arxiv: 2605.05565 · v1 · submitted 2026-05-07 · ✦ hep-ph · nucl-th

Squeezed spectra and back-to-back correlations of protons and antiprotons at RHIC energies

Yong Zhang This is my paper

Pith reviewed 2026-05-08 08:40 UTC · model grok-4.3

classification ✦ hep-ph nucl-th

keywords in-medium mass modificationproton antiproton correlationsback-to-back correlationsRHIC energiesyield ratiosource time distributionGaussian source modelfermion back-to-back correlation

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The pith

In-medium mass modification enhances the antiproton-to-proton yield ratio and raises the chance of detecting back-to-back correlations in proton-antiproton pairs at RHIC.

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

The paper first constrains the possible range of in-medium mass modifications for protons and antiprotons by matching theoretical calculations to measured transverse momentum spectra and the yield ratio of antiprotons to protons. It then uses a Gaussian source model that includes radial flow to predict the fermion back-to-back correlations of proton-antiproton pairs. The predicted correlation signal depends strongly on the form of the source time distribution, producing a high-momentum peak for a Lorentzian distribution and a low-momentum peak for an alpha-stable Levy distribution. The mass modification increases the antiproton-to-proton ratio, which in turn makes events with larger ratios more likely to show a clear back-to-back correlation signal. This approach suggests a way to observe in-medium effects through correlation measurements.

Core claim

The study shows that in-medium mass modification can be constrained using transverse momentum spectra and the pbar/p yield ratio at RHIC energies. Within a Gaussian source model with radial flow, the fermion back-to-back correlation of p pbar pairs exhibits strong sensitivity to the source time distribution, with Lorentzian forms giving pronounced high-momentum signals and alpha-stable Levy forms giving marked low-momentum signals. The modification enhances the yield ratio, implying that events with larger pbar/p ratios have a significantly higher probability of exhibiting a detectable fBBC signal.

What carries the argument

A Gaussian source model incorporating radial flow and in-medium mass modification, used to calculate fermion back-to-back correlations (fBBC) for proton-antiproton pairs, with source time distributions modeled as Lorentzian or alpha-stable Levy forms.

If this is right

The in-medium mass modification range is narrowed by fitting to experimental spectra and yield ratios.
fBBC signals appear at high momentum for Lorentzian time distributions.
fBBC signals appear at low momentum for alpha-stable Levy time distributions.
Events with higher pbar/p ratios are more likely to display detectable fBBC signals.

Where Pith is reading between the lines

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

Measurements of fBBC momentum dependence could help distinguish between different source time distribution models in heavy-ion collisions.
This correlation technique might be extended to other particle-antiparticle pairs to probe in-medium properties.
If confirmed, it offers an alternative experimental handle on mass modifications beyond direct yield measurements.

Load-bearing premise

The Gaussian source model with radial flow and the specific Lorentzian or alpha-stable Levy forms accurately describe the emission process and dynamics for protons and antiprotons in RHIC collisions.

What would settle it

Experimental data on the momentum dependence of proton-antiproton back-to-back correlations at RHIC that fails to show the predicted high-momentum or low-momentum signals corresponding to the assumed source time distributions, or spectra and yield ratios inconsistent with the constrained mass modification.

Figures

Figures reproduced from arXiv: 2605.05565 by Yong Zhang.

**Figure 1.** Figure 1: FIG. 1: (Color online) The transverse momentum spectra of pr view at source ↗

**Figure 2.** Figure 2: FIG. 2: (Color online) The left panel shows the fBBC strength view at source ↗

**Figure 3.** Figure 3: FIG. 3: (Color online) The left panel plots the transverse mo view at source ↗

**Figure 4.** Figure 4: FIG. 4: (Color online) Simulated fBBC strengths ( view at source ↗

read the original abstract

This study constrains the range of in-medium mass modification through a comparison of theoretical calculations with experimental transverse momentum spectra and the yield ratio {\bar{p}}/p of protons and antiprotons. Based on the constrained range and a Gaussian source model with radial ow, the theoretical predictions for the fermion back-to-back correlation (fBBC) of p{\bar{p}} pairs at RHIC energies are presented. The results reveal a strong sensitivity of the fBBC signal to the assumed source time distribution: a Lorentzian form generates a pronounced high-momentum signal, whereas an {\alpha}-stable L\'evy form leads to a marked low-momentum signal. Moreover, the in-medium mass modification is shown to enhance the yield ratio {\bar{p}}/p. Therefore, events characterized by a larger {\bar{p}}/p ratio are predicted to have a significantly higher probability of exhibiting a detectable fBBC signal. This study may propose a promising new direction for the experimental observation of this phenomenon

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.

Desk Editor's Note private letter to a colleague

The paper constrains in-medium mass shifts from spectra and yield ratios then predicts that higher pbar/p events are likelier to show fBBC, but the momentum dependence reverses between Lorentzian and Levy time distributions.

read the letter

The one thing to know is that this work ties in-medium proton mass shifts to an increased antiproton-to-proton yield ratio and then claims that events with larger ratios should show a clearer fermion back-to-back correlation signal. The fBBC momentum dependence also flips sign depending on whether the source time profile is taken as Lorentzian or as an alpha-stable Levy distribution. The new element is the specific prediction that mass modification enhances the yield ratio, which in turn raises the chance of detecting fBBC, combined with the strong sensitivity to the time distribution. Earlier papers on fBBC probably did not make this event-selection link or test these two time forms side by side after data constraints. The paper does well by first constraining the mass modification range against measured spectra and yield ratios before making the fBBC forecasts. That step keeps the parameter range from being completely free. The main limitation is the heavy reliance on the assumed source model. A Gaussian with radial flow plus one of the two time distributions is used throughout, and the opposite behaviors for the two time choices mean the results are exploratory rather than definitive. If the time distribution is not known independently, the fBBC predictions cannot be taken as firm. The approach is circular by construction because the outputs follow from the fitted inputs, but the authors present it as a way to guide future measurements rather than a closed prediction. This paper is for specialists in relativistic heavy-ion physics who follow two-particle correlation studies. Someone looking for new experimental strategies around in-medium modifications would find it useful. It is not a broad-impact result, but the modeling is transparent enough that it merits referee attention. I recommend sending it for peer review. The calculations appear reproducible from the described setup, and the community can evaluate whether the sensitivity findings hold up under different source assumptions.

Referee Report

3 major / 1 minor

Summary. The paper constrains the range of in-medium mass modification for protons and antiprotons by comparing theoretical calculations to RHIC transverse momentum spectra and the measured pbar/p yield ratio. Using a Gaussian source model with radial flow, it then predicts the fermion back-to-back correlation (fBBC) signal for p pbar pairs at RHIC energies, showing that the signal depends strongly on the assumed source time distribution (Lorentzian vs. alpha-stable Levy) and that in-medium mass modification enhances the yield ratio, implying higher fBBC detection probability in events with larger pbar/p ratios.

Significance. If the source model and time distributions hold, the work proposes a practical experimental handle—event selection by yield ratio—to improve observability of fBBC and links in-medium mass effects to correlation observables. The explicit demonstration of qualitative sensitivity to the time-distribution form is a useful contribution for guiding future measurements.

major comments (3)

[Abstract] Abstract: the central claim that in-medium mass modification enhances the pbar/p ratio and thereby raises the probability of a detectable fBBC signal rests on parameters constrained from spectra and yield data together with an assumed Gaussian source plus radial flow; this chain is not independent of the input choices and reduces in part to the outputs of those fitted or chosen ingredients.
[Abstract] Abstract: the reported strong sensitivity of the fBBC momentum dependence to the source time distribution (Lorentzian yielding a high-momentum signal, alpha-stable Levy a low-momentum signal) is correctly identified, yet this qualitative reversal underscores that the predictions are exploratory rather than robust; the manuscript must justify why either distribution is preferred or provide quantitative uncertainty bands before the event-selection recommendation can be considered load-bearing.
[Abstract] The weakest assumption is that the Gaussian source with radial flow plus the specific Lorentzian or Levy time forms accurately represent the emission process; without additional cross-checks against other observables or alternative source parametrizations, the link from mass modification to fBBC probability remains conditional on this model choice.

minor comments (1)

The abstract would be clearer if it stated the specific RHIC collision energies and the numerical range obtained for the in-medium mass modification after the fit to spectra and yield ratios.

Simulated Author's Rebuttal

3 responses · 1 unresolved

We are grateful to the referee for the thorough review and valuable suggestions. We have addressed the major comments point by point in the responses below. Revisions have been made to the manuscript to clarify assumptions, provide additional justifications, and discuss limitations, thereby improving the presentation of our results.

read point-by-point responses

Referee: [Abstract] Abstract: the central claim that in-medium mass modification enhances the pbar/p ratio and thereby raises the probability of a detectable fBBC signal rests on parameters constrained from spectra and yield data together with an assumed Gaussian source plus radial flow; this chain is not independent of the input choices and reduces in part to the outputs of those fitted or chosen ingredients.

Authors: We acknowledge that the predictions depend on the fitted parameters and the source model. However, the range of in-medium mass modification is constrained by direct comparison to RHIC data on transverse momentum spectra and the measured pbar/p yield ratio, making it data-driven. The Gaussian source with radial flow is a standard choice in the literature for modeling emission in heavy-ion collisions. In the revised manuscript, we have added a new subsection discussing the parameter constraints and performed a limited sensitivity analysis to source parameters, confirming that the enhancement of the pbar/p ratio persists. revision: partial
Referee: [Abstract] Abstract: the reported strong sensitivity of the fBBC momentum dependence to the source time distribution (Lorentzian yielding a high-momentum signal, alpha-stable Levy a low-momentum signal) is correctly identified, yet this qualitative reversal underscores that the predictions are exploratory rather than robust; the manuscript must justify why either distribution is preferred or provide quantitative uncertainty bands before the event-selection recommendation can be considered load-bearing.

Authors: The demonstration of sensitivity to the time distribution is deliberate, as it shows that the detailed momentum dependence of the fBBC signal requires careful modeling of the emission time profile. Both distributions are used in femtoscopy analyses: the Lorentzian for simple exponential time dependence and the Levy for more complex, possibly anomalous, emission. We have revised the abstract and main text to justify their use with references to prior works and to present results for both forms. The event-selection recommendation is based on the robust finding that in-medium mass modification enhances the pbar/p yield ratio independently of the time distribution; thus, events with larger ratios are expected to have higher fBBC visibility. We note the exploratory aspect in the revised discussion but maintain that this provides a useful guide for experiments. revision: yes
Referee: [Abstract] The weakest assumption is that the Gaussian source with radial flow plus the specific Lorentzian or Levy time forms accurately represent the emission process; without additional cross-checks against other observables or alternative source parametrizations, the link from mass modification to fBBC probability remains conditional on this model choice.

Authors: We concur that the source model is an important assumption. The Gaussian source with radial flow is selected because it provides a good description of the single-particle spectra and is consistent with hydrodynamic expectations at RHIC. References to supporting studies using similar models for other observables have been added. We have also included a dedicated paragraph in the conclusions acknowledging the conditional nature of the fBBC predictions on the source parametrization and suggesting future work with alternative models. However, performing new cross-checks with additional observables is beyond the scope of this paper. revision: partial

standing simulated objections not resolved

Performing dedicated cross-checks against other observables or alternative source parametrizations to further validate the model assumptions.

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper first constrains the range of in-medium mass modification by direct comparison of theoretical calculations to measured transverse momentum spectra and the experimental pbar/p yield ratio. It then adopts a Gaussian source model with radial flow plus one of two parametric source time distributions (Lorentzian or alpha-stable Levy) to compute the fBBC signal as a forward prediction for a distinct observable. Because the fBBC momentum dependence is shown to flip qualitatively between the two time-distribution choices, the calculation functions as a sensitivity study rather than a tautological output forced by the fitted inputs. No equations reduce by construction to the spectra or ratio data, no self-citation chain is invoked to justify uniqueness, and no ansatz is smuggled in; the derivation chain therefore remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard heavy-ion physics models (Gaussian source with radial flow) and data-constrained mass modification range, with no new entities postulated.

free parameters (2)

range of in-medium mass modification
Constrained through comparison of theoretical calculations with experimental spectra and yield ratio.
source time distribution parameters
Chosen as Lorentzian or alpha-stable Levy forms for the Gaussian source model.

axioms (1)

domain assumption Gaussian source model with radial flow accurately describes particle emission in RHIC collisions
Invoked to generate theoretical predictions for fBBC.

pith-pipeline@v0.9.0 · 5465 in / 1467 out tokens · 63071 ms · 2026-05-08T08:40:49.989639+00:00 · methodology

discussion (0)

Reference graph

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Here, m∗ ̸= m0 indicates that the mass of the fermions (antifermions) has been modiﬁed due to their interaction with the medium

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