The research program funded by this award will provide experimental data on nucleon structure that can be probed via the weak and the electromagnetic interactions. These objectives are sought through two major projects which are scheduled to take data at Jefferson Lab during the award period: the QWEAK and DVCS/Hall A experiments.
The QWEAK experiment is a precision measurement of the weak charge of the proton at very low energy scale. The weak charge of the proton at various energy scales is predicted by the Standard Model of Particle Physics, and its precise value at low energy scale would be sensitive to various physics processes beyond the Standard Model. Thus QWEAK may provide a measure of the influence of new particles which would be complimenatry to the direct observation at the LHC. The DVCS/Hall A experiment will study of the correlation between the momentum and spatial distribution of the quarks within the proton. This correlation provides a novel way to study the proton that bridges between two well explored avenues of nucleon studies: form factor (spatial) distributions and parton distribution (momentum) functions.
The research group supported by this award is responsible for the data acquisition and data analysis systems for QWEAK, and for a variety of hardware and software projects within the DVCS/Hall A experiment. These experiements provide outstanding opportunities for both graduate and undergraduate students to get hands-on experience with hardware and software tools and contribute to research at a major national laboratory.
The medium-energy nuclear experimental program supported by award ID 0969788 aimed to contribute information to answer the following questions: "What is the internal landscape of the nucleon?" and "What are the key ingredients of a ‘New Standard Model’?". Both areas of research have been identified in the 2007 Long Range Plan of the Nuclear Science Advisory Committee (NSAC) mandated by DOE and NSF, as research frontiers for today’s nuclear science. King and Roche use the electron beam of Jefferson Lab (JLab) to probe the nucleon with both the electromagnetic and weak interactions. The group’s work over the past funding cycle produced data for two experiments (DVCS/Hall A (E07-007) and QWEAK); the data taking for these experiments was completed during the funding cycle. The PIs and their students took active part in the analysis of the data. Over the past funding cycle, the PIs and the students working with them published 11 papers in peer-reviewed journals (2 also signed by students) and 10 internal documents (all of them signed by students). The members of the group delivered 19 presentations at conferences (6 invited talks, 4 talks by students) and 23 talks at collaboration meetings (11 by students). Finally, King, Roche and one of the graduate students working with them held leadership positions within the collaborations they worked with. The goal of DVCS experiments is to study the Generalized Partons Distributions (GPD) of the proton over a broad kinematic range. In the past fifteen years, the theoretical "discovery" of the GPDs has opened up a new exciting era of nuclear physics. The GPDs provide a unique framework based on a 3D tomographic image of the quark structure of the nucleon that links its momentum and coordinate quark distributions. Roche is a co-spokesperson of two experiments dedicated to the study of GPDs in Hall A at JLab. These experiments extend successful previous measurements of absolute cross sections; they will further explore the potential of Deeply Virtual Compton Scattering and Deeply Virtual Meson Production for GPDs measurements. One such experiment (E07-007) took data in the Fall of 2010. Roche’s participation to this data taking was made possible by award 0969788. Roche and her collaborators are working on the analysis of these data, of which publication is expected in 2015. In contrast to high-energy colliders, an alternative strategy to search for new physics is to perform precision measurements of interactions which can be reliably predicted by the Standard Model. While not directly exciting new forms of matter, any deviation from the prediction of the Standard Model provides a signature of these new forms of matter. It is in this low-energy domain where the QWEAK experiment contributes. QWEAK completed data taking in the summer of 2012. King, Roche and their two graduate students contributed software and data acquisition expertise. Subsequently, they took part to the analysis of the data resulting in the publication of the first peer review article from the collaboration. This paper presents the analysis of a small subset of the data demonstrating the overall quality of the data but not precise enough to test the prediction of the Standard Model. The analysis of the full data set is still on-going, with publication expected in 2015. The PhD work of the two graduate students supported by this award was cited in this initial peer review article. The broader impacts of this NSF award are twofold: training the next generation of scientists and raising the profile of minority scientists. Thanks to this support, four undergraduate students and four graduate students have worked with the PIs. Three of these eight students are female, four are first-generation college students and four are non-caucasian. Four of these students have worked directly at JLab (Virginia) and have had numerous personal contacts with national and international researchers. Two graduate students obtained PhDs for their work with the PIs, with one of them winning the 2014 JLab thesis prize. Both of them continued their career as postdoctoral fellows. Finally, this award supported the research of a woman physicist whose residence on campus and mentoring activities raised the profile of gender minorities within the larger public community.
