Speaker
Description
While QCD is regarded as a mature theory of interacting quarks, due to the complexity of the nucleon, a successful description of its spectrum of excited states remains a huge challenge. The photo-couplings to excited $N$ states provide benchmark tests for models. These require a determination of photo-production amplitudes and are extracted through detailed partial-wave analyses (PWA), which must be fit to many different polarization observables to control ambiguities.Since the electromagnetic interaction is not isospin invariant, the $N$ photo-couplings for neutron and proton targets are different. While there are considerable proton data, there are very little neutron target data and almost no spin-dependent data. As a result, the photo-couplings to states excited from neutrons are very poorly determined. To address this issue, the Jlab E06-101 ($\it{g14}$) experiment was performed during 2011-2012 using the CLAS detector in Hall B with circularly and linearly polarized photons incident on longitudinally polarized Deuterons in frozen-spin targets of solid Hydrogen-Deuteride (HD). First results will be discussed for the beam-target helicity asymmetry ($E$) in the $\gamma + n(p) \rightarrow \pi^- + p(p)$ reaction spanning the nucleon resonance region from invariant mass $W$= $1500$ to $2300$ MeV. These will be compared to PWA predictions with their associated photo-couplings $^1$. Other observables are under study and preliminary results will be presented.
- This work has been accecpted by Physical Review Letters; arXiv:1705.04713
