UM Physics Students Investigate Great Mysteries of the Universe

Staff Report

University of Mississippi

Four physics majors are working with a University of Mississippi professor and an international team of scientists to search for new particles and interactions that may help solve big questions about the universe. Along the way, they’re getting a head start on their own research careers.

The students – Paul Gebeline, Sakul Mahat, Matthew Mestayer and Wil Stacy – are working with Jake Bennett, an experimental elementary particle physicist and assistant professor in the UM Department of Physics and Astronomy. Bennett collaborates with more than 1,000 physicists and engineers from 26 countries on the Belle II experiment, a groundbreaking project at the SuperKEKB electron-positron accelerator in Tsukuba, Japan. 

The Belle II experiment aims to investigate great mysteries of particle physics, including: Why, if matter and antimatter should have been created in equal amounts after the big bang, is the universe filled almost entirely with matter?

“The experiment seeks to use massive data samples to make precise measurements of rare particle decays that offer clues to better understand the fundamental interactions of subatomic particles,” Bennett said. “Other experiments have seen hints of unexplained phenomena that Belle II will have the opportunity to clarify. UM students are contributing to several different aspects of the project.” 

The students also gain valuable skills and experience, said Gebeline, a senior from Kiln who also is double majoring in mathematics.

“I have learned post-graduate-level physics as an undergraduate, learned how to present – a very valuable skill in physics academia – and learned how to conduct academic research in general,” he said. “Research has brought me connections with professors/researchers from other schools and invaluable skills that make me an asset to any grad school program. 

“And finally, after a few more months of work, I may be able to publish my research before I’m even a graduate student, which is incredible!”

All the students use simulations and real data to either gauge the ability of Belle II to make measurements of interesting phenomena or to test the detector’s performance, Bennett said. 

“Precise measurements rely on a good understanding of the performance of the Belle II detector, which is strengthened by studies like those performed by Wil and Matthew,” Bennett said. “Paul and Sakul contributed to simulation studies, which are important to develop the necessary analysis tools and understand how well we can isolate and measure rare processes.”

Stacy, a senior from Southaven, has completed a study examining the performance of the Belle II detector to identify charged particles. 

The response of different detectors hints at the identity of charged particles that are created in the electron-positron collision. Those detector responses must be carefully calibrated and understood before precision measurements of interesting particle decays can be made, he explained.

“My goal was to measure the efficiency – what percentage of the time do we get it right – of the detectors to properly identify protons,” Stacy said. “This information was relayed to detector experts, to help them improve their software, and is made available to analysts so they can better understand how to get the most accurate data possible.”

Gebeline examines the lifetime of a subatomic particle called the Xi_c+ using simulations from the Belle II experiment. 

“It is an important analysis for two reasons: 1) It serves to confirm the most recent measurement made by the LHCb (Large Hadron Collider beauty) experiment, which is one of the world’s leading particle physics experiments, and 2) to prove the capability of Belle II to make precision measurements,” he explained. 

Mestayer, a junior from Ocean Springs, studies the asymmetry produced when a particle is measured with a different efficiency than its antimatter partner. This asymmetry must be well understood because it can hide behavior that violates the laws of physics and, therefore, indicate the presence of new particles and interactions. 

“I am studying a particle that clearly obeys the Standard Model in order to understand the detector well enough that we can search for particles that do not,” he said. 

Mestayer values his experience in the labs of both Bennett and Cecille Labuda, another UM associate professor of physics.

“It has given me direct proof of the material I am learning in class and gives me motivation to push myself in a challenging major,” he said.

Mahat, a senior from Dharan, Nepal, has been using simulated data to test the capability of the Belle II experiment to measure particle decays that show deviations from expected patterns. 

Most theories predict that certain particle decays that include leptons – electrons, muons and tauons – should proceed at the same rate, no matter the “flavor” of the lepton. Recent measurements hint that these predicted conservation laws are broken, suggesting new interactions may be at work.

“All the particles that we see around us and their interactions are described quite well by the Standard Model,” Mahat said. “The Standard Model explains how the basic building block of matter interact. However, there are some important missing pieces to the model. 

“‘Lepton universality’ is one of the fundamental assumptions of the Standard Model, and the overarching goal of my research is to contribute to the validity of this assumption by backing it up with the experimental data. 

“This research is important because if the experimental analysis/research does not back up the predicted value by the Standard Model, it might suggest a crack in the Standard Model.”

At many institutions, such cutting-edge research is limited to faculty researchers and graduate students, but Ole Miss undergraduates are encouraged to join research teams in many departments. For example, working in Bennett’s lab has been part of Gebeline’s entire education at UM.

“I was very lucky to get into research freshman year because I had my adviser as a professor for intro physics, and he likes to talk about his research. I found it interesting and asked to get involved, and I’ve been working with him for four years,” Gebeline said. 

The Ole Miss students are making scientific contributions as they learn in the lab, Bennett said. 

“These projects are valuable not just for the experience gained by the students, but also to the experiment,” he said. “Understanding the performance of the detector is vital to ensure accuracy of future results and provide necessary inputs for future studies.”

The students presented their findings at the annual meeting of the Southeastern Section of the American Physical Society in November 2021 at Florida State University. The 88th meeting of SESAPS covered a broad range of topics in physics research. 

The 89th SESAPS conference is scheduled for November 2022 at UM.

For more information, read Q&As with Paul Gebeline, Sakul Mahat, Matthew Mestayer and Wil Stacy.