In the Large Hadron Collider, hadrons are collided with one another and studied. At various instances, e.g. ALICE papers I come across this "charged particle multiplicity density." What exactly is this? I have searched so many forums. Nowhere is this answered. It would be awesome if anybody could give some basics for understanding this concept.
Multiplicity is a fancy way of saying "number of".
e.g. track multiplicity is just the number of tracks in an event.
Density will imply that this is normalised to a unit value of some quantity like volume/angle/solid-angle.