Two research teams working independently at two different particle accelerators have found evidence of what appears to be a four-quark particle that has come to be called Zc(3900). Both teams are made up of a large number of researchers affiliated with institutions from around the world and both have published their findings in separate papers in the journal Physical Review Letters.
The discovery of what appears to be a new particle has come about at the two sites (the Belle and BESIII experiments in Japan and China, respectively) as a result of research into Y(4260), a particle discovered in 2005. Physicists have been intrigued by Y(4260) as it appears to be made of a charmed quark, an anti-charmed quark and an extra gluon (in addition to the gluons holding the quarks together). In studying the decay of Y(4260)—which is found in the debris after smashing electrons and positrons together in their respective accelerators—both research teams noticed a spike of energy of about 3.9 gigaelectronvolts, which, as it turns out, is approximately four times the weight of a proton. That suggested evidence of a particle with four quarks, something that has never been seen before.
After much more study, both teams concluded that what their data was showing them was something both new and real. Initial indications are that Zc(3900) is indeed a previously unknown type of matter—a particle with four quarks. Combined, the research teams have found 460 examples of the Zc(3900) particle giving serious credence to their actual existence. Thus far, the particle appears to have an electric charge and at least one charm and one anti-charm quark. Both teams suspect that it also has an up and anti-down quark as well, giving it its full complement of four quarks.
Read more at: Phys.org