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Jefferson Lab Postdoc Characterizes a Class of Non-Ordinary Particles

Some particles are ordinary, like the protons and neutrons that make up the atomic nuclei of all the matter around us. They're stable under strong interactions and their basic properties are known. 

But Arkaitz Rodas studies particles that are much more elusive and mysterious at the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility. Specifically, the postdoctoral research associate at William & Mary characterizes a class of non-ordinary particles known as light mesons. 

"Most people don't know about them, but they exist in nature," he said.

As the recipient of the 2022 Jefferson Associates Postdoctoral Prize, Rodas will learn about the properties of these lesser-known particles, which will improve our understanding of how matter stays together.

Unstable Particles with Uncertain Properties

Just like protons and neutrons, light mesons are made up of smaller particles called quarks. However, instead of having three quarks each like a proton or neutron does, a light meson consists of only two: one quark and one antiquark. 

Many of these mesons are unstable and have a whole slew of different properties than protons and neutrons. And some of them can't be understood with simple quark models.

"Over many years, simplistic model pictures have arisen trying to gather information on these particles," Rodas said. "However, none of these are suited for high accuracy, and as a result, many of these non-ordinary mesons have remained controversial. Very little about their structure is known.

Rodas is a theorist, so for his prize-winning project, titled "Understanding exotic mesons from quantum chromodynamics," he'll characterize light mesons using computational mathematical tools.

"On an everyday basis, I touch a bit of math and spend a lot of time with supercomputers," he said. 

He needs to use supercomputers because he will be working with a complex theory called lattice quantum chromodynamics (lattice QCD). This theory will allow him to extract information about the fundamental properties of these light mesons, and maybe even offer a window to their inner structure. Calculations from lattice QCD are so complicated they require high-performance computers.

A better understanding of the properties of light mesons will shed light on the strong interaction, the fundamental force that binds quarks together to form the protons and neutrons found at the center of atoms.

"We want to know how we go from these tiny little quarks to the matter that creates us," Rodas said. "It's a very hard ask. So we, the experimentalists and theorists affiliated with Jefferson Lab, work on bridging the two."

Because the strong interaction also binds the quark couplets that make up light mesons, a better grasp of light mesons' properties will improve understanding of how the strong interaction works, and how it allows quarks to form both ordinary and exotic matter. 

"The ultimate goal is for us to be able to solve these strong interactions," Rodas said.

Rodas has been applying mathematical techniques to the study of light mesons since he began his doctorate at Complutense University of Madrid in Spain. During graduate school, in 2018, he came to Jefferson Lab for the first time for an internship.

He returned in 2019, when he started as a postdoc at William & Mary and scientific user at Jefferson Lab. His advisor and main collaborator is Jozef Dudek, a jointly appointed staff scientist at Jefferson Lab and associate professor of physics at William & Mary.

After this postdoc position, Rodas plans to stay in academia.

"I definitely want to be a researcher for the rest of my life," he said.

Prize Permits in-person Collaboration

The Jefferson Lab User Organization (JLUO) Board of Directors has awarded the JSA Postdoctoral Prize since 2008. The group represents the scientists who come to Jefferson Lab to conduct research with its unique facilities.

"Every year, the JLUO board has the pleasure to review excellent science projects submitted by postdoctoral researchers. They expand the wide range of physics studied at Jefferson Lab. The competition is very strong, and we are always impressed by the high quality work of our young colleagues," said JLUO Chair Carlos Munoz-Camacho. "This year, Arkaitz Rodas was the JSA Postdoc prize winner and we truly congratulate him for his outstanding contributions. We look forward to the conference that Arkaitz is planning to organize with the amount of the grant he has received. It will be a great opportunity to bring the community together and discuss recent progress in the field, as well as its future direction."

The board judges each applicant on their record of accomplishment in physics, proposed use of the research grant, and the likelihood of further accomplishments in the Jefferson Lab research fields. 

"It makes me very happy winning this award," Rodas said. "Considering the competition is outstanding, this award is reinforcement and gives you extra motivation. It really makes you work to the highest of your standards because you know you are supported by the lab."

The grant is funded by the Jefferson Science Associates Initiatives Fund program, which JSA provides to support programs, initiatives and activities that further the scientific outreach, and promote the science, education and technology missions of Jefferson Lab and benefit the laboratory's user community.

Rodas plans to use the $10,000 prize money to host a conference at Jefferson Lab that brings experimentalists and theorists together to focus on the study of light mesons and other exotic particles. Because COVID has impeded travel for the past two years, Rodas believes an in-person conference is now due. 

"Experimentalists and theorists need to work closely together, so I thought it would be a good idea to organize a small conference where we can discuss the future of our analyses," he said.

He hopes to hold this conference in the spring of 2023. He hopes to be able to share his own results from recent research at the conference. 

"When you suggest a new set of ideas, there is always excitement," he said. "But for the first few months, I was wondering if my ideas would end up producing final results, or if we'd get stuck at some point. Fortunately, they seem to be going pretty well, and I'm very excited about it."


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