John Price: “Spectrum” of Proton Research Explored at International Workshop

Associate professor of physics John Price co-organized an international workshop titled, "Cascade Physics: A New Window on Baryon Spectroscopy," at the Thomas Jefferson National Accelerator Facility in Newport News, VA in December. The “Jefferson Lab,” as it is known in the physics community, was chosen, according to Price, for its standing as the best facility for studying the structure and states of the proton.

Price presented “The Cascade Spectrum: What we've learned so far” to more than 50 colleagues from the fields of nuclear and high energy physics who attended from four continents. He describes the groundbreaking quality of eight years of research that revealed a new way to study cascade particles, which can help in the measurement of the proton and its properties.

“My talk itself was basically letting people know where we’re starting from as far as what we know about these cascades so far,” he says. “Of the 11 states of the cascade that we have found so far, we don’t know them very well and we haven’t really identified them, so there is a tremendous amount of work to do in this field. The first paper was published on this topic last June. It’s gaining momentum now and we wanted to start getting other people involved. So what we decided to do is put together a workshop to get the word out to the community that, ‘Hey, we’ve got this cool thing we can do,’ and to identify a group of people who are interested in working on this project.”

The organizing committee included Ben Nefkens of UCLA, and Dennis Weygand and David Richards, both of the Jefferson Lab. Price, who joined the CSUDH faculty last fall, previously conducted research at UCLA on methods used to determine what comprises the proton. Emphasizing the collaborative nature of scientific research, he often speaks in the plural when describing what findings have been made so far, since 1933, when protons were found to have both structure and size.

“After that, in nuclear physics, we started looking at what that structure is and, in the 1960s, we came up with a model. I say we – I of course, was barely four at that time,” he laughs. “But as a community, we came up with a model called the quark model. There are these particles called quarks, of which the proton is constructed. They’re held together by this other particle called the ‘gluon.’ Those of us in physics are not the most creative when it comes to naming particles; it ‘glues’ the quarks together, that’s all it means.

The quark model revealed excited states of the proton, which Price describes as revealing other related, but different states, including a higher mass that can be compared with the original model. He emphasizes the difficulty of measuring the short-lived excited states and the importance of the cascade particle.

“A trillionth of a trillionth of a second is how long they last,” he notes. “Because of that, we can’t really measure their masses very well, they have a fuzziness to them, called  ‘widths,’ which are something like 30 percent of the mass themselves. Because there are several of these excited states with similar masses, the widths tend to make them overlap, so I don’t even know which of these particles I’m looking at. That’s where we came in with this other particle called a cascade, that’s related to the proton. It has a similar structure, but its lifetime is much longer. Its width is much narrower by about a factor of 10, so we can better measure these things and have a more accurate idea of what they are.”

The results of similar work by physicists from Austria, Japan, Australia, and Poland were among the talks given at the conference. Price underscores the amount of work left to be done by noting that “We expect twice as many different states of the cascade as there are for the proton. As of now, we’ve found about half as many. What that’s telling us is that there is a lot for us to do.”

In October, Price delivered a plenary talk on cascade physics at the 10th International Workshop on the Physics of Excited Nucleons in Tallahassee, Fla., discussing the physics goals that could be pursued, showing how cascade physics is a complementary approach to the traditional methods that have been used by the community over the last fifty years.

-Joanie Harmon