We report the confirmation of a \textit{TESS}-discovered transiting super-Earth planet orbiting a mid-G star, HD 307842 (TOI-784). The planet has a period of 2.8 days, and the radial velocity (RV) measurements constrain the mass to be $9.67^{+0.83}_{-0.82}\ \rm{M_{\oplus}}$.
We also report the discovery of an additional planet candidate on an outer orbit that is most likely non-transiting. The possible periods of the planet candidate are approximately 20 to 63 days, with the corresponding RV semi-amplitudes expected to range from 3.2 to 5.4 m/s and minimum masses from $12.6$ to $31.1\ \rm{M_{\oplus}}$.
The radius of the transiting planet (planet b) is $1.93^{+0.11}_{-0.09}\ \rm{R_{\oplus}}$, which results in a mean density of $7.4^{+1.4}_{-1.2}\ \rm{g/cm^3}$ suggesting that TOI-784b is likely to be a rocky planet though it has a comparable radius to a sub-Neptune. We found TOI-784b is located at the lower edge of the so-called ``radius valley'' in the radius vs. insolation plane, which is consistent with the photoevaporation or core-powered mass loss prediction.
The \tess data did not reveal any significant transit signal of the planet candidate, and our analysis shows that the orbital inclinations of planet b and the planet candidate are ${88.60^{\circ}}^{+0.84}_{-0.86}$ and $\leqslant 88.3^{\circ}-89.2^{\circ}$, respectively. More RV observations are needed to determine the period and mass of the second object, and search for additional planets in this system.