Nuclear Physics Seminars This Term

The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for a thermal origin of dark matter sharpen this mass range to within about an MeV to 100 TeV. Most of the stable constituents of known matter have masses in the MeV to GeV range, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well, yet it remains largely unexplored. The Heavy Photon Search (HPS) at Jefferson Lab is a fixed target experiment that uses an electron beam to probe models of thermal dark matter involving sub-GeV dark photons. HPS searches for visibly decaying dark photons through two distinct methods - a resonance search in the e+e- invariant mass distribution and a displaced vertex search for long-lived dark photons. This seminar will give an overview of the theoretical motivations, the main experimental challenges and how they are addressed, the results for the 2016 Engineering Run, and future data and upgrades. In addition, an introduction to the Light Dark Matter eXperiment (LDMX), a planned next generation experiment at SLAC that will search for invisibly decaying dark photons through a missing-momentum experiment, will be presented.

In 1983, results published by the European Muon Collaboration (EMC) at CERN suggested that the quark structure of nucleons are modified when they are bound together in the nuclear environment. This modification, now called the EMC Effect, was largely unexpected and has been the subject of a significant amount of theoretical and experimental effort over the past 40 years to determine its underlying cause. Despite this effort, the exact mechanism that causes the EMC Effect has continued to elude physicists.

Experiment E12-10-008 at Jefferson Lab aims to shine a bright new light on this 40-year-old problem. Having collected data from September 2022 through February 2023, this experiment utilized the high luminosity 12 GeV electron beam of CEBAF to probe, with high precision, the quark structure of nearly 20 different nuclei. Data from this experiment will provide a significant contribution to the global set of EMC Effect data, producing the first measurements of the EMC Effect in many new nuclei and reducing uncertainty on previously studied nuclei. In this seminar, an overview of the EMC Effect will be given and the physics motivation of experiment E12-10-008 will be presented.