scene.launch('PauseMenu') then scene.pause(). The engine has two pauses and only one of them is any use here: setPaused freezes the whole loop and stops drawing, which would leave the menu floating over a black screen. Pausing a scene freezes it and keeps drawing it: the world stops mid-bounce and stays visible underneath.
Press Space to pause and resume, and S for slow motion, which is a different thing again: at timeScale: 0 the updates still run, they just run over no time at all.