Probes of Fundamental QCD Symmetries and BSM Physics Via the Neutral pion, eta and eta' Decays

University Of North Carolina At Wilmington, Wilmington NC

Investigators

Abstract

Fundamental symmetries of Quantum Chromodynamics (QCD) at low-energies and new physics Beyond the Standard Model (BSM) are two frontiers in physics. The primary goal of this project is to explore both fundamental topics with experimental sensitivities not previously achievable via two on-going experiments at Jefferson Lab: PrimEx-eta and JLab Eta Factory (JEF). The results from these experiments will shed light on some fundamental questions: How did the mass of visible matter emerge in the early universe? Why are quarks confined in “color neutral” particles? What is the nature of dark matter that constitutes 85% of matter and what is the cause for the asymmetry of matter-antimatter observed in the universe? The scope of this project, including hardware development, performance of the actual experiment and data analysis, will provide advanced training for a postdoctoral researcher and a group of undergraduate students. It will help them to acquire significant technical skills through hands-on experience, data analysis and computation, as well as critical thinking and problem-solving abilities. The opportunities for young researchers (postdoc and students) working at Jefferson Lab will enhance their international experience and global perspectives. The female PI of this project will help promote diversity and inclusion by attracting more women to the science, technology, engineering, and mathematics program. The PrimEx-eta experiment will measure the η radiative decay width via the Primakoff effect. It will shed light on a longstanding discrepancy (~4σ) between the previous experimental results using the Primakoff and the e+e- collisions; and will offer accurate determinations of the light quark-mass ratio and the η-η' mixing angle. The JEF experiment will measure various η/ηꞌ decays with emphasis on rare neutral modes, producing a clean dataset with background suppression by two orders of magnitude compared to previous experiments. In addition to the baseline GlueX apparatus, the JEF experiment requires an upgraded forward calorimeter (FCAL-II) with a high-granularity, high-resolution PbWO4 crystal core in the central region to minimize shower overlaps and to optimize resolutions of the reconstructed energy and position. The data from the JEF experiment will provide sensitive probes to: (a) explore the role of scalar meson dynamics in the chiral perturbation theory for the first time; (b) tighten the uncertainty in the light quark mass ratio using the η→3π Dalitz distributions; (c) search for various sub-GeV dark gauge boson candidates (including vectors, scalars and Axion-like particles) to improve the existing bounds by up to two orders of magnitude that is complementary to the ongoing worldwide efforts at high-energy collider and underground facilities; and (d) provide the best direct constraints for C-violating, P-conserving new forces. As a co-spokesperson, the PI will play a leadership role in carrying out these experiments. The PI and her team will: (1) analyze the PrimEx-eta experimental data to deliver the physics result; (2) commission the FCAL-II calorimeter and run the JEF experiment that is scheduled to start in Jan 2025. 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.