There is no doubt that particle physics has become big business. The latest and greatest in a long line of increasingly expensive particle accelerators is the Large Hadron Collider (LHC), which is due to switch on at CERN near Geneva next year. This multibillion euro accelerator with a circumference of 26 km will smash protons into one another with unprecedented energies – up to 14 TeV (14 × 1012 electron-volts) – producing enormous amounts of particle debris that thousands of scientists from across the globe will then analyse using vast detectors.
Physicists believe that achieving such energies will go a long way to help answer fundamental questions such as how particles acquire mass and how the four forces of nature can be unified. Indeed, most proposals to generalize the current theoretical framework describing the known elementary particles and their interactions – the so-called Standard Model – predict new heavy particles with masses of the order of 1 TeV (which is some 1000 times heavier than a proton). And one such proposal – known as supersymmetry – predicts a family of “weakly interacting massive particles” (WIMPs). The lightest WIMP could account for at least part of the mysterious dark matter believed to make up the vast majority of mass in the universe.
However, reaching higher and higher energies is not the only way of advancing our understanding of fundamental physics. New physics may also exist at energies below 1 eV. One example of such new “sub-eV” physics was revealed in 1998 – the observation that neutrinos oscillate between their three possible “flavours” and therefore have mass. Although we do not yet know the absolute mass of neutrinos, indirect measurements suggest that the masses are below a few tenths of an electron-volt.
In the August issue of Physics World, Axel Lindner and Andreas Ringwald describe how very weakly interacting sub-eV particles, or “WISPs”, can be sought in small, high-precision experiments the PVLAS experiment in Italy.
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