GENEVA — This Halloween, scientists celebrate a cosmic riddle of mysterious material known as “dark matter” they believe makes up most of the universe and holds it all together. Along with pumpkin-carving and trick-or-treating, it’s “Dark Matter Day” around the world.
Scientists, institutions and others gather at local events to talk about one of the hottest pursuits in particle physics: the hunt for dark matter, a theoretical material that does not emit light or energy and cannot be directly observed.
Researchers from the European Organization for Nuclear Research, or CERN, reported over summer in the scientific journal Physics Review Letters that they developed a more effective technique to search for clues among huge amounts of data generated at the world’s largest atom smasher.
The international organization operates the 27-kilometer Large Hadron Collider underground along the Swiss-French border near Geneva. As the world’s top particle physics lab, it was designed to push bunches of protons in opposite directions at close to the speed of light so they collide at four points.
The aim is to recreate conditions a split second after the Big Bang, which scientists theorize was the massive explosion that created the universe. The collider is getting a major upgrade to increase the number of proton collisions that can be used for experiments and to boost the probability of more discoveries about the universe’s fundamental properties.
All that data has to be processed and stored before it can even be evaluated. That is why researchers investigating dark matter and other mysteries had to figure out better ways to analyze the data CERN generates.
“If we are not careful, we could end up discarding data that contains clues to completely new particles of which we are not yet aware, such as particles that form dark matter,” said Caterina Doglioni, a particle physicist at Sweden’s Lund University and member of the ATLAS experiment at CERN, one of the two main teams there, each involving several thousand scientists.
The new technique for data analysis involves processing it faster so less of the information needs to be retained.
“We know that dark matter exists,” she said. “Normally it passes through our measurement instruments, but cannot be registered, but in the case of our research we hoped to see the products of particles connected to it.”
Holding it all together
Invisible dark matter makes up most of the universe, says CERN, but can only be detected from its gravitational effects.
Galaxies rotate so fast they should have torn themselves apart. The gravity generated by their observable matter could not hold them together. That is why scientists believe something that has not yet been directly observed — invisible dark matter — gives galaxies extra mass that generates the extra gravity to hold together.
The dark matter, unlike normal matter, does not interact with electromagnetic force, so it does not absorb, reflect or emit light. That makes it difficult to detect. Researchers infer the existence of dark matter only from the gravitational effect it seems to have on visible matter.
“Here’s a sobering fact: The matter we know and that makes up all stars and galaxies only accounts for 5 percent of the content of the universe!” CERN said in a statement.
On Dark Matter Day, scientific experts are offering educational activities and film presentations about the search for what Doglioni describes as unknown particles that could be carriers of forces that can create a connection between visible and dark matter. The day is hosted by Interactions Collaboration, an international organization of particle physics communication specialists.
“These new particles, which we call ‘mediator particles,’ can disintegrate into extremely short-lived pairs of quarks, i.e., the very building blocks of the protons and neutrons in atoms,” she said. “When quarks disintegrate, a type of particle shower is formed that we can actually detect with our instruments.”