New Class of Particles Called Pentaquarks Discovered

Posted on July 14, 2015

Pentaquark layout with five tightly bonded quarks

Researchers running the LHCb experiment at CERN’s Large Hadron Collider have reported the discovery a new class of particles called pentaquarks. An illustration of a possibly layout of quarks in a pentaquark particle is pictured above.

The researchers say the five quarks may be tightly bonded or they may be assembled into a meson (one quark and one antiquark) and a baryon (three quarks), weakly bonded together. The above illustration shows a layout with five tightly bonded quarks. LHCb researchers looked for pentaquark states by examining the decay of a baryon.

LHCb spokesperson Guy Wilkinson says in a statement, "The pentaquark is not just any new particle. It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over fifty years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we're all made, is constituted."

Murray Gell Mann proposed in 1964 that baryons are comprised of three fractionally charged objects called quarks, and that another category, mesons, are formed of quark-antiquark pairs. Gell-Mann was awarded the Nobel Prize in physics for this work in 1969. The quark model also allowed for the existence of other quark composite states, such as pentaquarks, but until now there has been no conclusive evidenec for the existence of pentaquarks.

LHCb physicist Tomasz Skwarnicki of Syracuse University, says in a statement, "Benefitting from the large data set provided by the LHC, and the excellent precision of our detector, we have examined all possibilities for these signals, and conclude that they can only be explained by pentaquark states. More precisely the states must be formed of two up quarks, one down quark, one charm quark and one anti-charm quark."

A BBC News story notes that past reported pentaquark discoveries turned out to be false signals. Because of this the researchers were very careful with today's pentaquark news and research paper. Patrick Koppenburg, physics co-ordinator for LHCb at Cern, told BBC News, "There is quite a history with pentaquarks, which is also why we were very careful in putting this paper forward."

The pentaquarks research paper can be found here in the journal, Physical Review Letters.

Image: Physical Review Letters