Scientists look for evidence of universe being simulation
Beane's experiment centers around observing high energy processes, such as those involving cosmic rays. These processes become smaller the more energetic they are. In a simulation, once the processes shrink to the size of the lattice, they cannot shrink further, and thus there should be a cutoff for how much energy can be applied to the system.
As it happens, there is indeed an upper limit to how much energy can be applied; this is what GZK is. It's a well studied phenomenon – when enough energy is applied to cosmic rays, background microwave radiation begins interacting with them, preventing them from attaining more energy. However, this doesn't necessarily mean we live in a simulation; it all has to do with how the physics surrounding the GZK behave. If they behave as they should, Beane believes his team will be able to see this; but he also believes that if we are simulated, that he should be able to see the lattice.
This is what GZK looks like
Of course, whether we find a lattice or not won't necessarily determine if we're simulated. There's no guarantee an advanced civilization would use technology even remotely similar to ours for their science projects.