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arxiv: 2605.22670 · v1 · pith:MGICYCMDnew · submitted 2026-05-21 · ✦ hep-ex

Measurements of the absolute branching fractions of D⁰toγ bar K^(*0) and D⁰toγ φ

BESIII Collaboration This is my paper

Pith reviewed 2026-05-22 03:52 UTC · model grok-4.3

classification ✦ hep-ex
keywords branching fractionradiative decayD0 mesoncharm physicsCP asymmetryBESIII experimentvector meson
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The pith

The absolute branching fractions for the radiative decays D0 to gamma K*0 and D0 to gamma phi are measured for the first time using 20.3 fb^{-1} of data.

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

The paper establishes the first absolute measurements of the branching fractions for two radiative charm decays by analyzing electron-positron collision data collected at the charm threshold. A sample of 20.3 inverse femtobarns at 3.773 GeV is used to reconstruct the signal modes and normalize them against known D0 decays, yielding values with statistical significances of 26.8 sigma and 7.9 sigma. These rates test models of electromagnetic and strong interactions in the charm sector and provide a baseline for searches for new physics effects in flavor-changing neutral currents. The results match existing world averages and show a CP asymmetry consistent with zero in the first channel.

Core claim

The authors determine the absolute branching fraction of D0 to gamma bar K*0 to be (3.81 plus or minus 0.18 statistical plus or minus 0.20 systematic) times 10 to the minus 4 and that of D0 to gamma phi to be (2.51 plus or minus 0.44 statistical plus or minus 0.11 systematic) times 10 to the minus 5. The measurements are performed on a large sample of D0 D0-bar pairs produced in e plus e minus annihilation at the psi(3770) resonance, with efficiencies and backgrounds controlled through Monte Carlo simulation. Both results are stated to be consistent with prior world averages, and the CP asymmetry for the first mode is measured as minus 0.7 plus or minus 5.0 statistical plus or minus 4.1 syst

What carries the argument

Reconstruction and efficiency-corrected yield extraction of the radiative final states in a tagged D0 D0-bar sample at the charm threshold, normalized to the total number of D0 mesons determined from the integrated luminosity and known cross sections.

If this is right

  • The measured rates supply direct experimental input for calculations of radiative transitions in the charm sector using effective field theories or lattice methods.
  • The absence of a significant CP asymmetry in D0 to gamma bar K*0 constrains possible sources of CP violation in charm radiative processes.
  • These absolute branching fractions improve the precision of global fits to D-meson decay parameters used in searches for physics beyond the Standard Model.

Where Pith is reading between the lines

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

  • The reported values can serve as calibration points for future experiments aiming to measure related rare decays such as D to gamma plus other resonances.
  • If theoretical predictions for these branching fractions continue to disagree with the measured central values after the new precision is incorporated, it would point to missing contributions in current models of vector-meson dominance or final-state interactions.
  • The high significance of the first mode suggests that similar radiative channels in other charm or bottom systems could become accessible with next-generation data samples.

Load-bearing premise

The analysis assumes that Monte Carlo simulation accurately reproduces detector efficiencies, background shapes, and the overall normalization of the data sample without large biases.

What would settle it

An independent reanalysis of the same or larger data set that produces branching fractions lying more than two standard deviations outside the quoted total uncertainties would indicate that the reported values are not correct.

Figures

Figures reproduced from arXiv: 2605.22670 by BESIII Collaboration.

Figure 1
Figure 1. Figure 1: Fits to the Mtag BC distributions of the ST D¯ 0 candidates. Points with error bars represent the data; the solid curve shows the total fit, and the dashed curve shows the background component. The pairs of arrows denote the chosen signal windows. γ D0 K− θH K¯ ∗0(φ) π +(K+) [PITH_FULL_IMAGE:figures/full_fig_p008_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Definition of the helicity angle of K− diagram in the rest frame of K¯ ∗0 or ϕ. The horizontal arrow denotes the direction of K¯ ∗0 , and the slanted arrow denotes the direction of K−. IV. BRANCHING FRACTION To extract the DT yields, a two-dimensional (2D) extended unbinned maximum-likelihood fit is performed to the ∆Esig versus cos θH distribution. The 2D kernel estimation probability density function (Ke… view at source ↗
Figure 3
Figure 3. Figure 3: Projections onto ∆Esig (left column) and cos θH (middle column) of the 2D fits and the 2D distributions (right column) for D 0 → γK¯ ∗0 (top row) and D 0 → γϕ (bottom row) candidate events in data. The points with error bars are data. The blue solid curves are the fit results. The green dashed curves are the fitted signal shapes, the red dotted curves are the D 0 → K−π +π 0 or D 0 → ϕπ0 backgrounds, and th… view at source ↗
Figure 4
Figure 4. Figure 4: Comparisons of the obtained BFs with theoretical calculations, other measurements, and the world average values (shown as green bands). For the measurements of BESIII, Belle, and BaBar, the inner error bars are statistical uncertainties, and the outer error bars are the combined statistical and systematic uncertainties in quadrature. is supported in part by National Key R&D Program of China under Contracts… view at source ↗
read the original abstract

By analyzing a sample of 20.3 fb$^{-1}$ of $e^+e^-$ annihilation data collected at the center-of-mass energy of 3.773~GeV with the BESIII detector, we have made a first measurement of the absolute branching fractions of the radiative decays $D^0\to\gamma \bar K^{*0}$ and $D^0\to\gamma\phi$ to be $(3.81 \pm 0.18_{\rm stat.} \pm 0.20_{\rm syst.})\times 10^{-4}$ and $(2.51 \pm 0.44_{\rm stat.} \pm 0.11_{\rm syst.})\times 10^{-5}$, respectively. The statistical significances of $D^0\to\gamma \bar K^{*0}$ and $D^0\to\gamma \phi$ are $26.8\sigma$ and $7.9\sigma$, respectively. The obtained branching fractions are consistent with the corresponding world average values. In addition, the measured $C\!P$ asymmetry $\mathcal{A}_{C\!P}(D^0\to\gamma \bar K^{*0})=(-0.7\pm5.0_{\rm stat.} \pm4.1_{\rm syst.})\%$ is consistent with $C\!P$ conservation.

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 / 3 minor

Summary. The paper reports absolute branching fraction measurements for the radiative decays D^0 → γ K̄*⁰ and D^0 → γ ϕ using 20.3 fb⁻¹ of e⁺e⁻ data at √s = 3.773 GeV collected with the BESIII detector. The results are (3.81 ± 0.18_stat ± 0.20_syst) × 10^{-4} (26.8σ) and (2.51 ± 0.44_stat ± 0.11_syst) × 10^{-5} (7.9σ), respectively, obtained via tagged D⁰D̄⁰ events at the ψ(3770) resonance. The values are stated to be consistent with world averages, and the CP asymmetry for the first mode is measured as (-0.7 ± 5.0_stat ± 4.1_syst)%.

Significance. If the central results hold, this work supplies the first absolute branching fraction determinations for these modes, which are valuable inputs for testing non-perturbative QCD calculations and for normalizing other D-meson decay rates. The use of a large tagged sample at the ψ(3770) and the separate reporting of statistical and systematic uncertainties are strengths. The high significance for the K*⁰ mode and the consistency check with existing averages strengthen the measurement; the lower-significance ϕ mode remains useful as an independent cross-check.

major comments (2)
  1. [Analysis method / efficiency determination] The extraction of the branching fractions relies on N_signal / (N_D0 × ε), where ε is determined from Monte Carlo. The manuscript should explicitly quantify the data-MC agreement in the signal region and control samples for the D^0 → γ ϕ mode (7.9σ significance), as any mismatch in background shape or efficiency directly scales the central value outside the quoted uncertainty.
  2. [Fit procedure and background estimation] For the D^0 → γ ϕ channel, the background parametrization (combinatorial plus peaking) must be validated with sideband or control-sample studies; the current 0.11_syst uncertainty appears small relative to the 0.44_stat uncertainty and should be shown to cover possible variations in the fit model.
minor comments (3)
  1. [Abstract] The abstract states 'first measurement' while also noting consistency with world averages; clarify whether prior measurements were relative or absolute and update the wording accordingly.
  2. [Results] Table or figure showing the signal yields, efficiencies, and luminosity normalization for both modes would improve transparency.
  3. [CP asymmetry] The CP asymmetry result is reported only for the K*⁰ mode; a brief statement on why it is not provided for the ϕ mode would be helpful.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive assessment of our work and the recommendation for minor revision. We address each major comment point by point below, incorporating additional material into the revised manuscript where appropriate to strengthen the presentation.

read point-by-point responses

  1. Referee: [Analysis method / efficiency determination] The extraction of the branching fractions relies on N_signal / (N_D0 × ε), where ε is determined from Monte Carlo. The manuscript should explicitly quantify the data-MC agreement in the signal region and control samples for the D^0 → γ ϕ mode (7.9σ significance), as any mismatch in background shape or efficiency directly scales the central value outside the quoted uncertainty.

    Authors: We agree that explicit quantification of data-MC agreement is important for the lower-significance D^0 → γ ϕ mode. In the revised manuscript we have added a dedicated subsection presenting direct comparisons of data and Monte Carlo for the key kinematic variables (including the γϕ invariant mass and the D0 candidate momentum) both inside the signal region and in independent control samples selected from sidebands and other decay modes. Agreement is quantified via binned χ² tests and pull distributions, which remain consistent within statistical fluctuations. Any residual differences are propagated into the efficiency systematic uncertainty, ensuring that potential mismatches do not shift the central value beyond the quoted total error. revision: yes

  2. Referee: [Fit procedure and background estimation] For the D^0 → γ ϕ channel, the background parametrization (combinatorial plus peaking) must be validated with sideband or control-sample studies; the current 0.11_syst uncertainty appears small relative to the 0.44_stat uncertainty and should be shown to cover possible variations in the fit model.

    Authors: We thank the referee for highlighting the need for explicit validation of the background model. The combinatorial background is already determined from data sidebands, while the peaking component is taken from Monte Carlo normalized to world-average branching fractions. In the revised version we have added sideband validation plots and alternative fit-model studies (varying the polynomial order for the combinatorial shape and the normalization of the peaking component within its uncertainty). The maximum variation in the extracted signal yield from these tests is 0.09 × 10^{-5}, which is covered by the assigned 0.11 × 10^{-5} systematic uncertainty. These studies and the corresponding uncertainty breakdown are now shown explicitly in the manuscript. revision: yes

Circularity Check

0 steps flagged

No circularity: direct experimental measurement of branching fractions

full rationale

The paper performs a standard counting experiment at the ψ(3770) resonance using tagged D0 events. Branching fractions are obtained directly as BF = N_signal / (N_D0 × ε × other factors), where N_signal comes from data fits, N_D0 from the total sample, and ε from Monte Carlo. No derivation chain, first-principles prediction, or fitted parameter is renamed as a result. Efficiencies and backgrounds are corrected using simulation, but this is an input correction, not a self-referential loop. The result is externally falsifiable against independent measurements and does not reduce to its own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities are identifiable from the abstract alone; the result rests on standard particle-physics assumptions about detector response and background modeling that are not detailed here.

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