Collaborative Research: Apparatus for Normalization and Systematic Control of the MOLLER Experiment

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A central goal of nuclear and particle physics is to obtain a complete understanding of the fundamental constituents of matter and the forces through which they interact. The Standard Model (SM) of particle physics has proven remarkably successful at describing the interactions of the known fundamental particles for the past 50 years. However, the SM is known to be incomplete, and there are compelling reasons to expect that the SM will eventually fail to describe some observed properties of matter. To address the question of whether there is new physics beyond the Standard Model, a precision measurement of the weak charge of the electron will be performed in a collaborative experiment at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. The electron’s weak charge is the weak force analog of the common electric charge of the electron, and it is precisely predicted in the SM. Any deviation of the measurement from this prediction would be evidence for undiscovered phenomena that represent new physics beyond our current understanding. The experiment is named MOLLER and it comprises a range of hardware design and construction activities as well as software development which will provide excellent training for students and young scientists. The experience of working in a collaborative modern science enterprise with state of the art technology provides a strong basis for a variety of careers.The funds provided by this project will support construction of essential apparatus for the MOLLER experiment (Measurement of a Lepton-Lepton Electroweak Reaction) at Jefferson Lab. MOLLER will measure the electron’s neutral weak charge by making a precision measurement of the parity-violating asymmetry in the elastic scattering of polarized electrons on unpolarized electrons at very low momentum transfer. This will result in a determination of the weak mixing angle at low energy with a precision comparable to the best determinations from high energy colliders, providing excellent sensitivity to physics scenarios that extend beyond the Standard Model. The MOLLER experiment consists of three major subsystems: 1) the beam/target/spectrometer to prepare the scattered Møller electrons to be observed, 2) apparatus to measure the raw parity-violating asymmetry to the needed statistical precision, and 3) apparatus for Normalization and Systematic Control to achieve sub-ppb and sub-% level systematic uncertainty and normalization control goals. The collaborative project described in this proposal will develop subsystem #3; namely the design, construction, and testing of the MOLLER Normalization and Systematic Control apparatus. The work will be done over the period December 2020 – November 2024. This includes the tracking system, background detectors, auxiliary asymmetry measurement detectors, and certain aspects of beam monitoring/control and beam polarimetry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.