Investigation of the conjectured nucleon deformation at low momentum transfer

We report new precise H$(e,e^{\mathrm{\prime }}p){\pi }^0$ measurements at the $\mathrm{\Delta }(1232)$ 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 ${\gamma }^{\ast }N\to \mathrm{\Delta }$ 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 $M^{3/2}{1+} = (41.4 \pm 0.3{stat+sys}\pm 0.4_{model})(10^{-3}/m_{\pi^+})$. They give credence to the conjecture of deformation in hadronic systems favoring, at low $Q^2$, the dominance of mesonic effects.