We report a direct measurement of the final-state energy spectrum in the electromagnetic dissociation of Si28 into p+ Al27 at an energy of 14.6 GeV/nucleon. The final-state energy is obtained through a calculation of the p-27Al invariant mass in kinematically reconstructed events. The final-state energy spectrum for all targets is peaked near the isovector giant-dipole resonance in Si28 and the dependence of the magnitude of the cross section on target charge confirms that the excitation is largely electromagnetic. By exploiting the expected scaling behavior on target Z and A, the background from nuclear interactions is evaluated and subtracted, leaving a pure electromagnetic dissociation final-state energy distribution. This distribution is well reproduced by simulated events, in which the photon spectrum calculated in the Weiszäcker-Williams approximation is combined with experimental data on the photonuclear reaction Si28(,p) Al27, and slight differences are observed only at low final-state energy.
ASJC Scopus subject areas
- Nuclear and High Energy Physics
- Physics and Astronomy(all)