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REVIEW 5 minor 40 references

Belle II sees no axion-like particles in three-photon events and sets the strongest photon-coupling limits yet over most of 0.17–5 GeV/c².

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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T0 review · grok-4.5

2026-07-10 17:51 UTC pith:J5MLTFXB

load-bearing objection Solid Belle II update that delivers the strongest photon-ALP limits in the 0.17–5 GeV window; incremental but clean and ready for citation.

arxiv 2607.07800 v1 pith:J5MLTFXB submitted 2026-07-08 hep-ex

Search for axion-like particles decaying to two photons at Belle II

Belle II Collaboration: M. Abumusabh , I. Adachi , A. Aggarwal , H. Ahmed , Y. Ahn , H. Aihara , M. Akdag , N. Akopov
show 444 more authors
S. Alghamdi M. Alhakami A. Aloisio N. Althubiti K. Amos M. Angelsmark N. Anh Ky C. Antonioli K. Arai D. M. Asner H. Atmacan T. Aushev 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. Baur 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 A. Biswas D. Biswas A. Bobrov D. Bodrov A. Bondar G. Bonvicini J. Borah A. Boschetti A. Bozek M. Bra\v{c}ko P. Branchini T. E. Browder A. Budano S. Bussino F. Callet Q. Campagna M. Campajola L. Cao M. Carminati G. Casarosa C. Cecchi M.-C. Chang 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 D. Crook S. Cuccuini J. X. Cui E. De La Cruz-Burelo S. A. De La Motte 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 C. Driver K. Dugic 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 A. Gale E. Ganiev M. Garcia-Hernandez A. Garmash L. G\"artner G. Gaudino V. Gaur V. Gautam A. Gaz P. Gebeline A. Gellrich G. Ghevondyan D. Ghosh H. Ghumaryan G. Giakoustidis D. Giesegh R. Giordano A. Giri P. Gironella Gironell A. Glazov B. Gobbo R. Godang O. Gogota W. Gradl E. Graziani D. Greenwald Y. Guan K. Gudkova I. Haide H. Haigh Y. Han K. Hayasaka H. Hayashii S. Hazra C. Hearty M. T. Hedges A. Heidelbach G. Heine I. Heredia de la Cruz M. Hern\'andez Villanueva T. Higuchi M. Hoek M. Hohmann R. Hoppe P. Horak X. T. Hou C.-L. Hsu T. Humair T. Iijima K. Inami G. Inguglia 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. Ketter C. Kiesling C. Kim D. Y. Kim H. Kim J.-Y. Kim K.-H. Kim H. Kindo K. Kinoshita P. Kody\v{s} T. Koga S. Kohani A. Korobov S. Korpar E. Kovalenko R. Kowalewski M. Krein P. Kri\v{z}an P. Krokovny T. Kuhr Y. Kulii D. Kumar K. Kumara T. Kunigo A. Kuzmin Y.-J. Kwon S. Lacaprara T. Lam J. S. Lange T. S. Lau R. Leboucher F. R. Le Diberder H. Lee M. J. Lee C. Lemettais 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 C. Lyu J. L. Ma Y. Ma M. Maggiora S. P. Maharana R. Maiti G. Mancinelli R. Manfredi E. Manoni M. Mantovano D. Marcantonio S. Marcello M. Marfoli C. Marinas C. Martellini 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 K. R. Nakamura M. Nakao Y. Nakazawa M. Naruki Z. Natkaniec A. Natochii M. Nayak M. Neu S. Nishida R. Nomaru S. Ogawa R. Okubo H. Ono Y. Onuki I. Ostrowski G. Pakhlova S. Pardi J. Park K. Park S.-H. Park A. Passeri S. Patra T. K. Pedlar R. Pestotnik 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 M. Remnev 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 J. Schmitz S. Schneider M. Schnepf K. Schoenning C. Schwanda Y. Seino K. Senyo J. Serrano M. E. Sevior 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 W. Song S. Spataro K. \v{S}penko B. Spruck M. Stari\v{c} P. Stavroulakis S. Stefkova R. Stroili M. Sumihama K. Sumisawa 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 P. Urquijo Y. Ushiroda S. E. Vahsen R. van Tonder K. E. Varvell M. Veronesi A. Vinokurova V. S. Vismaya L. Vitale V. Vobbilisetti R. Volk R. Volpe E. Waheed M. Wakai S. Wallner M.-Z. Wang X. L. 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 J. S. Zhou Q. D. Zhou X. Y. Zhou L. Zhu R. \v{Z}leb\v{c}\'ik
This is my paper
classification hep-ex
keywords axion-like particlesALP-photon couplingBelle IIthree-photon final statedi-photon mass spectrume+e- collisionsupper limits
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

This paper reports a search for axion-like particles produced together with a photon in electron-positron collisions and decaying promptly into two photons. Using 408 inverse femtobarns of Belle II data, the collaboration looks for a narrow peak in the di-photon mass spectrum between 0.17 and 9.80 GeV/c². No significant excess above Standard Model backgrounds appears. The resulting 95 percent confidence upper limits on the production cross section and on the ALP-photon coupling reach the 10^{-4} GeV^{-1} level and are the most restrictive to date over nearly the entire interval from 0.17 to 5 GeV/c², improving earlier bounds by as much as a factor of nine. A sympathetic reader cares because these limits close a large slice of previously allowed parameter space for a well-motivated portal between the visible and hidden sectors.

Core claim

No significant excess above background is observed in the three-photon final state. Consequently the analysis sets 95 percent confidence-level upper limits on the cross section for e^{+}e^{-} → γa (a → γγ) and on the coupling g_aγγ that are the most restrictive to date over nearly the full mass window 0.17 < m_a < 5.00 GeV/c² and improve previous results by up to a factor of nine.

What carries the argument

Reconstruction of the ALP as a narrow peak in the di-photon invariant-mass spectrum of three-photon events, after a kinematic fit that constrains the three-photon four-momentum to the known initial state and after a neural-network event classifier trained to reject the dominant e^{+}e^{-} → γγ(γ) continuum.

Load-bearing premise

The analysis assumes the ALP couples almost exclusively to photons, so that its branching fraction into two photons is exactly one; if that branching fraction is appreciably smaller the quoted coupling limits loosen by the same factor.

What would settle it

A statistically significant narrow peak appearing in the same di-photon mass distribution once substantially more Belle II luminosity is analyzed, or a laboratory or astrophysical measurement that independently demonstrates a non-unity branching fraction to two photons in the same mass range.

Watch this falsifier — get emailed when new claim-graph text bears on it.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

0 major / 5 minor

Summary. This Belle II letter reports a search for axion-like particles produced via e^{+}e^{-} → γa, a → γγ in 408 fb⁻¹ of SuperKEKB data. Three-photon events are selected with a kinematic fit, helicity-angle cut, π⁰ veto, and a neural-network classifier; the ALP is reconstructed as a narrow peak in the di-photon mass spectrum over 0.17 < m_a < 9.80 GeV/c². No significant excess is observed (largest local significance 3.3σ, global 1.4σ after the look-elsewhere effect). 95% CL upper limits are set on the production cross section and on the ALP–photon coupling g_aγγ (assuming BR(a → γγ) = 1), reaching ~10⁻⁴ GeV⁻¹ and constituting the most restrictive bounds over nearly the entire interval 0.17–5 GeV/c², improving prior results by up to a factor of nine.

Significance. The result is a high-impact, model-independent experimental constraint on photon-coupled ALPs in the MeV–GeV window. The analysis is blinded until selection and fit strategy are fixed, employs a kinematic fit that stabilizes the mass resolution, and reports both cross-section limits (Fig. 2) and coupling limits (Fig. 3). The factor-of-nine improvement over the earlier Belle II result and the coverage of previously less-constrained intermediate masses make the paper a clear reference for future ALP phenomenology and for comparisons with beam-dump, fixed-target, and collider reinterpretations.

minor comments (5)
  1. The abstract and introduction state that the limits improve previous results by “up to a factor 9.” A short quantitative statement (or a sentence in the caption of Fig. 3) identifying the mass region of maximum improvement would make the claim more transparent.
  2. Figure 1 shows the stacked MC background normalized to luminosity; the data/MC ratio panel exhibits a mild overall offset. A brief remark on residual normalization differences (already absorbed into the 4% selection-efficiency systematic) would help the reader.
  3. The combinatorial-signal fraction is fixed from simulation and reaches ~30% near 7 GeV/c². A one-sentence statement of how this fraction was validated (or of its uncertainty) would strengthen the description of the signal PDF.
  4. The paper is still labeled “Belle II (Preliminary)” in the figures. For the final journal version the preliminary designation should be removed and the arXiv identifier updated if necessary.
  5. Typographical slips: “determinedined” (efficiency paragraph) and occasional missing spaces around units (e.g., “GeV/c2”) should be corrected in production.

Circularity Check

0 steps flagged

No circularity: standard blinded experimental search yielding data-driven upper limits, not a derivation that reduces to its inputs

full rationale

This is a conventional high-energy physics search paper. Signal efficiencies, resolutions, and shapes are taken from simulation (MadGraph+Geant4, with data-driven beam-background overlays and efficiency corrections measured in radiative muon pairs); background is modeled by free polynomials whose order is fixed from MC; the signal yield is extracted by unbinned profile-likelihood fits in sliding mass windows; and 95% CL upper limits on the production cross section are obtained by a two-sided frequentist method. Conversion of those cross-section limits into g_aγγ uses only the theoretically computed rate for a fixed coupling (with the explicit assumption BR(a→γγ)=1). None of these steps is self-definitional, none reinterprets a fitted parameter as a prediction, and the comparison to the earlier Belle II result is purely comparative, not load-bearing for the new limits. The analysis is therefore self-contained against external benchmarks and exhibits no circular reduction.

Axiom & Free-Parameter Ledger

2 free parameters · 3 axioms · 0 invented entities

The central claim is an experimental upper limit. It rests on standard HEP assumptions (prompt decay, negligible width, BR=1 under the photon-only coupling hypothesis) plus the usual simulation-based efficiency and resolution models. No new free parameters are fitted to produce the limit; the only free parameters are the background polynomial coefficients that are profiled out.

free parameters (2)
  • background polynomial coefficients
    Order-2 or order-4 polynomials whose coefficients float freely in each mass-window fit; they absorb residual background shape but do not enter the signal yield extraction as fixed numbers.
  • combinatorial-signal fraction
    Relative normalisation of the combinatorial peaking component fixed from simulation (0–30% depending on mass); treated as a fixed shape parameter, not floated.
axioms (3)
  • domain assumption BR(a oγγ)=1 because the ALP-photon coupling dominates and g_aγZ is negligible
    Stated in the introduction and required to translate cross-section limits into g_aγγ limits; taken from the theoretical literature [4].
  • domain assumption ALP width is negligible compared with experimental resolution and the particle decays promptly
    Used to justify a zero-width signal PDF and the absence of lifetime-based selection; standard for the mass range under study.
  • domain assumption Signal efficiency and resolution can be reliably extracted from MadGraph+Geant4 simulation after beam-background overlay and data-driven corrections
    Core of every modern collider search; validated with radiative muon pairs and π⁰/η control samples.

pith-pipeline@v1.1.0-grok45 · 20816 in / 2567 out tokens · 30871 ms · 2026-07-10T17:51:05.185177+00:00 · methodology

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read the original abstract

Axion-like particles (ALPs) are predicted in many extensions of the Standard Model and provide a well-motivated portal between visible and hidden sectors through their coupling to photons. We search for ALPs produced in the process $e^{+}e^{-}\to\gamma a$, $a\to\gamma\gamma$, using a data sample corresponding to an integrated luminosity of $408~\mathrm{fb}^{-1}$ recorded by the Belle~II detector at the SuperKEKB $e^{+}e^{-}$ collider. Events containing three photons are used to reconstruct the ALP as a narrow peak in the di-photon invariant mass spectrum over the range $0.17 < m_{a} < 9.80~\mathrm{GeV}/c^{2}$. No significant excess above background is observed. We set 95\% confidence level upper limits on the production cross section and on the ALP-photon coupling $g_{a\gamma\gamma}$, reaching sensitivities at the level of $10^{-4}~\mathrm{GeV}^{-1}$. The limits are the most restrictive to date over nearly the entire mass range $0.17 < m_{a} < 5.00~\mathrm{GeV}/c^{2}$, and improve upon previous results by up to a factor 9.

Figures

Figures reproduced from arXiv: 2607.07800 by A. Aggarwal, A. Aloisio, A. Baur, A. Beaubien, A. Biswas, A. Bobrov, A. Bondar, A. Boschetti, A. Bozek, A. Budano, A. Di Canto, A. Frey, A. Gabrielli, A. Gale, A. Garmash, A. Gaz, A. Gellrich, A. Giri, A. Glazov, A. Heidelbach, A. Ishikawa, A. Johnson, A. Korobov, A. Kuzmin, A. L. Moreira de Carvalho, A. Lozar, A. Martens, A. Natochii, A. Passeri, A. Prakash, A. Rostomyan, A. Sibidanov, A. Soffer, A. Sokolov, A. Thaller, A. Vinokurova, A. Warburton, B. Bhuyan, B. D. Yabsley, Belle II Collaboration: M. Abumusabh, B. G. Cheon, B. G. Fulsom, B. Gobbo, B. Scavino, B. Shwartz, B. Spruck, B. Zhang, C. Antonioli, C. Cecchi, C. Cheshta, C. Driver, C. Finck, C. Hearty, C. Ketter, C. Kiesling, C. Kim, C. Lemettais, C.-L. Hsu, C. Li, C. Liu, C. Lyu, C. Marinas, C. Martellini, C. Miller, C. Praz, C. P. Shen, C. Santos, C. Schwanda, C. Sfienti, C. Wessel, C. Z. Yuan, D. A. Sanders, D. Biswas, D. Bodrov, D. Crook, D. Epifanov, D. Ghosh, D. Giesegh, D. Greenwald, D. Jacobi, D. Kumar, D. Liventsev, D. Marcantonio, D. M. Asner, D. Matvienko, D. Meleshko, D. Ricalde Herrmann, D. Shtol, D. V. Thanh, D. Y. Kim, E. Bertholet, E. De La Cruz-Burelo, E. Ganiev, E. Graziani, E.-J. Jang, E. Kovalenko, E. Manoni, E. Prencipe, E. Solovieva, E. Torassa, E. Waheed, F. Becherer, F. Bianchi, F. Callet, F. Forti, F. F. Trantou, F. Keil, F. Meier, F. R. Le Diberder, F. Simon, F. Testa, F. U. Bernlochner, F. Zeng, G. B. Mohanty, G. Bonvicini, G. Casarosa, G. De Nardo, G. De Pietro, G. Dujany, G. F. Benfratello, G. Finocchiaro, G. Gaudino, G. Ghevondyan, G. Giakoustidis, G. Heine, G. Inguglia, G. Karyan, G. Liu, G. Mancinelli, G. Pakhlova, G. Rizzo, G. Russo, H. Ahmed, H. Aihara, H. Atmacan, H. Bae, H. Chetri, H.-E. Cho, H. Ghumaryan, H.-G. Moser, H. Haigh, H. Hayashii, H. Kim, H. Kindo, H. Lee, H. Miyake, H. Murakami, H. Ono, H. Purwar, I. Adachi, I. Consigny, I. Haide, I. Heredia de la Cruz, I. Ostrowski, I. Prudiiev, I. Ripp-Baudot, I. Tsaklidis, I. Ueda, J. A. Colorado-Caicedo, J. A. McKenna, J. Baudot, J. Becker, J. Borah, J. B. Singh, J. Cochran, J. Dingfelder, J. Eppelt, J.-G. Shiu, J. H. Yin, J. Libby, J. Lin, J. L. Ma, J. M. Roney, J. Park, J. Schmitz, J. Serrano, J. Skorupa, J. S. Lange, J. S. Zhou, J. U. Rehman, J. V. Bennett, J. X. Cui, J. Yelton, J.-Y. Kim, J. Yuan, K. Amos, K. Arai, K. Chilikin, K. Chirapatpimol, K. Cho, K. Dugic, K. E. Varvell, K. Gudkova, K. Hayasaka, K. H. Kang, K.-H. Kim, K. Inami, K. Kinoshita, K. K. Joo, K. Kumara, K. Miyabayashi, K. Park, K. Ravindran, K. R. Nakamura, K. Schoenning, K. Senyo, K. Sumisawa, K. Tanida, K. Trabelsi, K. Unger, K. Uno, K. \v{S}penko, K. Yi, K. Yoshihara, L. Cao, L. Chen, L. Corona, L. E. Piilonen, L. G\"artner, L. K. Li, L. Massaccesi, L. Polat, L. Reuter, L. Salutari, L. Santelj, L. Vitale, L. Yuan, L. Zani, L. Zhu, M. Akdag, M. Alhakami, M. Angelsmark, M. Barrett, M. Bartl, M. Bertemes, M. Bessner, M. Bra\v{c}ko, M. Campajola, M. Carminati, M.-C. Chang, M. Destefanis, M. Dorigo, M. E. Sevior, M. Garcia-Hernandez, M. Hern\'andez Villanueva, M. H. Liu, M. Hoek, M. Hohmann, M. Iwasaki, M. J. Lee, M. Krein, M. Maggiora, M. Mantovano, M. Marfoli, M. Masuda, M. Maushart, M. Merola, M. Mirra, M. Nakao, M. Naruki, M. Nayak, M. Neu, M. Piccolo, M. Reif, M. Remnev, M. Schnepf, M. Stari\v{c}, M. Sumihama, M. Takahashi, M. Takizawa, M. T. Hedges, M. T. Prim, M. Uchida, M. Veronesi, M. Wakai, M. Watanabe, M. Zeyrek, M.-Z. Wang, N. Akopov, N. Althubiti, N. Anh Ky, N. Ipsita, N. K. Baghel, N. Mudgal, N. Rout, O. Gogota, O. Tittel, P. Bambade, P. Branchini, P. Cheema, P. Ecker, P. Feichtinger, P. Gagneja, P. Gebeline, P. Gironella Gironell, P. Horak, P. Jackson, P. Kody\v{s}, P. Kri\v{z}an, P. Krokovny, P. Leo, P. L. M. Podesta-Lerma, P. M. Lewis, P. Rados, P. Stavroulakis, P. Urquijo, Q. Campagna, Q. D. Zhou, Q. M. Li, Q. P. Ji, Q. Y. Liu, R. Ayad, R. de Sangro, R. Dhayal, R. Farkas, R. Giordano, R. Godang, R. Hoppe, R. Itoh, R. Kowalewski, R. Leboucher, R. Maiti, R. Manfredi, R. Mehta, R. Mizuk, R. Mussa, R. Nomaru, R. Okubo, R. Pestotnik, R. Stroili, R. Tiwary, R. van Tonder, R. Volk, R. Volpe, R. \v{Z}leb\v{c}\'ik, S. A. De La Motte, S. Alghamdi, S. Bahinipati, S. Bansal, S. Bettarini, S. Bussino, S. Choudhury, S. Chutia, S. Cuccuini, S. Dey, S. E. Vahsen, S. Hazra, S.-H. Park, S. H. Robertson, S.-J. Cho, S. Jia, S.-K. Choi, S. K. Maurya, S. Kohani, S. Korpar, S. Lacaprara, S. Lin, S. Longo, S. Marcello, S. Moneta, S. Nishida, S. Ogawa, S. Pardi, S. Patra, S. P. Maharana, S. Prell, S. Privalov, S. Raiz, S. Reiter, S. Saha, S. Sandilya, S. Schneider, S. Spataro, S. Stefkova, S. Uno, S. Wallner, S. Watanuki, Sw. Banerjee, S. X. Li, S. Yamada, T. Aushev, T. Bilka, T. E. Browder, T. Ferber, T. Fillinger, T. Higuchi, Th. Muller, T. Humair, T. Iijima, T. Kawasaki, T. Koga, T. K. Pedlar, T. Kuhr, T. Kunigo, T. Lam, T. Lueck, T. Martinov, T. Matsuda, T. Podobnik, T. Shillington, T. Shimasaki, T. S. Lau, T. Tien Manh, T. Uglov, U. Tamponi, V. Aushev, V. Babu, V. Bertacchi, V. Bhardwaj, V. Gaur, V. Gautam, V. Lisovskyi, V. Prasad, V. Savinov, V. S. Vismaya, V. Vobbilisetti, V. Zhilich, W. Gradl, W. P. Yan, W. Shan, W. Song, W. W. Jacobs, W. Yan, W. Z. Li, X. Dong, X. D. Shi, X. L. Wang, X. P. Xu, X. T. Hou, X. Y. Zhou, X. Zhao, Y. Ahn, Y. B. Li, Y. Guan, Y. Han, Y. Jin, Y.-J. Kwon, Y. Kulii, Y. Li, Y. Ma, Y. Nakazawa, Y. Onuki, Y. P. Liao, Y. Seino, Y. Unno, Y. Ushiroda, Y. Yusa, Z. Dole\v{z}al, Z. Liptak, Z. Mediankin Gruberov\'a, Z. Natkaniec, Z. Q. Liu.

Figure 1
Figure 1. Figure 1: Distribution of Mγγ together with the stacked con￾tributions from the various simulated SM background sam￾ples. Simulation is normalized to a luminosity of 408 fb−1 . Signal hypotheses are formed in the invariant di￾photon mass distribution Mγγ and are tested by extended unbinned maximum-likelihood fits. The signal probabil￾ity density function (PDF) consists of two components: a peaking contribution from … view at source ↗
Figure 2
Figure 2. Figure 2: Expected and observed upper limits (95% C.L.) [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Exclusion region (95% C.L.) in the plane of [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗

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