Pentaquark baryons are a natural expectation of an extended picture of hadrons where quarks and diquarks are the fundamental units. The parity/mass pattern observed, when compared to that of exotic mesons, appears as the footprint of a compact five-quark structure. What has been learned from the X , Y , Z phenomenology informs about the newly found pentaquark structure and suggests further experimental tests and directions to be explored.
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Maiani et al. (2015) studied this question.
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