Delta isobar in (h,t) reactions

We study the delta isobar problem found in the (h,t) reactions at E=2GeV. We find the nuclear medium effect is not expected large due to the fact that the (h,t) reactions can probe only the low density region at the nuclear surface. Instead, we find that the projectile delta process, hitherto neglected, is responsible in producing a different spectral shape for neutrons from that for protons. The experimental evidence for this prediction is seen in the spectrum for deuterons, which is different from that for protons. This is claimed to be the major source of the delta isobar problem for the case of the nuclear targets. The essential features of other experimental data concerning the delta isobar excitations are also understood by considering this mechanism. (author)