Strangeness can be hard to studyespecially on the atomic scale. But now a collaboration of 50 researchers from 15 different institutions has announced results that could make it easier for scientists to probe strange matter in the near future. Using the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratories, the team successfully produced structures containing one proton, one neutron and two lambda particles, each comprised of an up, a down and a strange quark. A full account of the structures, described as doubly strange for their twin strange quarks, will appear in an upcoming issue of the journal Physical Review Letters.
Making the doubly strange nuclei involved multiple steps: the AGS generates the world's most intense proton beam, which the physicists focused at a tungsten target. From the particles produced in that collision, they separated out a beam of negatively charged kaons and shot them at beryllium. When the kaons, which contain one strange quark and one up antiquark, interacted with the target's protons, new strange quarks and strange antiquarks emerged. These particles, in turn, recombined into a variety of particlesincluding, on occasion, a doubly strange nuclei.
"This is the first experiment to produce large numbers of these doubly strange nuclei," says Adam Rusek, a Brookhaven physicist and co-spokesperson for the collaboration. Out of 100 million potentially interesting products, the scientists winnowed down the number of definitively doubly strange nuclei to about 30 or 40. They did not observe the nuclei directly but instead picked up on hallmark patterns of pions, subatomic particles that the lambda particles emit as they decay. "[30 or 40 are] enough events to begin a study using statistical techniques," Rusek adds. Four earlier attempts at creating doubly strange nuclei yielded only one at a time at best.
The scientists want to create even more doubly strange nuclei. "We can use this nucleus as a laboratory in which the two lambdas can be held together long enough to study," Sidney Kahana of Brookhaven adds. In particular, they hope that interactions between lambda particles might shed light on neutron stars, the only places where strange matter presumably exists in a stable form.