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We studied the photoproduction of dileptons from strong electromagnetic fields generated by the nucleus in relativistic heavy-ion collisions. The production of dileptons is calculated based on the Equivalent Photon Approximation (EPA) method, which depends on the strength of the electromagnetic fields and the density of protons in the nucleus. With the EPA method, we construct the connections between dilepton photoproduction and the electromagnetic form factors in the nucleus. Finally, the nuclear proton densities can be determined with the dilepton photoproduction, which is employed to extract the neutron skin in the nucleus. Our calculations indicate that the dilepton photoproduction varies evidently with different proton densities in the nucleus, suggesting a deeper symmetry underlying the connections between proton density (or the neutron skin) and the dilepton photoproduction. This offers a new way to study the neutron skin in the nucleus. [ABSTRACT FROM AUTHOR]

The associated photoproduction of K Λ from the proton in the low energy region is studied using an isobar model in which the nonresonant contributions are obtained from the nonlinear sigma model with chiral SU(3) symmetry which predicts, in a natural way, the contact term with its coupling strength along with the coupling strengths of the various Born terms predicted by the nonlinear sigma model. The present model is an extension of the nonlinear sigma model with chiral SU(2) symmetry, used earlier to study the photo, electro, and neutrino productions of pions. In the resonance sector, the contributions from the well established nucleon resonances (R) in the s channel, the hyperon resonances ( Y ∗ ) in the u channel, and the kaon resonances ( K ∗ and K 1 ) in the t channel having spin ≤ 3 2 and mass < 2 GeV with a significant branching ratio in K Λ decay mode, have been considered. The strong and electromagnetic couplings of the s channel nucleon resonances are taken from experiments while the couplings for the resonances in the t and u channels are fitted to reproduce the current data on the associated photoproduction of K Λ in this energy region. The numerical results are presented for the total and differential cross-sections and are compared with the available experimental data from CLAS and SAPHIR as well as with some of the recent theoretical models. [ABSTRACT FROM AUTHOR]