Traces of theΘ+Pentaquark inK+-Nucleus Dynamics

Abstract

Long-standing anomalies in K(+)-nucleus integral cross sections could be resolved by extending the impulse-approximation trho optical-potential framework to incorporate K(+) absorption on pairs of nucleons. Substantially improved fits to the data at p(lab) approximately 500-700 MeV/c are obtained. An upper bound on the absorption cross section per nucleon is derived, sigmaabs((K(+))/A approximately 3.5 mb. We conjecture that the underlying microscopic absorption process is K(+) nN--> Theta+ N, where Theta(+) (1540) is the newly discovered exotic Y = 2, I = 0, Z = 1 pentaquark baryon, and estimate that sigma(K(+) d--> Theta(+) p) is a fraction of millibarn. Comments are made on Theta(+) production reactions on nuclei.

Strangeness in nuclei and neutron stars

“…[126] considered the interaction of the K + with the pion cloud of the nucleus, leading to a significant improvement of the differential and total K + nuclear cross sections. Alternatively, substantially improved fits to the data were achieved by incorporating the absorption of K + by nucleon pairs via the inclusion of the Θ + (1540) pentaquark [124,127,128], although the evidence of the pentaquark has faded away in the last years. An alternative way to determine the kaon optical potential is to analyze the formation and propagation of kaons in the dense medium created in pion-nucleus, proton-nucleus or nucleus-nucleus collisions for intermediate beam kinetic energies (GeV).…”

Partial-wave analysis ofK+-nucleon scattering

“…This fact has been useful for probing the possible changes in nucleon structure and/or K + N interaction in the nuclear medium [1, 2, 3, 4, 5,6,7,8]. Following the measurement of the ratio of total cross sections [4,5], a number of suggestions were made to explain the results, among the principal ones being a partial deconfinement of quarks, an interaction with exchanged mesons in the nucleus and a modification of the K + N interaction through exchanged mesons.…”

K+-nucleon amplitudes in the medium below 800 MeV/c

“…Peterson [15] showed in 1999 that the enhancement is reproduced by using in medium an increased average K + -nucleon S-wave phase-shift compared to free space, suggesting 'swelling' of bound nucleons. A possible link between the additional reactive content and K + interactions with two nucleons was explored in [16,17].…”