Mississippi State physicists net high impact experimental result on the weak force

Contact: Sarah Nicholas

Dipangkar Dutta (Photo by Russ Houston)James Dunne (Photo by Russ Houston)

STARKVILLE, Miss.—Two Mississippi State physicists are seeing more than a decade of research yield a new high-precision result that will expand scientists’ knowledge of the weak force in protons.

Published this month in the international journal of science, Nature, the Q-weak project conducted by the Jefferson Lab Q-weak Collaboration sought to precisely measure the proton’s weak charge, a quantity that signifies the influence the weak force exerts on protons. MSU Professors James Dunne and Dipangkar Dutta have worked with the consortia since 2004 and 2006, respectively.

Conducted at the Department of Energy’s Thomas Jefferson National Accelerator Facility in Newport News, Virginia, the experiment tests “the limits of our knowledge of the weak force,” and placed “very stringent constraints on the possibility of new, as yet unknown, types of forces and particles,” said Dunne.

Describing the Q-weak project, Dutta explained there are four known forces in nature: gravity, electromagnetic, weak and strong forces. “Gravity is what keeps us stuck to Earth and explains the motion of the planets and stars,” Dutta said, while the electromagnetic force is what “keeps our feet from going through the ground and is responsible for most other common everyday phenomena.”

“Just as the electromagnetic force is governed by the positive and negative charges, the strong and the weak forces also have charges associated with them,” Dutta said. “Since the weak force is so much weaker than the strong force and the electromagnetic force, it is very difficult to ‘feel’ or measure the effect of the weak charge.”

In order to measure the proton’s weak charge, an intense beam of electrons was directed onto a target containing cryogenic liquid hydrogen. The electrons scattered from this target were detected in a precise, custom-built measuring apparatus.

Dutta’s team built and operated the diamond-based electron detector used to continuously monitor the spin of the electron beam with the “highest precision ever achieved for the conditions of the Q-weak experiment,” Dutta said. MSU’s device was instrumental in creating a precise measurement of this beam property.

“A novel electron detector made out of diamonds was at the heart of this device and was the first of its kind to be used in a nuclear physics experiment,” Dutta said.

Dunne’s team helped build the Q-weak liquid hydrogen target, the highest power cryogenic target in the world. Describing the level of precision of the Q-weak experiment, Mark Novotny said to “think of having two piles, one with 10 million pennies and one with 10 million and two pennies.”

“Trying to measure which pile is larger is similar to the Q-weak experiment,” explained the professor and head of MSU’s Department of Physics and Astronomy.

“Working with a difference of two parts in 10 million is the same difference in the Q-weak measurement between the two electron spin orientations [in the Q-weak experiment],” Novotny said. 

“Better knowledge leads to a better understanding of nature, and ultimately sometimes to advanced devices,” Novotny added.

Part of a larger collaboration with more than 20 other institutions and approximately 100 scientists, Dunne and Dutta left a “noteworthy footprint” on the experiment, Novotny said. 

The Q-weak experiment is “truly an example of leading-edge science being performed by MSU faculty and students” and contributes to the “world-class education we offer to all our students,” said Novotny, calling Dunne and Dutta “strong assets” to the physics department. 

“The contributions they both have made to MSU undergraduate education, including directing research projects of undergraduates, to MSU graduate education, and to directing post-doctoral fellows, speaks to the heart and soul of MSU as the leading research university for the State of Mississippi,” Novotny said. 

Associate Dean for Research Giselle Thibaudeau said Dunne and Dutta’s contributions to MSU are a source of pride and “their research brings notoriety to the department, the college and the university, while having a significant positive impact on MSU’s research success portfolio and the discipline.”

Dunne and Dutta said they are excited to be part of a groundbreaking effort which has opened the door for even higher precision in the future and are “very proud about providing a world class challenging training ground for several MSU students and future scientists.”

MSU engineering/applied physics doctoral graduates Amrendra Narayan, Adesh Subedi and Luwani Ndukum played critical roles in the analysis of the data collected during the Q-weak experiment during their graduate programs. Narayan and Subedi used the Q-weak experiment for their Ph.D. theses. Subedi won the 2015 best thesis award at Jefferson Lab for his work. Post-doctoral researcher and current MSU lecturer Mitra Shabestari assisted with data collection. As an undergraduate student, 2010 physics graduate Daniel Brown assisted in the initial target development as part of the team designing and building the target’s high power heater that regulated the liquid hydrogen temperature.

MSU’s contribution to the experiment was funded by the U.S. Department of Energy Office of Science.

Dunne is a Grisham Master Teacher and director of the Center for Teaching and Learning.  He received his Ph.D. in 1995 from American University and has been a faculty member at MSU since 1998.

Dutta is an experimental nuclear physicist who has been at MSU since 2006.  He received his Ph.D. in 1999 from Northwestern University.

For more information on this project, visit https://www.jlab.org/news/stories/probing-protons-weak-side or https://www.nature.com/articles/d41586-018-05037-9.

MSU’s College of Arts and Sciences includes more than 5,200 students, 300 full-time faculty members, nine doctoral programs and 25 academic majors offered in 14 departments. Complete details about the College of Arts and Sciences and Department of Physics may be found at www.cas.msstate.edu or www.physics.msstate.edu

MSU is Mississippi’s leading university, available online at www.msstate.edu