Proceedings of Dielectron production in pp and Pb-Pb collisions with ALICE in Run 3, Quark Matter 2025

Florian Eisenhut (for the ALICE Collaboration)

REVIEW 3 major objections 4 minor 8 references

Proceedings of Dielectron production in pp and Pb-Pb collisions with ALICE in Run 3, Quark Matter 2025

T0 review · 3 major / 4 minor · reviewed 2026-08-04 · deepseek-v4-flash

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Pith's one-line read This paper reports the first dielectron production cross section in pp collisions at 13.6 TeV and shows that a displacement-based template fit separates prompt from heavy-flavour dielectron sources, uncovering a small prompt contribution in

desk verdict First 13.6 TeV dielectron cross section is new, but the DCAee prompt/non-prompt split is a promising hint, not yet a measurement. read the letter →

arxiv 2509.06613 v1 pith:E5RQISES submitted 2025-09-08 nucl-ex hep-ex

Florian Eisenhut (for the ALICE Collaboration) This is my paper

classification nucl-exhep-ex

keywords dielectronproductionpromptandnon-promptseparationDCAeeDrell-Yanheavy-flavourdecaysquark-gluonplasmathermalradiationALICERun3proton-protoncollisions

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

Dielectrons—electron–positron pairs—pass through the quark-gluon plasma without strong interactions, so their invariant mass and momentum carry information about when in the collision they were emitted. This paper reports the first measurement of the dielectron production cross section in proton–proton collisions at 13.6 TeV, based on a Run-3 data sample about 600 times larger than the previous measurement, and shows it agrees with the earlier 13 TeV result and with a hadronic cocktail. The paper's central new step is a template fit to a pair-level displacement variable, DCAee, that separates dielectrons produced promptly (Drell–Yan, light-flavour, prompt J/psi, possibly thermal) from those coming from displaced heavy-flavour decays. In the intermediate-mass region the fit favours a small prompt contribution, exactly the kind of signal needed to probe low-mass Drell–Yan and the onset of thermal radiation; the same DCAee separation is demonstrated in Pb–Pb collisions as a route to extracting QGP thermal radiation.

What carries the argument

The central object is the pair displacement variable DCAee = sqrt(1/2 * [(DCA_e1/sigma1)^2 + (DCA_e2/sigma2)^2]), the quadrature mean of each electron's distance of closest approach to the primary vertex, normalized by its resolution. Because heavy-flavour hadrons decay after traveling c*tau of roughly 150 micrometers (D mesons) or 470 micrometers (B mesons), their daughter electrons have broad DCAee distributions, while prompt dielectrons (Drell–Yan, light-flavour, prompt J/psi, and any thermal radiation) point back to the vertex. Monte Carlo templates for each source are fitted to the measured raw DCAee distribution in mass slices; the fit separates the invariant-mass spectrum into prompt

What would settle it

Re-extract the intermediate-mass prompt fraction after replacing the Monte Carlo DCAee templates for charm and beauty with shapes obtained from data regions enriched in displaced vertices, for example around the non-prompt J/psi peak; if the small prompt excess vanishes, the prompt claim is a template artifact.

Watch

Extended reading notes

Core claim

The paper reports the first dielectron production cross section in pp collisions at 13.6 TeV, from a Run-3 data sample ~600 times larger than the previous measurement, and finds it consistent with the 13 TeV result and with a hadronic cocktail. Its central new result is a template fit to the pair displacement variable DCAee that unfolds the dielectron spectrum into prompt and non-prompt sources: the non-prompt spectrum shows the soft heavy-flavour continuum and a non-prompt J/psi peak, while the prompt spectrum shows direct resonances and a small excess in the intermediate-mass region. This separation is also demonstrated in Pb–Pb collisions with simple DCAee selections, pointing toward extr

Load-bearing premise

The result depends on Monte Carlo templates reproducing the exact DCAee shapes of every dielectron source in real data; if a template shape is miscalibrated, the small prompt excess in the intermediate-mass region could be a fitting artifact rather than a real signal.

Editorial extensions

If this is right

The 13.6 TeV pp cross section becomes the new baseline for Run-3 Pb–Pb dielectron measurements, with the comparison to 13 TeV already used to validate detector effects.
Applying the DCAee template fit to Pb–Pb data should unfold the intermediate-mass spectrum into prompt and heavy-flavour components, isolating any QGP thermal radiation.
A prompt excess in the pp intermediate-mass region, if confirmed with the full data sample, can be confronted with low-mass Drell–Yan calculations, where perturbative QCD has large uncertainties.
The same template technique can be extended to finer mass and transverse-momentum bins, mapping the prompt contribution across the full mass range rather than only in the intermediate-mass region.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

Beyond the paper: if the small intermediate-mass prompt excess persists after systematics, it would be the first hint that a fraction of dielectrons at this energy are produced before any hadronic rescattering—possibly Drell–Yan or early thermal radiation—and its mass shape could help tell those apart.
Beyond the paper: the DCAee separation could also be used to measure the beauty-over-charm contribution to the continuum directly from data, providing a cross-check of the FONLL energy scaling used in the cocktail.
Beyond the paper: the same displacement-separation logic should apply to other dilepton channels and collision energies, so the method is not limited to electron final states or to LHC conditions.

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Editorial analysis

A structured set of objections, weighed in public.

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

Desk Editor's Note

read the letter

Quick take: this is an honest, preliminary ALICE proceedings that delivers one genuinely new thing—the 13.6 TeV dielectron cross section—and shows a plausible first cut at DCAee template unfolding. The measurement looks solid as far as it goes, but the interesting physics hint (a small prompt excess in the IMR) is not established: no significance, no closure, no systematics on the unfolded spectra. That's a fair criticism, but not a fatal one, because the paper itself says the signal 'appears' and warrants 'further investigations.'

What's good: the Run 3 sample is 600 times larger than Run 2; the ITS2 pointing resolution gives a cleaner DCAee; the raw cross section and the hadronic cocktail description are shown with data-to-cocktail agreement, aside from a 1.8σ η tension that is flagged. The DCAee template fit is demonstrated in pp and Pb–Pb, with raw spectra visibly separating prompt and non-prompt components. The paper is appropriately skeptical of its own result.

Soft spots: the paper is a proceedings, so it omits the full systematic breakdown and shows no uncertainty band on the cocktail. The DCAee template fit is shown for a single mass bin, with no χ2 or closure test. The stress-test point is well taken: because the heavy-flavour templates are tied to the Run 2 cocktail fit, agreement at 13.6 TeV is not an independent check of the charm/beauty DCA shapes. A miscalibrated template width could shift the small prompt excess either way. The paper also doesn't give the statistical significance of the prompt excess in the IMR. These are all genuine gaps, but they are the usual gaps of a conference proceeding, and the paper doesn't overclaim.

The Pb–Pb part is even more preliminary—raw spectra only, with DCAee selections. Fine for a proceedings, but not yet a physics result.

Who it's for: ALICE dielectron specialists, dilepton phenomenologists, and anyone tracking Run 3 performance. It's not a stand-alone physics paper, but it's a useful public record of a new measurement and a promising technique.

Recommendation: if this came in as a proceedings submission, a serious editor should send it to a referee to check that the ALICE preliminary numbers and the description of the method are consistent. It deserves refereeing, not desk rejection. But the physics claim about a prompt IMR excess should not be cited as established until the full analysis appears.

Referee Report

3 major / 4 minor

Summary. This proceedings paper reports the first measurement of the dielectron production cross section in pp collisions at sqrt(s)=13.6 TeV using ALICE Run 3 data, together with exploratory template fits to the DCA_ee distribution that unfold the spectrum into prompt and non-prompt contributions. The paper also shows raw Pb-Pb dielectron spectra and DCA_ee-selected distributions at sqrt(s_NN)=5.36 TeV, with future plans to apply the same unfolding technique. All results are labeled preliminary.

Significance. If established, the new 13.6 TeV measurement provides a precision baseline for heavy-ion studies at a new energy, and the DCA_ee unfolding method offers a promising route to separating prompt sources (e.g., Drell-Yan, thermal radiation) from the dominant heavy-flavour background. The paper benefits from a large Run 3 data sample (about 600 times the Run 2 dielectron sample), the upgraded ITS2/TPC pointing and readout capabilities, and a clear presentation of the template-fit concept. The strengths are the new data point and the demonstrable separation power of DCA_ee in both pp and Pb-Pb. However, the central claims are currently supported by preliminary comparisons lacking essential validation, so the significance is provisional.

major comments (3)

[Section 3, Fig. 1 (right)] The hadronic cocktail is described as being fitted to the Run 2 13 TeV measurement and using a preliminary eta/pi0 parametrization, and the comparison to the 13.6 TeV data is shown without an uncertainty band on the cocktail. The statement that data and cocktail agree 'within statistical and systematic uncertainties' is therefore unquantified and, because the cocktail is not independent of the Run 2 result, it does not validate the new measurement. A total uncertainty band (or a table of systematic components) and a quantitative chi2/ndf for the data-to-cocktail ratio are needed.
[Section 3, Fig. 2 (left)] The DCA_ee template fit is the core novelty of the paper, but the fit is only shown in one mass interval (2.1 < m_ee < 2.3 GeV/c^2) with a data-to-fit ratio consistent with unity. No chi2/ndf, closure test, or systematic uncertainties on the unfolded prompt/non-prompt spectra are reported. The claimed 'small contribution from prompt sources' in the IMR is a qualitative statement without a significance value. Without these, the extraction of prompt and non-prompt spectra is not established.
[Section 3, Fig. 2 (right)] The prompt/non-prompt separation relies on Monte Carlo templates for all dielectron sources, but the heavy-flavour templates are tied to PYTHIA6 and the cocktail is fitted to the Run 2 13 TeV spectrum. This does not validate the DCA_ee shapes at 13.6 TeV. A miscalibrated charm/beauty DCA_ee template or a missing prompt template in the IMR could move the small prompt excess in either direction. The authors should provide a robustness check, e.g., varying the HF cocktail or generator, or a control region dominated by non-prompt J/psi, to show that the IMR prompt excess is not a template artifact.

minor comments (4)

[Section 2] The statement that the Run 3 sample is '600 times larger' than the Run 2 dielectron sample should specify the comparison basis (events, integrated luminosity, or recorded statistics) to be reproducible.
[Section 3, Fig. 1 (right)] The bottom ratio panel appears to show no error bars on the data points; please clarify whether the ratio includes statistical and systematic uncertainties.
[Section 3, Eq. for DCA_ee] The text calls DCA_ee a 'quadratic mean' but the formula is the RMS of the normalized per-track DCA values. Also, Fig. 2 uses DCA_z_ee, while the definition in the text uses DCA_e1/2; please clarify the exact pair variable used in the fits.
[Introduction] The mass regions are defined as low (m_ee < 1.1 GeV/c^2), intermediate (1.1-2.7 GeV/c^2), and high (m_ee > 3.1 GeV/c^2), leaving the 2.7-3.1 GeV/c^2 interval unspecified. Please map the regions consistently with Fig. 1.

Circularity Check

0 steps flagged · score 1.0 of 10

No significant circularity: the 13.6 TeV measurement and DCAee prompt/non-prompt separation are data- and MC-driven, not derived from their own conclusions.

full rationale

The paper presents a new measurement of dielectron production in pp collisions at 13.6 TeV and a template-fit procedure for separating prompt and non-prompt sources. The only self-citation entering the analysis is the Run 2 dielectron result at 13 TeV [3], used to tune the hadronic cocktail's heavy-flavour components. This is not a circular step: the 13.6 TeV spectrum is an independent data set, and the energy extrapolation from 13 TeV to 13.6 TeV is supplied by external FONLL calculations [4], with Run 3 detector response applied. The agreement shown in Fig. 1 is therefore a cross-energy validation, not a prediction forced by the target measurement. The DCAee template fit in Section 3 constructs MC templates for each dielectron source and fits their amplitudes to the measured raw DCAee distribution. The template shapes come from simulations of known sources; they are not derived from the 13.6 TeV dielectron spectrum being unfolded. The 'small prompt contribution in the IMR' is a fit output, not an input, and the paper explicitly frames it as preliminary ('it appears that the fit favours...') without claiming a final significance. The absence of a closure test or systematic uncertainties on the unfolded spectra is a robustness concern, not a circularity of the kind defined here. No equation or claim reduces to its own input by construction, and no load-bearing argument rests on an unverified self-citation chain. Thus the circularity score is low.

Assumptions & free parameters 3 free parameters · 4 assumptions · 0 invented entities

No new physical entities are introduced. The central claim rests on fitted cocktail components and template-fit fractions, and the key assumption is that MC templates model the DCAee shape, since the prompt-source signal depends on it.

free parameters (3)

Preliminary eta/pi0 ratio parametrization = not quoted
Used in the hadronic cocktail; the paper notes a 1.8 sigma tension in the eta mass region which it attributes to this preliminary parametrization (Section 3, Figure 1).
PYTHIA6 heavy-flavour dielectron yields = not quoted (fitted to 13 TeV spectrum)
The charm and beauty dielectron components in the cocktail are fitted to the measured 13 TeV spectrum and then scaled to 13.6 TeV using FONLL; this fitted baseline is compared with the new data (Section 3).
Template source fractions in DCAee fits = not quoted (fit outputs)
The relative yields of prompt and non-prompt sources are fitted to the raw DCAee distribution in each mass interval; the claimed small prompt contribution in the IMR is a fit result (Section 3, Figure 2).

assumptions (4)

domain assumption MC templates for each dielectron source accurately describe the DCAee shapes in data
The template fits and the separation of prompt vs non-prompt sources rely on the measured DCAee distributions being correctly modeled by MC; stated in Section 3.
domain assumption The hadronic cocktail includes all significant dielectron sources
The comparison of data to cocktail assumes no missing source besides the Drell-Yan and thermal contributions under investigation; Section 3, Figure 1.
domain assumption Heavy-flavour production at 13.6 TeV can be estimated by scaling the 13 TeV fitted PYTHIA6 yields with FONLL
Used to extend the cocktail to the new energy; stated in Section 3.
standard math Standard model physics and perturbative QCD calculations for background processes
The analysis relies on standard dielectron production processes and PYTHIA/FONLL as background models; implicit in the cocktail construction.

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Cite this review

Pith. "Pith review of Proceedings of Dielectron production in pp and Pb-Pb collisions with ALICE in Run 3, Quark Matter 2025." pith.science (2026). https://pith.science/paper/E5RQISES

@misc{pith2026250906613,
  author       = {Pith},
  title        = {Pith review of: Proceedings of Dielectron production in pp and Pb-Pb collisions with ALICE in Run 3, Quark Matter 2025},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/E5RQISES}},
  note         = {Machine review of arXiv:2509.06613}
}

abstract

The measurement of dielectron production is a fundamental piece of the puzzle in the understanding of the hot and dense matter produced in ultra-relativistic heavy-ion collisions. The dielectron spectrum provides information that penetrates the veil of final-state hadronic interactions and gives direct access to the early phases of the collision. However, the interpretation of the measured spectra relies on a precise understanding of all the contributing sources. The measurement of dielectron production in proton-proton collisions, collected with the upgraded ALICE detector at $\sqrt{s}$ = 13.6 TeV is presented together with the status of the Pb-Pb analysis at $\sqrt{s_{\rm{NN}}}$ = 5.36 TeV. In particular, the extraction of prompt (and non-prompt) dielectron spectra over a wide mass range is explained. In addition it is discussed, in which way such analysis could help to understand the Drell-Yan process in a non-perturbative regime and to investigate the onset of thermal radiation.

Figures

Figures reproduced from arXiv: 2509.06613 by the authors.

**Figure 1.** Left: Comparison of dielectron production in pp collisions at √ s = 13.6 TeV (red) and 13 TeV (blue). The bottom panel shows the ratio between both energies. Right: Dielectron cross section compared to the hadronic cocktail with the ratio data over cocktail. (Using 2023 data sample.) surements of light-flavour mesons, as well as PYTHIA 6 calculations for the heavy-flavour components, fitted to the measured dielectro… view at source ↗

**Figure 2.** Left: Raw dielectron yield as a function of DCAz ee (DCAee in the beam direction) measured in pp collisions at √ s = 13.6 TeV in the IMR fitted with different templates. Right: Corresponding unfolded invariant-mass spectra for prompt and non-prompt sources based on DCAz ee template fits. (Using 2022 data sample.) J/ψ, possible thermal radiation) and non-prompt (heavy-flavour, non-prompt J/ψ) sources can be unfolded.… view at source ↗

**Figure 3.** Left: Raw dielectron signal as function of invariant mass, with selections of DCAz ee< 1σ (dark cyan), DCAz ee> 2σ (red) and the integrated DCAz ee (black) in Pb–Pb collisions at √ sNN = 5.36 TeV for the centrality class 10-90% and a pT,e > 0.4 GeV/c in Run 3. Right: Raw dielectron signal as function of DCAz ee selected in 0.08 < mee< 0.14 GeV/c 2 (dark cyan) and 1.1 < mee< 2.7 GeV/c 2 (red). (Using 2023 and 2024 da… view at source ↗

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8 extracted references · 3 canonical work pages

[1]

, " * write output.state after.block = add.period write newline

ENTRY address archive author booktitle chapter collaboration edition editor eid eprint howpublished institution isbn issn journal key month note number numpages organization pages publisher school series title type url doi volume year label extra.label sort.label short.list INTEGERS output.state before.all mid.sentence after.sentence after.block FUNCTION ...
[2]

write FUNCTION output.bibitem newline

" write FUNCTION output.bibitem newline " " " " * write cite write " " write newline "" before.all 'output.state := FUNCTION n.dashify 't := "" t empty not t #1 #1 substring "-" = t #1 #2 substring "--" = not "--" * t #2 global.max substring 't := t #1 #1 substring "-" = "-" * t #2 global.max substring 't := while if t #1 #1 substring * t #2 global.max su...
[3]

Acharya et al

S. Acharya et al. (ALICE), JINST 19, P05062 (2024), arXiv:2302.01238

arXiv 2024
[4]

Abelev et al

B. Abelev et al. (ALICE), J. Phys. G 41, 087002 (2014)

work page 2014
[5]

Dielectron and heavy-quark production in inelastic and high-multiplicity proton-proton collisions at $\sqrt{s}$ = 13 TeV

S. Acharya et al. (ALICE), Phys. Lett. B 788, 505 (2019), arXiv:1805.04407

work page Pith review arXiv 2019
[6]

Cacciari, M

M. Cacciari, M. Greco, P. Nason, M. Cacciari, S. Frixione, P. Nason, JHEP 9805 (1998) 007 and JHEP 0103 (2001) 006 (1998, 2001), hep-ph/9803400, hep-ph/0102134

arXiv 1998
[7]

Dielectron production in proton-proton collisions at $\sqrt{s}$ = 7 TeV

S. Acharya et al. (ALICE), JHEP 09, 064 (2018), arXiv:1805.04391

work page Pith review arXiv 2018
[8]

Acharya et al

S. Acharya et al. (ALICE) (2023), arXiv:2308.16704

arXiv 2023

Pith tools

Reviewed August 4, 2026 · model on record in the stance chip above.

[1] [1]

, " * write output.state after.block = add.period write newline

ENTRY address archive author booktitle chapter collaboration edition editor eid eprint howpublished institution isbn issn journal key month note number numpages organization pages publisher school series title type url doi volume year label extra.label sort.label short.list INTEGERS output.state before.all mid.sentence after.sentence after.block FUNCTION ...

[2] [2]

write FUNCTION output.bibitem newline

" write FUNCTION output.bibitem newline " " " " * write cite write " " write newline "" before.all 'output.state := FUNCTION n.dashify 't := "" t empty not t #1 #1 substring "-" = t #1 #2 substring "--" = not "--" * t #2 global.max substring 't := t #1 #1 substring "-" = "-" * t #2 global.max substring 't := while if t #1 #1 substring * t #2 global.max su...

[3] [3]

Acharya et al

S. Acharya et al. (ALICE), JINST 19, P05062 (2024), arXiv:2302.01238

arXiv 2024

[4] [4]

Abelev et al

B. Abelev et al. (ALICE), J. Phys. G 41, 087002 (2014)

work page 2014

[5] [5]

Dielectron and heavy-quark production in inelastic and high-multiplicity proton-proton collisions at $\sqrt{s}$ = 13 TeV

S. Acharya et al. (ALICE), Phys. Lett. B 788, 505 (2019), arXiv:1805.04407

work page Pith review arXiv 2019

[6] [6]

Cacciari, M

M. Cacciari, M. Greco, P. Nason, M. Cacciari, S. Frixione, P. Nason, JHEP 9805 (1998) 007 and JHEP 0103 (2001) 006 (1998, 2001), hep-ph/9803400, hep-ph/0102134

arXiv 1998

[7] [7]

Dielectron production in proton-proton collisions at $\sqrt{s}$ = 7 TeV

S. Acharya et al. (ALICE), JHEP 09, 064 (2018), arXiv:1805.04391

work page Pith review arXiv 2018

[8] [8]

Acharya et al

S. Acharya et al. (ALICE) (2023), arXiv:2308.16704

arXiv 2023