Particle physics experiments

How New Large Hadron Collider Experiments Could Change Physics Forever

After a After a three-year nap, the world’s largest particle collider is awake and ready to help physicists probe the limits of science itself, including the possible existence of a mysterious fifth force of nature.

Sam Harper has been a particle physicist and collaborator on the LHC’s Compact Muon Solenoid (CMS) experiment since 2007. He says new improvements to the collider over the past three years are now poised to bring scientists to the brink of the discovery of revelations that could forever alter our understanding of the smallest parts of our universe.

“We are really excited to follow [previous] anomalies,” says Harper. Reverse. “[But,] we are also very nervous to get everything right.

What is the Large Hadron Collider?

Located between the borders of France and Switzerland, the LHC is the largest (almost 25 kilometers long) and the most powerful particle accelerator in the world. This giant doughnut-shaped collider uses superconducting magnets and proton beams to crush known particles to extremely high energies (eg, 13.6 trillion electron volts).

This number may seem like a lot, but when converted into more common units of energy, like watts or joules, it’s not even enough to power a 100 watt light bulb for an hour (the energy of the LHC equals about 2.18 10^-6 Joules, whereas a 100 W light bulb needs 360,000 Joules for one hour of light.)

But don’t think you’ve been fooled – that might not be a lot of energy for a relatively heavy object like a light bulb, but it can propel incredibly light particles to speeds just below the speed of light.

Detectors spread around the loop then collect data from these collisions to watch the particles break into smaller fragments, revealing less understood areas of physics. These pieces can include things like quarks or even a class of particles called bosons. Bosons are a family of ultralight particles that include photons and are responsible for creating forces between particles, including strong and weak nuclear forces and electromagnetism. In the case of the famous Higgs boson, it is even responsible for giving mass to particles.

Beyond the excitement and curiosity that comes with smashing things together, Harper says scientists are using the LHC to explore the validity of the most important theory in particle physics: the Standard Model. Since its development in the 1970s, this theory has described nearly all of the behavior of subatomic particles that scientists have observed, but recent findings have challenged this supremacy, including a 2022 discovery from FermiLab data that suggests a certain boson, called the W boson, may be much heavier than predicted by the Standard Model.

With further upgrades to the LHC, scientists may finally be able to unravel this mystery, says Harper. If data from the new LHC run, Run 3, observes behavior not predicted by the Standard Model, this could be a telltale sign that there are forces or particles that are not yet known to the Standard Model.

“Voila, new physics discovered!” Harper said.

An experiment showing detections on the W boson.CERN

Why did the LHC stop working?

In the past, the operation of the LHC has caused concern among onlookers who once feared that a catastrophic accident at the collider would create a dangerous black hole (it wouldn’t have been), but skeptics can rest easy in knowing that the three-year break was nothing but planned upgrades and maintenance.

In fact, this isn’t the first or the last time such a stoppage will occur. According to an operating schedule, the LHC has two more planned shutdowns scheduled for the 2030s. The main purpose of these shutdowns, says Harper, is to gradually improve the energy capabilities of the proton beams projected inside the collider. to improve the chance of particle collision.

“Physicists want more collisions [and] no more collisions,” says Harper. “The LHC and its detectors are being upgraded to deliver and record as many as possible, which makes [for] happier physicists.

The LHC sent out two test beams last week, and the team intends to start collecting data for Run 3 in earnest later this summer. Aside from brief maintenance breaks along the way, Harper says Race 3 will last until the end of 2025.

What improvements has the LHC achieved?

During its most recent shutdown, which began at the end of 2018, the LHC benefited from two main improvements:

  • Increased energy capacities for its instruments allowing researchers to create more and faster collisions
  • More sensitive data collection software with improved capture rates to increase the number of collisions researchers can record and analyze

Together, these upgrades should create and register more collisions for detectors. According to CERN, the detector Harper is working on (CMS) should expect to observe “more collisions during this physics run than during the previous two physics runs combined”. Other ongoing experiments, including ATLAS, ALICE and LHCb, will likely see collisions up to fifty times the previous numbers.

In addition to upgrading existing experiments, Run 3 will also include two new experiments – FASER and [email protected] – specifically designed to research physics beyond the Standard Model.

The left shows a result in which two W bosons and a Z boson are released, while the other shows two Z bosons released. CERN

What discoveries could the LHC make now?

For Harper, one of the most exciting discoveries the LHC could make in Run 3 is to dig deeper into an anomaly observed by LHCb at the end of the last run that seemed to go beyond the physics of the standard model. In this data from Run 2, scientists saw a type of boson, called a B meson, decay into more electrons than predicted by the Standard Model.

If Harper and his colleagues can confirm this trend with more data, scientists believe this could be evidence that a new fifth force is acting on these particles.

“It’s too early to say anything. [certain,] but it makes us very excited, and we’re really looking forward to Run 3 being able to shed some more light on this,” says Harper.

In addition to exploring this anomaly, LHC experimenters also hope to dig deeper into other mysteries, including the particles that make up dark matter, by searching for missing momentum data from proton collisions. FASER, in particular, will focus on this hunt.

Yet despite all this tantalizing data at hand, Harper says there will still be a considerable lag time between collecting this data and actually concluding it. This might be the hardest part of the whole enterprise for passionate scientists like Harper.

“Unfortunately, we will have to wait while we carefully collect and analyze the data,” he says. “[It’s] hard for us because we are chomping at the bit to see the results ourselves!