When the Large Hadron Collider spins, the hopes of physicists rise

In April, outside Geneva, scientists at the European Center for Nuclear Research, or CERN, once again fired their spacecraft, the Large Hadron Collider. After a three-year shutdown for repairs and upgrades, the collider resumed shooting protons – the bare intestines of hydrogen atoms – around its 17-mile-long electromagnetic underground racetrack. In early July, the collider will begin to collide with these particles to form primordial energy sparks.

So the wonderful game of hunting for the mystery of the universe will be renewed again, against the backdrop of renewed hopes of new phenomena and particle physicists. Even before its renewal, the collider produced hints that nature might be hiding something spectacular. Mitesh Patel, a particle physicist at Imperial College London conducting an experiment at CERN, Describe his previous launch data as “the most interesting result I’ve seen in my professional life.”

Ten years ago, CERN physicists became world titles with the discovery of the Higgs boson, the long-awaited particle that gives mass to every other particle in the universe. What remains to be found? Almost everything, optimistic physicists say.

When the CERN collider was first launched in 2010, the world was ready. The machine, the largest and most powerful ever built, is designed to look for the Higgs boson. This particle is the cornerstone of the standard model, a set of equations that explains everything scientists have been able to measure about the subatomic universe.

But there are deeper questions about the universe that the standard model does not explain: Where did the universe come from? Why is it created from matter and not antimatter? What is the “dark matter” that fills the cosmos? How does a Higgs particle have mass?

Physicists hoped that some answers would be made in 2010 when the Big Collider was first turned on. Nothing appeared except Higgs – namely, no new particles that explained the nature of dark matter. It is unfortunate that the standard model has remained unshakable.

Collider closed at the end of 2018 for extensive upgrades and repairs. According to the current schedule, the collider will work until 2025 and then close for another two years to install other extensive upgrades. Among this set of upgrades is the improvement of giant detectors that stand at the four points of collision of proton beams and analyze collision debris. These detectors will stop working from July. Proton beams are compressed to become more intense, which increases the chance of protons colliding at intersection points – but creates confusion for detectors and computers in the form of multiple sprays of particles that must be distinguished from each other.

“The data will flow much faster than we were used to,” Dr. Patel said. Where once only a few collisions occurred at the intersection of each beam, there would now be more than five.

“It complicates our lives a bit because we have to be able to find what we are interested in in all those different interactions,” he said. “But that means you are more likely to see what you are looking for.”

Meanwhile, a variety of experiments have revealed possible cracks in the standard model – and pointed to a broader, deeper theory of the universe. These results include the rare behavior of subatomic particles whose names are unknown to most in cosmic bleaching.

Consider mion, a subatomic particle that briefly became known last year. Muons are often called fat electrons; They have the same negative electric charge but are 207 times more massive. “Who ordered this?” Physicist Isadore Rabbi said that when muons were discovered in 1936.

No one knows where the mions fit into the grand scheme of things. They are formed by the collision of cosmic rays – and in collider events – and they are radioactively dispersed in microseconds by a stream of electrons and electron particles called neutrinos.

Last year, a team of about 200 physicists affiliated with the National Laboratory of the Illinois Farm Accelerator announced that ions moving in a magnetic field would vibrate much faster than the standard model predicted.

The discrepancy with the theoretical predictions arose in the eighth decimal point of the parameter, called g-2, which describes how a particle reacts to a magnetic field.

Scientists have attributed the fractional but real difference to the quantum whisper of still unknown particles that briefly materialize around a mion and affect its properties. Confirmation of the existence of particles ultimately violates the standard model.

But two groups of theorists are still working to reconcile their predictions of what g-2 should look like before they expect more data from the Fermilab experiment.

“The g-2 anomaly is still very much alive,” said Aida X. El-Khadra, a physicist at the University of Illinois at Urbana-Champaign, who led a three-year effort to build a consensus forecast called the Muon g-2 Theory Initiative. “Personally, I am optimistic that the standard model cracks will add to the earthquake. However, the exact location of the cracks may still be a moving target. “

Mion also figures in another anomaly. The protagonist, or perhaps villain, in this drama is a particle called B quark, one of six quark species that form heavier particles such as protons and neutrons. B means lower or, perhaps, beauty. Such quarks are found in two quark particles known as B mesons. But these quarks are unstable and tend to collapse in a way that seems to break the standard model.

Some rare decays in quark B involve a chain of reactions chamomile ending in a different, lighter species of quark and a pair of light particles called leptons, electrons, or their rich cousins, muons. The standard model assumes that electrons and muons appear equally in this reaction. (There is a third, heavier lepton called a tau, but it disintegrates very quickly to go unnoticed.) But Dr. Patel and his colleagues found more electron pairs than a muon pair, which violates a principle called Lepton universality.

“It could be a standard model killer,” said Dr. Patel, whose team surveyed the B quarks with one of the Large Hadron Collider detectors, the LHCb. This anomaly, like the magnetic anomaly of a muon, indicates an unknown “influence” – a particle or force that interferes with a reaction.

Dr. Patel says one of the most dramatic possibilities, if these data are maintained in the future collider run, is a subatomic speculation called a leptocark. If a particle exists, it can bridge the gap between the two classes of particles that make up the material universe: light leptons — electrons, muons, and neutrons — and heavier particles, such as protons and neutrons, that make up quarks. It is amazing that there are six types of quarks and six types of leptons.

“We are moving in this perspective with more optimism that a revolution can take place,” Dr. Patel said. “ებიCrossed fingers.”

There is another particle in this zoo that behaves strangely: the W boson, which transmits the so-called weak force responsible for radioactive decay. In May, Fermilab Collider Detector physicists, or CDF, announced a 10-year effort to measure the mass of these particles based on the approximately 4 million watt boson collected as a result of the collision of Fermilab Tevatron, the world’s most powerful collider. Before building the Large Hadron Collider.

According to the standard model and previous measurements of mass, the W boson should weigh about 80.357 billion electron volts, a unit of mass energy preferred by physicists. By comparison, the Higgs boson weighs 125 billion electron volts, about as much as an iodine atom. But W’s CDF measurement, the most accurate ever made, was higher than the projected 80.433 billion. Experimenters calculated that there was only one chance in 2 trillion – 7 in sigma, in the slang of physics – that this discrepancy was a statistical error.

The W boson mass is related to the masses of other particles, including the infamous Higgs. So this new inconsistency, if it continues, could be another crack in the standard model.

Nevertheless, all three anomalies and the theorists’ hopes for a revolution can evaporate with more data. But for optimists, all three identical directions point to hidden particles or forces that interfere with “known” physics.

“So a new particle that can explain both g-2 and mass W may not be available in the LHC,” said Kyle Cranmer, a physicist at the University of Wisconsin who is working on other CERN experiments.

John Ellis, a theorist at CERN and King’s College London, noted that at least 70 papers have been published that offer an explanation for the new W-mass mismatch.

“Many of these explanations also require new particles that may be available to the LHC,” he said. “Did I mention dark matter?” So you have to pay attention to a lot of things! ”

Commenting on the upcoming race, Dr. Patel said: “It will be exciting. It will be hard work, but we really want to see what we have and whether there is anything really interesting in the data. ”

He added: “You can have a scientific career and you can not say it once. So it feels like a privilege. “

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