0000000000411870
AUTHOR
T. Lamparter
Quasifreeπ+production studied using theC12(γ, π+n)B11reaction in theΔ(1232)resonance region
Results are presented from a coincidence study of the {sup 12}C({gamma},{pi}{sup +}{ital n}){sup 11}B quasifree pion production reaction made in the {Delta}-resonance region using tagged photons. Cross sections for reactions originating on 1{ital p}-shell protons are found to be significantly larger than predicted by calculations based on quasifree pion production. It is suggested that more sophisticated calculations, perhaps including medium effects, may be required to reproduce the data. {copyright} {ital 1996 The American Physical Society.}
Investigation of multiparticle final states in12C photoreactions
The ${}^{12}\mathrm{C}(\ensuremath{\gamma},pn)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},ppp)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},p{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})$ reactions have been studied using tagged photons of energy ${E}_{\ensuremath{\gamma}}=250$--600 MeV. A model which includes all major absorption mechanisms and final state interactions gives results that agree well with the shapes of missing energy spectra, but for some channels the predicted cross sections are too large.
The angular distribution of the 12C(γ,pn) reaction for Eγ=120−150 MeV
The angular distribution of nucleons emitted in the 12C(γ,pn) reaction has been measured using tagged photons at the Mainz microtron MAMI. The variation of the reaction strength with the polar angles of the two emitted nucleons is reported for Eγ=120−150 MeV. The proton angular distribution peaks at more backward angles than the 2H(γ,p) differential cross section indicating a departure from the simple quasi-deuteron model of 2N photo-emission. The distribution shape is in reasonable agreement with microscopic theoretical models which include both π- and ρ-exchange.
Mechanisms in theC12(γ,pn)and(γ,pp)Reactions
${}^{12}\mathrm{C}(\ensuremath{\gamma},pn)$ and $(\ensuremath{\gamma},pp)$ cross sections have been measured in kinematics which emphasize direct $2N$ knockout for ${E}_{\ensuremath{\gamma}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}120--400\mathrm{MeV}$ and ${\ensuremath{\theta}}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}23\ifmmode^\circ\else\textdegree\fi{}--152\ifmmode^\circ\else\textdegree\fi{}$. The cross sections for both reactions peak strongly in the $\ensuremath{\Delta}$-resonance region. Theoretical calculations that account for the medium dependence of the $\ensuremath{\Delta}$ propagator predict a similar photon energy dependence to the data and describe the …
Proton photoproduction from 12C
Abstract The 12 C(γ,p) differential cross-section in the Δ-resonance region has been measured using tagged photons. Data are presented for 20 MeV wide photon energy bins at 200, 300, 400 and 500 MeV and for proton angles from 52° to 128°. The present 12 C(γ,p) measurements are compared with previous experiments carried out at Frascati, Tokyo and Bonn. Comparisons are also made with theoretical calculations developed at Gent and Valencia which provide an interpretation of the photon reaction mechanism in terms of the major contributing processes. Coincidence data with correlated neutrons, protons and pions are also presented.
The12C(γ,NN)reaction studied over a wide kinematic range
The ${}^{12}\mathrm{C}(\ensuremath{\gamma},np)$ and ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp)$ reactions have been studied using the Glasgow photon tagging spectrometer at the Mainz MAMI electron microtron for ${E}_{\ensuremath{\gamma}}=150--700$ MeV over a kinematic range which extends well beyond the approximately back-to-back detector arrangements of previous work. For ${}^{12}\mathrm{C}(\ensuremath{\gamma},np)$ the general trends of the missing energy distributions are reproduced over a wide range of kinematics and photon energies by the theory developed by the Valencia group. The corresponding ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp)$ channel is overestimated by a factor of \ensurem…
12C(γ,π+n) and 12C(γ,π+p) reactions across the Δ resonance region
Abstract Differential cross-sections from (γ,π+n) and (γ,π+p) experiments on 12C are presented together with a microscopic model calculation. The comparison of experimental data with theory confirms that quasifree pion production is the dominant process for the (γ,π+n) reaction. The comparison of (γ,π+p) with (γ,π+n) data shows the importance of final state interactions. first time to experimentally study the strength and the possible mechanisms involved in the final state interaction.
Nuclear pion photoproduction in theΔresonance region
A measurement of the /sup 12/C( gamma , pi /sup +/n)/sup 11/B reaction in quasifree pi -production kinematic regimes has been performed using tagged photons in conjunction with large solid angle pi and n detectors. The aim of the experiment was to investigate predicted modifications to the Delta excitation of nucleons and their subsequent propagation and decay, brought about by the nuclear medium. Differential cross sections are presented for photon energies spanning the Delta (1232) excitation region. The measurements are consistent with distorted wave impulse approximation calculations in which the amplitude for proton Delta excitation, followed by Delta propagation and decay to pi /sup +…