Investigation of the conjectured nucleon deformation at low momentum transfer

Abstract

We report new precise H$(e,e^{\prime }p){\pi }^0$ measurements at the $\Delta (1232)$ resonance at $Q^2=0.127$ (GeV/c)${}^2$ using the MIT/Bates out-of-plane scattering (OOPS) facility. The data reported here are particularly sensitive to the transverse electric amplitude ($E2$) of the ${\gamma }^{\ast }N\to \Delta$ transition. Analyzed together with previous data yield precise quadrupole to dipole amplitude ratios $EMR=(-2.3\pm 0.3_{stat+sys}\pm 0.6_{model})$ and $CMR=(-6.1\pm 0.2_{stat+sys}\pm 0.5_{model})$ and for $M_{1+}^{3/2}=(41.4\pm 0.3_{stat+sys}\pm 0.4_{model})(10^{-3}/m_{{\pi }^{+}})$. They give credence to the conjecture of deformation in hadronic systems favoring, at low $Q^2$, the dominance of mesonic effects.

4 pages, 1figure