Devin Powell in Nature:
Physicists have resurrected a particle that may have existed in the first hot moments after the Big Bang. Arcanely called Zc(3900), it is the first confirmed particle made of four quarks, the building blocks of much of the Universe’s matter.
Until now, observed particles made of quarks have contained only three quarks (such as protons and neutrons) or two quarks (such as the pions and kaons found in cosmic rays). Although no law of physics precludes larger congregations, finding a quartet expands the ways in which quarks can be snapped together to make exotic forms of matter.
“The particle came as a surprise,” says Zhiqing Liu, a particle physicist at the Institute of High Energy Physics in Beijing and a member of the Belle collaboration, one of two teams claiming the discovery in papers published this week in Physical Review Letters1, 2.
Housed at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan, the Belle detector monitors collisions between intense beams of electrons and their antimatter counterparts, positrons.