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Polarization observables $T$ and $F$ in the $γ p \to π^{0} p$ reaction at CLAS

H. Jiang ¹, S. Strauch², I. I. Strakovsky³, D. Rönchen⁴, R. Workman³, P. Achenbach⁴², J. S. Alvarado²⁵, H. Atac⁴¹, L. Baashen²⁶ et al. (CLAS Collaboration)

L. Baashen²⁶, N. A. Baltzell⁴², L. Barion¹⁹, M. Bashkanov⁴⁸, M. Battaglieri²⁰, F. Benmokhtar¹³, A. Bianconi^45,24, A. S. Biselli^14,36, M. Bondi^21,23, F. Bossù¹⁰, S. Boiarinov⁴², K.-T. Brinkmann³⁵, W. J. Briscoe³, J. Brock⁴², W. K. Brooks^44,42, V. D. Burkert⁴², T. Cao⁴², R. Capobianco¹², C. Carlin⁴², D. S. Carman⁴², J. C. Carvajal¹⁶, P. Chatagnon¹⁰, V. Chesnokov⁴⁰, G. Ciullo^19,15, P. L. Cole^28,42, M. Contalbrigo¹⁹, V. Crede¹⁷, A. D'Angelo^21,38, N. Dashyan⁵⁰, R. De Vita^20,*, M. Defurne¹⁰, A. Deur⁴², S. Diehl^35,12, C. Djalali^33,2, M. Dugger⁶, R. Dupre²⁵, H. Egiyan^42,31, A. El Alaoui⁴⁴, L. Elouadrhiri^42,11, P. Eugenio¹⁷, S. Fegan⁴⁸, I. P. Fernando⁴⁹, A. Filippi²², G. Gavalian^42,50, N. Gevorgyan⁵⁰, G. P. Gilfoyle³⁷, D. I. Glazier¹, R. W. Gothe², L. Guo¹⁶, K. Hafidi⁵, H. Hakobyan⁴⁴, M. Hattawy³⁴, T. B. Hayward²⁹, D. Heddle^11,42, A. Hobart²⁵, M. Holtrop³¹, Yu-Chun Hung³⁴, Y. Ilieva², D. G. Ireland¹, E. L. Isupov⁴⁰, H. S. Jo²⁷, C. D. Keith⁴², D. Keller⁴⁹, M. Khandaker^32,†, A. Kim¹², W. Kim²⁷, F. J. Klein^42,‡, V. Klimenko⁵, A. Kripko³⁵, V. Kubarovsky⁴², L. Lanza^21,38, P. Lenisa^19,15, X. Li³⁹, K. Livingston¹, S. Liyanaarachchi⁴², I. J. D. MacGregor¹, D. Marchand²⁵, V. Mascagna^45,24, M. Maynes³⁰, M. E. McCracken⁹, B. McKinnon¹, D. G. Meekins⁴², T. Mineeva⁴³, V. Mokeev⁴², C. Munoz Camacho²⁵, P. Nadel-Turonski², T. Nagorna²⁰, K. Neupane², D. Nguyen^42,47, S. Niccolai²⁵, M. Osipenko²⁰, A. I. Ostrovidov¹⁷, M. Ouillon³⁰, P. Pandey²⁹, L. L. Pappalardo^19,15, R. Paremuzyan^42,50, E. Pasyuk^42,6, S. J. Paul⁴⁶, W. Phelps¹¹, J. J. Pierce⁴², N. Pilleux⁵, S. Polcher Rafael¹⁰, J. W. Price⁷, Y. Prok³⁴, T. Reed¹⁶, J. Richards¹², M. Ripani²⁰, B. G. Ritchie⁶, J. Ritman¹⁸, G. Rosner¹, A. A. Rusova⁴⁰, S. Schadmand¹⁸, A. Schmidt³, R. A. Schumacher⁹, M. B. C. Scott³, M. L. Seely⁴², Y. G. Sharabian^42,50, E. V. Shirokov⁴⁰, S. Shrestha⁴¹, D. Sokhan¹, N. Sparveris⁴¹, M. Spreafico²⁰, J. A. Tan²⁷, M. Tenorio³⁴, N. Trotta¹², R. Tyson⁴², M. Ungaro⁴², D. W. Upton³⁴, S. Vallarino²⁰, L. Venturelli^45,24, H. Voskanyan⁵⁰, E. Voutier²⁵, Y. Wang²⁹, D. P. Watts⁴⁸, U. Weerasinghe³⁰, X. Wei⁴², M. H. Wood⁸, L. Xu²⁵, and N. Zachariou⁴⁸ (CLAS Collaboration)

¹University of Glasgow, Glasgow G12 8QQ, United Kingdom
²University of South Carolina, Columbia, South Carolina 29208, USA
³The George Washington University, Washington, DC 20052, USA
⁴Institute for Advanced Simulation (IAS-4), Forschungszentrum Jülich, 52425 Jülich, Germany
⁵Argonne National Laboratory, Argonne, Illinois 60439, USA
⁶Arizona State University, Tempe, Arizona 85287-1504, USA
⁷California State University, Dominguez Hills, Carson, California 90747, USA
⁸Canisius University, Buffalo, New York 14208, USA
⁹Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
¹⁰IRFU, CEA, Universit'e Paris-Saclay, F-91191 Gif-sur-Yvette, France
¹¹Christopher Newport University, Newport News, Virginia 23606, USA
¹²University of Connecticut, Storrs, Connecticut 06269, USA
¹³Duquesne University, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, USA
¹⁴Fairfield University, Fairfield Connecticut 06824, USA
¹⁵Universita' di Ferrara, 44121 Ferrara, Italy
¹⁶Florida International University, Miami, Florida 33199, USA
¹⁷Florida State University, Tallahassee, Florida 32306, USA
¹⁸GSI Helmholtzzentrum fur Schwerionenforschung GmbH, D-64291 Darmstadt, Germany
¹⁹INFN, Sezione di Ferrara, 44100 Ferrara, Italy
²⁰INFN, Sezione di Genova, 16146 Genova, Italy
²¹INFN, Sezione di Roma Tor Vergata, 00133 Rome, Italy
²²INFN, Sezione di Torino, 10125 Torino, Italy
²³INFN, Sezione di Catania, 95123 Catania, Italy
²⁴INFN, Sezione di Pavia, 27100 Pavia, Italy
²⁵Universit'e Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France
²⁶King Saud University, Riyadh, Kingdom of Saudi Arabia
²⁷Kyungpook National University, Daegu 41566, Republic of Korea
²⁸Lamar University, 4400 MLK Blvd, PO Box 10046, Beaumont, Texas 77710, USA
²⁹Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
³⁰Mississippi State University, Mississippi State, Mississippi 39762-5167, USA
³¹University of New Hampshire, Durham, New Hampshire 03824-3568, USA
³²Norfolk State University, Norfolk, Virginia 23504, USA
³³Ohio University, Athens, Ohio 45701, USA
³⁴Old Dominion University, Norfolk, Virginia 23529, USA
³⁵II Physikalisches Institut der Universitaet Giessen, 35392 Giessen, Germany
³⁶Rensselaer Polytechnic Institute, Troy, New York 12180-3590, USA
³⁷University of Richmond, Richmond, Virginia 23173, USA
³⁸Universita' di Roma Tor Vergata, 00133 Rome, Italy
³⁹Shandong University, Qingdao, Shandong 266237, China
⁴⁰Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119234 Moscow, Russia
⁴¹Temple University, Philadelphia, Pennsylvania 19122, USA
⁴²Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA
⁴³Universidad de La Serena, Avda. Juan Cisternas 1200, La Serena, Chile
⁴⁴Universidad Técnica Federico Santa María, Casilla 110-V Valparaíso, Chile
⁴⁵Universit'a degli Studi di Brescia, 25123 Brescia, Italy
⁴⁶University of California Riverside, 900 University Avenue, Riverside, California 92521, USA
⁴⁷University of Tennessee, Knoxville, Tennessee 37996, USA
⁴⁸University of York, York YO10 5DD, United Kingdom
⁴⁹University of Virginia, Charlottesville, Virginia 22901, USA
⁵⁰Yerevan Physics Institute, 375036 Yerevan, Armenia

^*Present address: Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
^†Present address: Idaho State University, Pocatello, Idaho 83209, USA.
^‡Present address: Catholic University of America, Washington, DC, 20064, USA.

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Phys. Rev. C 114, 015203 – Published 9 July, 2026

DOI: https://doi.org/10.1103/ml3y-pmb8

Abstract

Pion photoproduction in the $\vec{γ} \vec{p} \to π^{0} p$ reaction has been measured in the FROzen Spin Target (FROST) experiment at the Thomas Jefferson National Accelerator Facility. In this experiment, circularly polarized photons with energies up to 3.082 GeV impinged on a transversely polarized frozen-spin target. Final-state protons were detected in the Continuous Electron Beam Accelerator Facility (CEBAF) Large Acceptance Spectrometer. The polarization observables $T$ and $F$ have been extracted for $W$ from 1445 to 2525 MeV, of which the energy range is much broader, and the precision is better than the existing measurements in higher $W$ ranges. The data generally agree with predictions of present partial-wave analyses but also show marked differences for higher $W$ ranges. By incorporating the present data into the databases, the Scattering Analysis Interactive Data (SAID) fits have been improved with relatively small $χ^{2}$ and significant changes in the parameters of the $Δ (1910) 1 / 2^{+}$ and $N (2190) 7 / 2^{-}$ have been found with the JüBo model.

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References (30)

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Phys. Rev. C 114, 015203– Published 9 July, 2026

Vol. 114, Iss. 1 — July 2026

Received 30 August 2025
Accepted 19 May 2026

DOI: https://doi.org/10.1103/ml3y-pmb8

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.

Published by the American Physical Society

Physical Review C

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Polarization observables $T$ and $F$ in the $γ p \to π^{0} p$ reaction at CLAS

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Polarization observables T and F in the γp→π0p reaction at CLAS

Abstract

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References (30)

Polarization observables $T$ and $F$ in the $γ p \to π^{0} p$ reaction at CLAS