Sentence:  There were also particles no one had predicted that just <WSD>appeared</WSD>. Five of them [..., i]n order of increasing modernity, [...] are the neutrino, the pi meson, the antiproton, the quark and the Higgs boson. 
Meaning of the word marked with <WSD> tags:  To come or be in sight; to be in view; to become visible.