RUI: Precision Test of Fundamental Symmetries via Light Pseudoscalar Meson Decays

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Understanding how quarks are confined to form protons and neutrons and searching for physics beyond the standard model (BSM) are two of the most challenging and exciting frontiers in physics. The major goal of this project is to perform cutting-edge experiments at the Thomas Jefferson National Accelerator Facility (JLab) to explore both fundamental issues through precision tests of fundamental symmetries in the decay of particular subatomic particles, mesons. The results from these experiments have the potential to shed light on critical questions such as: the origin and dynamics of quark confinement, the nature of dark matter, and the mystery of the asymmetry of matter-antimatter in the universe. This project will also offer great opportunities to engage undergraduate students in research. It will create a research-enriched learning environment, explore new approaches to recruiting prospective students, and develop new courses which are research related. Students will work in an international collaboration, which will enhance their international experience and allow them to gain gain global perspectives.The major objectives of this project include: (1) publish the results from the PrimEx-II experiment (E-08-023), a precision measurement of the pi-zero lifetime; (2) prepare and perform the PrimEx-eta experiment to measure the eta radiative decay width (eta decay to two photons) (E-10-011); (3) develop an upgraded FCAL-II calorimeter for the newly approved JEF experiment (E12-12-002A) to study eta and eta-prime decays with emphasis on rare neutral modes in Hall D; and (4) continue the responsibility for maintaining and operating the low-granularity pair spectrometer detectors to control the photon beam in Hall D at JLab. The symmetries of QCD are manifested in their most unambiguous form in the sector of light pseudoscalar mesons pi-zero, eta, and eta-prime. Precision measurements of their properties are crucial to understanding the QCD symmetry structure at low energy, as well as the origin and dynamics of QCD confinement. In addition, the measurements of various rare and forbidden decays of the eta and eta-prime will provide sensitive probes for sub-GeV dark gauge bosons (a leptophobic vector B-prime and an electrophobic scalar meson) and C-violating, P-conserving new forces, which will extend our knowledge of the dark sector and explore new sources of CP violation needed to explain the matter and anti-matter asymmetry in the universe.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.