Jan 23 – 27, 2023
Bormio, Italy
Europe/Berlin timezone

Probing the X17 existence and properties using proton and neutron beams

Not scheduled
Bormio, Italy

Bormio, Italy

Short Contribution Wednesday Afternoon


Michele Viviani (INFN-Pisa)


Two striking anomalies have been observed recently in the emission of electron-positron pairs in 7Li(p, e+e-)8Be and 3H(p, e+e-)4He reactions [1-2]. These anomalies have been interpreted as the signature of a new particle, a boson with a mass of 17 MeV (hereafter X17 boson), not foreseen in the particle physics standard model. It has been speculated that the X17 boson could be a mediator of a fifth force, characterized by a strong coupling suppression of protons compared to neutrons (protophobic force). Even more interestingly, this scenario could explain, at least partially, the long-standing (recent) anomaly on the muon (electron) magnetic moment. Besides these speculations, it is clear that the possible existence of a new particle is of paramount importance in particle physics and cosmology.
This talk shows a new approach to clarify the present scenario by searching for the X17 boson in the decay of excited A=3,4 (Tritium, helium-3, helium-4) nuclei through reactions induced by protons or (for the first time) neutrons produced with n_TOF and Demokritos facilities, respectively at CERN and at NCSR, Athens. The study of the 3He(n, e+e-)4He and 3H(p, e+e-)4He reaction in a wide energy window would probe the X17 existence and, if the anomaly is confirmed, it allows for the determination of the relevant characteristics of the X17 boson such as its mass and quantic numbers. In the case of a positive result, the analysis of the 2H(n, e+e-)3He and 2H(p, e+e-)3H cross section ratio offers a unique opportunity to study the supposed protophobic nature of the fifth force. In this talk the physical motivations and the experimental approach are described. The achievable results are discussed on the base of recent of ab-initio calculations for A=3 and A=4 nuclei, in which the existence of a 17 MeV boson is considered [3,4].

[1] A.J. Krasznahorkay et al.:
"Observation of Anomalous Internal Pair Creation in 8Be: A Possible Indication of a Light, Neutral Boson". Physical Review Letters. 116 (42501): 042501 (2016).
[2] A.J. Krasznahorkay et al.:
"New evidence supporting the existence of the hypothetic X17 particle". 
PHYSICAL REVIEW C 104, 044003 (2021)
[3] M. Viviani et al.:
"X17 boson and the  3H(p,e+e-)4He and  3He(n,e+e-)4He processes: A theoretical analysis", PHYSICAL REVIEW C 105, 014001 (2022).
[4] M. Viviani et al:
“ Probing the coupling of X17 in 2H(p,e+e-)3He and  2H(n,e+e-)3H processes: a theoretical and experimental approach"
(In preparation).

Topic Fundamental Interactions

Primary author

Michele Viviani (INFN-Pisa)


Carlo Gustavino (INFN-Roma1)

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