Analytic parametrizations of the ${\gamma }^{*}N\to N(1440)$ form factors inspired by light-front holography

We present analytic parametrizations for the ${\gamma }^{*}N\to N(1440)$ form factors derived from light-front holography in leading twist approximation. The new parametrizations describe the electromagnetic form factors using analytic functions dependent on the masses of the $\rho$ meson and respective radial excitations, as well as the masses of the nucleon and the resonance $N(1440)$. The free parameters of the model, associated with three independent couplings, are interpreted as bare couplings, and are fixed by the nucleon data for large $Q^2$. The proposed parametrizations compare remarkably well with the empirical data for $Q^2>2{\mathrm{GeV}}^2$, corroborating the dominant role of the valence quark degrees of freedom in the ${\gamma }^{*}N\to N(1440)$ transition.

Figure 1

${\gamma }^{*}N\to N(1440)$ transition form factors $F_{1p}^{*}$ and $F_{2p}^{*}$. Data are from Refs. [34, 35].

Figure 2

${\gamma }^{*}N\to N(1440)$ helicity amplitudes. Data are from CLAS [34, 35] (solid circles), Particle Data Group [36] for $A_{1/2}$ (diamond) and A1 collaboration [37] for $S_{1/2}$ (square).

Figure 3

Proton and neutron electric and magnetic form factors. Data are from Refs. [28, 29, 30].

Figure 4

Ratios between proton electromagnetic form factors. Data are from Ref. [28].