  In this letter we present the first systematic spectroscopic measurements of
the Near-InfraRed (NIR) hydrogen recombination lines Paschen alpha
($Pa_{\alpha}$ $\lambda = 1.875 \mu m$) and Brackett beta ($Br_{\beta}$
$\lambda = 2.626 \mu m$), produced by pre-main-sequence (PMS) stars. These
stars, consisting of T Tauri and Herbig AeBe stars are located in the massive
Galactic star-formation region NGC 3603. The measurements were obtained from
JWST NIRSpec, using multi-object spectroscopy (MOS) mode. Utilising existing
empirical relations between $L_{acc}$ and $L_{Br_{\gamma}}$, we have used our
new measurements to formulate, for the first time, an empirical relationship
between the accretion luminosity $L_{acc}$ of the stars, and the line
luminosities $L_{line}$ of both $Pa_{\alpha}$ and $Br_{\beta}$. These
relationships are: $\log_{10}( \frac{L_{acc}}{L_{\odot}}) = 1.42 (\pm 0.18)
\times \log_{10}( \frac{L_{Pa_{\alpha}}}{L_{\odot}}) + 3.33 (\pm 0.42)$ and
$\log_{10}( \frac{L_{acc}}{L_{\odot}}) = 1.47 (\pm 0.18) \times \log_{10}(
\frac{L_{Br_{\beta}}}{L_{\odot}}) + 4.60 (\pm 0.57)$. These new relationships
are key for roughly estimating the accretion rates for large samples of PMS
stars with JWST.
