Higgs Boson

Scientists at the CERN research centre near Geneva, Switzerland,  unveiled their latest findings in their search for the Higgs boson, a subatomic particle key to the formation of stars, planets and eventually life after the Big Bang 13.7 billion years ago.

What is the Higgs boson?

The Higgs is the last missing piece of the Standard Model, the theory that describes the basic building blocks of the universe. The other 11 particles predicted by the model have been found and finding the Higgs would validate the model. Ruling it out or finding something more exotic would force a rethink on how the universe is put together.

The Standard Model and the Higgs boson

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Scientists believe that in the first billionth of a second after the Big Bang, the universe was a gigantic soup of particles racing around at the speed of light without any mass to speak of. It was through their interaction with the Higgs field that they gained mass and eventually formed the universe.

The Higgs field is a theoretical and invisible energy field that pervades the whole cosmos. Some particles, like the photons that make up light, are not affected by it and therefore have no mass. Others find it drags on them as porridge drags on a spoon.

The particle is theoretical, first posited in 1964 by six physicists, including Briton Peter Higgs.

The search for it only began in earnest in the 1980s, first in Fermilab’s now mothballed Tevatron particle collider near Chicago and later in a similar machine at CERN, but most intensively since 2010 with the start-up of the European centre’s Large Hadron Collider.

What is the standard model?

The Standard Model is to physics what the theory of evolution is to biology. It is the best explanation physicists have of how the building blocks of the universe are put together. It describes 12 fundamental particles, governed by four basic forces.

But the universe is a big place and the Standard Model only explains a small part of it. Scientists have spotted a gap between what we can see and what must be out there. That gap must be filled by something we don’t fully understand, which they have dubbed ‘dark matter’. Galaxies are also hurtling away from each other faster than the forces we know about suggest they should. This gap is filled by ‘dark energy’. This poorly understood pair are believed to make up a whopping 96 percent of the mass and energy of the cosmos.

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Confirming the Standard Model, or perhaps modifying it, would be a step towards the holy grail of physics – a ‘theory of everything’ that encompasses dark matter, dark energy and the force of gravity, which the Standard Model also does not explain. It could also shed light on even more esoteric ideas, such as the possibility of parallel universes.

CERN spokesman James Gillies has said that just as Albert Einstein’s theories enveloped and built on the work of Isaac Newton, the work being done by the thousands of physicists at CERN has the potential to do the same to Einstein’s work.

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A proton-proton collision event in the CMS experiment producing two high-energy photons (red towers). This is what we would expect to see from the decay of a Higgs boson but it is also consistent with background Standard Model physics processes.

What is the large hadron collider?

The Large Hadron Collider is the world’s biggest and most powerful particle accelerator, a 27-km (17-mile) looped pipe that sits in a tunnel 100 metres underground on the Swiss/French border. It cost 3 billion euros to build.

Two beams of protons are fired in opposite directions around it before smashing into each other to create many millions of particle collisions every second in a recreation of the conditions a fraction of a second after the Big Bang, when the Higgs field is believed to have ‘switched on’.

The vast amount of data produced is examined by banks of computers. Of all the trillions of collisions, very few are just right for revealing the Higgs particle. That makes the hunt for the Higgs slow, and progress incremental.

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What is the threshold for proof?

To claim a discovery, scientists have set themselves a target for certainty that they call “5 sigma”. This means that there is a probability of less than one in a million that their conclusions from the data harvested from the particle accelerator are the result of a statistical fluke.

The two teams hunting for the Higgs at CERN, called Atlas and CMS, now have twice the amount of data that allowed them to claim ‘tantalising glimpses’ of the Higgs at the end of last year and this could push their results beyond that threshold.

what’s so important about finding the Higgs boson?

In particle physics, there is a theory called the “Standard Model” that endeavors to explain all electromagnetic and nuclear reactions between particles. The “Standard Model”, derived in the 1970′s, explains that the universe is completely comprised of matter (fermions) and force (bosons). The brilliance of the “Standard Model” is that it has been able to successfully explain nearly all experimental physics.

Particle physics is the study of the individual elements that comprise our universe. As most know, atoms are composed of smaller components; neutrons, electrons and protons. When electrons jump between atoms, new substances are formed, but the nucleus of an atom generally remains unchanged unless it undergoes a nuclear reaction. The  neutron/proton nucleus is also known as a hadron, which is made up of quarks. Quarks come paired in six different varieties; up and down, charm and strange, top and bottom. Quarks can also be classified as first, second, or third generation.

According to the “Standard Model,” all matter consists of two different types of particles, quarks and leptons (i.e. electrons and neutrinos), held together by bosons. Bosons describe the force between particles.

There are three elementary bosons called gauge bosons; the photon (electromagnetic force), the W and Z boson (the weak force) and the gluons (the strong force). Then there are two additional suspected, yet unobserved, bosons, the Graviton and the Higgs.

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The Higgs boson was originally suggested in the 1960′s by British physicist Peter Higgs. Higgs postulated that a particle gains mass by passing through the Higgs field, a combination of an electromagnetic field and a solid. Before the Higgs portion of the “Standard Model,” it was assumed that W and Z bosons interacted with other elementary particles, however, the mass of those bosons was always so large that it unbalanced and broke the “Standard Model”.

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The LHC image from CERN

Thus, it was postulated that there had to be at least one other particle added to the mass equation, the Higgs boson. Ever since the search as been on to find the elusive Higgs, leading to the construction of the LHC.

The LHC is the world’s largest particle accelerator. Built by the European Organization for Nuclear Research (CERN), and situated along the border between France and Switzerland. LHC’s sole purpose is to be a platform in which to test particle physics theories. It is run by engineers and scientists from hundreds of universities and laboratories from over a hundred different countries.

One of the main objectives of the LHC, since its conception, is to find the Higgs boson. So how might the Higgs boson have been found? The Higgs boson is known to be unstable, decaying into certain particles based on its expected weight. The scientists designed their particle collision experiments in a way that will emit particles of a particular mass. If the particles within an expected range are more numerous then the collision alone can explain, then the rest of the observed particles are proof of the Higgs boson.

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Higgs Boson Basics

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