NUCLEON RESONANCES IN NUCLEI AND QUARK EXCHANGE

We investigate the photoexcitation of nucleon resonances in nuclei taking into account t quar structure of the nucleon. We calculate the total strength of the M1, E1, and E2 excitation in a two-nucleon system, considered as two three-quark clusters with a properly antisymmetrize w function. The calculations show that the resonance excitation in the deuteron is not modified with respect to the free nucleon case. In contrast, when the nucleon relative distance assumes typical nuclear values, quark exchange leads to a approximately 11% damping of the D13 resonance and approximately 23% of the F15, but it leaves the DELTA excitation practically unaffected, in agreement with the recent photoabsorption measurements.