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Physicists at the DESY laboratory in Germany discovered the first pentaquark, which contains a charm quark. The 1H collaboration team discovered evidence for the existence of a magic pentaquark with a mass of 3099 meU (megaelectron volts), created in collisions between electrons and protons at the HERA particle accelerator. However, another experiment in the accelerator, called "Zeus", failed to confirm the discovery.
Quarks and antiquarks come in six "flavors": up, down, strange, charm, top, bottom. For the most part quarks arrange themselves in pairs or triplets and form other particles. Mesons contain a quark and an antiquark, and baryons contain three quarks or three antiquarks. The proton, for example, contains two up quarks and one down quark. The negative kaon, on the other hand, contains a strange quark and an anti up quark.
Last year, evidence was discovered that there are two more particles, made up of four quarks - the Ds(2317) and the X(3872). Evidence was also discovered, supporting the existence of a third new particle, which contains five quarks. This penta quark (penta = five) contained two up quarks, two down quarks and one anti-strange quark. The discovery of this pentaquark has led theorists to think that there may be additional and heavier pentaquarks, such as the one containing the charm quark. Now, such a particle may be discovered in collisions between protons and electrons at the Hadron Electron Ring Accelerator HERA (Hadron Electron Ring Accelerator) in Hamburg.
The 1H team from HERA discovered events in which the collisions between the protons and electrons produced excited D-mesons (which contain a down quark and an anticharm quark) and protons or their antiparticles. When a graph is drawn of the number of these events as a function of the collision energy, a sharp jump in energy appears at 3099 MaU. The meaning of this jump is the creation of a particle, which contains two up quarks, two down quarks and an anti-charm quark or its anti-particle.
The HERA and ZEUS groups plan to conduct additional experiments in an attempt to confirm the discovery. Experiments to study the pentaquark will provide new insights into the strong nuclear force that holds quarks together.
Link to article on Physics Web
Link to press release from DESY
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