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arxiv: 2606.04496 · v1 · pith:45WTFPIXnew · submitted 2026-06-03 · ✦ hep-ex

Measurement of time-dependent CP violation parameters in B⁰ to K_(S)⁰ π⁰ γ decays at Belle and Belle II

Belle , Belle II Collaborations: M. Abumusabh , I. Adachi , A. Aggarwal , Y. Ahn , H. Aihara , M. Akdag , N. Akopov
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S. Alghamdi M. Alhakami N. Althubiti K. Amos M. Angelsmark N. Anh Ky C. Antonioli K. Arai H. Atmacan V. Aushev R. Ayad V. Babu H. Bae N. K. Baghel S. Bahinipati P. Bambade Sw. Banerjee S. Bansal M. Barrett M. Bartl J. Baudot A. Beaubien F. Becherer J. Becker G. F. Benfratello J. V. Bennett F. U. Bernlochner V. Bertacchi M. Bertemes E. Bertholet M. Bessner S. Bettarini V. Bhardwaj B. Bhuyan F. Bianchi T. Bilka D. Biswas A. Bobrov D. Bodrov A. Bondar G. Bonvicini J. Borah A. Boschetti A. Bozek M. Bra\v{c}ko P. Branchini N. Brenny R. A. Briere T. E. Browder A. Budano S. Bussino F. Callet Q. Campagna M. Campajola L. Cao M. Carminati G. Casarosa C. Cecchi P. Cheema L. Chen B. G. Cheon C. Cheshta H. Chetri K. Chilikin K. Chirapatpimol H.-E. Cho K. Cho S.-J. Cho S.-K. Choi S. Choudhury S. Chutia J. Cochran J. A. Colorado-Caicedo I. Consigny L. Corona H. Crotte Ledesma S. Cuccuini J. X. Cui S. Das E. De La Cruz-Burelo S. A. De La Motte G. de Marino G. De Nardo G. De Pietro R. de Sangro M. Destefanis S. Dey R. Dhayal A. Di Canto J. Dingfelder Z. Dole\v{z}al X. Dong M. Dorigo G. Dujany P. Ecker D. Epifanov J. Eppelt R. Farkas P. Feichtinger T. Ferber T. Fillinger C. Finck G. Finocchiaro F. Forti A. Frey B. G. Fulsom A. Gabrielli P. Gagneja E. Ganiev R. Garg G. Gaudino V. Gaur V. Gautam A. Gaz A. Gellrich G. Ghevondyan D. Ghosh H. Ghumaryan R. Giordano A. Giri P. Gironella Gironell B. Gobbo R. Godang O. Gogota W. Gradl E. Graziani D. Greenwald Y. Guan K. Gudkova I. Haide Y. Han K. Hayasaka H. Hayashii S. Hazra C. Hearty M. T. Hedges A. Heidelbach G. Heine I. Heredia de la Cruz T. Higuchi M. Hoek M. Hohmann R. Hoppe P. Horak X. T. Hou C.-L. Hsu T. Humair T. Iijima K. Inami N. Ipsita A. Ishikawa R. Itoh M. Iwasaki P. Jackson D. Jacobi W. W. Jacobs E.-J. Jang Q. P. Ji S. Jia Y. Jin A. Johnson K. K. Joo K. H. Kang G. Karyan T. Kawasaki F. Keil C. Kiesling C. Kim D. Y. Kim H. Kim J.-Y. Kim K.-H. Kim K. Kinoshita P. Kody\v{s} T. Koga S. Kohani A. Korobov S. Korpar E. Kovalenko R. Kowalewski P. Kri\v{z}an P. Krokovny T. Kuhr Y. Kulii R. Kumar K. Kumara T. Kunigo S. Kurokawa A. Kuzmin Y.-J. Kwon S. Lacaprara Y.-T. Lai T. Lam J. S. Lange T. S. Lau R. Leboucher H. Lee M. J. Lee P. Leo P. M. Lewis C. Li L. K. Li Q. M. Li S. X. Li W. Z. Li Y. Li Y. B. Li Y. P. Liao J. Libby J. Lin S. Lin Z. Liptak V. Lisovskyi C. Liu G. Liu M. H. Liu Q. Y. Liu Z. Q. Liu D. Liventsev S. Longo A. Lozar T. Lueck J. L. Ma Y. Ma M. Maggiora S. P. Maharana R. Maiti G. Mancinelli R. Manfredi E. Manoni M. Mantovano D. Marcantonio M. Marfoli C. Marinas A. Martens T. Martinov L. Massaccesi M. Masuda T. Matsuda D. Matvienko S. K. Maurya M. Maushart J. A. McKenna Z. Mediankin Gruberov\'a R. Mehta F. Meier D. Meleshko M. Merola C. Miller M. Mirra K. Miyabayashi H. Miyake R. Mizuk G. B. Mohanty S. Moneta A. L. Moreira de Carvalho H.-G. Moser N. Mudgal Th. Muller H. Murakami R. Mussa M. Nakao Y. Nakazawa Z. Natkaniec A. Natochii M. Neu S. Nishida R. Nomaru S. Ogawa R. Okubo H. Ono Y. Onuki G. Pakhlova S. Pardi J. Park K. Park S.-H. Park A. Passeri S. Patra T. K. Pedlar M. Piccolo L. E. Piilonen P. L. M. Podesta-Lerma T. Podobnik L. Polat A. Prakash V. Prasad C. Praz S. Prell E. Prencipe M. T. Prim S. Privalov I. Prudiiev H. Purwar P. Rados S. Raiz K. Ravindran J. U. Rehman M. Reif S. Reiter L. Reuter D. Ricalde Herrmann I. Ripp-Baudot G. Rizzo S. H. Robertson J. M. Roney A. Rostomyan N. Rout G. Russo S. Saha L. Salutari D. A. Sanders S. Sandilya L. Santelj C. Santos V. Savinov B. Scavino C. Schmitt J. Schmitz G. Schnell K. Schoenning C. Schwanda Y. Seino K. Senyo J. Serrano C. Sfienti W. Shan C. P. Shen X. D. Shi T. Shillington T. Shimasaki J.-G. Shiu D. Shtol B. Shwartz A. Sibidanov F. Simon J. B. Singh J. Skorupa A. Soffer A. Sokolov E. Solovieva S. Spataro K. \v{S}penko B. Spruck M. Stari\v{c} P. Stavroulakis S. Stefkova R. Stroili M. Sumihama M. Takahashi M. Takizawa U. Tamponi K. Tanida F. Testa A. Thaller D. V. Thanh T. Tien Manh O. Tittel R. Tiwary E. Torassa K. Trabelsi F. F. Trantou I. Tsaklidis M. Uchida I. Ueda T. Uglov K. Unger Y. Unno K. Uno S. Uno Y. Ushiroda R. van Tonder K. E. Varvell M. Veronesi A. Vinokurova V. S. Vismaya L. Vitale V. Vobbilisetti R. Volpe M. Wakai S. Wallner M.-Z. Wang A. Warburton M. Watanabe S. Watanuki C. Wessel X. P. Xu B. D. Yabsley S. Yamada W. Yan W. P. Yan J. Yelton K. Yi J. H. Yin K. Yoshihara C. Z. Yuan J. Yuan L. Yuan Y. Yusa L. Zani F. Zeng M. Zeyrek B. Zhang X. Zhao V. Zhilich Q. D. Zhou X. Y. Zhou L. Zhu R. \v{Z}leb\v{c}\'ik
This is my paper

Pith reviewed 2026-06-28 03:52 UTC · model grok-4.3

classification ✦ hep-ex
keywords CP violationB0 decaysradiative decaystime-dependent analysisBelle experimentBelle IIK*0 resonancepenguin decays
0
0 comments X

The pith

Belle and Belle II measure S = 0.09 ± 0.16 ± 0.02 and C = -0.09 ± 0.08 ± 0.04 for time-dependent CP violation in B0 → Ks0 π0 γ in the K*0 region.

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

The paper reports a measurement of time-dependent CP violation parameters S and C in the radiative decay B0 to Ks0 pi0 gamma. Data from roughly 772 million and 521 million Upsilon(4S) decays collected by Belle and Belle II are combined and split into a K*0(892) dominated mass region and a non-K*0 region. The extracted values in both regions agree with Standard Model expectations of small CP violation. The new results carry smaller uncertainties than earlier measurements and therefore tighten the experimental limits on this decay mode.

Core claim

Using the combined Belle and Belle II dataset, the time-dependent CP violation parameters are measured as S = 0.09 ± 0.16 ± 0.02 and C = -0.09 ± 0.08 ± 0.04 in the K*0(892) dominated region (M_Ks0 π0 in [0.8,1.0] GeV/c²) and S = -0.32 ± 0.33 ± 0.09 and C = -0.07 ± 0.17 ± 0.08 in the non-K*0 region (M_Ks0 π0 in [1.0,1.8] GeV/c²). These results are stated to be consistent with Standard Model predictions.

What carries the argument

Extraction of the CP parameters S and C from the time-dependent decay-rate asymmetry, performed separately in two intervals of the Ks0 π0 invariant mass.

If this is right

  • The measured values confirm that both direct and mixing-induced CP violation remain small in this b to s gamma penguin decay.
  • Tighter experimental bounds reduce the room for new-physics contributions that could alter the expected CP phases.
  • Separate results in resonant and non-resonant mass regions allow the underlying decay amplitudes to be probed in different kinematic regimes.
  • The improved precision can be used in global fits that combine multiple b to s gamma modes to test the overall consistency of the Standard Model.

Where Pith is reading between the lines

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

  • Future Belle II data taking could reduce the statistical uncertainties enough to begin testing small Standard Model contributions predicted by some QCD calculations.
  • The less precise result in the non-K*0 region suggests that improved modeling of non-resonant amplitudes will be needed before further gains in sensitivity are possible.
  • These measurements provide a reference point for comparing with theoretical predictions that include higher-order electroweak corrections.

Load-bearing premise

The chosen mass intervals for the Ks0 pi0 system cleanly separate the K*0 dominated and non-resonant contributions without significant cross-contamination or modeling errors that would bias the extracted S and C values.

What would settle it

An independent analysis or higher-statistics dataset that yields S or C values differing from the reported central values by more than three combined standard deviations would indicate the current results are not reproducible.

read the original abstract

We perform a measurement of time-dependent $CP$ violation parameters in $B^{0} \to K_{S}^{0} \pi^{0} \gamma$ decays using a dataset of approximately $772 \times 10^6$ and $521 \times 10^6$ $\Upsilon(4S)$ decays collected by the Belle and Belle II experiments, respectively. The measured parameters for the combined dataset in the $K^{*0}(892)$ dominated region ($M_{K_{S}^{0} \pi^{0}} \in [0.8,1.0] \mathrm{GeV}/c^2$) are $S = 0.09 \pm 0.16 \pm 0.02$ and $C = -0.09 \pm 0.08 \pm 0.04$. For the non-$K^{*0}(892)$ region ($M_{K_{S}^{0} \pi^{0}} \in [1.0,1.8] \mathrm{GeV}/c^2$), the corresponding values are $S = -0.32 \pm 0.33 \pm 0.09$ and $C = -0.07 \pm 0.17 \pm 0.08$. The first quoted uncertainties are statistical, while the second ones are systematic. These results are consistent with Standard Model predictions and more precise than previous measurements.

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

1 major / 0 minor

Summary. This paper measures time-dependent CP violation parameters S and C in B⁰ → K_S⁰ π⁰ γ decays at Belle and Belle II. Using combined data, it reports S = 0.09 ± 0.16 ± 0.02 and C = -0.09 ± 0.08 ± 0.04 in the K*⁰(892) dominated region (M_{K_S⁰π⁰} ∈ [0.8,1.0] GeV/c²), and S = -0.32 ± 0.33 ± 0.09 and C = -0.07 ± 0.17 ± 0.08 in the non-K*⁰ region (M ∈ [1.0,1.8] GeV/c²). The results are stated to be consistent with Standard Model predictions and more precise than earlier measurements.

Significance. These measurements test the Standard Model expectation of small S in b → sγ transitions. The combined dataset from two experiments provides higher precision, which can help in constraining new physics contributions if the analysis is robust against background and resonance modeling effects.

major comments (1)
  1. [Abstract (mass region definitions)] The non-K*0 region [1.0,1.8] GeV/c² necessarily includes higher-mass resonances (K*(1410), K2*(1430)) whose lineshapes, interference with the K*0 tail, and photon-polarization properties differ from the dominant K*0(892). The manuscript must specify how the signal PDF models these components (whether floated, constrained, or neglected) and how efficiency corrections are derived, to confirm the time-dependent fit yields unbiased S and C at the level of the quoted uncertainties. This directly affects the validity of the non-K*0 results.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful review and constructive feedback. We address the single major comment below, agreeing that additional clarity on the non-K*0 modeling is warranted.

read point-by-point responses

  1. Referee: The non-K*0 region [1.0,1.8] GeV/c² necessarily includes higher-mass resonances (K*(1410), K2*(1430)) whose lineshapes, interference with the K*0 tail, and photon-polarization properties differ from the dominant K*0(892). The manuscript must specify how the signal PDF models these components (whether floated, constrained, or neglected) and how efficiency corrections are derived, to confirm the time-dependent fit yields unbiased S and C at the level of the quoted uncertainties. This directly affects the validity of the non-K*0 results.

    Authors: We agree that explicit specification of the non-K*0 modeling is necessary for full transparency. The manuscript (Section 5) constructs the signal PDF for this region as an effective amplitude model that includes relativistic Breit-Wigner lineshapes for K*(1410) and K2*(1430), plus interference with the K*0(892) tail, with resonance parameters either fixed to world averages or constrained by sideband data. Photon polarization is incorporated via the SM expectation in the simulation. Efficiency corrections are obtained from large Monte Carlo samples generated with the full resonance content and reweighted to data. Toy Monte Carlo studies confirm that any residual bias in S and C lies well below the quoted uncertainties. To address the referee's point directly, we will expand the relevant section with a dedicated paragraph and a summary table of modeling choices in the revised manuscript. revision: yes

Circularity Check

0 steps flagged

No circularity: direct experimental extraction from data fits

full rationale

The paper reports S and C values obtained by fitting time-dependent decay distributions in two mass intervals of the K_S^0 π^0 system. These are empirical results from the Belle/Belle II datasets, not quantities derived from or forced by any internal equations, fitted parameters renamed as predictions, or self-citation chains. The abstract and reader's summary confirm the parameters are extracted directly from data with statistical and systematic uncertainties; no load-bearing step reduces by construction to prior inputs within the paper. This is the standard non-circular outcome for a measurement analysis.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Based solely on the abstract, the measurement rests on standard assumptions of B meson production, decay reconstruction, and background subtraction in e+e- collider experiments; no ad-hoc parameters or new entities are introduced in the provided text.

axioms (1)
  • domain assumption Standard Model expectations for CP violation parameters in b->s gamma radiative decays are small and near zero in the absence of new physics.
    The abstract states consistency with these predictions as the benchmark for the result.

pith-pipeline@v0.9.1-grok · 8075 in / 1499 out tokens · 66795 ms · 2026-06-28T03:52:24.992582+00:00 · methodology

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