[en] A high-gradient, meter scale Plasma Wakefield Accelerator (PWFA) module operating in the nonlinear, electron blow-out regime is demonstrated experimentally. The beam and plasma parameters are chosen such that the matched beam channels through the plasma over more than twelve beta functions without spreading or oscillating over a range of densities for observing both deceleration and acceleration. The wakefield decelerates the bulk of the initially 28.5 GeV beam by up to 155 MeV, however particles in the back of the same beam are accelerated by up to 280 MeV at a density of 1.9 x 10¹⁴ cm^-3 as the wakefield changes sign