X17: Status and Perspectives

Recently, a group directed by A. J. Krasznahorkay observed an anomaly in the emission of electron–positron pairs in three different nuclear reactions, namely, the 3H(p,e −e +) 4He, 7Li(p,e −e +) 8Be, and 11B(p,e −e +) 12C processes. Kinematics indicate that this anomaly might be due to the de-excitation of 4He, 8Be, and 12C nuclei with the emission of a boson with a mass of about 17 MeV, rapidly decaying into e −e + pairs. The result of the experiments performed with the singletron accelerator of ATOMKI is reviewed, and the consequences of the so-called X17 boson in particle physics and in cosmology are discussed. Forthcoming experiments designed to shed light on the possible existence of the X17 boson are also reported.