Baryon Structures and Hadron Interactions

Arizona State University, Scottsdale AZ

Investigators

Abstract

The fundamental particles and interactions in nature are currently described by the Standard Model, with the sector of strong interactions described by Quantum Chromodynamics (QCD). The quark mass eigenstates of QCD are related to the physical weak eigenstates of the Standard Model through the Cabibbo-Kobayashi-Maskawa (CKM) matrix. A requirement of this matrix is that the sum of the squares of the three elements across each row or each column be unity. Currently, the sum for the first row falls below unity by 2 to 2-1/2 standard deviations. The possible deficiency opens up the possibility for new physics, such as additional quark families or super-symmetry models. One of these matrix elements can be determined by a measurement of the decay rate of the K meson into a pion, a positron, and a neutrino, known as Ke3. Experiment E927 at Brookhaven National Laboratory will use the Crystal Ball spectrometer to make a new, high-precision measurement of the Ke3 decay rate. This improvement by about a factor of 3 over the current value, along with new neutron decay experiments, will permit a critical test of CKM unitarity. Experiment E927 will also provide data concerning weak interactions in hadrons, and may help with the interpretation of recent related data on the production of neutron mesons from nucleons and nuclei.