12 | New Scientist | 1 January 2022

Preview of 2022

THE Large Hadron Collider

(LHC) at CERN near Geneva,

Switzerland, will start running

again after a three-year

shutdown and delays due to the

covid-19 pandemic. The particle

collider – known for its role in

the discovery of the Higgs boson,

which gives mass to all other

fundamental particles – will

return in 2022 with upgrades

that give it a power boost.

Work has been under way to

conduct tests on the collider and

calibrate new equipment. Now, it

is gearing up for experiments that

could give physicists the data

needed to expand the standard

model, our best description of

how particles and forces interact.

Phil Allport at the University

of Birmingham in the UK says

the upgrades could allow new

measurements that give us

insight into the way the Higgs

boson decays, leading to a

better understanding of how

it fits into the standard model.

“These measurements

shed light on what’s happening

at the highest energies that we

can reach, which tells us about

phenomena in the very early

universe,” he says. They will

also allow us to test ideas

that try to account for things

that aren’t fully described by

the standard model, he says.

This includes mysteries that

have plagued physicists for

decades, such as the so-called

hierarchy problem, which deals

with the vast discrepancy

between the mass of the Higgs

and those of other fundamental

particles, plus dark energy and

dark matter, the unexplained

phenomena that make up most

of the universe.

“All of these things require

extensions to the standard

model of particle physics to

accommodate, and all of those

theories make predictions. And

the best place to look to test

those predictions is usually in

the highest energies achievable,”

says Allport. He says the LHC

upgrades also pave the way to

entirely new observations that

signal a departure from the

standard model.

Part of the upgrade work

has been to increase the power

of the injectors that supply

highly accelerated particle

beams to the collider. Prior

to the last shutdown in 2018,

protons could reach an energy

of 6.5 teraelectronvolts, but the

upgrades mean this can now be

pushed to 6.8 teraelectronvolts.

Rende Steerenberg at CERN

says that these more powerful

beams will cause collisions at

higher energies than ever before,

and other upgrades in the future

will also allow more particles

to be collided at the same time.

There are already plans for

further improvements in 2024,

which will narrow the LHC’s

beams and drastically increase

the number of collisions that

take place. The 2018 run saw

around 40 collisions every time

a pulse of protons passed each

other, but upgrades will push this

to between 120 to 250. At that

point, the LHC will take on a new

name, the High Luminosity Large

Hadron Collider, and it should

begin experiments in 2028.

There are still many tests to be

run before the power of the new

components can be unleashed.

Scientists at CERN hope to finish

these by late February and then

slowly ramp up to a small number

of full-power collisions in May.

The frequency of these collisions

will be increased in June, which

is when Steerenberg says

“meaningful” physics will begin.  ❚

Matthew Sparkes

The Large Hadron Collider

comes back online

4

The Large Hadron Collider

has been shut down for

upgrades since 2018

Particle physics

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