Researchers dig deep underground in hopes of finally observing dark matter

This text was initially printed at The Dialog. The publication contributed the article to House.com’s Skilled Voices: Op-Ed & Insights.

Physicists like me do not absolutely perceive what makes up about 83% of the matter of the universe — one thing we name “darkish matter.” However with a tank filled with xenon buried almost a mile underneath South Dakota, we’d sooner or later have the ability to measure what darkish matter actually is.

Within the typical mannequin, darkish matter accounts for many of the gravitational attraction within the universe, offering the glue that permits buildings like galaxies, together with our personal Milky Method, to kind. Because the photo voltaic system orbits across the middle of the Milky Method, Earth strikes by means of a darkish matter halo, which makes up many of the matter in our galaxy.

I am a physicist fascinated by understanding the character of darkish matter. One fashionable guess is that darkish matter is a brand new sort of particle, the Weakly Interacting Huge Particle, or WIMP. “WIMP” captures the particle’s essence fairly properly – it has mass, which means it interacts gravitationally, however it in any other case interacts very weakly – or hardly ever – with regular matter. WIMPs within the Milky Method theoretically fly by means of us on Earth on a regular basis, however as a result of they work together weakly, they simply don’t hit something.

Trying to find WIMPs

Over the previous 30 years, scientists have developed an experimental program to attempt to detect the uncommon interactions between WIMPs and common atoms. On Earth, nevertheless, we’re continuously surrounded by low, nondangerous ranges of radioactivity coming from hint parts – primarily uranium and thorium – within the surroundings, in addition to cosmic rays from house. The objective in attempting to find darkish matter is to construct as delicate a detector as potential, so it may see the darkish matter, and to place it in as quiet a spot as potential, so the darkish matter sign might be seen over the background radioactivity.

With outcomes printed in July 2023, the LUX-ZEPLIN, or LZ, collaboration has performed simply that, constructing the most important darkish matter detector thus far and working it 4,850 ft (1,478 meters) underground within the Sanford Underground Analysis Facility in Lead, South Dakota.

On the middle of LZ rests 10 metric tons (10,000 kilograms) of liquid xenon. When particles go by means of the detector, they might collide with xenon atoms, resulting in a flash of sunshine and the discharge of electrons.

In LZ, two huge electrical grids apply an electrical discipline throughout the quantity of liquid, which pushes these launched electrons to the liquid’s floor. Once they breach the floor, they’re pulled into the house above the liquid, which is crammed with xenon gasoline, and accelerated by one other electrical discipline to create a second flash of sunshine. 

Two massive arrays of sunshine sensors gather these two flashes of sunshine, and collectively they permit researchers to reconstruct the place, vitality and sort of interplay that came about.

Decreasing radioactivity

All supplies on Earth, together with these utilized in WIMP detector development, emit some radiation that might doubtlessly masks darkish matter interactions. Scientists due to this fact construct darkish matter detectors utilizing probably the most “radiopure” supplies – that’s, freed from radioactive contaminants – they’ll discover, each inside and out of doors the detector.

For instance, by working with metallic foundries, LZ was ready to make use of the cleanest titanium on Earth to construct the central cylinder – or cryostat – that holds the liquid xenon. Utilizing this particular titanium reduces the radioactivity in LZ, creating a transparent house to see any darkish matter interactions. Moreover, liquid xenon is so dense that it truly acts as a radiation defend, and it’s straightforward to purify the xenon of radioactive contaminants that may sneak in.

In LZ, the central xenon detector lives inside two different detectors, known as the xenon pores and skin and the outer detector. These supporting layers catch radioactivity on the way in which in or out of the central xenon chamber. As a result of darkish matter interactions are so uncommon, a darkish matter particle will solely ever work together one time in all the equipment. Thus, if we observe an occasion with a number of interactions within the xenon or the outer detector, we will assume it’s not being attributable to a WIMP.

The hunt continues

Within the consequence simply printed, utilizing 60 days of knowledge, LZ recorded about 5 occasions per day within the detector. That is a couple of trillion fewer occasions than a typical particle detector on the floor would file in a day. By wanting on the traits of those occasions, researchers can safely say that no interplay to date has been attributable to darkish matter. The result’s, alas, not a discovery of latest physics – however we will set limits on precisely how weakly darkish matter should work together, because it stays unseen by LZ.

These limits assist to inform physicists what darkish matter just isn’t – and LZ does that higher than any experiment on this planet. In the meantime, there’s hope for what comes subsequent within the seek for darkish matter. LZ is accumulating extra information now, and we count on to take greater than 15 occasions extra information over the subsequent few years. A WIMP interplay might already be in that information set, simply ready to be revealed within the subsequent spherical of study.

This text was first printed by The Dialog.