US-Germany Cooperative Research: The Crystal Ball at MAMI Project

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

0341791 Nefkens This award supports Bernard Nefkens and students from University of Californis-Los Angeles in a collaboration with Reinhard Beck of the Institute for Nuclear Physics at the University of Mainz, Germany. This award supports a new program of study being undertaken at the Mainz Microtron (MAMI) in Mainz, Germany with the Crystal Ball (CB) detector, the TAPS spectrometer as a forward endcap. Additional equipment includes the Glasgow photon tagger, the Mainz/Bonn polarized target, and the DAPHNE wire chamber. This apparatus will enable a multifaceted physics program involving the measurement of several fundamental quantities related to the structure of the nucleon. Nucleon structure models make specific predictions for not only the masses and decay branching ratios of the states, but also their magnetic moments. The collaboration in Mainz is uniquely situated to measure the magnetic moments of D+(1232) and N+(1535). The only similar previous study is a measurement of uD++(1232) performed at Los Alamos in 1978. The intellectual merit of this program lies in the ability to relate measurements of fundamental quantities such as the magnetic moments of the D(1232) and the N(1535) to the structure of the proton and the neutron, the two basic particles that together make up well over 99% of the visible mass of the known universe. The UCLA group is well qualified to participate in this endeavor, having led an international collaboration using the Crystal Ball detector at the Brookhaven AGS for similar studies with pion and kaon beams. The German group at the Mainz facility plans to devote 2000 hours of beam time per year to this effort over the next five years. The impact of this research will extend far beyond the goals stated in this proposal. In addition to training several physics Ph.D. students engaged in original research projects, this program will contribute to the education of many undergraduate and masters-level students. The Crystal Ball Collaboration has an excellent record of diversity; the students who earned their doctoral dissertations with this detector include not only a woman, but also students from Bangladesh, Thailand, Canada, and Russia. By participating in this program, the various member institutions will enhance their laboratory and data analysis capabilities, thus improving their research and educational infrastructure.