Photoproduction of [rho]⁰ Mesons on complex nuclei

Abstract

An experiment was performed on the reaction y + A + A + p0 + A + [pi]+ + [pi]- the DESY 7.5 GeV electron synchrotron. Using a double arm magnetic spectrometer, approximately 106 dipion events were detected on thirteen complex nuclei covering a range from Beryllium to Uranium. The events were in a kinematic region defined by 20 intervals in dipion mass from 400 to 1000 MeV/c 2, 10 intervals in the po resonance momentum from 3.5 to 7 GeV/c, and 20 intervals in the transverse momentum transfer from 0.0 to -0.04 (GeV/c) . The data were corrected for systematic effects and differential cross-sections da/dndm(A,m,p,t) were extracted, revealing the predominant dynamical features of the data. Further analysis was carried out using current models for photoproduction and scattering on complex nuclei. The aim of this analysis, was to: 1) study nuclear density distributions by fitting the t-dependence of the cross-sections for each A to determine the nuclear radii seen by the po meson. 2) extract the absolute and relative forward po production cross-sections by fixing A, p, and t and studying the dipion spectrum as a function of invariant mass. This gives a determination of the po line-shape and background. 3) extract the po-nucleon cross-section apN and the y-p coupling constant y2 /4r. pN By studying the nuclear density p distributions and the A-dependence of the production cross-sections, one determines the rate of reabsorption of po by nuclear matter and the effective single-nucleon forward production cross-section Ifo12 and the two quantities above in a self-consistent manner. Results of the analysis are: ... Cross-sections and resonance parameters are detailed in the text.