Scientists have discovered a new particle — the latest member to be added to the exotic species of particle known as tetraquarks. Credit: Artwork by Fermilab
Scientists on the DZero collaboration at Fermilab have discovered a new particle – the latest member to be added to the exotic species of particle known as tetraquarks. Quarks are point-like particles that typically come in packages of 2 or 3, the most familiar of which are the proton and neutron (each is made of 3 quarks). There are 6 types, or “flavors,” of quark to choose from: up, down, strange, charm, bottom and top. Each of these also has an antimatter counterpart. Over the last 60 years, scientists have observed hundreds of combinations of quark duos and trios.
In 2008 scientists on the Belle experiment in Japan reported the first evidence of quarks hanging out as a foursome. Since then physicists have glimpsed a handful of different tetraquark candidates, including now the recent discovery by DZero – the first observed to contain 4 different quark flavors. DZero is one of 2 experiments at Fermilab’s Tevatron collider. Although retired in 2011, the experiments continue to analyze billions of previously recorded events from its collisions. As is the case with many discoveries, the tetraquark observation came as a surprise when DZero scientists first saw hints in July 2015 of the new particle, called X(5568), named for its mass – 5568 megaelectronvolts.
While all other observed tetraquarks contain at least two of the same flavor, X(5568) has four different flavors: up, down, strange and bottom.
This latest discovery comes on the heels of the first observation of a pentaquark announced last year by the LHCb experiment at the Large Hadron Collider. Scientists will sharpen their picture of the quark quartet by making measurements of properties such as the ways X(5568) decays or how much it spins on its axis. It will provide another window into the workings of the strong force that holds these particles together.
75 institutions from 18 countries collaborated on this result from DZero. http://www.symmetrymagazine.org/article/fermilab-scientists-discover-new-four-flavor-particle
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