MSU physicist first to observe formation of rare ‘strange matter’

STARKVILLE, Miss.—A ��ɫ��Ƶ physicist and her colleagues are the first scientists to observe how subatomic particles—known as lambda particles—are formed, helping researchers learn more about their production and formation in atomic nuclei, deepening the overall understanding of the dynamics of subatomic structure that governs most of the visible matter in the universe.

Lamiaa El Fassi, an associate professor in MSU’s Department of Physics and Astronomy, published the results in a recent edition of .

Lambda particles—comprised of up and down quarks—are common building blocks that make up most of the visible matter in the universe, and a rarer particle called a strange quark, known as “strange matter.” While strange matter only exists in extreme circumstances like high-energy particle collisions and the cores of the densest stars in the universe, by studying strange matter, scientists can glean information on how subatomic particles are formed—as well as acquire better understanding on how the universe operates.

“It hasn’t been an easy journey, but I am pleased with its outcome. These classes of studies help build a story, analogous to a motion picture, of how the struck quark turns into hadrons. In this paper, we report the first-ever observation of lambda baryon production in the forward and backward fragmentation regions,” said El Fassi.

The discoveries happened after more than 10 years of analyzing data collected from a 2004 experiment carried out using the Continuous Electron Beam accelerator Facility (CEBAF) Large Acceptance Spectrometer (CLAS) housed in the Experimental Hall B at the Thomas Jefferson National Accelerator Facility.

El Fassi’s team produced the lambda particles by shooting the CEBAF’s electron beam at different fixed-target nuclei such as carbon, iron and lead. When the high-energy electron from the accelerator collides with one of the target’s nuclei, it would break its protons and/or neutrons and thus probe their building blocks, called quarks. These quarks would then move around freely inside the nucleus prior to joining with other quark subconstituents to form the new composite particles, which would sometimes be a lambda.��

“The study reveals the possibility of a different mechanism responsible for the production and formation of lambda particles. Instead of the exchanged virtual photon between the beam and target nucleus being absorbed by a single struck quark, sometimes it’s absorbed by paired quarks, called a diquark. This is also the first experimental hint of its kind, opening the door for new theoretical and experimental development to fully understand the measured trend,” El Fassi said.

Through their observations, the team hypothesized the existence of a diquark—a pair of quarks that will sometimes absorb the exchanged virtual photon and bond with the strange quark to create the lambda particle. The observation of the diquark deepens scientists’ understanding of how three-quark composite particles—such as lambda particles—are formed.

El Fassi's work is supported in part by the U.S. Department of Energy; Office of Science; Office of Nuclear Physics Award No. DE-FG02-07ER41528.

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