Jefferson Lab: Partnership Contributes Toward Sharp Eyes For Moller Experiment

Thirteen universities working on a new experiment to be carried out at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility have recently been awarded new grants totaling more than $9 million. The grants come from the National Science Foundation and the Canadian Foundation for Innovation, with a matching award for the CFI grant from Research Manitoba. The grants benefit the Measurement of a Lepton-Lepton Electroweak Reaction Experiment, called MOLLER.

MOLLER is an experiment designed to precisely measure the electron’s weak charge, a gauge of how much influence the weak force exerts on the electron. MOLLER’s precision measurement will test the theory that describes the particles and interactions that make up everyday matter.

The experiment will be carried out in Jefferson Lab’s Continuous Electron Beam Accelerator Facility, a DOE Office of Science user facility. In the experiment, polarized electrons from CEBAF will interact with electrons from atoms inside a liquid hydrogen target. After the interactions, electrons that come flying out of the target will be bent by spectrometer magnets. These magnets separate the electron-electron scattering signal events from background events, where the beam electrons scatter off of the protons rather than the electrons in the target. The signal events will be collected in state-of-the-art detector systems in Jefferson Lab’s Experimental Hall A.

The MOLLER research program was established at Jefferson Lab as a DOE Major Item of Equipment (MIE) project to support the experiment. Preparation for this high-priority experiment kicked into high gear in December 2020, when the MOLLER MIE project received a designation of Critical Decision 1, or CD-1, from the DOE. CD-1 allowed the project to engage in design and prototyping of equipment.

Now, a new partnership forged between the DOE, the National Science Foundation and the Canadian Foundation for Innovation to support this important experiment is propelling work forward with new grants.

James Fast is Jefferson Lab’s MOLLER MIE project manager. He says the new grants provided by the NSF and CFI with matching award from Research Manitoba (CFI/RM) will go toward critical detector components. The grants also lower the DOE total project cost from $57.6 million to $48.2 million.

“The partnership between the DOE, the NSF and the CFI/RM will enable MOLLER scientists to make a more precise measurement. It contributes to the proposed design of the detector systems. That upgrade will enable an even higher-statistics measurement than initially thought,” Fast said. “It allows them to pin down normalization and systematic uncertainties by mapping the scattered electron distributions.”

NSF Support for MOLLER

In the partnership, NSF in-kind contributions will go toward the design and construction of key beam characterization, detector, tracking and data acquisition systems. The CFI/RM will contribute toward obtaining the precision needed to achieve important aspects of the MOLLER measurement.

The NSF Midscale Physics Projects program grant includes individual grants totaling $5.7 million to researchers at nine institutions. These include Idaho State University, Louisiana Tech University, Muskingum University, Ohio University, Syracuse University, the University of Massachusetts Amherst, the University of Virginia, Virginia Tech, and William & Mary.

The lead principal investigator on the NSF collaborative grant for MOLLER is Mark Pitt. Pitt is a professor and chair of the Department of Physics at Virginia Tech.

He says the NSF grant will support the design and construction of MOLLER’s tracking system, background detectors, main detector mechanics, auxiliary asymmetry detectors, the data acquisition system, and certain aspects of beam monitoring and polarimetry.

“We’re pleased that the NSF has made this award to support a variety of different systems that will contribute to the experiment,” Pitt explained. “Each institution will design, build and test their system. Then we’ll bring them all together at Jefferson Lab, integrate them, and run the experiment.”

The NSF grant will also support graduate students and postdoctoral researchers. These early-career scientists will benefit from crucial training, hands-on research and leadership opportunities.

CFI/RM Support for MOLLER

In the partnership, the CFI/RM grant totals $3.7 million (converted to U.S. dollars) for detector hardware contributions.

The Canadian team who received the MOLLER grant is led by researchers from the University of Manitoba, with Principal Investigators Michael Gericke and Juliette Mammei and Co-Investigator Wouter Deconinck. The team also includes the University of Winnipeg, the University of Northern British Columbia, the Memorial University of Newfoundland, and TRIUMF.

According to Gericke, the CFI/RM grant will be used to design and construct a high-resolution detector. This detector will allow for detailed measurements of the particles that emerge from the electrons’ interactions.

Additional grant funds provided by the Natural Sciences and Engineering Research Council of Canada will support postdocs and students. These funds will also provide support for travel and small equipment needs for MOLLER.

Unlocking the Electron’s Secrets

All of these nuclear physicists are excited about the possibilities that MOLLER’s precision measurement of the electron may unlock.

“The electron’s weak charge is a fundamental prediction of the Standard Model that we currently have to explain particles and their interactions. It’s a fundamental property of the electron. By measuring it precisely, we are sensitive to a whole range of physics possibilities beyond the Standard Model,” Pitt explained.

“The electron is currently considered to be a so-called point or fundamental particle, which means that no one has ever observed it to have any excited states or spatial extent.” Gericke said. “MOLLER is potentially sensitive to effects of electron structure, and there are hints that the point particle picture may not hold at arbitrarily small distance scales.”

In 2009, the MOLLER experiment was highly rated in its review by the Jefferson Lab Program Advisory Committee. This group reviews the scientific merits and technical feasibility of proposed experiments. In 2011, the committee awarded the experiment its full beamtime request of 344 days of running, pending full funding and following completion of the 12 GeV CEBAF Upgrade project, which concluded in 2017.

More than 100 nuclear physicists from more than 30 institutions are actively involved in the MOLLER experimental collaboration.