With the upgrade of the world’s most advanced particle accelerator, scientists believe they may discover a new (fifth) force of nature and evidence of so-called dark matter.
Deep in the Alps, scientists can barely contain their excitement. They mutter about discoveries that would radically alter our understanding of the Universe.
“I’ve been looking for the fifth force (of nature) since I’ve been a particle physicist,” says Sam Harper.
“Maybe this is the year.”
For the past 20 years, Sam has been trying to find evidence of a fifth force of nature — gravity, electromagnetic, and the two nuclear forces being the four that physicists already know.
He’s pinning his hopes on a major overhaul of the Large Hadron Collider (LHC). It’s the world’s most advanced particle accelerator — a massive machine that crushes atoms to break them apart and find out what’s inside them.
It was upgraded even more in a three-year renovation. Its instruments are more sensitive, allowing researchers to study the collision of particles inside atoms with greater definition; its software has been updated to be able to receive data at a rate of 30 million times per second; and their beams are narrower, which greatly increases the number of collisions.
What all this means is that there is now a greater chance that the LHC will find subatomic particles that are completely new to science. He is expected to make discoveries that will spark the biggest revolution in physics in a hundred years.
In addition to believing they can discover a new (fifth) force of nature, the researchers hope to find evidence of an invisible substance that makes up most of the Universe, called dark matter.
There is enormous pressure on researchers to present results. Many expected the LHC to have already found evidence of a new realm of physics.
New experimental chain
The LHC is part of the European Organization for Nuclear Research, known as Cern, on the Franco-Swiss border outside Geneva.
As you get closer, it looks like an ordinary complex — blocks of 1950s office and dormitory buildings set amid manicured lawns and winding lanes named after renowned physicists.
But 100 meters underground is a cathedral for science. I managed to get to the heart of the LHC, to one of the giant detectors that made one of the greatest discoveries of our generation, the Higgs boson, a subatomic particle without which many of the other particles we know would have no mass.
The Atlas detector is 46m long and 25m high. It is one of four instruments at the LHC that analyze the particles created by it.
There are 7 thousand tons of metal, silicon, electronics and wiring, gathered in a complex and precise way. It is a thing of great beauty. “Majesty” is the word used by Marcella Bona of Queen Mary University of London, UK, one of the scientists using the Atlas detector for her experiments.
I watch in ecstasy as Marcella tells me about the improvements made to the detector during the three years since the LHC shut down.
“It will be two to three times better, in terms of our experiment’s ability to detect, collect and analyze data,” she says.
“The entire experimental chain has been updated.”
Amidst the noise of engineers finishing up the Atlas, I find it hard to imagine that something this big is needed to detect particles that are much smaller than an atom.
The LHC has four of these detectors, each doing different experiments. It is at the very center of these gigantic detectors that particles known as protons, found in the nuclei of atoms, collide after being accelerated to close to the speed of light around a ring 27 km in circumference.
The collisions generate even smaller particles that fly off in different directions. Its trajectory and energy are tracked by detector systems, and it’s this trail that tells scientists what kind of particle it is — sort of like determining an animal’s species and characteristics from its footprints.
Almost all the smaller particles resulting from collisions are already known to science. What physicists are looking for here is evidence of new particles that can emerge from collisions, but are thought to be created very rarely.
It is these as-yet-unknown particles that physicists believe are the key to unlocking a completely new view of the Universe. Their discovery could bring about the biggest shift in physics thinking since Einstein’s theories of relativity.
Engineers have spent the last three years upgrading the LHC to produce more collisions in a shorter amount of time. The reformed machine has a much better chance of generating and finding the new rarely created particles. Much of this work was led by Rhodri Jones, who rejoices in his title of “chief of the sheaves”.
Encounter Rhodri in CERN’s magnetic assembly area, which resembles a large aircraft hangar. Here, engineers are renovating the 15-meter-long cylindrical magnets that bend the particle beams around the accelerator. It’s precision work with absolutely no margin for error.
Rhodri tells me that his team has narrowed the beams so that more particles are squeezed into a smaller area. This greatly increases the chances of the particles colliding with each other.
“We’re looking at very rare processes, so the greater the number of collisions, the greater the chance of actually finding what’s going on and seeing small anomalies,” he says.
“The improvement in the beam means that for all the physics we’ve done since the beginning of the time the LHC has been in operation, we’re going to be able to get the same amount of collisions in the next three years that we got in those ten years.”
Another major improvement was in the capture and processing of collision data. In the revamped LHC, data is collected from each of the four detectors at a staggering rate of 30 million times per second.
Of course, this is too much for the human mind to take in, but any one of the collisions could contain crucial evidence for the existence of one of the new particles that scientists are looking for.
The LHC’s software has been updated to automatically search through all collected data and, using the latest artificial intelligence techniques, identify and save readings that may be of potential interest for scientists to analyze.
Doubts about gravity
The current theory of subatomic physics is called the Standard Model. Although it has a rather unimaginative name, the theory has been brilliant at explaining how subatomic particles come together to create atoms that make up the world around us.
The Standard Model also explains how particles interact through forces of nature, such as electromagnetic and nuclear forces that hold the components of atoms together.
But the Standard Model cannot explain how gravity works, nor how the invisible parts of the Universe, which physicists call dark matter and dark energy, behave.
Scientists know that these invisible particles and forces exist from the movement of galaxies in space — and together they make up 95% of the Universe. But no one has yet been able to prove their existence and determine what they are.
The LHC was built to detect these particles that could explain how much of the cosmos works. Marcella Bona told me that there is now real hope that updates will make this possible.
“It’s a really exciting time,” she smiles.
“We’ve been working for the last three years updating the machinery. Now we’re ready.”
Marcella has spoken passionately from the moment I met her. But her enthusiasm increases when I ask whether the discovery of a dark matter particle would be one of the greatest discoveries in physics.
“I’d say so,” she laughs, her eyes widening. “Yes, without a doubt, that would be amazing,” she says, allowing herself, momentarily, to revel in the real prospect of this happening in the coming months.
No less enthusiastic is Sam Harper, the scientist who has spent the last two decades hunting the “fifth force” of nature. He works on another of the LHC’s four detectors, the so-called CMS, located at the other end of the Cern complex.
Results from the LHC before it was shut down for refurbishment and from several other particle accelerators around the world revealed tantalizing clues to this fifth force. But with the LHC’s extra oomph, Sam believes his scientific quest may soon end.
And just like Marcella, the emotion in his voice is heightened as he says aloud what cannot be formally said in scientific circles until there is solid evidence.
“It would shake the structures of the field. It would be the biggest discovery of the LHC, the biggest discovery in particle physics since, since…”
Sam pauses, trying to find the words.
“It will be bigger than the Higgs.”
CERN will celebrate the tenth anniversary of the discovery of the Higgs boson later this year. But the festivities draw attention to the fact that the £3.6bn LHC, with an annual cost of £1.1bn , has not made any major discoveries since.
Many expected, and some hoped, that the world’s most powerful particle accelerator had by now discovered dark energy, the fifth force, or some other paradigm-shifting particle.
Much will depend on the results the researchers get over the next few years, as CERN will soon come up with proposals for an even larger hadron collider.
The most ambitious plan, the so-called Future Circular Collider (FCC), would have a ring 100 km in circumference, which would pass under Lake Geneva.
The FCC could cost around 20 billion pounds (about R$125 billion). The current machine has at least another ten years to go, and several other upgrades that will offer even more power to try to discover the particles that will change physics forever.
But CERN’s scientific leaders will submit their application for the next phase of particle physics experiments soon. And persuading member country governments to commit to a big increase in funding will be more difficult if the latest update fails to even find a sense of the new particles in the next two or three years.
Sam Harper admits to feeling “a little terrified” as the LHC embarks on its next series of experiments.
“We’re desperately trying to get everything ready and we’re working really hard to make sure we don’t miss any possible new physics. Because the worst thing in the world would be for new physics to be there and not find it.”
But far greater than Sam’s dread is his excitement about what the next few years hold.
“What drives all particle physicists is that we want to discover the unknown, which is why things like the fifth force and dark matter are so exciting, because we have no idea what it could be or if it even exists and we really want to find that out. .”
What could be the first crack in the Standard Model was discovered by researchers at Fermilab, the US equivalent of the LHC, earlier this month.
In the coming months and years, LHC researchers will try to confirm their result and find many more cracks in the current theory until it collapses to make way for a new, unified and more complete theory of how the Universe works.