We report the first measurement of the $(e,e'p)$ reaction cross-section
ratios for Helium-3 ($^3$He), Tritium ($^3$H), and Deuterium ($d$). The
measurement covered a missing momentum range of $40 \le p_{miss} \le 550$
MeV$/c$, at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$
(GeV$/c$)$^2$) and $x_B>1$, which minimized contributions from non
quasi-elastic (QE) reaction mechanisms. The data is compared with plane-wave
impulse approximation (PWIA) calculations using realistic spectral functions
and momentum distributions. The measured and PWIA-calculated cross-section
ratios for $^3$He$/d$ and $^3$H$/d$ extend to just above the typical nucleon
Fermi-momentum ($k_F \approx 250$ MeV$/c$) and differ from each other by $\sim
20\%$, while for $^3$He/$^3$H they agree within the measurement accuracy of
about 3\%. At momenta above $k_F$, the measured $^3$He/$^3$H ratios differ from
the calculation by $20\% - 50\%$. Final state interaction (FSI) calculations
using the generalized Eikonal Approximation indicate that FSI should change the
$^3$He/$^3$H cross-section ratio for this measurement by less than 5\%. If
these calculations are correct, then the differences at large missing momenta
between the $^3$He/$^3$H experimental and calculated ratios could be due to the
underlying $NN$ interaction, and thus could provide new constraints on the
previously loosely-constrained short-distance parts of the $NN$ interaction.
