“Extracting the number of short-range correlated nucleon pairs from inclusive electron scattering data” published in Physical Review C

Comparisons of inclusive quasi-elastic cross sections in “x_B>1 kinematics” have long been interpreted as a measure of the relative number of high-momentum nucleons in different nuclei. This interpretation relies on a the effect of a kinematic envelope relating the inclusive scattering parameter Bjorken-x, x_B, and the minimum nucleon momentum. In our latest paper, “Extracting the number of short-range correlated nucleon pairs from inclusive electron scattering data,” we argue that the picture is a bit more subtle.

In quasi-elastic scattering (in which the electron ejects an intact proton or neutron from the nucleus) not all combinations of x_B and nucleon momentum legally conserve energy and momentum. In order to satisfy this conservation, scattering at high x_B can only happen from a nucleon with high momentum. There is an envelope (shown in the figure above), above which the reaction can proceed, below which it is forbidden.

To determine the number of high-momentum nucleons in a nucleus, say carbon, one could compare the high-x_B inclusive cross section in electron-carbon scattering to the same quantity in electron-deuterium scattering. By requiring high-x_B, one is directly probing high-momentum nucleons. The ratio of cross sections can be interpreted as a ratio of the number of high-momentum nucleons in the nucleus.

However, we point out that nuclear effects, such as the way the high-momentum of the nucleon is balanced, as well as the residual excitation energy of the nuclear remnant after the scattering interaction can change the kinematic envelope. We argue that such effects can distort any extraction.

We follow this up with calculations, built around the tool called “Generalized Contact Formalism” that show the wide-range of combinations of nuclear parameters that are consistent with the data from previous scattering experiments.

This paper was a result of the hard work of several collaborators: Hebrew University (Jerusalem) graduate student Ronan Weiss, as well as MIT graduate students Andrew Denniston (pictured below) and Jackson Pybus.