What is the differece between a pomeron and a glueball? What is the differece between a pomeron and a glueball?   I thought that glueballs were states made only of gluons, and pomerons were states of an even number of gluons. But apparently there is a difference that I am missing.
 A: One has to remember that back in the 1960's the dominant theory to model the plethora of resonances found in elemenary particle studies was Regge theory

In quantum physics, Regge theory  is the study of the analytic properties of scattering as a function of angular momentum, where the angular momentum is not restricted to be an integer multiple of ħ but is allowed to take any complex value.

In this review's figures are the experimental  trajectories with their fit to theory.
The Pomeron was a  Regge trajectory where there was just a type of elastic scattering.
At present the quark model and QCD calculations  dominate the theory , and  there is an effort to identify Regge trajectories with QCD concepts, for example this,  does connect "glueball"  states with the Pomeron trajectory as poles on it. Glueballs as far as I can gather exist in other trajectories too.
So in current research the Pomeron is a trajectory on which glueballs can be modeled in order to reproduce the experimental successes of the 1960's Regge trajectories.
Just a note, that AFAIK string theories also are able to embed the successes of the Regge trajectories
