Where should we look for the deviation from quantum mechanics?

We argue that the experimental measurement of the lifetime and decay law of metastable helium is a promising way to find a deviation from quantum mechanics. We analyze the decay of the metastable state for a quartic deformation of quantum mechanics. We find that the absolute change of the mean lifetime can be significant even if the modification is small. We show that, in the Wigner–Weisskopf approximation, the deviation from the exponential law in the modified theory can occur on time scales comparable with the lifetime.