ANOMALOUS MASS-NUMBER DEPENDENCE OF NUCLEAR TRANSPARENCY

We examine the target mass number (A) dependence of the nuclear transparency calculated for (e, e' p) reactions. Generally, the transparency is proportional to A(-1/3) for large A's and has weaker A-dependence as A decreases. The conventional nuclear physics calculation yields a transparency whose A(-1/3) dependence is reached in rather light nuclei (around A = 20). If either the proton mean-free path in nuclei becomes substantially longer, or the internal structure of the proton is explicitly incorporated in the calculation, however, the A(-1/3) dependence is reached only in extremely heavy nuclei. The A-dependence should thus serve as a signature of the so-called color-transparency phenomenon.