The Star Garden
12th June 2011 2 Comments
A lead-lead collision in the Large Hadron Collider Image credit: ALICE/CERN
Earlier this year, Rolf-Dieter Heuer, director general of the European Organisation for Nuclear Research (CERN) announced that if they have not discovered the Higgs boson by the end of next year, then physicists should give up on finding it and reconsider the Standard Model of particle physics.
The Standard Model was developed in the early 1970s in order to explain how all known particles interact. It divides particles into fermions, which can combine to form atoms, and bosons which carry forces. Fermions are further divided into quarks, which can form protons and neutrons, and leptons which include electrons and neutrinos. Components of the Standard Model were theorised using quantum theories of fields, this concept, which combines quantum mechanics and special relativity, was first developed by English physicist Paul Dirac in 1927.
world to look for evidence of it. These are the Tevatron particle accelerator in Illinois and the Large Hadron Collider (LHC), which is run by CERN and situated beneath the Franco-Swiss border. The LHC produces the most energy and the Tevatron is due to shut down in September as it has been made obsolete.
The Standard Model predicts that collisions in the LHC should produce a Higgs boson every few hours. At this rate, it should take two to three years to collect enough data to guarantee that one is detected and another year to analyse the results. The LHC has been running successfully since late 2009 and this means that if the Higgs boson exists, then it should be discovered by the end of 2012. After this, the LHC is to be shut down in order to produce collisions that are twice as energetic in 2014.
The Higgs boson is often called 'the God particle' after Nobel prize winning physicist Leon Lederman's book 'The God Particle: If the Universe is the Answer, What Is the Question?'. This name is not popular among physicists however, because it overstates the importance of the discovery.
If the Higgs Boson is not found in the next year and a half then physicists will be faced with the problem of explaining how particles acquire mass, given that the rest of the Standard Model has been proven correct. However this is not the only fundamental question which remains unanswered, the discovery of the Higgs boson would not explain why the Standard Model predicts exactly twelve fermions, nor would it show whether they are truly fundamental or if they can be further divided into smaller objects. It would not provide a quantum field theory of gravitation and, perhaps most importantly, it would not explain the origin of dark matter or dark energy, leaving 95% of the universe unaccounted for.
It will be many years before we discover a 'theory of everything' if this is even possible, the discovery of the Higgs boson would prove that we are on the right path but the failure to find it may be even more exciting as this could lead to the development of completely new laws of physics.
Related articles; Einstein's theory of Special Relativity (1905), The Big Bang (1900s), Quantum Mechanics (1900-1927) and Quantum Gravity (1900s).
Quarks
There are six types, or flavours, of quarks known as; up, down, charm, strange, top and bottom, and every quark has an antimatter partner with an opposite charge. The up and down quarks are the lightest and this means they are the most stable. The top and bottom quarks are the most massive, they can only be created in high energy collisions like those produced by particle accelerators and soon decay into up and down quarks.
Quarks are never found in isolation but combine to form particles called hadrons which are held together by the strong force. Hadrons are split into two groups, baryons which are made of three quarks and mesons which are composed of one quark and one antiquark. All hadrons are unstable except for protons and neutrons when they are inside atomic nuclei. A proton is composed of two up quarks and one down quark, which add up to have a charge of one, and a neutron is made of one up and two down quarks which have no overall charge.
The quantum field theory of electromagnetism, known as quantum electrodynamics, was developed in the 1940s and 1950s. It explains how the electromagnetic force holds leptons, like electrons, to the nuclei of atoms. Electroweak theory is a quantum field theory of the weak force, the force carried by W and Z bosons. It was developed in the 1960s and explains radioactive decay. The Standard Model was completed in 1973 with the development of quantum chromodynamics. This is a quantum field theory of the strong force, the force carried by gluons, and explains how quarks stick together in order to form hadrons like protons and neutrons.
The Standard Model Image credit: Wiki Commons
By the time the Standard Model was formed, the up, down and strange quarks had already been experimentally verified using particle accelerators and all but two of the leptons had been discovered. Since then, every elementary particle predicted by the Standard Model has been verified except for the infamous Higgs boson, which is thought to carry mass in the same way that other bosons carry forces.
The Higgs boson is only produced in high energy collisions and physicists are currently using the two highest energy particle accelerators in the
Leptons
There are six flavours of leptons known as; electrons, electron neutrinos, muons, muon neutrinos, taus and tau neutrinos. The electron, muon and tau leptons are negatively charged and have positively charge antimatter partners. The neutral leptons are known as neutrinos. Whilst the charged leptons can interact with hadrons via the electromagnetic force, neutrinos rarely interact with anything. As with quarks, the heavier muon and tau leptons can only be created in high energy collisions and soon decay. Electrons are the most stable leptons and attach to atomic nuclei, neutralising atoms.
Bosons
At least six bosons are needed in order to explain how fermions can interact. Bosons are particles which carry forces, the photon carries the electromagnetic force, the gluon carries the strong force and the W and Z bosons carry the weak force. The two remaining bosons have both yet to be observed, these are the Higgs boson which allows objects to have mass and the graviton which is thought to carry the force of gravitation. The graviton is not part of the Standard Model but is predicted by theories of quantum gravity which are needed to explain how quantum mechanics can be reconciled with general relativity.
HTML Comment Box is loading comments...
