After a two-year shutdown, the atom-smashing machine known as the Large Hadron Collider has embarked on a renewed quest to probe some of the biggest puzzles about the universe, such as dark matter and the possible presence of other dimensions.
In the collider’s first run from 2010 to 2013, physicists discovered the Higgs boson, a breakthrough that closed a long-standing gap in the theory about how subatomic particles behave. Now, scientists hope to break new ground with the souped-up collider.
“We hope to find light in the dark universe,” said Rolf Heuer, director general of the European Organization for Nuclear Research, or CERN, in an interview. CERN, based in Geneva, operates the collider.
At a physics conference in Vienna on Monday, CERN will brief 700 scientists about the collider’s second run, which began earlier this month and extends until 2018. CERN will also present fresh data about the Higgs, a fundamental particle that gives mass to other particles.
“We’ve done more precise measurements about the Higgs and have more information about its properties,” said Dr. Heuer.
The collider smashes protons together at close to the speed of light. These collisions are mini-versions of the primordial blast known as the big bang that brought the universe into being 13.8 billion years ago. Scientists sift through the debris of the collisions to learn how the subatomic world is put together.
Since the collider was shut down in February 2013 hundreds of engineers and technicians have been upgrading the machine to prepare for particle collisions at far higher energy levels.
This time, the collider will run day and night and ramp up to 13 tera-electron-volts, an energy level about 70% greater than the first run. It will also reach one billion collisions per second. The higher power and greater number of collisions should make it possible to probe even deeper into the subatomic world.
One big enigma is dark matter. With the discovery of the Higgs, physicists more or less completed the description of visible matter. But visible matter makes up only 4% of the universe, while an unseen “dark matter” makes up 23%. (The rest is something called dark energy, another mystery.)
Scientists hypothesize that dark matter may be built from relatively large, ethereal particles known as “wimps”—weakly interacting massive particles—which barely interact with normal matter.
Scientists hope to catch a glimpse of the elusive wimp at the souped-up collider. It requires higher levels of energy to produce larger particles, such as the wimp, something the collider can now do. There is also a greater chance of spotting wimps when there are more collisions to study.
“We needed more than 100 billion collisions to produce the Higgs,” noted Dr. Heuer.
The Higgs is a crucial piece of the Standard Model, a 40-year-old theory that predicts the behavior of subatomic particles. But it is incomplete because it doesn’t explain gravity.
Physicists have put forward a theory called supersymmetry, or SUSY, that could extend the Standard Model. According to SUSY, every particle in the Standard Model has a partner. Thus, the electron’s SUSY partner would have the same electric charge as the electron but a different spin.
If SUSY exists, some of the partner particles—with names such as Higgsinos and winos—may be seen in the detritus of the proton collisions.
“We’ll have four to eight times more data in the second run compared to what we had in the first,” said Ian Hinchliffe, physicist at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and a CERN scientist.
Physicists also hope the collider will help unearth evidence for the existence of extra dimensions, beyond the three of space and one of time. Although scientists searched for evidence in the first run, they came up with nothing.
“These extra dimensions might exist at very small distances,” said Dr. Hinchliffe. “But now, at higher and higher energies of the collider, I can probe shorter and shorter distance scales.”
In the collider’s first run, scientists notched several successes, including the Higgs and the discovery of two new subatomic particles.
Researchers also observed the rare decay of a particle known as the strange B meson, the subject of a 30-year quest. Earlier this month, they said they had stumbled on an exotic particle called the pentaquark, which helps explain how everyday matter is constituted.
Still, scientists made one major misstep with the collider. In 2011, CERN said it had recorded ghostly particles called neutrinos traveling faster than the speed of light—a claim that threatened to undermine a key theory of Einstein’s notion that nothing travels faster than light. The claim turned out to be false.