Long-awaited boosts to the world’s most powerful collider could spur breakthroughs in the hunt for physics beyond the Standard Model
In their final moments, the last protons flew at nearly the speed of light. They completed the 27-kilometer loop underneath the Alpine countryside 11,245 times a second until they were released from their metal coil and slammed into a giant steel-coated graphite block. Since December 2018, other than a few tests here and there, the Large Hadron Collider has been offline. But on April 22 the LHC fired up again and commenced its third run.
As Run 3 begins, particle physicists face a number of tantalizing anomalies, from the new, unexpectedly hefty measurements of the W boson mass to the long-standing muon g−2 discrepancy, but they lack firm evidence of new physics. “There aren’t any obvious flashing lights,” says Nishita Desai, a theorist at the Tata Institute of Fundamental Research in India. “It’s not like ‘this is where you will get a discovery.
Theorists in the 1960s posited that particle mass arose from an imperceptible field permeating all of space: the more a particle interacts with this field, the greater its mass. Peter Higgs, a British theorist, suggested that the field would have an associated particle—the Higgs boson. Discovering it would confirm the mechanism that gave elementary particles their mass.
“There’s a certain generation of physicists who were told that, as soon as the accelerator turned on, they would see SUSY [and] find new physics.” Blekman says. “But there is no reason why it should be so easy.” After each multiyear run, the LHC’s equipment requires refurbishing.. José Miguel Jiménez, CERN’s head of technology, who oversaw the second long shutdown, ticks off a rapid-fire list of areas that needed work: “technical infrastructure, cooling, ventilation, electrical distribution, electrical safety, elevators, cranes, all these fancy door access systems [and] fire detection.”
This density is crucial because it determines how many collisions the detectors at the LHC will eventually see, says Bettina Mikulec, a senior physicist at CERN, who led the injector upgrade. If the beam is not dense at the start, it will not be dense later. When it is running, the LHC—not just the magnets and beam but also computers and cryogenics and vacuum systems—consumes an astonishing amount of energy: about 800 gigawatt-hours per year, or about half that of the entire city of Geneva. “We are, in a certain way, the electrical utility for CERN,” says Mario Parodi, head of electrical project management. CERN’s electricity comes primarily from France, where about 80 percent of the grid relies on nuclear energy.
Dealing with increased luminosity requires taking faster and better data, Blekman says. Both ATLAS and CMS have revamped their “triggers”—systems that use software and hardware to recognize particle events, such as a Higgs boson decaying to two photons. Sifting legible events from a mishmash early on is crucial for later analysis.
Whereas ATLAS and CMS underwent moderate upgrades, the Large Hadron Collider beauty detector, which is use particles called beauty quarks, or b quarks, to search for rare decays will be completely changed. “We are going to start commissioning a completely new detector,” says Patrick Koppenburg, an experimental particle physicist at LHCb. “We need a better resolution just so that we can tell [particles] apart.
FASER is essentially a mostly empty tube full of trackers designed to detect a dark sector particle decaying. FASERnu uses the opposite strategy. “We want as dense of a material as possible to get the neutrinos to actually interact,” Feng says. The detector is essentially made from camera film interleaved with 1,000 tungsten plates. Tungsten’s high density—nearly twice that of lead—gives neutrinos more targets to scatter off.
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Large Hadron Collider hits world record proton accelerationChelsea “Foxanne” Gohd joined Space.com in 2018 and is now a Senior Writer, writing about everything from climate change to planetary science and human spaceflight in both articles and on-camera in videos. With a degree in Public Health and biological sciences, Chelsea has written and worked for institutions including the American Museum of Natural History, Scientific American, Discover Magazine Blog, Astronomy Magazine and Live Science. When not writing, editing or filming something space-y, Chelsea 'Foxanne' Gohd is writing music and performing as Foxanne, even launching a song to space in 2021 with Inspiration4. You can follow her on Twitter chelsea_gohd and foxannemusic.
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