Towards a precise measurement of the $\Lambda_c^+/D^0$ ratio at RHIC

Joseph D. Osborn

REVIEW 2 major objections 3 minor 7 references

Towards a precise measurement of the $\Lambda_c^+/D^0$ ratio at RHIC

T0 review · 2 major / 3 minor · reviewed 2026-08-04 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

Pith's one-line read sPHENIX's first p+p data show a Λ_c+ invariant-mass peak at about 3σ, putting the first RHIC Λ_c+/D0 ratio within reach.

desk verdict Genuine first look at Λc+ in p+p at RHIC, but the forward-looking precision projection rests on an unstated scaling assumption and should be read as a status report, not a measurement. read the letter →

arxiv 2509.10772 v1 pith:7H3LIQ5P submitted 2025-09-13 nucl-ex hep-ex

Joseph D. Osborn This is my paper

classification nucl-exhep-ex

keywords Λ_c+baryonD0mesonheavy-flavorhadronizationp+pcollisionsRHICsPHENIXstreamingreadoutopenheavyflavor

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

These proceedings report that the sPHENIX tracking system, running in streaming readout, has reconstructed the Λ_c+ baryon in p+p collisions at √s=200 GeV for the first time at RHIC, with a peak at roughly 3σ significance in about one hour of early-calibration data. The same sample yields a D0 peak at 5.6σ with 2484 candidates, and a constant K0s reconstruction efficiency across beam crossings, indicating the streaming readout chain works. The paper argues that the full Run-24 streamed sample of 2.9 pb−1 of unbiased p+p collisions will support the first measurement of the Λ_c+/D0 ratio at RHIC, the missing vacuum baseline needed to interpret baryon-vs-meson hadronization in heavy-ion collisions. This matters because no p+p baseline exists at RHIC energies and current Monte Carlo generators disagree widely on the ratio.

What carries the argument

The central mechanism is the hybrid streaming readout of the four sPHENIX tracking detectors (MVTX pixel vertex detector, INTT silicon strip, TPC, and TPOT micromegas), which records unbiased p+p collisions at ~200 kHz without a hardware trigger for low-pT heavy-flavor hadrons. Tracks are reconstructed with the Acts Kalman filter and resonances are formed with KFParticle; the invariant-mass reconstruction of Λ_c+ → pKπ and D0 → Kπ carries the argument. The constant K0s → π+π− yield across beam crossings is the diagnostic that the streamed data are unbiased and that reconstruction efficiency is stable, which is what licenses the projection to the full dataset.

What would settle it

Compare the Λ_c+ invariant-mass peak in the full 2.9 pb−1 sample with the one-hour calibration result: if the yield does not scale roughly with luminosity (from 101 candidates toward ~10^4 with unchanged selection) or the peak width at ~3.6 MeV degrades, the scaling projection is wrong.

Watch

Extended reading notes

Core claim

On its own terms, the paper's claim is that the sPHENIX detector and streaming-readout tracking chain can reconstruct both Λ_c+ → pKπ and D0 → Kπ in p+p at √s=200 GeV, and that the first peaks are already visible in a single hour of calibration data: the D0 at about 5.6σ and the Λ_c+ at about 3σ, with mass resolutions around 2.1 MeV and 3.6 MeV respectively. The Λ_c+ peak, shown in Fig. 3 (left), is reported as the first such measurement in p+p at RHIC. The paper further projects that with the full 2.9 pb−1 streamed sample, the Λ_c+/D0 ratio can be measured with the precision shown in Fig. 3 (right), providing the missing p+p baseline.

Load-bearing premise

The projection assumes that the one-hour, early-calibration sample represents the full Run-24 dataset: tracking efficiency, mass resolution, and background levels scale linearly with integrated luminosity to 2.9 pb−1, with no degradation from the uncorrected TPC space-charge distortions.

Editorial extensions

If this is right

The full Run-24 streamed p+p sample (2.9 pb−1) is expected to yield the first Λ_c+/D0 ratio measurement at RHIC, with statistical precision comparable to the projection in Fig. 3 (right).
The ratio will provide the missing vacuum baseline for interpreting baryon-to-meson enhancement in Au+Au collisions at RHIC energies.
The measurement will discriminate between current Monte Carlo hadronization models, which give widely different Λ_c+/D0 predictions at these energies.
The success of streaming readout for heavy-flavor reconstruction opens the same analysis path for the 7.2 nb−1 Au+Au dataset sPHENIX is collecting in 2025.

Reading between the lines

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

If the one-hour signal scales with integrated luminosity, the full sample should contain on the order of 10^4 Λ_c+ candidates; comparing that yield with the projection is a direct check of the scaling assumption, independent of any ratio extraction.
The same streaming-data analysis could be applied to the 2025 Au+Au dataset to give the in-medium Λ_c+/D0 ratio at matching pT, turning the p+p baseline into a direct medium comparison rather than a standalone number.
Because the paper's K0s efficiency is flat across beam crossings, the streamed sample is unbiased with respect to the hardware trigger; this implies the final measurement can reach low pT where baryon/meson differences are largest, a regime the paper motivates but does not quantify.
The projection uses no explicit systematic error budget; a reader should expect the final ratio paper to add feed-down and efficiency-correction uncertainties that could widen the Fig. 3 (right) bands.

Share X Bluesky LinkedIn Reddit HN

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

Take it for what it is: a status report from a collaboration that just got its tracking chain working. The two genuinely new experimental bits are the first Λc+ invariant-mass peak in p+p at RHIC at about 3 sigma and the first sPHENIX D0 peak at 5.6 sigma. The peaks are internally sane—D0 mass 1862.6±2.1 MeV, Λc+ mass 2285±3.6 MeV, yields consistent with stated significances—and the K0s vs beam-crossing plot shows streaming readout is working. The missing p+p Λc+/D0 baseline at RHIC is a real gap, and the generators disagree wildly, so even a modest measurement has physics value. Credit goes to the collaboration for stating plainly that the first calibrations are limited by TPC space-charge distortions and that the ratio measurement is still a projection.

The soft spot is exactly where the stress-test note points. Figure 3 (right) says the projection is 'based on the total integrated luminosity' but gives no scaling law, no efficiency evolution, no systematics. The peaks come from one hour of early-calibration data. If the full 2.9 pb^-1 dataset under real running conditions has somewhat worse momentum resolution—which the paper itself says is dominated by space-charge distortions—the per-event significance drops and a simple sqrt(N) projection overstates what the full dataset will deliver. A 12.8 MeV width growing to 15 MeV is enough to matter. This isn't circular reasoning; the yields are measured and the projection is an explicit scale-up of them. It is just an unstated representativeness assumption.

There is also no run-by-run stability check, and the Λc+ peak at 3 sigma is marginal. That is fine for a proceedings, but the paper's headline promise—a precise Λc+/D0 ratio—should be read as conditional. The references are appropriate: CLEO and ALICE for the physics, the ACTS papers for the software. No citation inflation.

Who should read this: heavy-ion experimentalists and hadronization folks tracking sPHENIX commissioning. It is not a physics result yet. I would send it to peer review as a proceedings/status note, and require the authors to either spell out the scaling assumptions and uncertainties or soften the projection. I would not cite it as evidence of a measured ratio, but I would cite it as the first demonstration of Λc+ reconstruction in p+p at RHIC.

Referee Report

2 major / 3 minor

Summary. The paper reports the status of the first open heavy-flavor reconstruction in sqrt(s)=200 GeV p+p collisions with the sPHENIX streaming readout. Using approximately one hour of early-calibration data, it shows a K0s invariant-mass peak that is stable across beam crossings, a D0 -> K pi peak at 5.6 sigma with yield 2484 +/- 44 and mean 1862.6 +/- 2.1 MeV, and a Lambda_c+ -> p K pi peak at about 3 sigma with yield 101 +/- 33 and mean 2285 +/- 4 MeV. It then projects the (Lambda_c+ + c.c.)/(D0 + c.c.) ratio for the full Run-24 sample of 2.9 pb^-1. The abstract claims this is the first Lambda_c+ invariant-mass peak in p+p at RHIC.

Significance. If the results hold, the paper demonstrates that the sPHENIX tracking and streaming-readout chain can reconstruct charm hadrons in p+p at RHIC energies, opening the way to the first Lambda_c+/D0 baseline measurement at RHIC. The internal consistency is good: the D0 mass agrees with the PDG value, the yields are internally consistent, and the K0s stability is a useful streaming-readout validation. The paper is commendably explicit about the dominant current limitation, TPC space-charge distortions. The main quantitative promise, however, rests on an extrapolation that is not documented.

major comments (2)

[Section 3, Fig. 3 (right)] The projection of the Lambda_c+/D0 ratio for the full Run-24 dataset is described only as 'based on the total integrated luminosity.' No scaling law, reconstruction-efficiency evolution, background scaling, or systematic uncertainties are given. The one-hour sample is explicitly an early-calibration sample dominated by TPC space-charge distortion uncertainties. If the mass resolution or tracking efficiency changes as calibration improves or as running conditions vary, the projected significance may not scale as sqrt(integrated luminosity). Please either supply the scaling details and a run-by-run stability check, or reframe the figure as an illustration with caveats.
[Section 3, Fig. 3 (left)] The claim of a 'first measurement' of the Lambda_c+ invariant-mass peak at 3 sigma significance is load-bearing, but the paper does not define how the significance is computed (e.g., likelihood ratio, fitted yield over background error), nor whether systematic variations of the fit model (background shape, binning, mass resolution) are included. The fit mean and width are consistent with expectations, but the quoted mass uncertainty and the 3 sigma significance need a stated procedure to support the 'measurement' claim. Add the significance definition and a check of fit-model dependence.

minor comments (3)

[Throughout] There are several formatting and wording issues: the Lambda_c+ symbol is occasionally broken as 'Lambda + c' in the header; 'the first initial calibrations' in Sec. 3 is redundant. Please use proper LaTeX and rephrase.
[Fig. 3 (right) label] The label 'p+p str. -12.9 pb' is unclear. Define 'str.' (streaming?) and explain the negative sign, or use a standard notation for the integrated luminosity.
[References] For a baseline claim, the paper could briefly mention existing RHIC heavy-ion Lambda_c measurements (e.g., STAR in Au+Au) to better contextualize the novelty of the p+p measurement.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the D0 and Lambda_c+ peaks are direct measured reconstructions, and the Run-24 projection is an explicit luminosity scaling of the one-hour sample, not a disguised input.

full rationale

The paper's central evidence is a set of measured invariant-mass peaks: the D0 peak at 5.6 sigma (yield 2484) and the Lambda_c+ peak at ~3 sigma (yield 101), with K0s stability across beam crossings shown as a streaming-readout check. These are direct reconstructions from data, not outputs of a fitted model that is then relabeled as a prediction. The only forward-looking element is the Figure 3 (right) projection, which the text explicitly states is 'based on the total integrated luminosity from the 2024 streaming readout data collection period' (Sec. 3). That is a transparent statistical scaling of measured yields, not a hidden reuse of the same quantity as an independent prediction. No equation in the paper defines the projection in terms of the measured ratio in a way that is disguised as a derivation; the scaling assumption is stated, albeit without explicit systematic-error propagation. The self-citations (Refs. [5,6] for ACTS implementation and Ref. [7] for public results) are implementation and data references, not load-bearing uniqueness theorems or ansatz sources. The acknowledged TPC space-charge calibration limitation affects the achievable momentum resolution and therefore the projected precision, but that is an uncertainty/correctness risk rather than a circularity. There is no self-definitional step, no fitted input renamed as a prediction, and no imported uniqueness claim. Accordingly the circularity score is 0.

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

The central feasibility claim rests on two measured peaks and the K0s stability curve, plus four assumptions: standard heavy-quark production physics, sample unbiasedness, correctness of the external software stack, and representativeness of the calibration sample for the projection. No new particles, forces, or conserved quantities are introduced. The softest uncharged input is the projection scaling, which is not derived anywhere in the text.

free parameters (3)

D0 peak fit parameters (mean, width, yield) = mean 1862.6 +/- 2.1 MeV, width 10.5 +/- 1.7 MeV, yield 2484 +/- 44
Gaussian plus background fit to the D0 invariant mass peak, Fig. 2 (right). These are measurement outputs, not model inputs, but they seed the sensitivity projection.
Lambda_c+ peak fit parameters (mean, width, yield) = mean 2285 +/- 3.6 MeV, width 12.8 +/- 4 MeV, yield 101 +/- 33
Fit to the Lambda_c+ invariant mass peak, Fig. 3 (left). The ~3 sigma yield is the basis for the projected ratio measurement in Fig. 3 (right).
Projection scale from ~1 hour sample to full Run-24 streaming dataset = not stated in text
The Fig. 3 (right) projection is described only as 'based on the total integrated luminosity'; the assumed scaling of yields, backgrounds, and efficiency is not specified, so the projected uncertainties cannot be independently reproduced.

assumptions (4)

domain assumption Charm quarks are produced in hard partonic scattering early in the collision and therefore experience the full hadronization process
Invoked in the Introduction to motivate the measurement; standard QCD factorization assumption for heavy flavor, not derived in the paper.
domain assumption The streaming readout sample is an unbiased p+p sample at 200 GeV
Central to yield scaling from the streamed data; partially supported by Fig. 2 (left), which shows approximately constant K0s reconstruction efficiency versus beam crossing.
domain assumption The ACTS tracking and KFParticle packages reconstruct tracks and decays correctly under sPHENIX conditions
The reconstruction chain is taken from Refs. [5,6] without in-paper validation of software assumptions; the author is a co-author of Ref. [5].
ad hoc to paper The ~1 hour calibration sample is representative of the full Run-24 dataset for signal and background scaling
The projection in Fig. 3 (right) requires yields to scale with luminosity under unchanged efficiency and resolution; the paper does not defend this and states that initial calibrations are limited by TPC space charge distortion knowledge.

how reviews work

0 comments

Cite this review

Pith. "Pith review of Towards a precise measurement of the $\Lambda_c^+/D^0$ ratio at RHIC." pith.science (2026). https://pith.science/paper/7H3LIQ5P

@misc{pith2026250910772,
  author       = {Pith},
  title        = {Pith review of: Towards a precise measurement of the $\Lambda_c^+/D^0$ ratio at RHIC},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/7H3LIQ5P}},
  note         = {Machine review of arXiv:2509.10772}
}

abstract

sPHENIX is a next-generation experiment at RHIC for jet and heavy-flavor physics which was fully commissioned during 2023 and 2024. Using its novel streaming-readout-capable, precision tracking system, sPHENIX collected 100 billion unbiased $p$$+$$p$ collisions, and a further sample of minimum-bias Au-Au collisions, in Run-24. A key measurement of the sPHENIX heavy flavor physics program is the comparison of $\Lambda_c^+$ to $D^0$ differential yields in both Au+Au and $p$$+$$p$ collisions, which probes questions related to the hadronization of heavy-flavor baryons compared to mesons in the Quark-Gluon Plasma medium and in vacuum. At RHIC energies, there is no previous measurement of the $\Lambda_c^+/D^0$ baseline in $p$$+$$p$ collisions, modern Monte Carlo event generators give widely different predictions, and the ratio in Au+Au is only poorly known. These proceedings present the status of measurement from sPHENIX of the $\Lambda_c^+/D^0$ ratio in $p$$+$$p$ collisions.

Figures

Figures reproduced from arXiv: 2509.10772 by the authors.

**Figure 1.** The dE/dx distribution as a function of particle momentum times charge, showing the dE/dx performance of the TPC with initial calibrations. sPHENIX was constructed in the years 2020-2022 and was commissioned using Au+Au beams in 2023 and p+p collisions in 2024 at √ s = 200 GeV. After commissioning, sPHENIX collected a large sample of unbiased p+p collisions using its unique streaming readout capabilities, described… view at source ↗

**Figure 2.** (left) The invariant mass of reconstructed K 0 s → π +π − decays as a function of streaming readout beam crossing number in √ s = 200 GeV p+p collisions. (right) The invariant mass of reconstructed D 0 → πK decays in ∼1 hour of data with initial calibrations. fraction is limited only by the total data volume readout from the TPC to storage, where the limitation comes from the available storage. The streaming mode o… view at source ↗

**Figure 3.** (left) The first measurement of the Λ + c → pKπ baryon in p+p collisions at RHIC energies at 3σ significance. (right) Projections for measurements of the Λ + c /D 0 ratio from the sPHENIX p+p data collected in 2024. A rich heavy flavor physics program at the sPHENIX experiment has begun with the first physics quality unbiased p+p data at √ s =200 GeV data collected in 2024. The streaming tracking detectors and recon… view at source ↗

Discussion (0). Sign in to comment.

Reference graph

Works this paper leans on

7 extracted references · 2 canonical work pages

[1]

Adare et al

A. Adare et al. (PHENIX collaboration), An Upgrade Proposal from the PHENIX Col- laboration (2015),1501.06197. https://arxiv.org/abs/1501.06197

arXiv 2015
[2]

Artuso et al

M. Artuso et al. (CLEO collaboration), Charm meson spectra ine +e− annihilation at 10.5-GeV c.m.e., Phys. Rev. D70, 112001 (2004). 10.1103/PhysRevD.70.112001

doi:10.1103/physrevd.70.112001 2004
[3]

Acharya et al

S. Acharya et al. (ALICE collaboration),Λ + c production in pp collisions at √s= 7 TeV and in p-Pb collisions at √sNN =5.02 TeV, JHEP04, 108 (2018). 10.1007/JHEP04(2018)108

doi:10.1007/jhep04(2018)108 2018
[4]

Acharya et al

S. Acharya et al. (ALICE collaboration),Λ + c production in Pb-Pb collisions at √sNN = 5.02 TeV, Phys. Lett. B793, 212 (2019). 10.1016/j.physletb.2019.04.046

work page doi:10.1016/j.physletb.2019.04.046 2019
[5]

Osborn, A.D

J.D. Osborn, A.D. Frawley, J. Huang, S. Lee, H.P. Da Costa, M. Peters, C. Pinkenburg, C. Roland, H. Yu, Implementation of ACTS into sPHENIX Track Reconstruction, Com- put. Softw. Big Sci.5, 23 (2021). 10.1007/s41781-021-00068-w

work page doi:10.1007/s41781-021-00068-w 2021
[6]

Ai et al., A Common Tracking Software Project, Comput

X. Ai et al., A Common Tracking Software Project, Comput. Softw. Big Sci.6, 8 (2022). 10.1007/s41781-021-00078-8

doi:10.1007/s41781-021-00078-8 2022
[7]

sPHENIX Public Results, https://www.sphenix.bnl.gov/index.php/PublicResults, ac- cessed: 2025-08-31

2025

Pith tools

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

[1] [1]

Adare et al

A. Adare et al. (PHENIX collaboration), An Upgrade Proposal from the PHENIX Col- laboration (2015),1501.06197. https://arxiv.org/abs/1501.06197

arXiv 2015

[2] [2]

Artuso et al

M. Artuso et al. (CLEO collaboration), Charm meson spectra ine +e− annihilation at 10.5-GeV c.m.e., Phys. Rev. D70, 112001 (2004). 10.1103/PhysRevD.70.112001

doi:10.1103/physrevd.70.112001 2004

[3] [3]

Acharya et al

S. Acharya et al. (ALICE collaboration),Λ + c production in pp collisions at √s= 7 TeV and in p-Pb collisions at √sNN =5.02 TeV, JHEP04, 108 (2018). 10.1007/JHEP04(2018)108

doi:10.1007/jhep04(2018)108 2018

[4] [4]

Acharya et al

S. Acharya et al. (ALICE collaboration),Λ + c production in Pb-Pb collisions at √sNN = 5.02 TeV, Phys. Lett. B793, 212 (2019). 10.1016/j.physletb.2019.04.046

work page doi:10.1016/j.physletb.2019.04.046 2019

[5] [5]

Osborn, A.D

J.D. Osborn, A.D. Frawley, J. Huang, S. Lee, H.P. Da Costa, M. Peters, C. Pinkenburg, C. Roland, H. Yu, Implementation of ACTS into sPHENIX Track Reconstruction, Com- put. Softw. Big Sci.5, 23 (2021). 10.1007/s41781-021-00068-w

work page doi:10.1007/s41781-021-00068-w 2021

[6] [6]

Ai et al., A Common Tracking Software Project, Comput

X. Ai et al., A Common Tracking Software Project, Comput. Softw. Big Sci.6, 8 (2022). 10.1007/s41781-021-00078-8

doi:10.1007/s41781-021-00078-8 2022

[7] [7]

sPHENIX Public Results, https://www.sphenix.bnl.gov/index.php/PublicResults, ac- cessed: 2025-08-31

2025