- 3556 - LARGE HADRON COLLIDER - The world's largest particle collider is getting ready to smash atoms even harder in 2022. 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.
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- If all initial tests and checks starting in March, 2022, go well, scientists will begin experiments in June and slowly ramp up to full power by the end of July.
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- 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.
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- The completion of the will deploy the countless, both preventive and corrective, maintenance operations, which are required to operate such a 27-kilometer-long (17 miles) complex machine.
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- 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.
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- 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.
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- 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. ATLAS will be on the hunt for a proposed left-handed relative to the neutrino called a “heavy neutral lepton“.
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- The upcoming LHC run will also introduce two new physics experiments: the Scattering and Neutrino Detector (SND) and the Forward Search Experiment (FASER).
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- The LHC produces 1.7 billion collisions per second.
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- 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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- A decade ago, physicists wondered whether the discovery of the Higgs boson at the Large Hadron Collider would point to a new frontier beyond the Standard Model of subatomic particles. So far, that’s not been the case but a new measurement of a different kind of boson at a different particle collider might do the trick.
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- Fresh findings from the Collider Detector at Fermilab, or CDF, one of the main experiments that made use of the Tevatron particle collider at the U.S. Department of Energy’s Fermilab in Illinois. The CDF team has a newly reported value for the mass of the “W boson“.
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- Bosons are force-carrying particles that transfer discrete amounts of energy between particles of matter. The electromagnetic force is carried by “bosons” known as “photons“, while the “Higgs boson” is responsible for transferring the force that endows particles with mass.
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- The W boson plays a role in the “weak nuclear force“, which comes into play in radioactive decay as well as nuclear fusion, that process that makes the sun shine. The particle was discovered decades ago at Europe’s CERN research center, which is now home to the Large Hadron Collider, and its mass has been the subject of study ever since.
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- The W boson about 80 times heavier than a proton. Knowing the precise weight of the W boson is a big deal because that value is factored into the finely tuned equations that are woven into the Standard Model, one of the most successful theories in science. The theory explains how atoms are put together, and its predictions, including the prediction of the existence of the Higgs boson, have been repeatedly confirmed.
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- And yet, there’s a lot the Standard Model doesn’t explain. This has to do with the nature of dark matter and dark energy, which together make up more than 95% of the universe’s content. If there’s some measurement that runs counter to the Standard Model, that may point to an opening for revising the theory.
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- Physicists have analyzed huge amounts of data collected at the Tevatron between 1985 and 2011, and came up with a mass measurement that carries a precision of 0.01%. That’s twice as precise as the best previous measurement. Fermilab says it’s like measuring the weight of an 800-pound gorilla to within 1.5 ounces.
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- The only problem is, the 800-pound gorilla appears to tip the scales at three-quarters of a pound overweight. The expected value for the W boson’s mass was 80,357 mega electron volts, or MeV, plus or minus 6 MeV. The CDF’s value is 80,433 MeV, plus or minus 9 MeV.
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- The CDF researchers say their findings carry a confidence level of 7 sigma, which translates to a 1-in-390 billion chance that they could be explained away as a statistical fluke. If the findings hold up, theoretical physicists will have to turn their firepower toward figuring out how to explain the discrepancy.
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- Although the statistical analysis sounds impressive, there’s still a chance that something threw off the measurement. That was the case for the claim in 2011 that neutrinos could travel faster than light. When those findings were first announced, researchers claimed a confidence level nearly as high as what the CDF team is claiming now. But upon review, the researchers found glitches in their experimental setup, including a fiber-optic cable that was mis-attached. Those faster-than-light neutrinos actually weren’t.
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- The CDF findings alone aren’t enough to force a full rethinking of the Standard Model.
It’s now up to the theoretical physics community and other experiments to follow up on this and shed light on this mystery. If the difference between the experimental and expected value is due to some kind of new particle or subatomic interaction, which is one of the possibilities, there’s a good chance it’s something that could be discovered in future experiments.
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April 24, 2022 LARGE HADRON COLLIDER 3556
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