After a 3-Year Break, The Large Hadron Collider Restarts to Smash Some More Atoms
The world's largest particle collider is getting ready to smash atoms harder than ever before.
Following a three-year break of scheduled maintenance, upgrades, and pandemic delays, the Large Hadron Collider (LHC) is preparing to power up for its third, and most powerful yet, experimental period.
If all initial tests and checks starting this month go well, scientists will begin experiments in June and slowly ramp up to full power by the end of July, experts told Live Science.
The new run could finally reveal the long-sought "right-handed" versions of ghostly particles called neutrinos; find the elusive particles that make up dark matter, which exerts gravity but does not interact with light; and even help to explain why the universe exists at all.
"The completion of the so-called Long Shut-down 2, initially planned for two years but extended by one year due to the COVID-19 pandemic, provided the opportunity to deploy the countless, both preventive and corrective, maintenance operations, which are required to operate such a 27-kilometer-long [17 miles] complex machine," Stephane Fartoukh, a physicist at the European Organization for Nuclear Research (CERN), which operates the LHC, told Live Science.
Since 2008, the LHC has smashed atoms together at incredible speeds to find new particles, such as the Higgs boson, an elementary particle and the last missing piece in the Standard Model that describes fundamental forces and particles in the universe.
Related: Could misbehaving neutrinos explain why the universe exists?
In the upcoming third run, the collider's upgraded capabilities will focus on exploring the properties of particles in the Standard Model, including the Higgs boson, and hunting for evidence of dark matter.
In addition to other tasks, the ATLAS experiment, the largest particle detector at the LHC, will try to answer a question that has puzzled scientists for decades: Why are all the neutrinos detected so far southpaws?
Most particles come in left- and right-handed flavors – which describe how the particles spin and move – and are thought to have antimatter twins – which have the same mass but the opposite electric charge.
In theory, right-handed neutrinos should exist, but no one has ever found an elusive right-handed neutrino, a left-handed antineutrino, or an antimatter twin to an ordinary neutrino, for that matter, according to Fermilab.
ATLAS will be on the hunt for a proposed left-handed relative to the neutrino called a heavy neutral lepton, according to a statement from the ATLAS Collaboration.
"I'm excited to get data again and see what we can see in the different searches," Rebeca Gonzalez Suarez, a CERN physicist, an education and outreach coordinator for the ATLAS Collaboration, and an associate professor at Uppsala University in Sweden, told Live Science. "Maybe there will be a surprise in there."
The upcoming LHC run will also introduce two new physics experiments: the Scattering and Neutrino Detector (SND) and the Forward Search Experiment (FASER).
FASER will use a detector located 1,575 feet (480 meters) from the collision site for the ATLAS experiment, with the goal of collecting unknown exotic particles that can travel long distances before decaying into detectable particles – for instance, potential weakly interacting massive particles that barely interact with matter and could make up dark matter.
FASER's subdetector, FASERν, and SND will aim to detect high-energy neutrinos, which are known to be produced at the collision site but have never been detected. Such detections will help scientists understand these particles in greater detail than ever before.
And they may also address another conundrum. Matter and antimatter are thought to have been produced in equal amounts at the Big Bang. In theory, that means they should have annihilated on contact, leaving nothing behind. Yet our universe exists and is mostly matter.
"These two experiments attempt to solve some of the biggest puzzles in physics, such as the nature of dark matter, the origin of neutrino masses, and the imbalance between matter and antimatter in the present-day universe," Fartoukh told Live Science via email.
The new upgrades will allow the LHC to smash particles harder than ever before – up to an energy of 6.8 teraelectronvolts, an increase over the previous limit of 6.5 teraelectronvolts – which could enable the LHC to see new types of particles.
The LHC will also smash atoms together more often, which should make it easier for scientists to find uncommon particles that are very rarely produced during collisions.
The LHC's detector upgrades will enable its instruments to gather high-quality data on this new energy regime. But while the LHC experiments will deliver terabytes of data every second, only a fraction can be saved and studied.
So scientists at CERN have improved the automated systems that first process the data and select the most interesting events to be saved and later studied by scientists.
"[LHC] produces 1.7 billion collisions per second. It's impossible to keep all that data, so we need to have a strategy to pick the events that we think are interesting," Gonzalez Suarez told Live Science. "For that, we use specific parts of our hardware that send signals when something looks like it's interesting."
The third run is scheduled to last until the end of 2025. Already, scientists are discussing the next round of upgrades to be implemented after Run 3 for the LHC's High Luminosity phase, which will further increase the number of simultaneous collisions and energies, and improve instrument sensitivities.
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