The researchers added a stack of two types of insulating materials, designed to make it more likely that the system could search for a type of hypothetical dark matter particle known as a dark photon. The SNSPD experiment consisted of a small square array of nanowires, each 140 nanometers (nm, or billionths of a meter) in diameter and spaced 200 nm apart, confined within a light-tight box. The current generates a brief but measurable voltage -a signal that part of the nanowire heated up by interacting with a photon or, perhaps, a dark matter particle. With the flow of current through the nanowire now obstructed, the current travels along a second path connected to an electrical amplifier. That way, even a tiny amount of energy deposited by an incoming particle will produce enough heat to develop electrical resistance in the wire. Researchers operate SNSPDs at a temperature just below the threshold required for the nanowires to become superconducting.

Systems of such wires, formally known as superconducting nanowire single-photon detectors (SNSPDs), are exquisitely sensitive to extremely small amounts of energy imparted by photons (particles of light) and perhaps dark matter particles when they collide with the detectors. “Superconducting” refers to a property that some materials, such as tungsten silicide, have at ultralow temperatures: zero resistance to the flow of electrical current. In the superconducting detector study, NIST scientists Jeff Chiles and Sae Woo Nam and their collaborators used tungsten silicide superconducting nanowires only one-thousandth the width of a human hair as dark-matter detectors. Another NIST team has proposed that trapped electrons, commonly used to measure properties of ordinary particles, could also serve as highly sensitive detectors of hypothetical dark matter particles if they carry charge. The study has already placed new limits on the possible mass of one type of hypothesized dark matter.

In one study, a prototype for a much larger experiment, researchers have used state-of-the-art superconducting detectors to hunt for dark matter. Researchers at NIST are now exploring new ways to search for the invisible particles. In underground laboratories and at particle accelerators, scientists have been searching for this dark matter with no success for more than 30 years. Some kind of invisible, unknown type of subatomic particle, dubbed dark matter, must provide the extra gravitational glue. Numerous astronomical observations indicate that the visible mass in the universe is not nearly enough to hold galaxies together and account for how matter clumps. For decades, astronomers and physicists have been trying to solve one of the deepest mysteries about the cosmos: An estimated 85% of its mass is missing.

Dark matter a novel