the paper in Sect. \[sect:summary\].

Holographic Confinement plus One-Gluon Exchange {#sec:ingredients}
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We extend light-front holography by introducing realistic QCD interactions such as the one-gluon exchange interaction with running coupling [@Li:2015zda]. In addition we include finite quark masses, important for heavy flavors, as well as a longitudinal confining potential to complement the transverse holographic confining potential. Spin structure and excited states (radial and angular) naturally emerge from the one-gluon exchange and its non-perturbative interplay with the confining potential [@Li:2016wwu]. The effective Hamiltonian $H_\text{eff}\equiv P^+P^-_\text{eff}-\vec P^2_\perp$ reads, $$\begin{gathered}
\label{eqn:Heff}
H_\mathrm{eff} = \frac{\vec k^2_\perp + m_q^2}{x} + \frac{\vec k^2_\perp+m_{\bar q}^2}{1-x}
+ \kappa^4 \vec \zeta_\perp^2 - \frac{\kappa^4}{(m_q+m_{\bar q})^2} \partial_x\big( x(1-x) \partial_x \big)  \\
- \frac{C_F4\pi\alpha_s(Q^2)}{Q^2}\bar u_{s'}(k')\gamma_\mu u_s(k) \bar v_{\bar s}(\bar k) \gamma^\mu v_{\bar s'}(\bar k').\end{gathered}$$ where $\vec \zeta_\perp \equiv \sqrt{x(1-x)} \vec r_\perp$ is Brodsky and de Téramond’s holographic variable [@Brodsky:2014yha], $\partial_x f(x, \vec\zeta_\perp) = \partial f(x, \vec \zeta_\perp)/\partial x|_{\vec\zeta}$, $C_F = (N_c^2-1)/(2N_c)=4/3$ is the color factor for the color singlet state. $\kappa$ is the strength of the confinement, and $m_q$ ($m_{\bar q}$) is the mass of the quark (anti-quark). $Q^2 = -(1/2) (k'-k)^2- (1/2) (\bar k'-\bar k)^2$ is the average 4-momentum squared carried by the exchanged gluon. In terms of kinematical variables, $$Q^2 