To fully capitalize on the Jefferson Lab 12 GeV upgrade, the proposed SoLID (Solenoidal Large Intensity Device) experiment in Hall A can offer an unprecedented combination of luminosity and acceptance, unlocking access to measurements that cannot be performed anywhere else. Developing this spectrometer (Figure 4.5-1) would entail a confluence of the core competencies of the Medium Energy Physics (MEP) group, which combines leadership of a cutting- edge physics program, detector development for high- luminosity environments, development of software and analysis infrastructure for large-scale electron scattering experiments, and access to world-class engineering resources.

The baseline program of the SoLID experiment consists of three configurations. The first configuration will focus on precision measurements of proton and neutron structure in terms of their internal quark dynamics. In particular, the transverse momentum structure of the neutron will be studied through scattering off a transversely polarized 3He target.

The second configuration will focus on a study of the non-perturbative gluonic structure of the proton through near-threshold J/ψ production. These measurements will shed light on the emergence of the proton mass, constrain the properties of a QCD Van der Waals binding force, and constrain the properties of possible five-quark states discovered by the LHCb experiment.

In its third configuration, SoLID will allow us to study parity, one of the most fundamental properties of nature. In its simplest form, parity conservation means that a process, when viewed in a mirror, should behave the same as it would without the mirror. This seemingly simple property is violated, albeit rarely, by particle interactions involving the weak force. We will use an ultra-precise measurement of parity-violating deep inelastic scattering, measured with the SoLID spectrometer, to test the framework in which we understand the weak force, searching for signatures of beyond the Standard Model.

The MEP group is responsible for the design and construction of several critical system in the SoLID spectrometer. To ensure the high-rate capabilities of the detector and data acquisition system, we conduct targeted pre-R&D measurements through a series of parasitic experiments in Hall C. Furthermore, we provide for leadership in the software development for detector simulations and reconstruction, leveraging Argonne’s capability for high-performance computing.