# How can a meson beam be created?

I was reading this thread where the answer states that to use deep inelastic scattering on mesons, we have to

"generate a meson beam (which is a bit of a trick in and of itself) and direct it into either a fixed baryon target or another beam (electrons, say) in collider mode"

But how can a meson beam even be created? I tried to search for an answer but it's pretty difficult to find. Could someone explain? Thanks.

• I believe Don Lincoln describes it in one of his videos on the Dune experiment. Such a beam is used to create neutrinos. Feb 25 at 6:51

It is an engineering problem. A brief description is here.

In this experiment, a beam of ∼ 100 GeV proton from the Super Proton Synchrotron (SPS) are used to produce pions off a conventional solid target, which later are collected and focused by magnetic horn and quadrupole magnets before being transported to a storage ring. This storage ring is optimized for utilizing a 3.8 GeV/c muon momentum with 15% momentum acceptance.

It goes into details of how the pion beam is produced.

• Not very many engineers know how to do this. It's a real, concrete physics problem for experimental physicists. Feb 25 at 18:40
• Is it done so fast the pions don't decay? Feb 26 at 2:43
• @Sʨɠɠan Yes. It is part of the calculations Feb 26 at 3:30

I didn't find a video by Don Lincoln, but here is one by Kristy Duffy, who is also from FermiLab. How do particle accelerators make neutrinos?

The process starts with Hydrogen. Atoms are ionized so they can be manipulated by electromagnetic fields. The electrons are stripped off, leaving a beam of protons.

The proton beam is smashed into a target, producing a spray of particles like pions and kaons. These are gathered into a horn which focuses the positively charged particles and defocuses the negative ones. Or vice versa, depending on the experiment.

This answers your question, but at Fermilab the purpose is to create a neutrino beam (or anti-neutrino beam, if negatively charged particles were kept.) To do this, they simply wait until the particles decay. Then the beam hits a concrete or steel target. This stops all the particles except the neutrinos.

The neutrinos are on their own at this point. They are neutral so they can't be steered. They don't interact with matter, so they exit the accelerator and fly through whatever is in their way to the detector. For Dune, this is through the earth to a detector a mile underground several states away.