Close Nucleon Encounters

HIC for FAIR Colloquium

Prof. Mark Strikman

Pennsylvania State University

Prof. L. von Smekal

Importance of short-range nucleon correlations (SRC) for microscopic description of the nuclear structure was understood already in the fifties by the leaders of the nuclear theory such as H.Bethe. Numerous attempts to observe SRC experimentally in the sixties have failed. So, by late seventies the task experimental observation of SRCs was considered hopeless. We have argued in late seventies that the problem was with the use of processes in which energy and momentum transfer to the nucleus were not high enough. Price to pay for use of high energy processes is the need to account for dominance of the space – time evolution of high energy processes along the light cone, which required development of the light cone quantum mechanics of nuclei. Unfortunately, no appropriate experimental facilities were available at that time. The recent progress described in the talk is due to the studies of two classes of hard high momentum transfer reaction – inclusive (e,e’) scattering at xBj > 1, and quasielastic knockout of high momentum nucleons by protons and electrons. The studies directly confirmed a) the presence of universal high momentum proton – neutron and proton - proton SRCs (total probability ~20% for A> 10) , b) dominance of SRC at high nucleon momenta, c) the dominance of pn SRCs in a wide momentum range. Open questions will be outlined and the need for complementary experiments using proton, photon and antiproton beams will be emphasized.

I will also outline briefly the recent developments in the experimental studies of the EMC effect which suggest that the proton - neutron SRC play dominant role in the EMC effect. In combination with experimental evidence that the SRC are predominantly nucleonic these observations lead to even more stringent restrictions on the theoretical models than the ones which were discussed in the analyses of the nineties. Example of the model which is not killed experimentally will be presented.