Observation of parametric X-rays produced by 400 GeV/c protons in bent crystals - Scandale, W; Arduini, G; Assmann, R; Cerutti, F; Gilardoni, S; Christiansen, J; Laface, E; Losito, R; Masi, A; Metral, E; Mirarchi, D; Montesano, S; et al. (PHYSICS LETTERS B, 2011)