Photoproduction of π0-Mesons from the Nucleon and Deuteron

Abstract

The photoproduction of π 0 -mesons from the nucleon and deuteron has been studied for incidents of photon energies up to 1.5 GeV. By using the MAID-2007 model for the process on the nucleon, we predict results for the unpolarized and helicity-dependent total cross sections of the semi-exclusive reaction γd→π 0 X (X=np+d) with the inclusion of rescattering effects. We find that rescattering effects yield a substantially large contribution. The extracted results are compared with the available experimental data and a satisfactory agreement is obtained. In addition, the contribution of γd→π 0 X (X=np+d) to the finite GDH integral has been evaluated by explicit integration up to 1.5 GeV and a total value of 256.96 µb has been obtained. Convergence of the GDH integral has been reached. AbstrakFotoproduksi Meson-π0 dari Nukleon dan Deuteron. Fotoproduksi meson-π 0 dari nukleon dan deuteron telah dipelajari untuk energi-energi foton datang hingga 1.5 GeV. Dengan menggunakan model MAID-2007 untuk proses produksi pada nukleon, kami meramalkan hasil-hasil perhitungan penampang lintang total tidak-terpolarisasi dan penampang lintang total bergantung-helisitas dari reaksi semi-eksklusif γd→π 0 X (X=np+d) dengan memasukkan efek rescattering. Hasil studi memperlihatkan bahwa efek rescattering memberikan kontribusi sangat besar. Perbandingan hasil-hasil ekstraksi dengan data eksperimen yang tersedia memperlihatkan kecocokan yang memuaskan. Sebagai tambahan, kontribusi dari proses γd→π 0 X (X=np+d) pada integral GDH berhingga telah dihitung dengan menggunakan integrasi eksplisit hingga 1.5 GeV dan nilai total sebesar 256.96 µb telah diperoleh. Konvergensi dari integral GDH telah tercapai.

Partial wave analysis for KΣ photoproduction on the nucleon valid from threshold up to W = 2.8 GeV

“…To conclude this section, although the present models yield different contributions to the GDH sum rule, the small contribution of KΣ channels implies that the contribution of pion and two-pion channels should be larger than those predicted by previous calculations [7][8][9]. Otherwise, we need to search for additional contributions, e.g.…”

“…For the sake of comparison with the previous calculations, instead of using equation (55) we use the definition of GDH integral Obviously, the largest contribution to the photoabsorption cross sections originates from the pion and two-pion photoproductions since the corresponding cross sections are almost two order of magnitude larger than that of kaon photoproduction. However, as shown in [7][8][9], equation (55) would be convergent if the contribution of kaon photoproduction on the proton was nearly +4 μb. It is shown in [5,6] that the contribution of Kaon-Maid for the proton anomalous magnetic moment is 2.93 μb, where the contribution of both K + Σ 0 and K 0 Σ + channels is 1.68 μb.…”

“…This sum rule connects the anomalous magnetic moment of the nucleon to the total absorption cross section of circularly polarized photon on longitudinally polarized nucleon. With the help of meson photoproduction data, it was shown that the sum rule converges [4][5][6][7][8][9]. Nevertheless, all related studies of GDH indicate that such a conclusion depends considerably on the phenomenological models used to explain the meson productions.…”

Different vertex parameterizations and propagators for the Δ contribution inπ-photoproduction

“…Since the pioneering work of Chew, Goldberger, Low and Nambu [3], extensive work during more than fifty years has shown that, below 0.45 GeV incident photon energy, the dominant mechanisms of the N N g p  reaction are the background and the Δ-resonant excitation. After that, high efforts have been carried out both experimentally (see for π and [31][32][33][34][35][36][37][38][39][40][41] for η-photoproduction and references therein) and theoretically (regarding π photoproduction see for example models developed in [42][43][44][45][46][47][48][49][50][51][52][53], MAID model [54][55][56], Bonn-Gatchina model [57,58], chiral Lagrangian based models [59][60][61], quark model [62], and [63][64][65] for η-photoproduction) to study the cross sections of π and η mesons photoproduction reactions, arriving in the present to higher incident photon energies of the order of 1.2 GeV. By this reason, to obtain a good theoretical description of the experimental data we need: (i) to add to the Δ resonance the contribution of those ones belonging to the second resonance region; and (ii) to perform a consistent description of the Δ resonance, nondivergent at energies well above its peak.…”