Canadian researchers played a major role in an international collaboration that has gained new insight into the most elusive of the four fundamental forces in nature, the weak force. The Q-weak experiment has revealed the strength of the weak force’s grip on the proton, by measuring the proton’s weak charge to high precision. The research was carried out using the high quality polarized electron beam available at the Continuous Electron Beam Accelerator Facility, at the US Department of Energy’s Thomas Jefferson National Accelerator Facility. The result, published in the May 10 issue of Nature, significantly narrows the search for new particles that could influence the behavior of matter at sub-nuclear distance scales.
“The Q-weak experiment, initiated in 2001, represents the sustained effort of a large, international team of about 100 scientists from 25 institutions over nearly two decades,” said Dr. Shelley Page, a co-spokesperson and NSERC PI for the experiment. “The Canadian group was a founding member and represents approximately 15% of the Qweak collaboration; it was a leading contributor to the equipment design and construction, data production, and analysis efforts,” she said.
More than $3M of support has been provided through the NSERC subatomic physics Project Grant program to the Canadian group, which includes scientists from the Universities of Manitoba, Northern BC, Winnipeg, and TRIUMF. These funds were used to build equipment and to support student and postdoctoral researchers’ salaries and travel to carry out the measurements at Jefferson Laboratory. Vital technical and engineering support was provided by TRIUMF, and detector development was carried out in CFI-funded laboratories at the Universities of Manitoba and Winnipeg. The Canadian group’s primary contributions include the design, fabrication, and field mapping of the large spectrometer magnet, the design and construction of the main electron detector package, development of a novel diamond microstrip detector used for precise Compton electron beam polarimetry, design and construction of low noise detector readout electronics, extensive systematic error simulations and data analysis.
The successful completion of the Q-Weak experiment is an important milestone in parity violating electroweak physics and sets the stage for a new measurement of the weak charge of the electron, at even higher precision the MOLLER experiment –which is currently under development and in which a Canadian subatomic physics group from the University of Manitoba has again a strong position of leadership.
The experiment was funded by the United States Department of Energy, the National Science Foundation, the Natural Sciences and Engineering Research Council of Canada, and the Canadian Foundation for Innovation, with matching and in-kind contributions from a number of the collaborating institutions.