Measurement of the p(γ,π^{0}) cross section at threshold

Abstract

Differential and absolute cross sections for the reaction /?(y,/r°) have been measured with energydefined photons in the threshold region (i^r = 131.4-157.2 MeV). The Eo+ amplitude has been extracted out of the data. The values found are in disagreement with predictions of low-energy theorems.

Threshold Neutral Pion Photoproduction on the Proton

“…There have been many studies of the pion photoproduction data near threshold in the past few decades [1][2][3][4][5][6][7][8][9], which were in good agreement with the data existing at the time [10,11]. While ChPT models very well describe the charged channels of pion photoproduction even at tree level, this is not the case for the neutral channels, where the inclusion of higher orders and loop diagrams leads to important contributions.…”

Threshold pion electroproduction at large momentum transfers

“…Twenty years later, a renewed interest to threshold pion production was trigged by the extensive data that became available on γp → π 0 p [6,7] and, most importantly, γ * p → π 0 p, at the photon virtuality Q 2 ∼ 0.04 − 0.1 GeV 2 [8]. At the same time, the advent of chiral perturbation theory (CHPT) has allowed for the systematic expansion of low-energy physical observables in powers of the pion mass and momentum.…”

Aspects of near-threshold neutral pion photoproduction off protons

“…First, over the last decade fairly precise differential and total cross section data have been obtained at MAMI [3,4,5] and SAL [6,7,8]. A further experiment involving linearly polarized photons was performed at MAMI, which not only improved the differential cross sections but also gave the first determination of the photon asymmetry [9].…”