# Why are there fixed target experiments?

Collider experiments put all their energy into $$\sqrt{s} = 2E$$ while target experiments only provide $$\sqrt{s} = \sqrt{2Em+m^²}$$.

Yet, there are fixed target experiments. Why?

• Well, they are a lot easier to arrange for random mixes of incident particle and target. Not quite sure how Geiger and Marsden would have arranged a collider experiment. – Jon Custer Aug 19 '19 at 21:28
• :D I doubt that the Rutherford experiment (didn't hear it as Geiger and Marsden before) is a "particle accelerator", seen in a current technical manner ;) But yet, it is true – Ben Aug 19 '19 at 21:35
• Luminosity, cost, the option of continuous operation (no fill-n-spill), ... If your exposure to particle physics had been mostly through the popular press then you probably have a very warped impression of what particle physics consists of. – dmckee --- ex-moderator kitten Aug 19 '19 at 21:35
• The experimental paper was authored by Geiger and Marsden, who worked in Rutherford's lab. en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment – Jon Custer Aug 19 '19 at 21:38
• As an aside, the limitations of using natural alpha sources were the motivation for Cockroft and Walton, as well as Van de Graaff, to develop high voltage electrostatic accelerators. Ditto for Wideroe (linac) and Lawrence (cyclotron). Note that none of those were originally colliders yet lots of useful nuclear and particle physics were done with them. – Jon Custer Aug 19 '19 at 21:56