& & 16\
& & & & 1.390 & 4.901 & 39 & 7 & & 24\
& & & & 1.389 & 4.902 & 38 & 8 & & 32\

Decay Constants {#sec:decay}
---------------

Decay constants are defined as the local vacuum-to-hadron matrix elements: $$\begin{aligned}
 \langle 0 | \overline \psi(0) \gamma^+\gamma_5 \psi(0) | P(p) \rangle =\,& \imag p^+ f_P,  \\
 \langle 0 | \overline \psi(0) \gamma^+ \psi(0) | V(p, \lambda) \rangle =\,& e^+_\lambda M_V f_V.
 \end{aligned}$$ Here only the “good” currents (the “+” component) are used. The corresponding LFWF representation reads [@Lepage:1980fj], $$\label{eqn:dc}
\frac{f_{P,V}}{2 \sqrt{2N_c}} =  \int_0^1 \frac{\dd x}{2\sqrt{x(1-x)}} \int\frac{\dd^2k_\perp}{(2\pi)^3}
\psi^{(\lambda=0)}_{\uparrow\downarrow\mp\downarrow\uparrow}(x, \vec k_\perp).$$ For this calculation, we choose $N_{\max}=8$ for charmonium and $N_{\max}=32$ for bottomonium, roughly corresponding to $\Lambda_\textsc{uv}
\triangleq \kappa \sqrt{N_{\max}} \approx 1.7 m_q$, where $\Lambda_\textsc{uv}$ is the UV regulator, and $m_q$ is the heavy quark mass. This choice is motived by the competition between the needs for both a better basis resolution and a lower UV scale since our model does not incorporate radiative corrections. We also provide an indicator for sensitivity by altering the basis truncation parameter $N_{\max}$. The resulting charmonium and bottomonium decay constants are shown in Fig. \[fig:decay\], which also collects PDG values converted 