Double polarisation observable G for single pion photoproduction from the proton

Abstract

We report measurements of π+ and π0 meson photoproduction from longitudinally spin-polarised protons by an energy tagged (0.73-2.3 GeV) and linearly polarised photon beam. A close to complete solid angle coverage for the reaction products was provided by the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The double-polarisation observable G is extracted from Maximum Likelihood fits to the data, enabling the first accurate determination for the reaction γ→p→→π+n, while also significantly extending the kinematic coverage for γ→p→→π0p. This large data set provides an important constraint on the properties and spectrum of excited nucleon states decaying to Nπ in the mass range from 1.4 to 2.2 GeV, as well as for background (non-resonant) photoproduction processes. The considerable improvement achieved in the description of the observable G within the SAID and Bonn-Gatchina approaches after implementation of our data, illustrates that the partial-wave analyses now significantly extend the knowledge on Nπ photoproduction amplitudes at W>1.8 GeV. A partial-wave analysis using the new high-precision data set has a large impact on the extracted properties of high-spin nucleon excited states.

Metadata

Funding Information: This work has been supported by the U. K. Science and Technology Facilities Council (ST/P004385/2, ST/T002077/1, and ST/L00478X/2) grants, as well as by the Department of Energy (DE-SC0016582) grant. We also acknowledge the outstanding efforts of the staff of the Accelerator and Physics Divisions at Jefferson Lab that made this experiment possible. This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Awards No. DE?SC0016583 and DE?SC0016582 and Contract No. DE?AC05?06OR23177. Further support was provided by the U.S. National Science Foundation, the Italian Istituto Nazionale di Fisica Nucleare, the Chilean Comisi?n Nacional de Investigaci?n Cient?fica y Tecnol?gica (CONICYT), the French Centre National de la Recherche Scientifique, the French Commissariat ? l'?nergie Atomique, and the National Research Foundation of Korea. Funding Information: This work has been supported by the U. K. Science and Technology Facilities Council ( ST/P004385/2 , ST/T002077/1 , and ST/L00478X/2 ) grants, as well as by the Department of Energy ( DE-SC0016582 ) grant. We also acknowledge the outstanding efforts of the staff of the Accelerator and Physics Divisions at Jefferson Lab that made this experiment possible. This work was supported in part by the U.S. Department of Energy , Office of Science, Office of Nuclear Physics under Awards No. DE–SC0016583 and DE–SC0016582 and Contract No. DE–AC05–06OR23177 . Further support was provided by the U.S. National Science Foundation , the Italian Istituto Nazionale di Fisica Nucleare , the Chilean Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), the French Centre National de la Recherche Scientifique , the French Commissariat à l'Énergie Atomique , and the National Research Foundation of Korea . Publisher Copyright: © 2021 The Author

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