Search for the X17 particle in $$^{7}\textrm{Li}(\textrm{p},\textrm{e}^+ \textrm{e}^{-}) ^{8}\textrm{Be}$$ processes with the MEG II detector

作者：K. Afanaciev, A. M. Baldini, S. Ban, H. Benmansour, G. Boca, P. W. Cattaneo, G. Cavoto, F. Cei, María Cecilia Chiappini, A. Corvaglia, G. Dal Maso, A. de Bari, M. De Gerone, L. Ferrari Barusso, M. Francesconi, L. Galli, G. Gallucci, F. Gatti, L. Gerritzen, F. Grancagnolo, E. G. Grandoni, M. Grassi, D. N. Grigoriev, M. Hildebrandt, F.V. Ignatov, F. Ikeda, T. Iwamoto, S.V. Karpov, P. -R. Kettle, N. V. Khomutov, Alexander Kolesnikov, N. Kravchuk, В. А. Крылов, N. Kuchinskiy, F. Leonetti, Weiyuan Li, V. Malyshev, A. Matsushita, M. Meucci, S. Mihara, W. Molzon, T. Mori, D. Nicolò, H. Nishiguchi, A. Ochi, W. Ootani, A. Oya, D. Palo, M. Panareo, A. Papa, V. Pettinacci, A.S. Popov, F. Renga, S. Ritt, M. Rossella, A. Rozhdestvensky, S. Scarpellini, P. Schwendimann, G. Signorelli, Masato Takahashi, Y. Uchiyama, A. Venturini, B. Vitali, C. Voena, Kensuke Yamamoto, Ryoji Yokota, T. Yonemoto · 发表于：The European Physical Journal C · 年份：2025 · DOI：10.1140/epjc/s10052-025-14345-0 · 被引用次数：6 · 研究领域：Particle physics theoretical and experimental studies、Dark Matter and Cosmic Phenomena、Quantum Chromodynamics and Particle Interactions

Abstract The observation of a resonance structure in the opening angle of the electron-positron pairs in the $$^{7}$$ 7 Li(p,e $$^+$$ + e $$^-$$ - ) $$^{8}$$ 8 Be reaction was claimed and interpreted as the production and subsequent decay of a hypothetical particle (X17). Similar excesses, consistent with this particle, were later observed in processes involving $$^{4}$$ 4 He and $$^{12}$$ 12 C nuclei with the same experimental technique. The MEG II apparatus at PSI, designed to search for the $$\mu ^+ \rightarrow \textrm{e}^+ \gamma $$ μ + → e + γ decay, can be exploited to investigate the existence of this particle and study its nature. Protons from a Cockroft–Walton accelerator, with an energy up to 1.1 MeV, were delivered on a dedicated Li-based target. The $$\gamma $$ γ and the e $$^{+}$$ + e $$^{-}$$ - pair emerging from the $$^8\textrm{Be}^*$$ 8 Be ∗ transitions were studied with calorimeters and a spectrometer, featuring a broader angular acceptance than previous experiments. We present in this paper the analysis of a four-week data-taking in 2023 with a beam energy of 1080 keV, resulting in the excitation of two different resonances with Q-value 17.6 and 18.1 MeV. No significant signal was found, and limits at 90% C.L. on the branching ratios (relative to the $$\gamma $$ γ emission) of the tw...