones.

Core claim

The central claim is that the reduction in angularity for D0-tagged jets at low angular weights demonstrates the QCD dead-cone effect caused by the mass of the charm quark, with the modification localized to the jet core rather than its periphery.

What carries the argument

Jet angularity, a substructure observable with a tunable angular exponent that controls sensitivity to collinear versus wide-angle radiation.

Load-bearing premise

The observed difference between D0-tagged and inclusive jet angularities is driven primarily by the charm-quark mass rather than by jet reconstruction efficiency, background subtraction, or the choice of the inclusive reference sample.

What would settle it

A measurement showing that the angularity distributions of D0-tagged and inclusive jets become statistically identical once all non-mass differences in reconstruction and selection are corrected would falsify the dead-cone interpretation.

Figures

Figures reproduced from arXiv: 2606.20028 by ALICE Collaboration.

Figure 1
Figure 1. Figure 1: Left: Invariant-mass distribution of D0 -jet candidates for 10 < p ch. jet T < 20 GeV/c, with D0 -meson candidates in 8 < p D 0 T < 12 GeV/c and R = 0.4. The total fit function is depicted by the dashed blue line, while the solid red line represents the background fit function. The blue and green shaded areas correspond to the signal and sideband regions, respectively. Right: The distribution of the raw D0… view at source ↗
Figure 2
Figure 2. Figure 2: Non-prompt (feed-down) fraction of D0 -tagged jets from beauty-hadron decays as a function of λα=1 for jets with R = 0.4 and 10 < p ch. jet T < 20 GeV/c [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Solid markers represent data, while the dashed lines correspond to PYTHIA 8 Monash 2013 [51] calculations. The λα=1 distribution (upper left panel) for D0 -tagged jets peaks at lower values than inclusive jets with a leading-track pT requirement; inclusive jets without a leading track requirement peak at an even larger value. This indicates that the transverse momentum carried by the jet fragments in D0 - … view at source ↗
Figure 4
Figure 4. Figure 4: The mean (left panel) and RMS (right panel) values extracted from the angularity distributions shown in [PITH_FULL_IMAGE:figures/full_fig_p012_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Comparison of jet angularity distributions for D0 -tagged (red), quark-initiated (blue), and gluon-initiated (green) jets from PYTHIA 8 Monash simulations with R = 0.4 in the 10 < p ch. jet T < 20 GeV/c range, shown for λα=1 (left) and λα=3 (right). wide-angle radiation, indicating that the impact of the dead-cone effect decreases at larger α, thereby enhancing sensitivity to color-charge (Casimir) differe… view at source ↗
Figure 6
Figure 6. Figure 6: The D0 -tagged jet-angularity distributions, measured by ALICE in pp collisions at √ s = 5.02 TeV (red markers), compared to PYTHIA 8 Monash (red line), SHERPA AHADIC (green line), and SHERPA LUND (blue line) using R = 0.4 in 10 < p ch. jet T < 20 GeV/c, for λα=1 (left) and λα=3 (right). λα=3. Among the tested generators, PYTHIA 8 Monash, which employs the Lund string model, provides the best description o… view at source ↗
read the original abstract

The ALICE Collaboration presents the first measurements of ${\rm D}^0$-tagged jet angularities in proton$-$proton (pp) collisions at $\sqrt{s} = 5.02$ TeV. Jet angularities are powerful substructure observables that characterize the angular and momentum distributions of particles within jets via tunable weighting parameters. Varying the angular parameter in jet angularities allows for a systematic probe of the sensitivity to collinear and soft radiation, enabling the study of flavor-dependent fragmentation and hadronization through comparisons of jets initiated by different partons. This paper reports ${\rm D}^0$-tagged and inclusive (gluon-dominated) charged-particle jet angularities with a resolution parameter $R=0.4$ in the low jet transverse momentum range ($10 < p_{\rm T}^{\rm ch. \, jet} < 20$ GeV/$c$), where charm-quark mass effects are most significant. At low angular weight, which emphasizes collinear radiation, ${\rm D}^0$-tagged jets exhibit smaller angularity values than inclusive jets. This provides evidence for the radiation suppression from massive quarks -- a phenomenon known as the QCD dead-cone effect. As the angular weight increases, giving more emphasis to wide-angle radiation, the difference between ${\rm D}^0$-tagged and inclusive jet distributions decreases. This indicates that the modification is concentrated within the jet core rather than its edge. PYTHIA 8 simulations qualitatively reproduce both the angularity of ${\rm D}^0$-tagged and inclusive charged-particle jets, but reproduce the ${\rm D}^0$-tagged jet distributions better than those of inclusive jets, offering a powerful new constraint for models. These results provide insight into flavor-dependent fragmentation and establish an essential baseline for future studies of jet modifications in the quark-gluon plasma produced in heavy-ion collisions.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The ALICE Collaboration reports the first measurements of D0-tagged charged-particle jet angularities (R=0.4) in pp collisions at 5.02 TeV for 10 < pT^ch jet < 20 GeV/c. At low angular weight (emphasizing collinear radiation), D0-tagged jets show smaller angularity values than inclusive jets, interpreted as evidence for the QCD dead-cone effect due to charm-quark mass suppression. The difference decreases at higher angular weights. PYTHIA 8 qualitatively reproduces both distributions, with better agreement for D0-tagged jets than inclusive jets.

Significance. If the central interpretation holds, this provides the first experimental probe of flavor-dependent jet substructure via tunable angularities in the low-pT regime where mass effects are prominent, serving as an essential baseline for heavy-ion studies of jet quenching. The qualitative PYTHIA comparison offers a new constraint on fragmentation models, though the lack of quantitative distributions and uncertainties in the presented results limits immediate impact.

major comments (1)
  1. [Abstract and results section] Abstract and results section: The claim that smaller angularity values provide evidence for the dead-cone effect assumes the D0-tagged vs. inclusive difference is driven by charm mass rather than D0 reconstruction biases (vertex reconstruction, pT/PID cuts on daughters). The manuscript notes qualitative PYTHIA agreement but does not isolate or quantify the contribution of tagging-induced selection effects on fragmentation or efficiency, which could suppress wide-angle radiation independently of mass.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading and constructive feedback on our manuscript. We address the major comment below and will make targeted revisions to strengthen the discussion of potential biases.

read point-by-point responses

  1. Referee: [Abstract and results section] Abstract and results section: The claim that smaller angularity values provide evidence for the dead-cone effect assumes the D0-tagged vs. inclusive difference is driven by charm mass rather than D0 reconstruction biases (vertex reconstruction, pT/PID cuts on daughters). The manuscript notes qualitative PYTHIA agreement but does not isolate or quantify the contribution of tagging-induced selection effects on fragmentation or efficiency, which could suppress wide-angle radiation independently of mass.

    Authors: We agree that isolating the charm-mass contribution from tagging-induced selection effects is important for a robust interpretation. The D0-tagged sample applies the same reconstruction (vertexing, pT and PID requirements on daughters) to both data and PYTHIA 8, which includes the full detector response and charm-quark mass. The observed difference between D0-tagged and inclusive jets is therefore compared to a simulation that already incorporates tagging biases; the qualitative agreement with PYTHIA supports that the mass-dependent suppression (dead-cone) is the primary driver. Nevertheless, the manuscript does not provide an explicit decomposition (e.g., PYTHIA runs with massless charm or with tagging cuts removed). We will add a dedicated paragraph in the results section and a supplementary figure quantifying the tagging bias contribution by comparing massive vs. massless charm simulations under identical reconstruction, thereby addressing the referee’s concern directly. revision: partial

Circularity Check

0 steps flagged

No circularity: direct experimental measurement

full rationale

The paper reports first measurements of D0-tagged jet angularities compared to inclusive jets in pp collisions. No derivation, ansatz, or parameter fitting is present that reduces to its own inputs. The central result is the observed difference in angularity distributions at low angular weight, interpreted as possible dead-cone evidence, but this follows from the data collection and reconstruction rather than any self-referential equation or self-citation chain. PYTHIA comparisons are external model checks, not load-bearing for the measurement itself. The paper is self-contained against external benchmarks with no self-definitional or fitted-input reductions.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The measurement relies on standard high-energy physics assumptions for jet finding and particle identification; no new free parameters or invented entities are introduced in the abstract.

axioms (1)
  • domain assumption Standard QCD parton shower and hadronization models (PYTHIA 8) provide a valid reference for vacuum fragmentation
    Used to interpret the difference between data and simulation

pith-pipeline@v0.9.1-grok · 5892 in / 1156 out tokens · 27694 ms · 2026-06-26T15:14:53.263640+00:00 · methodology

discussion (0)

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Reference graph

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