Manufacturing Bits: May 30

Looking for heavy photons
The SLAC National Accelerator Laboratory and others have embarked on a mission to find hypothetical particles called heavy photons.

In 2015, researchers from the so-called Heavy Photon Search (HPS) group started the experiment at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility. Researchers installed a particle detector half a millimeter away from a powerful electron beam within Jefferson Lab’s Continuous Electron Beam Accelerator Facility (CEBAF).

Jefferson Lab’s accelerator is shaped like an oval racetrack and is located 25 feet below ground. (Source: Jefferson Lab)

Recently, researchers conducted the first tests with the system. The goal is to find “dark sector” particles like heavy photons. These theoretical sub-atomic particles could help unravel the mystery of the universe and perhaps provide a clue about the composition of the materials on earth.

Dark sector particles fall in the category of dark matter. In theory, some 4.9% of the universe consists of observable matter, such as protons, neutrons and electrons.

Then, some 68.3% of the universe is dark energy, while the remaining 26.8% is dark matter. An unknown form of energy, dark energy permeates outer space. In theory, dark matter exists in the universe, but it is invisible to the entire electromagnetic spectrum. Thus, researchers have failed to directly observe or detect dark matter.

Specifically, the HPS group is looking for a dark sector version of the photon. Photons are particles of light. They carry the fundamental electromagnetic force in particle physics. “Analogously, the dark photon would be the carrier of a force between dark-sector particles,” according to SLAC. “But unlike the regular photon, the dark photon would have mass. That’s why it’s also called the heavy photon.”

To find heavy photons, researchers used a continuous beam of electrons from Jefferson Lab’s CEBAF facility. In the lab, the electrons hit a tungsten target, which, in turn, could produce heavy photons.

So far, though, researchers have not found dark or heavy photons in the first-run or early experiments. But the early results are promising, according to Mathew Graham of SLAC. “In addition to figuring out if we can actually do the experiment, the first run also helped us understand the background signals in the experiment and develop the data analysis tools we need for our search for dark photons,” he said.

Searching for dark matter
In a separate project, researchers from the XENON Collaboration have been looking for an elusive part of the makeup of the universe—dark matter.

As stated above, dark matter exists in the universe. However, it is invisible to the electromagnetic spectrum. As a result, researchers have been unable to directly observe or detect dark matter.

Recently, the XENON Collaboration, a group of researchers from several countries, has released the first results from a dark matter experiment. For this, the group developed a giant liquid xenon detector, dubbed the XENON1T. The detector is installed underground within the Laboratory Nazionali del Gran Sasso in central Italy. The 3.2-ton system is based on a dual-phase time projection chamber. The chamber resides in a mountain to shield the detector from cosmic rays.

XENON1T installation in the underground hall of Laboratori Nazionali del Gran Sasso. The three story building on the right houses various auxiliary systems. The cryostat containing the detector is located inside the large water tank on the left. (Photo by Roberto Corrieri and Patrick De Perio)

The chamber itself is situated within a cryostat in the middle of a water tank. The tank maintains the xenon at a temperature of -95°C.
In the system, there is a particle interaction with the liquid xenon. This leads to tiny flashes of light. “A 62 kg liquid xenon target is operated as a dual phase (liquid/gas) time projection chamber to search for interactions of dark matter particles,” according to the XENON Collaboration.

Following this step, researchers then examine the energy of the interacting particles. Then, they can determine whether it might be dark matter or not.

Many dark matter experiments are searching for so-called weakly interacting massive particles (WIMPs). So far, though, the early results have not shown any signs of dark matter. “WIMPs did not show up in this first search with XENON1T, but we also did not expect them so soon,” said Elena Aprile, a professor at Columbia University. “The best news is that the experiment continues to accumulate excellent data which will allow us to test quite soon the WIMP hypothesis in a region of mass and cross-section with normal atoms as never before. A new phase in the race to detect dark matter with ultra-low background massive detectors on Earth has just began with XENON1T.”

Big laser
The European XFEL–the world’s biggest X-ray laser–has reached the last major milestone before its grand opening in September.

The 3.4 km long facility has generated its first X-ray laser light. The light has a wavelength of 0.8nm. The first laser had a repetition rate of one pulse per second, which will later increase to 27,000 per second.

The European XFEL is located in the German federal states of Hamburg and Schleswig-Holstein. It comprises three large sites above ground and several underground tunnels. Using the X-ray flashes of the European XFEL, researchers will be able to map the atomic details of viruses, cells, materials and chemical reactions.