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)