I have a question about the spectrum of particles predicted in string theory. Assuming I have this correct here goes. If I look only at open strings I can predict the particle spectrum and I can get scalars, vectors, spinors, maybe spin 3/2, but no spin 2 particles. We can then look at the closed string particle spectrum and the graviton shows up along with the rest. Here is where I get confused. When I calculated this spectrum, I got all the particles in the standard model (SM), yet I never included excited modes of the string. When I do look at excited modes of the string the energies are so high we would never see these particles today correct? If so, how do we see all the different particles in the SM, if they are all represented by a string in its ground state? Does it have to do with the string being constrained to some of the 26 dimensions, or how the space is compactified. For example, an electron and a muon would both be produced by the string in its ground state. So how do I determine which particle is which in the context of string theory? I realize this isn't completly physical since I didn't include SUSY, but I think the concept is the same if we include SUSY and look at 10d.