Electromagnetic dissociation of relativistic 28Si by nucleon emission

A detailed study of the electromagnetic dissociation of 28Si by nucleon emission at Elab/A = 14.6 GeV/nucleon was carried out with 28Si measurements were made in the fixed target relativistic heavy ion experiment E814 operating at the Brookhaven National Laboratory. The E814 apparatus consists of detectors in the target area which measure the energy and charged multiplicity, and a forward spectrometer which measures the position, momentum and energy of the reaction fragments. The exclusive electromagnetic dissociation cross sections for decay channels having multiple nucleons in the final state have been measured with the aid of the E814 apparatus which enables the selection of events produced in pure electromagnetic interactions. The measured cross sections agree well with previous measurements obtained for the removal of a few nucleons with the E814 apparatus as well as with measurements on total charge removal cross section on the target charge ZT and the target mass AT confirms that for higher Z targets the excitation is largely electromagnetic. Direct measurements of the excitation energy for the electromagnetic dissociation of 28Si → p + 27Al and 28Si → n +27Si have been obtained through a calculation of the invariant mass in kinematically reconstructed events. The excitation energy spectrum for all targets peak near the isovector gain dipole resonance in 28Si have been investigated with cross section measurements as well as with excitation energy reconstruction. Effects due to the surviving peripheral nuclear interactions and the contribution from double interactions on experimental observations are discussed