Have Pentaquark States Been Seen?

Abstract

The status of the search for pentaquark baryon states is reviewed in light of new results from the first two dedicated experiments from CLAS at Jefferson Lab and of new analyses from several labs on the Θ + (1540). Evidence for and against the heavier pentaquark states, the Ξ(1862) and the Θ 0 c (3100) observed at CERN and at HERA, respectively, are also discussed. I conclude that the evidence against the latter two heavier pentaquark baryons is rapidly increasing making their existence highly questionable. I also conclude that the evidence for the Θ + state has significantly eroded with the recent CLAS results, but still leaves room for a state with an intrinsic width of Γ < 0.5 MeV. New evidence in support of a low mass pentaquark state from various experiments will be discussed as well.

Observation of a narrow baryon resonance with positive strangeness formed inK+Xe collisions

“…More recently, observation of a narrow peak near 1.54 GeV in the missing mass of the K 0 S meson in the reaction γp → K 0 S K 0 L p was reported by a group from the CLAS Collaboration [9]. Other searches for the + baryon in different reactions and experimental conditions yielded both positive and negative results; see the review papers [10] and [11] and references therein. The bulk of null results can be probably explained by the extreme smallness of the + width that implies the smallness of production cross sections [12].…”

K*couplings for the antidecuplet excitation

“…Various collaborations give either positive results on its observation, or null results casting doubts on existence of the Θ + and on correctness of its positive evidences (see recent experimental reviews [1,2]). There are, however, no data of different groups with exactly overlapping conditions (initial and/or final states, kinematical regions, and so on).…”

Search forΣ50,N50, andΘQiang1, Annand2, Arrington3 et al. 2007Phys. Rev. C10080View full textAdd to dashboardCite

“…For recent reviews of the experimental evidence, see Refs. [5,6,7]. If confirmed, the Θ + could be the lowest-mass member of an antidecuplet of pentaquark states, predicted within the framework of the Chiral Quark Soliton Model [8].…”