The
Large Hadron Collider (LHC) is the biggest and most powerful particle
accelerator in the world. It is located at the European particle physics
laboratory CERN, in Switzerland.
Scientists
use the LHC to test theoretical predictions in particle physics, particularly
those associated with the "Standard Model". While the Standard Model
can explain almost all results in particle physics there are some questions
left unanswered such as what is dark matter and dark energy? Why is there more
matter than antimatter? The LHC is designed to help answer such questions.
The LHC
can reproduce the conditions that existed within a billionth of a second of the
Big Bang. The colossal accelerator allows scientists to collide high-energy
subatomic particles in a controlled environment and observe the interactions.
One of the most significant LHC breakthroughs came in 2012 with the discovery
of the Higgs Boson.
If you
see a news headline about exotic new subatomic particles, the chances are the
discovery was made at CERN, the European Organization for Nuclear Research,
located near Geneva in Switzerland.
A recent
example occurred in January 2022, when CERN scientists announced "evidence
of X particles (opens in new tab) in the quark-gluon plasma produced in the
Large Hadron Collider." Hiding behind that technospeak is the eye-popping
fact that CERN succeeded in recreating a situation that hasn't occurred
naturally since a few microseconds after the Big Bang.
When Run
3 commences we can expect a whole new spate of discoveries, so it's a good time
to take a closer look at what makes the LHC — and the rest of CERN — so unique.
The LHC
is a particle accelerator — a device that boosts subatomic particles to
enormous energies in a controlled way so that scientists can study the
resulting interactions, according to the CERN LHC fact sheet (opens in new
tab). The 'large' that the L stands for is an understatement; the LHC is by far
the biggest accelerator in the world right now, occupying a circular tunnel
nearly 17 miles (27 kilometers) in circumference. The middle letter, H, stands
for 'hadron', the generic name for composite LHC particles such as protons that
are made up of smaller particles called quarks. Finally, the C stands for
‘collider’ — the LHC accelerate two particle beams in opposite directions, and
all the action takes place when the beams collide.
Like all
physics experiments, the LHC aims to test theoretical predictions — in this
case, the so-called Standard Model of particle physics — and see if there are
any holes in them. As strange as it sounds, physicists are itching to find a
few holes in the Standard Model because there are some things, such as dark
matter and dark energy, that can't be explained until they do.
The LHC
smashes particles together at high speeds, creating a cascade of new particles,
including the infamous Higgs boson.
The
LHC's biggest moment came in 2012 with the discovery of the Higgs boson.
Although widely referred to as the "God particle", it's not really as
awesome in itself as that name might suggest. Its huge significance came from
the fact that it was the last prediction of the Standard Model that hadn't yet
been proven. But the Higgs boson is far from being the LHC's only discovery.
According
to the physics magazine CERN Courier (opens in new tab), the LHC has also found
around 60 previously unknown hadrons, which are complex particles made up of
various combinations of quarks. Even so, all those new particles still lie
within the bounds of the Standard Model, which the LHC has struggled to move beyond
(opens in new tab), much to the disappointment of the numerous scientists who
have spent their careers working on alternative theories.
The
first tantalizing hints that a breakthrough might be just around the corner
came in 2021 when analysis of LHC data revealed patterns of behavior (opens in
new tab) that indicated small but definite departures from the Standard Model.
According
to CERN, the LHC opened for business in 2009, but CERN's history goes back much
further than that. The organization was established in 1954(opens in new tab)
following a recommendation by the European Council for Nuclear Research — or
Conseil Européen pour la Recherche Nucléaire in French, from which it gets its
name. Between its creation and the opening of the LHC, CERN was responsible for
a series of groundbreaking discoveries, including weak neutral currents, light
neutrinos and the W and Z bosons. As soon as the LHC is back up and running, we
can expect discoveries to continue.
As the
name suggests, Run 3 is the third science run of the LHC and will begin on July
5, 2022. It will build on LHC's discoveries made during its Run 1 (2009-2013)
and Run 2 (2015 to 2018) and perform experiments through 2024.
On the
precipice of new physics, scientists are keen to make use of the LHC's new
upgrades to investigate the Higgs boson, explore dark matter and potentially
expand our understanding of the standard model, the leading theory describing
all known fundamental forces and elementary particles in the universe.
With the
new upgrades, CERN has increased the power of the LHC's injectors, which feed
beams of accelerated particles into the collider. At the time of the previous
shutdown in 2018, the collider could accelerate beams up to energy of 6.5
teraelectronvolts, and that value has been raised to 6.8 teraelectronvolts,
according to a statement from CERN (opens in new tab).
For
reference, a single teraelectronvolt is equivalent to 1 trillion electron volts
(an electron volt, a unit of energy, is equivalent to the work done on an
electron accelerating through the potential of one volt.)
To
increase the energy of the proton beams to such an extreme level, "the
thousands of superconducting magnets, whose fields direct the beams around
their trajectory, need to grow accustomed to much stronger currents after a
long period of inactivity during LS2(opens in new tab)," the same CERN
statement read. Getting the equipment up to speed in this upgrade is a process
that CERN calls "magnet training" and which is made up of about
12,000 individual tests.
With
LHC's magnets "trained" and the proton beams more powerful than ever,
the LHC will be able to create collisions at higher energies than ever before,
expanding the possibilities for what scientists using the upgraded equipment
might find.
Once Run
3 concludes in 2024, CERN scientists will shut it down for another planned
overhaul that will include more upgrades for the massive particle accelerator.
Once complete, those upgrades will allow scientists to rename LHC the
"High Luminosity Large Hadron Collider" once it reopens in 2028.
The
Compact Muon Solenoid (CMS) pictured here can capture images of particles up to
40 million times per second.
As huge
as it is, the LHC can't function without the help of other machines around it.
Before particles, which are usually protons but for some experiments are much
heavier lead ions, are injected into it, they're passed through a chain of
smaller accelerators that progressively boost their speed; according to a CERN
LHC report (opens in new tab). Smaller is just a relative term; the last step
in the injector chain, the Super Proton Synchrotron, is almost 4.3 miles in
circumference (6.9 km). The result is two beams traveling in opposite
directions around the LHC at virtually the speed of light, according to CERN (opens
in new tab).
The
beams are kept on their circular trajectories by a strong magnetic field, which
has the effect of bending the path of electrically charged particles. At four
points around the LHC's vast ring, the opposing beams are brought together and
made to collide, and that's where all the science happens.
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