Hoke Ahmed - The Large Hadron Collider

DESY, Notkestr. 85, 22607 Hamburg, Germany

Thomas Schrner-Sadenius

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The LHCor the option of a hadron collider in the tunnel of the Large Electron-Positron Collider (LEP) at CERNwas reportedly first mentioned [].

By 1977, electron-positron colliders were well established, but hadron accelerators had so far exclusively been working in fixed-target modeexcept for the Intersecting Storage Rings (ISR) at CERN, which, since 1971, were colliding protons with beam energies of up to 31.4 GeV (see Sect. ).

Lepton colliders had already provided interesting results, like the co-discovery (together with a fixed-target hadron machine) of the and thus of charm in 1974. However, the wish of particle physicists to go to ever higher centre-of-mass energies posed a severe problem to lepton colliders: The energy loss due to synchrotron radiation increases with the fourth power of a particles energy. The fact that the energy loss per turn also scales with the inverse of the bending radius favours large acceleratorslike LEP. Since there are, naturally, restrictions to the possible size of accelerators, also the achievable energy is limited for circular lepton colliders. However, the energy loss also goes with the inverse of the particle mass to the fourth power. So one way to realise collisions at higher energies is to choose protons as beam particles. Hadron collidersso it seemedare the only way towards the discovery of new physics phenomena at highest energies. And ideas for such new phenomena abounded already in the late 1970s!

By 1977, a large fraction of what came to be known as the Standard Model (SM) of particle physics was well established. At the same time, numerous questions remained unanswered, which were at the top of the research agenda of high energy physics.