# LHC particle combinations and colliding neutral particles

In high-energy particle accelerators, we have limited possibilities for what kinds of particles we can collide due to their charge, radiation properties etc. I understand that in LHC we collide high-mass particles such as protons or lead nuclei because they are electrically charged so we can use electromagnetic methods. They are massive as well so their radiation output is not that large as well.

Is there a possibility to attach some emitter of different particles like electrons or neutrons to some of the detectors "from the side" to have new kinds of collisions on high-energy? (True that it would be still only 6.5 TeV collision and not full 13 because emitter would not have its own accelerator, nevertheless we could then have the possibility of neutron-proton collisions and many others.)

Is it technically difficult or even tested to collide particles perpendiculary to the synchrotron beam?

Is or why wasn't this scheme used in the construction of LHC?

## 1 Answer

Determining the fixed-target beam energy needed to produce some process and comparing that to the collider beam energy needed for the same process is a standard exercise that we give to particle physics students (and, indeed I give a simplified version of it to my modern physics students). It really only calls for special relativity.

But the result is that a fixed target experiment using one beam from a collider is not half as energetic as a the collider experiment; it is a lot less energetic because much of the energy is thrown away in the form of the resultant spray having a large overall momentum in the lab frame. In other words, don't be thinking $6.5\,\mathrm{TeV}$ here.

There are exploratory plans to fund and build a electron-ion collider. Both Brookhaven and Jefferson lab are competing to get the nod using their existing facilities for one part of the infrastructure. (At RHIC they have the hadron beam, and JLAB the electron beam). But that is a two beam project.

Finally, the detector systems at the LHC are designed with proton-proton, proton-ion, and ion-ion collisions in mind. For electron-ion work you would build similar devices but some details of the design would be different.

• And even if we used an emitter shooting in a tangent direction against the beam, the energy of LHC is still too much higher and resultant losses would be still uneconomical as well, correct? Sep 24 '16 at 21:34
• Yes. Both the IEC designs have the two beams running nearly opposite each other. Sep 24 '16 at 21:36
• Just to put a number to what you say about fixed-target collisions, the value of $\sqrt{s}$ for a 7 TeV proton colliding with a stationary proton is about 115 GeV Sep 27 '16 at 13:35