The Nuclear and Particle Physics group at Norfolk State University (NSU) is involved in experimentally exploring the basic interaction that keeps the nucleus together, namely, the strong interaction. The group's research efforts are focused in the study of the structure of the nucleon and of other sub-atomic particles (hadrons). This research is carried out at the Thomas Jefferson National Accelerator Facility, Virginia. Through this program NSU faculty and students will be involved in experiments at the forefront of research in the field, thereby strengthening the national participation of minorities in nuclear and particle physics research.

Project Report

The research pursued by Norfolk State University’s (NSU) Nuclear Physics group is directed to the study of the strong interactions. More specifically, we study the quantum field theory of the strong interactions, QCD, at energies where is most relevant and less understood, on the scale of the nucleon (intermediate energies). To this end, we perform experiments at Jefferson Lab, Newport News, VA. NSU faculty and undergraduate students participate in the construction of hardware and analysis of data from experiments in the forefront of intermediate energy nuclear physics, and in doing so, strengthening the participation of minorities in nuclear and particle physics research. Symmetries and their spontaneous breaking effects play a fundamental role in our understanding of Nature. In particular, the neutral pion, π0, contains fundamental information about chiral symmetry breaking, and its radiative decay is primarily defined by the chiral anomaly. Theoretical activities in this domain for the past several years have resulted in a high precision (1% level) prediction for the decay rate of the π0 into two photons. A new experiment (PRIMEX) was performed at Jefferson Lab in Hall B using the high precision photon tagging facility in combination with a newly developed high-resolution electromagnetic calorimeter. The π0 decay width in this experiment was extracted from the pion photoproduction differential cross sections measured at forward angles (the Primakoff process) for two nuclear targets. The result from this experiment, with its 2.8% total uncertainty, is a factor of 2.5 more precise than the currently accepted average value of the π0 lifetime and directly confirms the validity of chiral anomaly at the few percent level. Protons and neutrons (collectively called nucleons) are fundamental building blocks of the atomic nuclei, and they are held together inside nuclei by the strong force. Precise knowledge of the proton's radius is critically important for understanding nucleons in terms of the underlying quarks and gluons, which are the degrees of freedom of the accepted theory of the strong force called quantum chromodynamics (QCD). High precision measurement of the proton's radius is also warranted by the recent controversy over the size of the proton, triggered by the new ultra-high precision measurement in muonic hydrogen, which is significantly smaller than the commonly accepted value obtained from measurement in normal (electronic) hydrogen. To address this proton radius puzzle, we have developed a novel electron scattering experiment that can achieve an unprecedented precision and an almost model independent extraction of the proton charge radius for the first time in electron scattering experiments using a high resolution calorimeter and a windowless gas flow target. Lattice QCD calculations are providing a mass spectrum of light-mass hadrons and they are posed to obtain scattering properties. Therefore, it is time for improving our experimental determination of the poorly known light meson spectrum to compare with predictions. One main question in meson spectroscopy is: Can we find hints of the glue in the meson spectrum? We performed and are now analyzing several meson spectroscopy experiment performed at CLAS in the last several years, and we are planning for new experiments at CLAS12, the Jefferson Lab upgrade. The first PWA results have been published and more PWA results are progressing in several channels. We have searched for the suspected JPC = 1-+ exotic mesons p1(1400) and p1(1600). These new CLAS results show that those mesons are not photoproduced at the expected levels from calculations based on them being hybrids. These new results made an important contribution to the future prospectives on exotic searches at Jefferson Lab. The future of hadron spectroscopy at CLAS12 will be pursued using quasireal photoproduction. The CLAS12 high intensity quasireal photon beam (including knowledge of the beam polarization) on protons and nuclear targets will create new opportunities in hadron spectroscopy that our group had initiated and is now pursuing.

National Science Foundation (NSF)
Division of Physics (PHY)
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Bradley D. Keister
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Norfolk State University
United States
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