paper

Very narrow excited baryons

arXiv:1703.07774 · doi:10.1103/PhysRevD.95.114012

Abstract

Recently LHCb reported the discovery of five extremely narrow excited baryons decaying into . We interpret these baryons as bound states of a -quark and a -wave -diquark. For such a system there are exactly five possible combinations of spin and orbital angular momentum. The narrowness of the states could be a signal that it is hard to pull apart the two -quarks in a diquark. We predict two of spin 1/2, two of spin 3/2, and one of spin 5/2, all with negative parity. Of the five states two can decay in -wave and three can decay in -wave. Some of the -wave states might be narrower than the -wave states. We discuss relations among the five masses expected in the quark model and the likely spin assignments and compare with the data. A similar pattern is expected for negative-parity excited states. An alternative interpretation is noted in which the heaviest two states are excitations with and , while the lightest three are those with expected to decay via -waves. In this case we expect states around 2904 and 2978 MeV.

18 pages, 4 figures (expanded text, appendices, and references)

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