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New high-statistics measurement of the $π^{0} \to e^{+} e^{-} γ$ Dalitz decay at the Mainz Microtron

S. Prakhov^1,*, L. Heijkenskjöld¹, S. Abt², P. Achenbach¹, P. Adlarson¹, F. Afzal³, Z. Ahmed⁴, K. Altangerel¹, J. R. M. Annand⁵ et al. (A2 Collaboration)

J. R. M. Annand⁵, M. Bashkanov⁶, R. Beck³, M. Biroth¹, N. S. Borisov^7,†, A. Braghieri⁸, W. J. Briscoe⁹, F. Cividini¹, C. Collicott¹, S. Costanza⁸, A. Denig¹, M. Dieterle², A. S. Dolzhikov⁷, E. J. Downie⁹, P. Drexler¹, S. Fegan⁶, S. Gardner⁵, D. Ghosal², D. I. Glazier⁵, I. Gorodnov⁷, W. Gradl¹, M. Günther², G. M. Gurevich¹⁰, D. Hornidge¹¹, G. M. Huber⁴, A. Käser², V. L. Kashevarov^1,7, S. J. D. Kay⁴, M. Korolija¹², B. Krusche^2,†, A. Lazarev⁷, K. Livingston⁵, S. Lutterer², I. J. D. MacGregor⁵, D. M. Manley¹³, P. P. Martel¹, R. Miskimen¹⁴, M. Mocanu⁶, E. Mornacchi¹, C. Mullen⁵, A. Neganov⁷, A. Neiser¹, M. Ostrick¹, P. B. Otte¹, D. Paudyal⁴, P. Pedroni⁸, A. Powell⁵, E. Rickert¹, T. Rostomyan², V. Sokhoyan¹, K. Spieker³, O. Steffen¹, I. I. Strakovsky⁹, Th. Strub², I. Supek¹², M. Thiel¹, A. Thomas¹, Yu. A. Usov⁷, S. Wagner¹, D. P. Watts⁶, D. Werthmüller⁶, J. Wettig¹, M. Wolfes¹, and N. Zachariou⁶ (A2 Collaboration)

¹Institut für Kernphysik, University of Mainz, D-55099 Mainz, Germany
²Institut für Physik, University of Basel, CH-4056 Basel, Switzerland
³Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, D-53115 Bonn, Germany
⁴University of Regina, Regina, Saskatchewan S4S 0A2, Canada
⁵SUPA School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom
⁶Department of Physics, University of York, Heslington, York Y010 5DD, United Kingdom
⁷Joint Institute for Nuclear Research, 141980 Dubna, Russia
⁸INFN Sezione di Pavia, I-27100 Pavia, Italy
⁹The George Washington University, Washington, DC 20052-0001, USA
¹⁰Institute for Nuclear Research, 125047 Moscow, Russia
¹¹Mount Allison University, Sackville, New Brunswick E4L 1E6, Canada
¹²Rudjer Boskovic Institute, HR-10000 Zagreb, Croatia
¹³Kent State University, Kent, Ohio 44242-0001, USA
¹⁴University of Massachusetts, Amherst, Massachusetts 01003, USA

^*Contact author: prakhov@ucla.edu
^†Deceased.

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Phys. Rev. C 113, 065202 – Published 5 June, 2026

DOI: https://doi.org/10.1103/9tk1-2dxp

Abstract

The Dalitz decay $π^{0} \to e^{+} e^{-} γ$ has been measured with the highest statistical accuracy obtained so far in the $γ p \to π^{0} p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value of the slope parameter for the $π^{0}$ electromagnetic transition form factor, $a_{π} = 0.0315 \pm 0 . 0026_{stat} \pm 0 . 0010_{syst}$ , is obtained from the analysis of $2.4 \times 10^{6}$ $π^{0} \to e^{+} e^{-} γ$ observed decays. Within experimental uncertainties, it is in agreement with existing measurements and theoretical calculations, with its own uncertainty being smaller than previous results based on the analysis of $π^{0} \to e^{+} e^{-} γ$ decays.

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Phys. Rev. C 113, 065202– Published 5 June, 2026

Vol. 113, Iss. 6 — June 2026

Received 4 December 2025
Revised 18 March 2026
Accepted 4 May 2026

DOI: https://doi.org/10.1103/9tk1-2dxp

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP³.

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New high-statistics measurement of the $π^{0} \to e^{+} e^{-} γ$ Dalitz decay at the Mainz Microtron

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New high-statistics measurement of the π0→e+e−γ Dalitz decay at the Mainz Microtron

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Physics Subject Headings (PhySH)

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References (70)

New high-statistics measurement of the $π^{0} \to e^{+} e^{-} γ$ Dalitz decay at the Mainz Microtron