A new electron scattering experiment (E12-21-003) to verify and understand the nature of hidden sector particles, with particular emphasis on the so-called X17 particle, has been approved at Jefferson Lab. The search for these particles is motivated by new hidden sector models introduced to account for a variety of experimental and observational puzzles: excess in \(e^+e^-\) pairs observed in multiple nuclear transitions, the 4.2\(\sigma\) disagreement between experiments and the standard model prediction for the muon anomalous magnetic moment, and the small-scale structure puzzle in cosmological simulations. The aforementioned X17 particle has been hypothesized to account for the excess in \(e^+e^-\) pairs observed from the \(^8\)Be M1, \(^4\)He M0, and, most recently, \(^{12}\)C E1 nuclear transitions to their ground states observed by the ATOMKI group. This experiment will use a high resolution electromagnetic calorimeter to search for or set new limits on the production rate of the X17 and other hidden sector particles in the \(3 - 60\) MeV mass range via their \(e^+e^-\) decay (or \(\gamma\gamma\) decay with limited tracking). In these models, the \(1 - 100\) MeV mass range is particularly well-motivated and the lower part of this range still remains unexplored. Our proposed direct detection experiment will use a magnetic-spectrometer-free setup (the PRad apparatus) to detect all three final state particles in the visible decay of a hidden sector particle for an effective control of the background and will cover the proposed mass range in a single setting. The use of the well-demonstrated PRad setup allows for an essentially ready-to-run and uniquely cost-effective search for hidden sector particles in the \(3 - 60\) MeV mass range with a sensitivity of 8.9\(\times\)10\(^{-8}\) - 5.8\(\times\)10\(^{-9}\) to \(\epsilon^2\), the square of the kinetic mixing interaction constant between hidden and visible sectors.