Search for theΘ+Pentaquark in the Reactionγd→pK−K+n

Abstract

A search for the Theta+ in the reaction gammad --> pK-K+n was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow Theta+ resonance. The present experiment, with more than 30 times the integrated luminosity of our earlier measurement, does not show any evidence for a narrow pentaquark resonance. The angle-integrated upper limit on Theta+ production in the mass range of 1.52-1.56 GeV/c2 for the gammad --> pK-Theta+ reaction is 0.3 nb (95% C.L.). This upper limit depends on assumptions made for the mass and angular distribution of Theta+ production. Using Lambda(1520) production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary gamman --> K-Theta+ reaction is estimated to be a factor of 10 higher, i.e., approximately 3 nb (95% C.L.).

A Personal Journey Through Hadronic Exotica

“…In a high-statistics repeat of their own measurement, JLab found that their own earlier observation of Θ + was false and no evidence for the existence of the pentaquark exists [10]. However, rumor has it that Nakano et al claim that they still see the pentaquark in a high-statistics remeasurement.…”

Heavy molecules and one- σ/ω -exchange model

“…Ever since the observations of X(3872) [1] and Θ + [2], much evidence has been reported for new types of structures that are beyond the minimalqq mesons and qqq baryons, although the observation of Θ + have been criticized by subsequent experiments [3,4]. Hence, they are called the exotic hadrons, like X(3872) [1], Z b (10610)/Z b (10650) [5], P c (4380)/P c (4450) [6], and so on.…”

Observation of a narrow structure in1H(γ,KS0)Amaryan1, Gavalian2, Nepali3 et al. 2012Phys. Rev. CSelf Cite

“…It was not until 2004 that the CLAS Collaboration performed dedicated high statistics photoproduction experiments both on deuterium and hydrogen targets. It was found, first of all, that the previous measurement on the deuterium target by CLAS [4] was not reproduced in the new measurement, despite an order of magnitude higher statistics [15]. It is now understood [15] that the level of background in the first paper was underestimated and therefore the observed signal was statistically not so significant.…”