Fixed-target experiment

A fixed-target experiment in particle physics is an experiment in which a beam of accelerated particles is collided with a stationary target. The moving beam (also known as a projectiles) consists of charged particles such as electrons or protons and is accelerated to relativistic speed. The fixed target can be a solid block or a liquid or a gaseous medium. These experiments are distinct from the collider-type experiments in which two moving particle beams are accelerated and collided. The famous Rutherford gold foil experiment was one of the first fixed-target experiments, in which the alpha particles were targeted at a thin gold foil.

The energy involved in a fixed target experiment is 4 times smaller compared to that in collider with the dual beams of same energy. More over in collider experiments energy of two beams is available to produce new particles, while in fixed target case a lot of energy is just expended in giving velocities to the new particles. This clearly implies that fixed target experiments are not quite helpful when it comes to increasing the energy scales of experiments.

However, the fixed target experiments have a significant advantage for experiments that require higher luminosity (rate of interaction). The High Luminosity LHC which is an upcoming, upgraded collider of the Large Hadron Collider at CERN will attain total integrated luminosity of around $\mathrm {5\times 10^{35}cm^{-2}s^{-1}}$ in its run. While luminosity scale of about $\mathrm {5\times 10^{34}cm^{-2}s^{-1}}$ have already been approached by much older fixed target experiments such at the E288 lead by Leon Lederman at Fermilab.

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