The Hunt for the Higgs Boson
Table of Contents
The Standard Model of Elementary Particles 3
The Higgs Theory (Boson, Mechanism and Field) 3/4
Discovery of the Higgs 4
Possibilities of Decay 5
Large Hadron Collider 5
The ATLAS detector 6
The G.R.I.D 7
The Aim and Benefits of the LHC 7
The Standard Model of Elementary Particles
The ‘Standard Model of Particle Physics’ describes the interactions between particles, where the fundamental force carriers are treated as mass-less particles. It is the theoretical framework that is used to explain the relations between complex particles and forces. The theory was first introduced by Sheldon Glashow through the electromagnetic and weak interactions, but was then developed on Steven Weinberg and Abdus Salam. Although the Standard Model is able to explain the interactions between quarks, leptons and bosons, it does not include an integral property of particles, mass.
In 1964, Peter Higgs showed how to give mass to fundamental particles through the Higgs mechanism. The Higgs mechanism is where the symmetry of mass-less particles is broken and non-zero masses become possible.
This is just a hypothetical theory but if true, an extra particle called the Higgs boson should exist. A disturbance in the Higgs field is in actual fact a Higgs boson. When particles interact with the Higgs field they cause a clustering effect and thus, gain mass. The more massive the particle the more it’ll interact with the Higgs field and according to the Higgs mechanism, the more mass it will acquire. Many experiments around the world have illustrated Higgs’ ideas but the presence of one mysterious particle has been predicted. Although years of work have established ‘The Standard Model’, they have also predicted the existence of an unknown particle, named today as the Higgs particle.
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What is the Higgs Boson?
The Higgs boson, also known as ‘The God Particle’, can be defined as:
A hypothetical, electrically neutral, massive and scalar elementary particle.
It was first proposed by the English theoretical physicist Peter Higgs, at his time at the University of Edinburgh, when Higgs came up with the theory of the Higgs field.
What is the Higgs Field?
The Higgs Field is defined as:
A field hypothesized to account for spontaneous symmetry breaking in the standard model.
Particles in the standard model acquire mass from interactions with the Higgs field. Massive particles (‘massive’ meaning a particle with mass) interact with the Higgs field and it is that interaction that gives them their mass. Particles such as photons don’t interact with the Higgs field and thus have no mass. The Higgs field is included in the Higgs Mechanism.
What is the Higgs Mechanism?
The Higgs mechanism can be defined as:
A theoretical framework which explains how the masses of the W and Z bosons of the standard model, arise through spontaneous electroweak symmetry breaking (the Higgs field).
The Higgs mechanism then explains how massive, sub-atomic particles obtain mass. Different particles interact with the Higgs field differently with different strengths; hence some particles are heavier than others.
The whole Higgs ‘theory’ supposedly sums up the mystery of mass but it has not been discovered yet. Physicists and engineers at the Large Hadron Collider and Fermilab Tevatron have been working on the discovery of the Higgs boson. There are speculations that the Higgs boson can be discovered in more ways than one. There are ways such as detecting the boson through super symmetry and the unlikely case of a visible Higgs boson to be detected but most believe the most reliable way will be through the decay of other subatomic particles.
How to discover the Higgs Boson
As the Higgs ‘theory’ is centrally related to mass, physicists such as Din Lincoln claim that the Higgs boson is most likely to decay into one of the three top heaviest subatomic particles; the bottom quarks, W and Z bosons, and top quarks. Other physicists agree that the boson will decay into the top quark and some agree that it will decay into the W and Z boson so there is quite a lot of speculation and uncertainty as to what the Higgs boson will definitely decay into. The reason being that there are so many pairs of particles that the Higgs boson can decay, that it is quite impossible at this moment in time to definitively decide on an absolute correct decay. This solely depends on the actual mass of a Higgs boson, predicted at 114 – 115 GeV. And even that’s uncertain.
Possibilities of Higgs Decay
The Hunt for the Discovery of the Higgs
As the Higgs boson has so many daughter particles that decay themselves, every scientist has to take this into account when attempting to trace the boson. Physicists at the Tevatron in American and the LHC in Geneva look at all these possible decays of the Higgs boson and also its daughter particle’s decays. This means that it will take quite some time until any real developments are made on the Higgs boson as there is no direct evidence supporting the Higgs boson.
Physicists at Fermilab in America have helped in the discovery of the Higgs as they have narrowed the range of mass that the Higgs boson hypothetically can be found at. They have narrowed the range down to 160-170 GeV as it was detected by their CDF detector. This then allows physicists to test for the Higgs boson in a much more precise way, allowing a possible discovery of the Higgs boson. The Tevatron in America has also contributed in the theoretical ‘Standard Model’ as it has proved the existence of particles such as the bottom quark and the top quark.
At the moment, the LHC seems to be the collider with enough power to reach the range of mass discovered by the Tevatron and so researchers will be looking for the hypothesized daughter decay particles to be able to identify a Higgs Boson.
Large Hadron Collider
The large hadron collider is located near Geneva, 100 metres beneath the Swiss/French border, weighting at 38000 tonnes and running for 27km in a circle. It is the largest collider built to date and it can collide protons at energy levels of 7 TeV. The LHC accelerates two beams of particles in opposite directions around the 27km collider. At 4 points when the beams have reached their maximum speeds, they are collided and produce thousand of new particles. Detectors placed at these points allow researchers to follow and identify the particles that are of distinctive behaviour and interest.
The ATLAS Detector
The specific detectors that are used have to be built around the collision points and are very large, taking the ATLAS for example which is the size of a 5 storey building. Their large size is in hope to trap high energy particles and to allow the tracks of charged particles to be curved by the magnets within the detector. Detectors include a powerful magnet that affects the motion of charged particles. From the effects it has, researchers can measure the charge and the momentum of the affected particles.
Detectors are made up of layers, each layer detecting different properties of particles. The layers nearest to the collision are designed to track the motion and detect the energy of short-lived particles that are of most interest. Subsequent layers track the movement of more common, long-lived particles with more energy. Components such as calorimeters measure and detect energy released by particles in the collision.
An example of a major detector is the ATLAS detector at CERN, used with the LHC for the experiments of the Higgs boson. The ATLAS detector is ‘A Toroidal LHC ApparatuS’ where it searches for traces of daughter particles of the Higgs boson. The ATLAS is specifically designed for tremendous high energy collisions of protons.
The G.R.I.D is a way of bringing supercomputing power to desktops. By linking desktop computers in a global network, the G.R.I.D provides enough computing power to process data from major detectors at CERN. This process would normally take days to complete whereas with the computing power of the G.R.I.D, this will only take a matter of hours providing the results from experiments.
Aim and Benefits
With the LHC, researchers aim to be able to produce conditions suitable enough for the production of a Higgs boson. As explained before, the only way of tracing a Higgs boson is through its decay daughter particles. This means that there are many, many options and outcomes the Higgs can take but hopefully, the LHC will detect most, if not, all of these. This then means that the LHC is our best chance at discovering the Higgs boson or tracking its presence.
Although the LHC cost £3.4billion, it allows testing of theories and ideas such as the Higgs theory. The social impact of this is that the questions asked and also the answers found as a result, can be so fundamental that they can only be applied in the future, if at all. Yet there is a possibility of a discovery that can be applied almost immediately such as medical, consumer and industrial technologies.
The discovery of the Higgs boson would shine light on the origin of mass and would widen our knowledge. It would prove key theories in particle physics and quantum dynamics. It is the last remaining particle of the ‘Standard Model’ that has not been detected; all other particles have been proven to exist through experiments. If the LHC was to develop enough energy for an observable Higgs boson then we would understand why matter has mass. From that point then we can move onto proving other theories and ideas using the principle of the Higgs Boson.