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New Theories About the Forces and Particles that Determine the Destiny of the Universe
:: 22 July, 2008
The world’s biggest scientific experiment, designed to re-create in miniature the conditions of the early universe shortly after the Big Bang 14bn years ago, is scheduled to start in late August.
Cern, the European particle physics centre outside Geneva, will send the first beam of hydrogen nuclei (protons) around the 27km circular tunnel of its new atom smasher, the $8bn (€5bn, £4bn) Large Hadron Collider (LHC), at almost the speed of light.
Lyn Evans, project leader, told the EuroScience Open Forum in Barcelona that the LHC’s first collisions would follow seven or eight weeks later, in early autumn, when Cern races two beams round the tunnel in opposite directions and smashes them together.
Physicists expect these super-energetic collisions between protons – and later between far heavier lead nuclei – to produce a cornucopia of subatomic particles never before seen on Earth. The results will lead to new theories about the forces and particles that determine the destiny of the universe.
Mr Evans and other Cern scientists were giving an update on the LHC, a global facility that has been built over the past 14 years with substantial involvement by the US, Russia and Asian countries as well as Cern’s core European membership.
Before the LHC can start, 50,000 tonnes of equipment have to be cooled to just 1.8ºKelvin above absolute zero with superfluid liquid helium – by far the largest cryogenic project in history. Five of the machine’s eight segments are already at that temperature and the remaining three are almost there, Mr Evans said.
Fabiola Gianotti, a senior Cern scientist, told the meeting that “new physics” – manifestations of particles and forces never observed before – might show up almost as soon as the LHC starts, though researchers would probably need at least six months of observations at the experiment’s four giant particle detectors before they could confidently go public with their discoveries.
The likely discovery of the Higgs particle, which is posited to give matter its mass, has received most attention. But according to Ms Gianotti, the experiment’s first significant scientific achievement will probably be to prove or disprove “supersymmetry” – the theory that every subatomic particle has a far heavier partner or “superparticle”.
About Supersymmetry
In particle physics, supersymmetry (often abbreviated SUSY) is a symmetry that relates elementary particles of one spin to another particle that differs by half a unit of spin and are known as superpartners. In other words, in a supersymmetric theory, for every type of boson there exists a corresponding type of fermion, and vice-versa.
As of 2008 there is no direct evidence that supersymmetry is a symmetry of nature. Since superpartners of the particles of the Standard Model have not been observed, supersymmetry, if it exists, must be a broken symmetry allowing the 'sparticles' to be heavy.
If supersymmetry exists close to the TeV energy scale, it allows the solution of two major puzzles in particle physics. One is the hierarchy problem - on theoretical grounds there are huge expected corrections to the particles' masses, which without fine-tuning will make them much larger than they are in nature. Another problem is the unification of the weak interactions, the strong interactions and electromagnetism. Another advantage of supersymmetry is that supersymmetric quantum field theory can sometimes be solved. Supersymmetry is also a feature of most versions of string theory, though it can exist in nature even if string theory is wrong.
One reason that physicists explored supersymmetry is because it offers an extension to the more familiar symmetries of quantum field theory. These symmetries are grouped into the Poincaré group and internal symmetries and the Coleman-Mandula theorem showed that under certain assumptions, the symmetries of the S-matrix must be a direct product of the Poincaré group with a compact internal symmetry group or if there is no mass gap, the conformal group with a compact internal symmetry group. In 1975, the Haag-Lopuszanski-Sohnius theorem showed that considering symmetry generators which satisfy anticommutation relations allows for such nontrivial extensions of space-time symmetry. This extension to the Coleman-Mandula theorem prompted some physicists to study this wider class of theories.
Tags: Little Big Bang to redefine physics , Big Bang , beam of hydrogen nuclei (protons) , Large Hadron Collider (LHC) , supersymmetry ,
