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Hunting for a Very Important Subatomic Component of Matter as the "God Particle"

By any stretch of imagination the Large Hadron Collider, which is nearing completion deep underground close to Geneva, is the mother of all machines.

Built at a cost of about four billion euros, it's expected to become operational later this year when researchers from over three dozen countries can finally begin conducting what are already being billed as some of the greatest experiments ever in the history of particle physics. One of them is the hunt for a very important subatomic component of matter which has remained so elusive till now that scientists refer to it fancifully as the "god particle" - otherwise known as the Higgs boson.

The Collider's colossal 27-kilometre-long circular tunnel is designed to speed up protons to more than 99.99 per cent of the velocity of light and then smash them together head-on with a combined energy of around one trillion electron volts to find out what's inside them. It's the essence of experimental particle physics: smash stuff together and see what other stuff comes out. Back in 1964, Peter Higgs, a British physicist, had predicted it could be the particle named after him. If so, it would fill a gaping hole in the benchmark theory - the Standard Model - for understanding the universe and confirm some predictions while filling in "missing links".

For example, without the Higgs boson, the theory has not been able to explain how other elementary particles acquire properties such as mass. Or for that matter why there's so much "extra" mass in the universe in the form of unseen "dark matter" which, in fact, makes up 96 per cent of all matter anywhere but about which scientists are themselves totally in the dark.

Not only could the Collider provide answers to some of these ultimate questions about the cosmos but also throw new light on mini black holes, describe the extra dimensions predicted by theory and give clues about how the Big Bang which brought everything into existence happened.

Physics is on the brink of so many breakthroughs that some scientists believe it's on the verge of the biggest revolution since Einstein and Planck, possibly since Galileo and Newton. Others think the Collider is a genesis machine which may take them as close to the creation of the universe as is humanly possible and - who knows - even let them read the mind of God?

Note for Large Hadron Collider
The Large Hadron Collider (LHC) is a particle accelerator and hadron collider located at CERN, near Geneva, Switzerland (46°14′N, 6°03′E). It is currently in the final stages of construction, and commissioning, with some sections already being cooled down to its final operating temperature of ~4 K (−269 °C). The first beams are due for injection mid June 2008 with the first collisions planned to take place 2 months later. The LHC will become the world's largest and highest-energy particle accelerator. The LHC is being funded and built in collaboration with over two thousand physicists from thirty-four countries as well as hundreds of universities and laboratories. When activated, it is theorized that the collider will produce the elusive Higgs boson, the observation of which could confirm the predictions and 'missing links' in the Standard Model of physics and could explain how other elementary particles acquire properties such as mass. The verification of the existence of the Higgs boson would be a significant step in the search for a Grand Unified Theory, which seeks to unify all of the four fundamental forces: electromagnetism, the strong nuclear force, the weak nuclear force and gravitation. The Higgs boson may also help to explain why gravitation is so weak compared to the other three forces. In addition to the Higgs boson, other theorized novel particles that might be produced, and for which searches are planned, include strangelets, micro black holes, magnetic monopoles and supersymmetric particles.

The collider is contained in a circular tunnel with a circumference of 27 kilometres (17 mi) at a depth ranging from 50 to 175 metres underground. The tunnel, constructed between 1983 and 1988, was formerly used to house the LEP, an electron-positron collider.

The 3.8 metre diameter, concrete-lined tunnel crosses the border between Switzerland and France at four points, although the majority of its length is inside France. The collider itself is located underground, with many surface buildings holding ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants.

The collider tunnel contains two pipes enclosed within superconducting magnets cooled by liquid helium, each pipe containing a proton beam. The two beams travel in opposite directions around the ring. Additional magnets are used to direct the beams to four intersection points where interactions between them will take place. In total, over 1600 superconducting magnets are installed, with most weighing over 27 tonnes.

The LHC physics program is mainly based on proton-proton collisions. However, shorter running periods, typically one month per year, with heavy-ion collisions are included in the programme. While lighter ions are considered as well, the baseline scheme deals with lead (Pb) ions. This will allow an advancement in the experimental programme currently in progress at the Relativistic Heavy Ion Collider (RHIC).

The construction of LHC was originally approved in 1995 with a budget of 2.6 billion Swiss francs, with another 210 million francs (140 M€) towards the cost of the experiments. However, cost over-runs, estimated in a major review in 2001 at around 480 million francs (300 M€) in the accelerator, and 50 million francs (30 M€) for the experiments, along with a reduction in CERN's budget pushed the completion date out from 2005 to April 2007. 180 million francs (120 M€) of the cost increase has been the superconducting magnets. There were also engineering difficulties encountered while building the underground cavern for the Compact Muon Solenoid. The total cost of the project is anticipated to be between $5 and $10 billion.

Note for Standard Model
The Standard Model of particle physics is a theory that describes three of the four known fundamental interactions between the elementary particles that make up all matter. It unifies the electroweak theory and quantum chromodynamics into a structure denoted by the gauge groups SU(3)×SU(2)×U(1). It is a quantum field theory developed between 1970 and 1973 which is consistent with both quantum mechanics and special relativity. To date, almost all experimental tests of the three forces described by the Standard Model have agreed with its predictions. However, the Standard Model falls short of being a complete theory of fundamental interactions, primarily because of its lack of inclusion of gravity, the fourth known fundamental interaction, but also because of the eighteen numerical parameters (such as masses and coupling constants) that must be put "by hand" into the theory (rather than being derived from first principles).

In physics, the dynamics of both matter and energy in nature is presently best understood in terms of the kinematics and interactions of fundamental particles. To date, science has managed to reduce the laws which seem to govern the behavior and interaction of all types of matter and energy we are aware of, to a small core of fundamental laws and theories. A major goal of physics is to find the 'common ground' that would unite all of these into one integrated model of everything, in which all the other laws we know of would be special cases, and from which the behavior of all matter and energy can be derived (at least in principle). "Details can be worked out if the situation is simple enough for us to make an approximation, which is almost never, but often we can understand more or less what is happening." (Feynman's lectures on Physics, Vol 1. 2-7)

The standard model is a grouping of two major theories – quantum electroweak and quantum chromodynamics – which provides an internally consistent theory describing interactions between all experimentally observed particles. Technically, quantum field theory provides the mathematical framework for the standard model. The standard model describes each type of particle in terms of a mathematical field. For a technical description of the fields and their interactions, see standard model (mathematical formulation).

For ease of description, the standard model can be divided into three parts – covering particles of matter, force mediating particles, and the Higgs boson.

Note for Higgs boson
The Higgs boson is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. It is the only Standard Model particle not yet observed, but would help explain how otherwise massless elementary particles still manage to construct mass in matter. In particular, it would explain the difference between the massless photon and the relatively massive W and Z bosons. Elementary particle masses, and the differences between electromagnetism (caused by the photon) and the weak force (caused by the W and Z bosons), are critical to many aspects of the structure of microscopic (and hence macroscopic) matter; thus, if it exists, the Higgs boson has an enormous effect on the world around us.

As of 2008, no experiment has directly detected the existence of the Higgs boson, but this may change as the Large Hadron Collider (LHC) at CERN becomes operational. The Higgs mechanism, which gives mass to vector bosons, was theorized in 1964 by Peter Higgs, François Englert and Robert Brout, working from the ideas of Philip Anderson, and independently by G. S. Guralnik, C. R. Hagen, and T. W. B. Kibble. Higgs proposed that the existence of a massive scalar particle could be a test of the theory, a remark added to his Physical Review letter at the suggestion of the referee. Steven Weinberg and Abdus Salam were the first to apply the Higgs mechanism to the electroweak symmetry breaking. The electroweak theory predicts a neutral particle whose mass is not far from the W and Z bosons.

The particle called the Higgs boson is the quantum of one of the components of a Higgs field. In empty space, the Higgs field acquires a non-zero value (or non-zero vacuum expectation value), which permeates every place in the universe at all times. The existence of this non-zero vacuum expectation value plays a fundamental role: it gives mass to every elementary particle, including to the Higgs boson itself. In particular, the acquisition of a non-zero vacuum expectation value spontaneously breaks the electroweak gauge symmetry, a phenomenon known as the Higgs mechanism. This is the simplest mechanism capable of giving mass to the gauge bosons that is also compatible with gauge theories.

In the Standard Model, the Higgs field consists of two neutral and two charged component fields. Both of the charged components and one of the neutral fields are Goldstone bosons, which are massless and become, respectively, the longitudinal third-polarization components of the massive W+, W-, and Z bosons. The quantum of the remaining neutral component corresponds to the massive Higgs boson. Since the Higgs field is a scalar field, the Higgs boson has spin zero and has no intrinsic angular momentum. The Higgs boson is also its own antiparticle and is CP-even.

The Standard Model does not predict the value of the Higgs boson mass. If the mass of the Higgs boson is between 115 and 180 GeV, then the Standard Model can be valid at energy scales all the way up to the Planck scale (1016 TeV). Many theorists expect new physics beyond the Standard Model to emerge at the TeV-scale, based on unsatisfactory properties of the Standard Model. The highest possible mass scale allowed for the Higgs boson (or some other electroweak symmetry breaking mechanism) is around one TeV; beyond this point, the Standard Model becomes inconsistent without such a mechanism because unitarity is violated in certain scattering processes. Many models of Supersymmetry predict that the lightest Higgs boson (of several) will have a mass only slightly above the current experimental limits, at around 120 GeV or less.