Elong-16-02-19

PAC 43

The PAC43 Report gave the Azz and T20 experiment C2 approval.

Motivation

The motivation of the proposed experiment is to probe short-range repulsion and tensor force in nucleon-nucleon interaction by measuring tensor asymmetries from quasi-elastic and elastic deuteron scattering - tensor asymmetries are predicted to be sensitive to the D state probability in the deuteron wave function, as well as relativistic effects. The additional proposed measurement on T20 will also provide data for this observable.

Measurement and Feasibility

The proposed measurements will be carried out in Hall C using a tensor polarized deuteron target, the HMS, and the SHMS spectrometers. The proposed kinematic settings were chosen to cover both the quasi-elastic and elastic kinematics in order to provide data on T20 as well as calibration of the tensor polarization measurement using an existing data point from NIKHEF at low momentum transfer squared. The proposed measurements appear feasible and there are no major technical issues with the assumption that a tensor polarization of 30% or more will be achieved before the proposed experiment will run.

Issues

The measurements, as proposed, will rely solely on positive tensor polarization due to the current UVa target setup. This has two drawbacks: (i) lower positive tensor polarization compared with the negative case; (ii) potential systematic issue associated with the ability to measure tensor asymmetries with only positive tensor polarization. The proponents are strongly encouraged to investigate techniques to obtain negative tensor polarization in addition to the positive tensor polarization. While the proposed measurements are important, the PAC believes more work is needed to demonstrate the impact of the measurements in the following two areas: (i) higher tensor polarization, particularly the negative one, should reduce uncertainties in the region that is sensitive to short-range repulsion and tensor force; (ii) provide quantitative comparison between the proposed tensor asymmetry and unpolarized measurements regarding sensitivity to the D-state probability. The NMR technique using line shape analysis for the tensor polarization determination needs to be further developed.

Recommendation

Conditional approval (C2)