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arxiv: 2606.12158 · v2 · pith:3ZMAPCJKnew · submitted 2026-06-10 · ✦ hep-ex · hep-ph

Hidden-sectors search and probe of discrete symmetries at the REDTOP experiment

The REDTOP COllaboration This is my paper

Pith reviewed 2026-06-27 07:46 UTC · model grok-4.3

classification ✦ hep-ex hep-ph
keywords eta decayshidden sectorsbeyond standard modelCP violationT invariancelepton universalitytransition form factorsmuon g-2
0
0 comments X

The pith

The proposed facility collecting 10^14 eta mesons enables searches for hidden sector physics and tests of discrete symmetries.

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

This paper evaluates how a proposed facility collecting O(10^14) eta and O(10^12) eta-prime mesons can search for physics beyond the standard model. The studies assess sensitivity to new particles coupling through the vector, scalar, axion-like and heavy lepton portals. The statistics also enable precise tests of charge parity and time reversal invariance as well as lepton universality. They further improve the eta and eta-prime transition form factors needed for accurate calculations of the muon anomalous magnetic moment. This scale is much larger than previous experiments which collected around 10^9 eta events.

Core claim

The proposed facility targets O(10^14) eta and O(10^12) eta-prime mesons, enabling broad searches for physics beyond the Standard Model through the vector, scalar, axion-like, and heavy lepton portals, while also allowing precise tests of CP and T invariance and lepton universality and improving the eta and eta-prime transition form factors crucial for the hadronic light-by-light contribution to the muon anomalous magnetic moment.

What carries the argument

The high event rates of eta and eta-prime meson decays, which act as sensitive probes for new physics because their decay dynamics are strongly constrained as nearly Goldstone bosons.

If this is right

  • Searches for dark photons via the vector portal reach new sensitivity levels.
  • Higgs-mixing scalars can be probed via the scalar portal.
  • Axion-like particles become accessible via the axion-like portal.
  • Heavy leptons can be searched via the heavy lepton portal.
  • Precision tests of CP and T invariance and lepton universality become possible.

Where Pith is reading between the lines

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

  • The improved form factors could help resolve tensions in the calculation of the muon g-2 if they are a limiting factor.
  • Such an experiment could serve as a complement to direct searches at colliders for hidden sector particles.
  • The portal framework allows systematic coverage of different types of new physics couplings.

Load-bearing premise

The sensitivity projections assume the experimental setup achieves the required event rates and background rejection without significant systematic uncertainties dominating.

What would settle it

If background rejection proves insufficient or the number of collected eta events falls well below 10^14, the claimed sensitivities for rare processes would not hold.

read the original abstract

The $\eta$ and $\eta^{\prime}$ mesons are nearly unique in the particle universe since they are nearly Goldstone bosons, and their decay dynamics are strongly constrained. While earlier experiments collected samples of order $\sim 10^{9}$ $\eta$, the proposed REDTOP (Rare Eta Decays To Observe Physics Beyond the Standard Model) facility targets $\mathcal{O}(10^{14})$ $\eta$ and $\mathcal{O}(10^{12})$ $\eta'$, enabling broad searches for physics beyond the Standard Model. In this work, we present studies evaluating REDTOP sensitivity to processes that couple the Standard Model to New Physics through four portals: the Vector (dark photon), the Scalar (Higgs-mixing), the Axion-like, and the Heavy Lepton. In parallel, the proposed statistics allow precise tests of $CP$ and $T$ invariance and lepton universality and improve determinations of the $\eta/\eta'$ transition form factors, which are crucial inputs to the hadronic light-by-light contribution to the muon anomalous magnetic moment $(g-2)_\mu$.

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

2 major / 0 minor

Summary. The manuscript proposes the REDTOP facility to collect O(10^14) η and O(10^12) η' events, enabling searches for BSM physics through the Vector (dark photon), Scalar (Higgs-mixing), Axion-like, and Heavy Lepton portals, together with precision tests of CP and T invariance, lepton universality, and improved η/η' transition form factors relevant to (g-2)_μ.

Significance. If the projected event samples and background rejection can be realized, the statistics would represent a two-to-five order-of-magnitude advance over existing η/η' data sets and could meaningfully constrain hidden-sector models while supplying improved inputs to the hadronic light-by-light contribution to (g-2)_μ. The manuscript, however, supplies no supporting calculations, efficiencies, or background models, so the significance cannot yet be evaluated.

major comments (2)
  1. [Abstract] Abstract: the statement that 'studies evaluating REDTOP sensitivity to processes that couple the Standard Model to New Physics through four portals' have been performed is unsupported; no production rates, luminosities, efficiencies, background models, or systematic-error budgets are shown, rendering the claimed reaches for portal-mediated rare decays unverifiable.
  2. [Abstract] Abstract: the central claim that O(10^14) η statistics will enable the listed symmetry tests and form-factor improvements assumes that systematic uncertainties remain sub-dominant, yet no error analysis or background-rejection study is provided to justify this assumption.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and constructive comments. We agree that the abstract requires revision to align more closely with the content of the manuscript, which is a high-level proposal outlining projected capabilities rather than a detailed sensitivity analysis with full simulations.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the statement that 'studies evaluating REDTOP sensitivity to processes that couple the Standard Model to New Physics through four portals' have been performed is unsupported; no production rates, luminosities, efficiencies, background models, or systematic-error budgets are shown, rendering the claimed reaches for portal-mediated rare decays unverifiable.

    Authors: We agree that the phrasing in the abstract implies a level of detailed supporting calculations that is not present in the manuscript. The projections are based on the targeted event yields and order-of-magnitude assumptions about acceptance and efficiency. We will revise the abstract to state that the reaches are estimated from the projected statistics under standard assumptions for detector performance, without claiming that full studies with production rates, background models, or systematic budgets have been completed in this work. revision: yes

  2. Referee: [Abstract] Abstract: the central claim that O(10^14) η statistics will enable the listed symmetry tests and form-factor improvements assumes that systematic uncertainties remain sub-dominant, yet no error analysis or background-rejection study is provided to justify this assumption.

    Authors: The referee correctly identifies that the manuscript does not provide an error analysis or background-rejection study to support the assumption that systematics remain sub-dominant. The large statistics are presented as the primary enabling factor, but control of systematics is indeed essential. We will revise the abstract to qualify the expected improvements as contingent on successful management of systematic uncertainties through the experimental design, and we will add a brief discussion in the main text on the detector features intended to suppress backgrounds and control systematics. revision: yes

Circularity Check

0 steps flagged

No circularity: forward-looking sensitivity projections with no derivations or self-referential fits

full rationale

The manuscript is a proposal paper presenting sensitivity estimates for rare decays and symmetry tests at a future facility. No equations, parameter fits, or derivations are described that reduce by construction to the paper's own inputs. No self-citations are invoked as load-bearing uniqueness theorems or ansatze. The content consists of projected reach statements based on assumed statistics, which are external benchmarks rather than tautological redefinitions. This matches the default expectation of no significant circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The abstract introduces no explicit free parameters, axioms, or invented entities; it relies on standard BSM portal models and experimental assumptions not detailed here.

pith-pipeline@v0.9.1-grok · 5716 in / 1134 out tokens · 26776 ms · 2026-06-27T07:46:56.476945+00:00 · methodology

discussion (0)

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