It's probably nitpicking, but 'discovery' isn't the right word in this context.
String theory is a purely mathematical construct, which has as of now no way to be confirmed empirically or experimentally. We can't check and look for strings, they're too small (Planck scale). The only foreseeable confirmation (not 'proof') would be the discovery -here it's appropriate- of the supersymmetric cousins of the known particles. These are predicted by the maths and are orders of magnitude heavier than their known counterparts. But the energies involved in discovering them are thus far eluding our tools (heavier particles are, perhaps counterintuitively, more difficult to observe because of the E=mc² relation between matter and energy, see 'particle accelerators' for a full explanation).