DarkLight experiment

DarkLight experiment
Name	DarkLight experiment
Collaboration	Massachusetts Institute of Technology, Jefferson Lab, University of Massachusetts Amherst, Arizona State University
Accelerator	CEBAF
Location	Newport News, Virginia
Energy	100 MeV
Detector	HPS
Spokesperson	Richard G. Milner

DarkLight experiment. The DarkLight experiment is a particle physics search designed to detect a hypothetical particle known as a dark photon, which could act as a portal between normal matter and dark matter. Proposed to run at the Thomas Jefferson National Accelerator Facility, it aims to probe a specific, unexplored region of parameter space by studying the decay of an electron beam hitting a fixed target. The collaboration involves researchers from several major institutions, including Massachusetts Institute of Technology and University of Massachusetts Amherst.

Overview

The experiment was conceived to investigate forces beyond the Standard Model, particularly those that might explain the nature of dark matter. It is specifically designed to search for the dark photon, also referred to as A' or U-boson, by looking for its decay products in a precise energy range. The proposal leverages the high-intensity, continuous-wave electron beam available at the CEBAF accelerator to achieve unprecedented sensitivity. This effort is part of a broader global initiative in particle physics to uncover evidence of new fundamental interactions.

Experimental design

The core design involves directing a 100 MeV electron beam from CEBAF onto a fixed target made of high-density tungsten or tantalum. The experiment is configured to detect the hypothesized process where a dark photon is produced and subsequently decays into an electron-positron pair, a signature known as a resonance. Key to this design is the use of a compact, high-rate spectrometer system capable of operating in an intense background environment. This setup requires sophisticated trigger systems and precise vertex reconstruction to identify the rare signal events amidst substantial backgrounds from quantum electrodynamics processes like trident production.

Physics goals and motivation

The primary physics goal is to either discover the dark photon or constrain its properties, specifically its mass and its coupling strength to the ordinary photon. Such a discovery would provide a compelling candidate for a force carrier mediating interactions with the dark sector, potentially explaining anomalies like the discrepancy in the measured muon g-2. The experiment is motivated by theoretical frameworks including string theory and models with a hidden U(1) gauge symmetry. Success would have profound implications for our understanding of cosmology and could illuminate the composition of the universe's missing mass.

Technical specifications and components

The experiment's detector, often referred to as the HPS, includes a silicon vertex tracker for precise measurement of decay vertices, a lead-tungstate calorimeter for energy measurement, and a magnet for momentum analysis. The beamline incorporates a high-power water-cooled target capable of withstanding the intense beam current. Critical technical challenges involve managing high rates of background events, which necessitates fast electronics and advanced data acquisition systems developed in collaboration with engineers from Jefferson Lab. The entire apparatus is designed for high luminosity to maximize the chance of observing the rare decay process.

Results and status

An initial proof-of-principle run was conducted, demonstrating the feasibility of the detection technique in the challenging beam environment. While the full proposed experiment has not yet been completed, these early results helped refine the design and background rejection strategies. The collaboration has published technical design reports and physics sensitivity projections in journals like Physical Review Letters. The future status of the experiment depends on securing further beam time and funding within the broader priorities of the US Department of Energy nuclear physics program.

Collaboration and funding

The collaboration is led by principal investigators from Massachusetts Institute of Technology and includes scientists from Jefferson Lab, University of Massachusetts Amherst, and Arizona State University. Funding and support have been provided by the US Department of Energy Office of Nuclear Physics and the National Science Foundation. The project also benefits from the infrastructure and technical expertise of the Thomas Jefferson National Accelerator Facility, a key national user facility for nuclear physics research in the United States.

Category:Particle physics experiments Category:Dark matter Category:Jefferson Lab