Positive and negative pions, denoted \(\pi^{+}\)and \(\pi^{-}\), are antiparticles of each other. Each has a rest mass of \(140 \mathrm{MeV} / \mathrm{c}^{2}\). Suppose a collision between an electron and positron, each with kinetic energy \(K\), produces a \(\pi^{+}, \pi^{-}\)pair. What is the smallest possible value for \(K\) ?