A new detection set-up to search the X17 boson

An excess of electron-positron pairs at large relative angle emitted in the 3H(p,e+e−)4He, 7Li(p,e+e−)8Be, and 11B(p,e+e−)12C nuclear processes has been recently observed. These anomalies are compatible with the creation of a boson with mass of about 17 MeV, not foreseen in the standard model. To probe the possible existence of the so called X17 boson, we propose to study for the first time the 3He(n,e+e−)4He reaction at the n_TOF facility at CERN. The experimental program and performance of the detector prototype are discussed.