Chris Willman Senior Music Writer and Chief Music Critic U2 will begin its two-residency at Las Vegas’ Sphere with at least one new song to perform: “Atomic City,” a Vegas-themed tune that is expected to be released on or before the band’s Sept. 29 opening-night show. Filming a music video, the foursome repeatedly played through the song Saturday while positioned on a flatbed trailer that had come to a halt on Fremont Street in the city’s neon-filled downtown area.