X(17): What Next?

Monday 13 Apr 2026, 15:00 → 17:30 Europe/Rome

Aula Conversi (Dipartimento di Fisica-Ed.Marconi)

In the past decade, experiments performed with the ATOMKI pair spectrometer in Debrecen, Hungary, have reported anomalies in the angular distributions of electron–positron pairs emitted in the decays of excited states of ⁸Be, ¹²C, and ⁴He nuclei. These observations have been interpreted as possible evidence for a new boson with a mass of about 17 MeV, referred to as “X(17)”. In this afternoon, we review the current experimental status of X17 searches, with particular emphasis on the activities carried out at INFN Roma 1.

 

 

 

 

Organizzatori: Valerio Ippolito, Francesco Pandolfi, Mauro Valli

15:00 → 15:20 Theoretical introduction

Speakers: Claudio Toni (Istituto Nazionale di Fisica Nucleare), Claudio Toni, Claudio Toni (Sapienza)

X17_Sapienza.pdf

15:25 → 15:37 MEG-II

Speaker: Francesco Renga (Istituto Nazionale di Fisica Nucleare)

renga_X17Roma.pdf

15:40 → 15:52 Probing the existence and properties of the X7 boson using proton and neutron beams

Three significant anomalies have been observed in the emission of electron-positron pairs in the 7Li(p,e+e−)8Be, 3H(p,e+e−)4He and 11B(p,e+e−)12C nuclear reactions [1-3]. These anomalies have been interpreted as the signature of the existence of a boson (hereafter referred to as X17) of mass MX17 = 16.8 MeV/c2 that could be a mediator of a fifth force, characterised by a strong coupling suppression of protons compared to neutrons (protophobic force).
In this talk is presented a new experimental 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 neutrons. The study of the 3He(n,e+e−)4He and 3H(p,e+e−)4He reaction, in a wide energy window and using a detector with a large angular acceptance would probe the X17 existence and quantic numbers. In the case of a positive result, the study of the 2H(n,e+e−)3He and 2H(p,e+e−)3H would show the kinematic onset of the X17 channel at Ebeam~>16 MeV and offers the opportunity to shed light on the isospin dependence of the X17-nucleon coupling. The achievable results are discussed on the base of ab-initio calculations, in which the existence of a 17 MeV boson is considered [4,5].

[1] A. J. Krasznahorkay et al., Phys. Rev. Lett. 116, (2016) 042501.
[2] A. J. Krasznahorkay et al., Phys. Rev. C 104, (2021) 044003.
[3] A. J. Krasznahorkay et al., Phys. Rev. C 106, (2022) 061601.
[4] M. Viviani et al., Phys. Rev. C 105, 014001 (2022), arXiv:2104.07808 [nucl-th].
[5] M. Viviani et al., submitted to Phys. Rev. C. arXiv:2408.16744.

Speaker: Carlo Gustavino (Istituto Nazionale di Fisica Nucleare)

Gustavino_Sapienza.pdf

15:55 → 16:10 Other initiatives and PADME

Speaker: Mauro Raggi (Istituto Nazionale di Fisica Nucleare)

Raggi_PomTemRM1.pdf

16:15 → 16:35 X17 production and electron motion pitfalls

Speakers: Luc DARME (IP2I - Lyon 1 University), Dr Luc Darmé (Laboratori Nazionali di Frascati), Luc Jean Marie Darmé

X17andElectronMotion.pdf

16:40 → 17:00 Discussion

17:00 → 17:30 Coffee break