Traces of Theta^+ pentaquark in K^+ nucleus dynamics

Abstract

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