Photoexcitation of the quasi-bound Δ nuclear state in the <Superscript>12</Superscript>C(γ, π<Superscript>−</Superscript>pp) reaction

Photoproduction of negative pions on the carbon nucleus in the (γ, π^?p) and (γ, π^?pp) reactions was experimentally studied. The measurement results are explained within the framework of a model which supposes formation of an intermediate quasi-bound Δ nuclear state (Δ nucleus) decaying with emission of a pion and a nucleon. The mass and width of the Δ nucleus ¹¹B_Δ are evaluated.     

Photoproduction of pion-nucleon pairs on nuclei in the Δ(1232)-resonance region

Data from three experiments performed at the linear accelerator in Saclay, the Tomsk synchrotron, and the MAMI accelerator in Mainz and devoted to studying single pion photoproduction on light nuclei that is accompanied by nucleon emission are analyzed. The behavior of respective experimental cross sections, which is inexplicable in the impulse approximation, is interpreted within a model where the formation of an intermediate quasibound isobar-nucleus state is followed by its decay to a final state involving a pion and a nucleon.     

Estimate of the Δ(1232) component in the 12C nucleus

The cross section for the ¹²C(γ, π⁺ p) reaction was measured in the range of the Δ(1232) isobar. The data were analyzed using the models taking into account the nucleon and isobaric degrees of freedom of the ¹²C nucleus. The conclusion is drawn that in the large-momentum transfer range the π⁺ p pairs are produced in the course of the direct knocking-out of Δ⁺⁺ isobar from the nucleus. The probability of finding the Δ isobar in the ground-state ¹²C nucleus is estimated at 0.018±0.005 Δ isobars per nucleon.     

Formation of two pions on nuclei in A(γ, ππN)B reactions

A model is proposed for double pion photoproduction on nuclei that is accompanied by nucleon emission. Simple models that faithfully reproduce single-particle differential cross sections are used to describe photon interactions with intranuclear nucleons. The calculated cross sections for pion photoproduction on ¹²C nuclei are compared with inclusive pion spectra measured in the second resonance region of photon energies.     

Measurements of the Mean Free Paths of the Proton and Pions in the Nuclear Matter

The results of measuring the yields of neutral and charged pions in the (, p) reaction on Li, C, and Al nuclei are presented as functions of the proton energy and azimuth angle of pion emission. The experiment was performed in the second resonance region of the photon energy. The measurements are analyzed within the model of single and double quasi-free pion photoproduction. The energy dependences of the mean free path of the proton and neutral and charged pions are obtained based on the dependence of the reaction yield on the atomic number of the target nucleus.     

Delta-isobar configurations in 12C and 16O nuclei

The differential yield of the reaction ¹⁶O(γ, π ⁺ p) at the maximum photon energy of 450 MeV was measured in the region of high momentum transfers to the residual nuclear system. The experimental results obtained for the ¹⁶O nucleus and the cross section measured earlier for the reaction ¹²C(γ, π ⁺ p) were analyzed on the basis of a model that takes into account the admixture of isobar states in the nuclear wave function. The probabilities for the delta-isobar configurations in the ground states of the carbon and oxygen nuclei per nucleon were estimated empirically at 0.012 ± 0.003 ± 0.002 and 0.019 ± 0.003 ± 0.003, respectively.