Research in Intermediate Energy Physics

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

This project addresses certain basic aspects of the electroweak and strong interactions reflected in the properties of mesons and nucleons (particles found inside atomic nuclei) and their interactions at low energies. The strong and weak interactions are responsible for the structure of matter at the smallest known scale, a femtometer (size of the hydrogen nucleus) or less. The research is motivated by the fact that the present comprehensive theory -- the Standard Model (SM) -- is known to be incomplete. The rare decay of the pi-meson (pion) into an electron and a neutrino, occurring once in about ten thousand ordinary pion decays, provides a theoretically extraordinarily clean window to certain possible extensions of the SM, at a very large mass scale not directly accessible at any existing or planned accelerators. The PEN experiment, mounted at the Paul Scherrer Institute, Switzerland, by an international collaboration of seven institutions led by the University of Virginia (UVa) group, builds on the success of the PIBETA experiment which improved by about an order of magnitude the accuracy of several rare decay modes of the pion and muon (a massive relative of the electron) in a series of measurements from 1999 through 2004. A new project, encompassing experiments "Nab" and "abBA," has been initiated at the Spallation Neutron Source at Oak Ridge National Lab in Tennessee, with the aim to measure precisely and simultaneously several of the decay parameter of the neutron beta decay. Through their precision, these experiments will explore similarly interesting possible extensions to the SM. During the past five years this program has resulted in four doctoral degrees at UVa. Two UVa Ph.D. students are currently working towards their theses, plans call for a third to join the group soon. Each year typically one to two undergraduate students are engaged in research on this project, thus gaining practical laboratory experience.