Scientists are gearing up to once more push the boundaries of the cutting edge of particle physics with the reopening of the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland after a three-year shutdown.
After its successful second run ended in December of 2018, the LHC was purposefully shut down for updates while teams prepared for Run 3, which is set to begin soon, as the new run will begin this spring (earlier reports from CERN expected Run 3 to begin as soon as early March). During the shutdown, which also included delays due to the COVID-19 pandemic, CERN team members have been preparing for new experiments with the collider as major upgrades are made to boost its power and capabilities.
On the precipice of new physics, scientists are eager to harness the LHC's new upgrades to investigate the Higgs boson, explore dark matter and potentially expand our understanding of the standard model, the leading theory describing all known fundamental forces and elementary particles in the universe.
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Now, while there were some delays in work due to the COVID-19 pandemic, LHC's latest shutdown was pre-planned for these upgrades. But "the fact that there hasn't been so much news coming out of the LHC in the last year or so, I think would have happened anyway because the thing wasn't making collisions," John Ellis, a theoretical physicist at CERN, told Space.com.
However, the LHC will soon be back doing what it does best: accelerating protons (or ions) to near the speed of light and smashing them into one another.
"These measurements shed light on what's happening at the highest energies that we can reach, which tells us about phenomena in the very early universe," Phil Allport, a particle physics detector expert at the University of Birmingham in the UK, told NewScientist about what experiments with the LHC could allow scientists to do.
These high-energy collisions could also allow researchers to think outside of the box with their experiments and try to make sense of things that the standard model doesn't fully explain.
When physicists explore unknowns like dark matter and dark energy, "these things require extensions to the standard model of particle physics to accommodate, and all of those theories make predictions. And the best place to look to test those predictions is usually in the highest energies achievable," Allport added.
Ellis is especially interested in exploring one particular finding that actually came during the LHC shutdown, he shared.
"One thing, which by the way, it did come out during the shutdown period, which certainly intrigues me, is this evidence that when bottom quarks decay, they may do so in a way that discriminates between electrons and muons," Ellis said, adding that within the standard model "we expect electrons and muons to behave in exactly the same way."
However, findings like those during the LHCb experiment, which investigates the differences between matter and antimatter, "indicate that they actually don't behave in the same way. There's quite a significant difference," Ellis said.
Ellis specified that there is still much work to be done before these findings are confirmed as a concrete discovery. However, "it's certainly very intriguing," and "would be a major, major discovery if confirmed."
With the new upgrades, CERN has increased the power of the LHC's injectors, which feed beams of accelerated particles into the collider. At the time of the previous shutdown in 2018, the collider could accelerate beams up to an energy of 6.5 teraelectronvolts, and that value has been raised to 6.8 teraelectronvolts, according to a statement from CERN.
For reference, a single teraelectronvolt is equivalent to 1 trillion electron volts (an electron volt, a unit of energy, is equivalent to the work done on an electron accelerating through the potential of one volt.)
To increase the energy of the proton beams to such an extreme level, "the thousands of superconducting magnets, whose fields direct the beams around their trajectory, need to grow accustomed to much stronger currents after a long period of inactivity during LS2," the same CERN statement read. Getting the equipment up to speed in this upgrade is a process that CERN calls "magnet training" and which is made up of about 12,000 individual tests.
With LHC's magnets "trained" and the proton beams more powerful than ever, the LHC will be able to create collisions at higher energies than ever before, expanding the possibilities for what scientists using the upgraded equipment might find.
As part of its ongoing upgrades, the LHC team is even considering implementing graphics processing units (GPUs) to be used as efficient computer processors for the collider, as it analyzes and processes an incredible wealth of data.
"The LHC's ambitious upgrade programme poses a range of exciting computing challenges; GPUs can play an important role in supporting machine-learning approaches to tackling many of these," Enrica Porcari, head of the CERN IT department, said in a statement.
After Run 3, the LHC will be upgraded again in 2024 to narrow the colliders' proton beams. This will allow more collisions to take place, increasing the number of collisions from 40 in 2018 to between 120 and 250, NewScientist reported. These collective upgrades will transform the LHC so dramatically that it will be renamed to the High Luminosity Large Hadron Collider. The HL-LHC is set to come "online" in 2028.
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