* Astronomy

First particle containing four quarks is confirmed.

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 Universes 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.
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The new observed particle "Zc(3900).", which decays into an electrically charged pi-meson plus a neutral J/psi and, thus, must itself carry an electric charge. Since it decays to a J/psi, the Zc(3900), which has a mass slightly higher than that of a helium atom, must contain a charmed quark and an anti - charmed quark. Different theoretical models have been proposed that attempt to explain how this could come about. The positively charged Zc(3900) particle could be a tightly bound four quark composite of a charmed and anti-charmed quark plus an additional up quark and anti-down quark. Or, perhaps, the Zc(3900) is a molecule-like structure comprised of two mesons, each of which contain a charmed quark (or anti-charmed quark) bound to a lighter anti-quark (or quark). Another scenario is that the Zc(3900) is an artifact of the interaction between these two mesons. In any case, the appearance of such an exotic state in the decay of another exotic state was unanticipated by most researchers.
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