The existence of the Higgs boson completes the standard model of particle physics.
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Artist's
illustration of the Higgs boson being produced by two colliding protons. (Image
credit: MARK GARLICK/SCIENCE PHOTO LIBRARY via Getty Images) |
The Higgs boson is the fundamental force-carrying
particle of the Higgs field, which is responsible for granting other particles
their mass. This field was first proposed in the mid-sixties by Peter Higgs —
for whom the particle is named and his colleagues.
The particle was finally discovered on July 4, 2012,
by researchers at the Large Hadron Collider (LHC) — the most powerful particle
accelerator in the world — located at the European particle physics laboratory
CERN, Switzerland.
The LHC confirmed the existence of the Higgs field and
the mechanism that gives rise to mass and thus completed the standard model of
particle physics — the best description we have of the subatomic world.
As scientists approached the end of the 20th Century advances
in particle physics had answered many questions that surrounded the fundamental
building blocks of nature. Yet, as physicists steadily populated the particle
zoo with electrons, protons, bosons, and all flavors of quarks, some pressing
questions remained stubbornly unanswered. Amongst these, why do some particles
have mass?
The story of the Higgs boson is motivated by this
question.
WHAT IS THE HIGGS BOSON?
The Higgs boson has a mass of 125 billion electron
volts(opens in new tab) — meaning it is 130 times more massive than a
proton , according to CERN(opens in new tab). It is also chargeless with zero
spin — a quantum mechanical equivalent to angular momentum. The Higgs Boson
is the only elementary particle with no spin.
A boson is a "force carrier" particle that
comes into play when particles interact with each other, with a boson exchanged
during this interaction. For example, when two electrons interact they exchange
a photon — the force-carrying particle of electromagnetic fields.
Because quantum field theory describes the microscopic
world and the quantum fields that fill the universe with wave mechanics, a
boson can also be described as a wave in a field.
So a photon is a particle and a wave that arises from
an excited electromagnetic field and the Higgs boson is the particle or
"quantized manifestation" that arises from the Higgs field when
excited. That field generates mass via its interaction with other particles and
the mechanism carried by the Higgs boson called the Brout-Englert-Higgs
mechanism.
WHY IS THE HIGGS BOSON CALLED THE 'GOD PARTICLE?'
The ATLAS detector
(A Toroidal LHC Apparatus) is one of the LHC’s general-purpose detectors. ATLAS, along with the CMS detector first
detected the Higgs boson. (Image credit:
xenotar via Getty Images) |
The Higgs boson's nickname "the God
Particle" was solidified upon its discovery, namely as a result of the
popular media. The origin of this is often connected to Nobel Prize-winning
physicist Leon Lederman referring to the Higgs boson as the "Goddamn
Particle" in frustration with regards to how difficult it was to detect.
Business Insider(opens in new tab) says that when
Lederman authored a book on the Higgs boson in the 1990s the title was to be
"The Goddamn Particle" but the publishers changed this to "The
God Particle" and a troublesome connection with religion was drawn, one
which bothers physicists to this day.
Still, it's hard to overestimate the importance of the
Higgs boson and the Higgs field in general, as without this aspect of nature no
particles would have mass. That means no stars, no planets, and no us —
something which may help warrant its hyperbolic nickname.
WHY IS THE HIGGS BOSON IMPORTANT?
In 1964, researchers had begun to use quantum field
theory to study the weak nuclear force(opens in new tab) — which determines
the atomic decay of elements by transforming protons to neutrons — and its
force carriers the W and Z bosons.
The weak force carriers should be massless, and if
they weren't this risked breaking a principle of nature called symmetry which
— just like the symmetry of a shape ensures it looks the same if it is turned
or flipped — ensures the laws of nature are the same however they are viewed.
Putting mass arbitrarily onto particles also caused certain predictions to
trend towards infinity.
Yet, researchers knew that because the weak force is
so strong over short distance interactions — much more powerful than gravity
— but very weak over longer interactions, its bosons must have mass.
The solution proposed by Peter Higgs François Englert,
and Robert Brout, in 1964 was a new field and a way to "trick" nature
into breaking symmetry spontaneously.
An article from CERN(opens in new tab) compares this
to a pencil standing on its tip — a symmetrical system — suddenly tipping
to point in a preferred direction destroying its symmetry. Higgs and his fellow
physicist proposed that when the universe was born it was filled with the Higgs
field in a symmetrical, but unstable state — like the precariously balanced
pencil.
The field quickly, in just fractions of a second,
finds a stable configuration, but this in the process breaks its symmetry. This
gives rise to the Brout-Englert-Higgs mechanism which grants mass to the W and
Z bosons.
What was later discovered about the Higgs field was
that it would not only give mass to the W and Z bosons but that it would grant
mass to many other fundamental particles. Without the Higgs field and the
Brout-Englert-Higgs mechanism, all fundamental particles would race around the
universe at the speed of light. This theory doesn't just explain why particles
have mass but also, why they have different masses.
Particles that interact — or "couple" — with
the Higgs field more strongly are granted greater masses. Even the Higgs boson
itself gets its mass from its own interaction with the Higgs field. This has
been confirmed by watching how Higgs boson particles decay.
One particle not granted mass by the Higgs field is
the basic particle of light — the photon. This is because spontaneous
symmetry breaking doesn't happen for photons as it does for its fellow
force-carrying particles the W and Z bosons.
This mass-granting phenomenon also only applies to
fundamental particles like electrons and quarks. Particles like protons —
made up of quarks — get most of their mass from the binding energy that holds
their constituents together.
While all this conforms well to theory, the next step
was to discover evidence of the Higgs field by detecting its force-carrying
particle. Doing this would be no simple task, in fact, it would require the
largest experiment and most sophisticated machine in human history.
In this way, the search for the Higgs boson itself has
pushed both particle accelerator and detector technology to its limits — with
the ultimate expression of this being the Large Hadron Collider (LHC).
Refereence: US Department of Energy
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