Electromagnetic matrix elements for negative parity nucleons

Abstract

Here we present preliminary results for the evaluation of the electromagnetic form factors for the lowest-lying negative-parity, spin-$\frac{1}{2}$ nucleons, namely the $S_{11}(1535)$ and $S_{11}(1650)$, through the use of the variational method. We find that the characteristics of the electric form factor, $G_E$, are similar between these states, however significant differences are observed between the quark-sector contributions to the magnetic form factor, $G_M$. Within simple constituent quark models, these states are understood to be admixtures of $s=\frac{1}{2}$ and $s=\frac{3}{2}$ states coupled to orbital angular momentum $\ell =1$. Our results reveal a qualitative difference in the manner in which the singly-represented quark sector contributes to these baryon magnetic form factors.

Comments: 7 pages, 5 figures; talk presented at the 32nd International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia University, New York, USA