Pentaquarks: review of the experimental evidence

Pentaquarks, namely baryons made by 4 quarks and one antiquark have been predicted and searched for since several decades without success. Theoretical and experimental advances in the last 2 years led to the observation of a number of pentaquark candidates. We review the experimental evidence for pentaquarks as well as their non-observations by some experiments, and discuss to which extend these sometimes contradicting informations may lead to a consistent picture.Comment: Contribution to the International Conference on 'Strangeness in Quark Matter', 15-21 Sept. 2004, Cape Tawn, South Afric

Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)Sigma0 reactions at Egamma=1.5-2.4 GeV

Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0 reactions are measured for the first time for Egamma=1.5-2.4 GeV and 0.6<cos(theta_cm(K+))<1.0 by using linearly polarized photons at the Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are positive and gradually increase with rising photon energy. The data are not consistent with theoretical predictions based on tree-level effective Lagrangian approaches. Including the new results in the development of the models is, therefore, crucial for understanding the reaction mechanism and to test the presence of baryon resonances which are predicted in quark models but are sofar undiscovered