![]() Teasing out the subtle signal of lambda decay-the particles are too short-lived for direct detection-required more than 10 years of effort. At the time, El Fassi was conducting separate research with the dataset, but she eventually chose to seek evidence of lambda particles within it as well. This subatomic alchemy took place at the Thomas Jefferson National Accelerator Facility way back in 2004. The resulting energetic kick can send quarks pinballing through the nucleus, where they combine with other quarks to create lambdas and other “composite” particles. Instead the impinging electrons release “virtual” photons, so called because they scarcely exist at all: these photons are reabsorbed by the quarks almost as fast as they are emitted. Yet despite these elaborate efforts, the arcane laws of quantum mechanics dictate that, even here, the electrons do not interact directly with the quarks. This involves shooting an electron beam at a nucleus, which transfers energy to the quarks within the protons and neutrons inside, stimulating lambda production. Lambda particles have been studied before, but in the new paper, the researchers relied on a special process called semi-inclusive deep inelastic scattering to create them inside a nucleus. ![]() ![]() “So part of the reason that strange quarks are interesting is because, at least in this naive picture, they’re not there at the beginning. “Our naive picture of a proton and a neutron is that they involve up and down quarks,” he says. The scarce, slippery nature of strange quarks is precisely what makes them so appealing for researchers, says Daniel Brandenburg, an assistant professor of physics at the Ohio State University, who was not involved in the new work. Strange quarks are heavier, rarer beasts than their up and down siblings, and the particles they form are correspondingly far less stable, tending to decay very quickly. The vast majority of quarks are of the up or down varieties, says Lamiaa El Fassi, lead author of the new study and an associate professor of experimental nuclear physics at Mississippi State University. Lambda particles are baryons, which means they’re a type of hadron made of three quarks: one up quark, one down quark and one strange quark. This is the force that binds quarks together to make larger particles such as protons and neutrons and that holds those protons and neutrons within an atom’s nucleus. Hadrons are subatomic particles that are made of quarks and subject to the strong force. “This data is the first time we study the lambda in the nucleus, and we look at what we call hadronization, the process of producing hadrons,” says study co-author Kawtar Hafidi, associate laboratory director for physical sciences and engineering at Argonne National Laboratory. In this particular case, a group of researchers focused on one variety of strange matter, called lambda particles. Probing the details of strange matter’s emergence is part of a broader effort by nuclear physicists to understand the fundamentals of how subatomic particles form. “Strange” here refers, in part, to a profound remoteness from our everyday lives: strange matter only seems to show up in truly extreme circumstances such as high-energy particle collisions and perhaps the enormously dense and pressurized cores of neutron stars. Strange matter is any matter containing the subatomic particles known as strange quarks. A new physics result two decades in the making has found a surprisingly complex path for the production of strange matter within atoms.
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