Why build the Large Hadron Collider? - page 8
Keywords: Physics Report Large Hadron Collider Basic Introduction Grand Unified Theory Cosmic Rays Anti Matter Extra Dimensions String Theory Dark Matter Higgs Boson
By Jenny on 02/07/2009
Level: A Level (Year 13)
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matter’. The other 96% of the Universe seems to be made up of both dark matter and ‘dark energy’; dark matter accounts for about 26% and dark energy about 70%. [1][7]
We only know about the existence of dark matter because the effect of its gravity makes galaxies spin faster than expected. In computer models of stars moving in spiral galaxies, without a massive ‘halo’ of dark matter around the galaxies they are unstable, with the dark matter the spiral form persists. [4]
Dark matter is unlikely to be ordinary matter such as stellar remnants as due to effects in the Big Bang the observed ratio of hydrogen to helium in the universe is proportional to a certain amount of protons and neutrons. The known proportion of hydrogen to helium is compatible with the amount of observed visible matter in the Universe and more than ten times this amount existing is ruled out. Therefore most of the dark matter must be in some starnfe new form. [4]
According to the best theories dark matter is made up of particles called ‘WIMPs’ (weakly interacting massive particles) and both the ATLAS and CMS detectors are hoping to find some. If we can find out what exactly dark matter is made of then it will help us understand how it works, and allow its behaviour to be simulated which would help clear up a number of problems associated with it in astronomy.
The theory suggests that WIMPs are at least 100 times more massive than a proton, which would be why no other accelerators have produced them yet. [7]
The theory of ‘supersymmetry’ says that for every particle that we know of in the Standard Model there is another heavier counterpart (known as a ‘sparticle’) in order that the equations of quantum mechanical theory stay the same when fermions are replaced by bosons or the other way around.[3][7]
All of these supersymmetric particles are massive and don’t react very much with matter but the lightest one (the "neutralino") is considered to be the most likely to be the dark matter WIMP particle, because it is stable.[7]
If it exists then the LHC will have enough energy to detect this particle. If it is found and is proved to be the cause of dark energy then 22% of the Universe will have turned up; while if no WIMPs at all are found by the LHC then the Big Bang couldn’t
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