Time, experiments and search for unknown physics

on july 5, under the suburbs of Geneva, Switzerland, will launch the world’s largest particle accelerator and begin collecting data again. And what they might find has the potential to explode particle physics wide open.

After nearly four years of shutdown, extended by Covid-induced delays, Large Hadron Collider (LHC) is about to kick off the third round of experiments: briefly mentioned, Run 3† CERN will commemorate the launch with a live stream at 10 a.m. Eastern time.

Physicists have high hopes for Run 3. They hope to unlock new particles and new mechanisms that they have never been able to see. Recent physics research has revealed a possible fifth force and challenges for the Standard model of physics. Run 3 could be

What does the Large Hadron Collider do?

The LHC is a particle accelerator. The name accurately describes what LHC does: It crushes particles — mostly protons, but it can also collide larger particles that physicists call “heavy ions.” Usually that means ions of lead, the heaviest non-radioactive element.

To do this, the LHC first shoots two beams of particles into its ring, traveling in opposite directions. They spin around and around, accelerated and guided by powerful electromagnets, until they come very close to the speed of light. Then, after they get up to speed, they collide head-on.

The ALICE experiment at CERN, which deals with large ions. Ronald Patrick/Getty Images News/Getty Images

Those collisions cause the guts of the fast-moving particles – the smaller particles that act as their building blocks – to explode. Some bump into each other. And in the energetic, high temperature and extreme conditions during a collision, all kinds of foreign particles can come out of the woodwork.

Scientists study the waste that is left behind. Their highly sophisticated detectors can search through the rubble and find the tracks, traces and fingerprints all those particles leave behind.

Large Hadron Collider target

Smashing up particles sounds like a rough way to learn about it: a bit like smashing complex electronic devices together and hoping to learn how they work from the mangled components that are left behind. But it’s the best way for physicists to look at the quantum world, at scales millions of times smaller than even atoms.

But in those collisions, many of these particles are phantoms, barely interacting with the world or lasting fractions of a second. Most of the time they would go unseen even if you look at them with very powerful detectors. But scientists can find the telltale features of those particles in the high-energy soup that emerges for a moment in a particle accelerator like LHC.

The LHC’s upgrades during its shutdown have boosted its energy, giving it even more power to reveal this subatomic world.

Large Hadron Collider Size

The LHC is a behemoth. It is housed in a circular tunnel, 27 kilometers (17 mi) in circumference and 4 meters (13 ft) wide, buried several floors underground. From CERN’s headquarters in the outskirts of Geneva, this tunnel runs under the towering Jura Mountains, along the undulating French-Swiss border, and then comes back again.

LHC is so large because, with a larger circumference that a particle beam can accelerate through, particles can move closer and closer to the speed of light and therefore carry higher energies. With higher energies, physicists can see more particles when beams collide.

As massive as the LHC is, scientists aren’t afraid to dream even bigger. If some scientists have their way, LHC will have a future successor — a so-called Future circular collider – that’s almost four times the circumference.

The computational grid for the LHC, responsible for processing the petabytes of information produced by the experiments.FABRICS COFFRINI/AFP/Getty Images

Great Hadron Collider Discoveries

Perhaps LHC’s most striking discovery to date is the… Higgs boson† According to particle physics, this ghostly particle is a product of something known as the Higgs field, which gives mass to certain particles, the W and Z bosons. These particles direct the weak nuclear force that controls some forms of radioactivity.

By finding the Higgs boson, particle physicists were able to confirm that much of their theory about how the universe works on a small scale was correct. But the Higgs boson is very unstable and observing it has to do with the fact that it will disintegrate almost immediately.

The Higgs boson was first proposed in the 1960s, and scientists have searched for it for decades until it was finally discovered at the LHC in 2012. In fact, the search for the Higgs boson was one of the reasons LHC was built in the first place. Earlier particle accelerators didn’t have the energy needed to find it.

Although scientists have found a Higgs boson, they don’t quite understand its properties. Doing that is on their wish list.

What are the new Large Hadron Collider experiments?

There aren’t necessarily *new* experiments — but they build on existing experiments looking for unknown physics.

LHC is not just another big experiment. It actually houses multiple experiments. Each is looking for different particles or exploring different physics. Each has its own detector somewhere along the accelerator loop. Each is supported by as many as hundreds of scientists around the world.

There are four major. ATLAS and CMS are “general purpose” experiments looking at a wide variety of particles passing through the examination of their respective detectors. These two experiments found the Higgs boson.

Images of the CMS and ATLAS detectors. Everything about Space Magazine/Future/Getty Images

ALICE hopes to study a quirky phase of matter known as “quark-gluon plasma,” where atoms literally melt into a super-hot soup. Cosmologists believe that quark-gluon plasma dominated the universe for a brief moment early in its history.

LHCb (short for “LHC beauty”) aims to investigate a particular particle called the beauty quark† Scientists think the beauty quark could teach them more about the differences between matter and its destructive twin with opposite charges: antimatter. When matter and antimatter touch, they destroy each other. The Big Bang should have created matter and antimatter in equal amounts, but it seems to have created an excess of matter – the matter that surrounds us. This imbalance has no explanation.

There are several smaller experiments, many of which look at other specific particles or other elements of physics.

What do CERN scientists hope to find?

For decades, particle physics has been living and dying through the so-called Standard model† It’s a diagram that neatly depicts the fundamental particles of the universe – 17 of them – and how they interact with each other. It controls three of the four fundamental forces of the universe: the strong nuclear force, which holds particles together in the nucleus of an atom; the weak nuclear force, which directs some forms of radioactivity; and electromagnetism.

For decades, particle physics seems to have almost always obeyed the predictions of the Standard Model — almost.

Particle physicists increasingly believe that the Standard Model is not all there is. There are a few curiosities that the Standard Model does not meet. For example, the model does not answer the fourth fundamental force: gravity. Nor has it (so far) provided a satisfactory culprit for dark matter, which is more than five times greater in abundance than “normal” matter.

Some of these unanswered questions have led scientists to suspect that there is a fifth fundamental force lurking somewhere out there. One idea is that this fifth force is somehow related to dark energy, a mysterious form of energy that seems to be speeding up the universe.

Some experiments have suggested that particles are beyond the Standard Model, perhaps the carriers of physics beyond scientists’ current understanding.

Recently, scientists have delved into old data from another particle accelerator in suburban Chicago’s Fermilab found it that one particle, the W boson, has a higher mass than expected. It sounds insignificant, but it is a serious violation of the standard model. Physicists hope LHC can help them test this.

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