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Measurement of the Gerasimov-Drell-Hearn integrand for the proton and deuteron from 200 to 1400 MeV

P. Pedroni ^1,*, F. Afzal², S. Abt³, P. Achenbach⁴, J. R. M. Annand⁵, H. J. Arends⁴, S. D. Bass^6,7, M. Biroth⁴, R. Beck² et al. (A2 Collaboration at MAMI)

R. Beck², N. Borisov^8,†, A. Braghieri¹, W. J. Briscoe⁹, F. Cividini⁴, C. Collicott⁴, A. S. Dolzhikov⁸, E. Downie⁹, S. Fegan¹⁰, A. Fix¹¹, D. Ghosal³, I. Gorodnov⁸, W. Gradl⁴, G. Gurevich^12,†, L. Heijkenskjöld⁴, D. Hornidge¹³, G. M. Huber¹⁴, V. L. Kashevarov⁴, S. J. D. Kay¹⁰, M. Korolija¹⁵, B. Krusche^3,†, A. Lazarev⁸, K. Livingston⁵, S. Lutterer³, I. J. D. MacGregor⁵, D. M. Manley¹⁶, P. P. Martel⁴, R. Miskimen¹⁷, M. Mocanu¹⁰, E. Mornacchi⁴, C. Mullen⁵, A. Neganov⁸, A. Neiser⁴, M. Oberle³, M. Ostrick⁴, P. B. Otte⁴, D. Paudyal¹⁴, A. Powell⁵, T. Rostomyan^3,‡, V. Sokhoyan⁴, K. Spieker², O. Steffen⁴, I. I. Strakovsky⁹, T. Strub³, M. Thiel⁴, A. Thomas⁴, Yu. A. Usov⁸, S. Wagner⁴, D. P. Watts¹⁰, D. Werthmüller^10,‡, J. Wettig⁴, L. Witthauer³, M. Wolfes⁴, and N. Zachariou¹⁰ (A2 Collaboration at MAMI)

¹INFN Sezione di Pavia, I-27100 Pavia, Italy
²Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, D-53115 Bonn, Germany
³Department für Physik, Universität Basel, CH-4056 Basel, Switzerland
⁴Institut für Kernphysik, University of Mainz, D-55099 Mainz, Germany
⁵SUPA School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom
⁶Kitzbühel Centre for Physics, Kitzbühel, Austria
⁷Marian Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland
⁸Joint Institute for Nuclear Research, 141980 Dubna, Russia
⁹The George Washington University, Washington, DC 20052-0001, USA
¹⁰Department of Physics, University of York, Heslington, York Y010 5DD, United Kingdom
¹¹Budker Institute of Nuclear Physics, 630090 Novosibirsk, Russia
¹²Institute for Nuclear Research, 125047 Moscow, Russia
¹³Mount Allison University, Sackville, New Brunswick E4L 1E6, Canada
¹⁴University of Regina, Regina, Saskatchewan S4S 0A2, Canada
¹⁵Rudjer Boskovic Institute, HR-10000 Zagreb, Croatia
¹⁶Kent State University, Kent, Ohio 44242-0001, USA
¹⁷University of Massachusetts, Amherst, Massachusetts 01003, USA

^*Contact author: pedroni@pv.infn.it
^†Deceased.
^‡Present address: Paul Scherrer Institute (PSI), CH-5232 Villigen PSI, Switzerland.

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Phys. Rev. C 114, 045203 – Published 1 October, 2026

DOI: https://doi.org/10.1103/smhf-nl99

Abstract

New data for the total inclusive helicity-dependent cross section for the proton and deuteron were obtained in the photon energy interval $200 - 1400 MeV$ . The experiment was performed at the A2 tagged-photon facility of the Mainz Microtron (MAMI) using a circularly polarized photon beam and longitudinally polarized proton and deuteron targets. The reaction products were detected using the large-acceptance Crystal Ball/TAPS calorimeter, which covers 97% of the full solid angle. These new results, obtained with fine energy binning, significantly expand both the quantity and the quality of the available data for these observables and enable a detailed comparison with state-of-the-art theoretical calculations. From the combination of the results for the deuteron and the proton, important information could also be extracted for the neutron. Based on these data, and using existing models to evaluate the missing contributions from unmeasured photon energy regions, the validity of the Gerasimov-Drell-Hearn (GDH) sum rule has been verified for the proton, the neutron, and the deuteron. These new data provide a precise experimental benchmark for theoretical models used to study nucleons, both in their free state and when embedded in the nuclear medium.

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Phys. Rev. C 114, 045203– Published 1 October, 2026

Vol. 114, Iss. 4 — October 2026

Received 10 April 2026
Revised 27 June 2026
Accepted 27 July 2026

DOI: https://doi.org/10.1103/smhf-nl99

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.

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Measurement of the Gerasimov-Drell-Hearn integrand for the proton and deuteron from 200 to 1400 MeV

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