First Measurement Using Elliptically Polarized Photons of the Double-Polarization Observable E for γp→pπ^{0} and γp→nπ^{+}

F Afzal; K Spieker; P Hurck; S Abt; P Achenbach; P Adlarson; Z Ahmed; C S Akondi; J R M Annand; H J Arends; M Bashkanov; R Beck; M Biroth; N Borisov; A Braghieri; W J Briscoe; F Cividini; C Collicott; S Costanza; A Denig; M Dieterle; E J Downie; P Drexler; S Fegan; S Gardner; D Ghosal; D I Glazier; I Gorodnov; W Gradl; D Gurevich; L Heijkenskjöld; D Hornidge; G M Huber; V L Kashevarov; S J D Kay; M Korolija; B Krusche; A Lazarev; K Livingston; S Lutterer; I J D MacGregor; R G Macrae; D M Manley; P P Martel; R Miskimen; M Mocanu; E Mornacchi; C Mullen; A Neganov; A Neiser; M Oberle; M Ostrick; P B Otte; D Paudyal; P Pedroni; A Powell; G Reicherz; T Rostomyan; C Sfienti; V Sokhoyan; O Steffen; I I Strakovsky; T Strub; I Supek; A Thiel; M Thiel; A Thomas; Yu A Usov; S Wagner; N K Walford; D P Watts; D Werthmüller; J Wettig; L Witthauer; M Wolfes; N Zachariou; A2 Collaboration at MAMI

doi:10.1103/PhysRevLett.132.121902

First Measurement Using Elliptically Polarized Photons of the Double-Polarization Observable E for γp→pπ^{0} and γp→nπ^{+}

Phys Rev Lett. 2024 Mar 22;132(12):121902. doi: 10.1103/PhysRevLett.132.121902.

Authors

F Afzal¹, K Spieker¹, P Hurck², S Abt³, P Achenbach⁴, P Adlarson⁴, Z Ahmed⁵, C S Akondi⁶, J R M Annand², H J Arends⁴, M Bashkanov⁷, R Beck¹, M Biroth⁴, N Borisov⁸, A Braghieri⁹, W J Briscoe¹⁰, F Cividini⁴, C Collicott¹¹, S Costanza^{9

12}, A Denig⁴, M Dieterle³, E J Downie¹⁰, P Drexler^{4

13}, S Fegan⁷, S Gardner², D Ghosal³, D I Glazier², I Gorodnov⁸, W Gradl⁴, D Gurevich¹⁴, L Heijkenskjöld⁴, D Hornidge¹⁵, G M Huber⁵, V L Kashevarov^{4

8}, S J D Kay⁷, M Korolija¹⁶, B Krusche³, A Lazarev⁸, K Livingston², S Lutterer³, I J D MacGregor², R G Macrae², D M Manley⁶, P P Martel^{4

15}, R Miskimen¹⁷, M Mocanu⁷, E Mornacchi⁴, C Mullen², A Neganov⁸, A Neiser⁴, M Oberle³, M Ostrick⁴, P B Otte⁴, D Paudyal⁵, P Pedroni⁹, A Powell², G Reicherz¹⁸, T Rostomyan³, C Sfienti⁴, V Sokhoyan⁴, O Steffen⁴, I I Strakovsky¹⁰, T Strub³, I Supek¹⁶, A Thiel¹, M Thiel⁴, A Thomas⁴, Yu A Usov⁸, S Wagner⁴, N K Walford³, D P Watts⁷, D Werthmüller⁷, J Wettig⁴, L Witthauer³, M Wolfes⁴, N Zachariou⁷; A2 Collaboration at MAMI

Affiliations

¹ Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, D-53115 Bonn, Germany.
² SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom.
³ Department of Physics, University of Basel, Ch-4056 Basel, Switzerland.
⁴ Institut für Kernphysik, University of Mainz, D-55099 Mainz, Germany.
⁵ University of Regina, Regina, SK S4S0A2, Canada.
⁶ Kent State University, Kent, Ohio 44242, USA.
⁷ Department of Physics, University of York, Heslington, York, Y010 5DD, United Kingdom.
⁸ Joint Institute for Nuclear Research, 141980 Dubna, Russia.
⁹ INFN Sezione di Pavia, I-27100 Pavia, Pavia, Italy.
¹⁰ Center for Nuclear Studies, The George Washington University, Washington, DC 20052, USA.
¹¹ Department of Astronomy and Physics, Saint Mary's University, E4L1E6 Halifax, Canada.
¹² Dipartimento di Fisica, Università di Pavia, I-27100 Pavia, Italy.
¹³ II. Physikalisches Institut, University of Giessen, D-35392 Giessen, Germany.
¹⁴ Institute for Nuclear Research, RU-125047 Moscow, Russia.
¹⁵ Mount Allison University, Sackville, New Brunswick E4L1E6, Canada.
¹⁶ Rudjer Boskovic Institute, HR-10000 Zagreb, Croatia.
¹⁷ University of Massachusetts, Amherst, Massachusetts 01003, USA.
¹⁸ Institut für Experimentalphysik, Ruhr Universität, 44780 Bochum, Germany.

PMID: 38579200
DOI: 10.1103/PhysRevLett.132.121902

Abstract

We report the measurement of the helicity asymmetry E for the pπ^{0} and nπ^{+} final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. The results agree very well with data that were taken with a circularly polarized photon beam, showing that it is possible to simultaneously measure polarization observables that require linearly (e.g., G) and circularly polarized photons (e.g., E) and a longitudinally polarized target. The new data cover a photon energy range 270-1400 MeV for the pπ^{0} final state (230-842 MeV for the nπ^{+} final state) and the full range of pion polar angles, θ, providing the most precise measurement of the observable E. A moment analysis gives a clear observation of the pη cusp in the pπ^{0} final state.