Paul E. Ulmer

My research focusses on studies of few-body atomic nuclei, in particular the deuteron and ⁴He.  Using electron scattering at Jefferson Lab these nuclei are broken up and an emitted proton is detected in coincidence with the scattered electron. 

The deuteron, consisting of a proton and neutron, is the simplest nucleus except for the proton itself.   It therefore provides the clearest window into the force between nucleons, which is a manifestation of the strong force governed by Quantum Chromodynamics (QCD).  Studies of the "break-up" reaction, wherein the neutron and proton within the deuteron become free, can provide constraints on models of the nucleon-proton force.  Further, by looking at the distribution of emitted protons and the "asymmetry" of this distribution about the direction of the momentum transfer of the electron, we can constrain relativistic models of the deuteron.   At Jefferson Lab the combination of high beam energy, beam current and duty factor allow studying this reaction at very short distance scales. Further, the high resolution spectrometers of Hall A allow precise determination  of the kinematics of the final state minimizing systematic uncertainties and permitting a clean theoretical interpretation.  We have recently performed a very extensive study of the deuteron breakup reaction in (e,e'p) and are now analyzing these data (click here for the experiment summary).

For ⁴He we examine the polarization of the emitted proton after scattering by polarized electrons.   This polarization is sensitive to the (electromagnetic) structure of the proton.  By comparing the reaction on ⁴He to that for a hydrogen (proton) target, we can infer the extent to which the proton structure is modified by the nuclear medium.  This information has been long sought for but has proved elusive using other techniques.  In contrast, the polarization experiments are expected to be much more cleanly interpretable and hold promise for unraveling "medium modifications" from more conventional effects.  For results from our previous experiment click here.  For an article (in German) about our previous experiment click here.  For the latest approved proposal click here.

The data from these experiments will be compared to various state-of-the-art theoretical models.  For this purpose, I have written a simulation program,
MCEEP,  allowing folding of theoretical models over the experimental acceptance.