Abstract
The first experimental investigation of the near-threshold cross section for incoherent $\pi^-$ photoproduction on the deuteron $\gamma$ d -> $\pi^-$ pp is presented. The experimental technique involved detection of the ~131 MeV gamma ray resulting from the radiative capture of photoproduced $\pi^-$ in the target. The total cross section has been measured using an unpolarized tagged-photon beam, a liquid-deuterium target, and three very large NaI(Tl) spectrometers. The data are compared to theoretical models that give insight into the elementary reaction $\gamma$ n -> $\pi^-$ p and pion-nucleon and nucleon-nucleon final-state interactions.
Highlights
Incoherent pion photoproduction on the deuteron, γ d → π NN, provides information on the elementary reaction on the nucleon γ N → π N and on pion-nucleon (π N) and nucleon-nucleon (NN) final-state interactions (FSI)
Used to obtain values for this and other photoproduction amplitudes. These are vital inputs to low-energy descriptions of hadron physics based on dispersion relations [3] or chiral perturbation theory (χ PT) [4]. The latter, which is used for comparison with experimental data in this article, is an effective field theory of quantum chromodynamics (QCD), where hadrons, instead of quarks and gluons, act as relevant degrees of freedom. χ PT emerges from the QCD Lagrangian in the chiral limit of vanishing up and down quark masses and offers a way to investigate the fundamental symmetries and interactions of the strong force in an energy regime where QCD is nonperturbative
The data acquisition was triggered by an energy deposition greater than ≈50 MeV in any NaI(Tl), which initiated the readout of the analog-to-digital converters (ADCs) and started the to-digital converters (TDCs)
Summary
Incoherent pion photoproduction on the deuteron, γ d → π NN, provides information on the elementary reaction on the nucleon γ N → π N and on pion-nucleon (π N) and nucleon-nucleon (NN) final-state interactions (FSI). The near-threshold cross section for the elementary reaction is sensitive to the E0+ amplitude, which has a long history of theoretical studies closely related to measurements of near-threshold pion photoproduction [1]. Used to obtain values for this and other photoproduction amplitudes These are vital inputs to low-energy descriptions of hadron physics based on dispersion relations [3] or chiral perturbation theory (χ PT) [4]. The latter, which is used for comparison with experimental data in this article, is an effective field theory of quantum chromodynamics (QCD), where hadrons, instead of quarks and gluons, act as relevant degrees of freedom. The well-understood radiative capture (RC) reaction on the deuteron, π −d → γ nn [14], with an endpoint photon-energy of 131.4 MeV, is exploited in a novel way for the yield determination of the photoproduced π −
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