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

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Main Authors:	The MEG II collaboration, Afanaciev, K., Baldini, A. M., Ban, S., Benmansour, H., Boca, G., Cattaneo, P. W., Cavoto, G., Cei, F., Chiappini, M., Corvaglia, A., Maso, G. Dal, De Bari, A., De Gerone, M., Barusso, L. Ferrari, Francesconi, M., Galli, L., Gallucci, G., Gatti, F., Gerritzen, L., Grancagnolo, F., Grandoni, E. G., Grassi, M., Grigoriev, D. N., Hildebrandt, M., Ignatov, F., Ikeda, F., Iwamoto, T., Karpov, S., Kettle, P. -R., Khomutov, N., Kolesnikov, A., Kravchuk, N., Krylov, V., Kuchinskiy, N., Leonetti, F., Li, W., Malyshev, V., Matsushita, A., Meucci, M., Mihara, S., Molzon, W., Mori, T., Nicolò, D., Nishiguchi, H., Ochi, A., Ootani, W., Oya, A., Palo, D., Panareo, M., Papa, A., Pettinacci, V., Popov, A., Renga, F., Ritt, S., Rossella, M., Scarpellini, A. Rozhdestvensky. S., Schwendimann, P., Signorelli, G., Takahashi, M., Uchiyama, Y., Venturini, A., Vitali, B., Voena, C., Yamamoto, K., Yokota, R., Yonemoto, T.
Format:	Preprint
Published:	2024
Subjects:	Nuclear Experiment High Energy Physics - Experiment
Online Access:	Acceder al recurso
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_version_	1866910695784710144
author	The MEG II collaboration Afanaciev, K. Baldini, A. M. Ban, S. Benmansour, H. Boca, G. Cattaneo, P. W. Cavoto, G. Cei, F. Chiappini, M. Corvaglia, A. Maso, G. Dal De Bari, A. De Gerone, M. Barusso, L. Ferrari Francesconi, M. Galli, L. Gallucci, G. Gatti, F. Gerritzen, L. Grancagnolo, F. Grandoni, E. G. Grassi, M. Grigoriev, D. N. Hildebrandt, M. Ignatov, F. Ikeda, F. Iwamoto, T. Karpov, S. Kettle, P. -R. Khomutov, N. Kolesnikov, A. Kravchuk, N. Krylov, V. Kuchinskiy, N. Leonetti, F. Li, W. Malyshev, V. Matsushita, A. Meucci, M. Mihara, S. Molzon, W. Mori, T. Nicolò, D. Nishiguchi, H. Ochi, A. Ootani, W. Oya, A. Palo, D. Panareo, M. Papa, A. Pettinacci, V. Popov, A. Renga, F. Ritt, S. Rossella, M. Scarpellini, A. Rozhdestvensky. S. Schwendimann, P. Signorelli, G. Takahashi, M. Uchiyama, Y. Venturini, A. Vitali, B. Voena, C. Yamamoto, K. Yokota, R. Yonemoto, T.
author_facet	The MEG II collaboration Afanaciev, K. Baldini, A. M. Ban, S. Benmansour, H. Boca, G. Cattaneo, P. W. Cavoto, G. Cei, F. Chiappini, M. Corvaglia, A. Maso, G. Dal De Bari, A. De Gerone, M. Barusso, L. Ferrari Francesconi, M. Galli, L. Gallucci, G. Gatti, F. Gerritzen, L. Grancagnolo, F. Grandoni, E. G. Grassi, M. Grigoriev, D. N. Hildebrandt, M. Ignatov, F. Ikeda, F. Iwamoto, T. Karpov, S. Kettle, P. -R. Khomutov, N. Kolesnikov, A. Kravchuk, N. Krylov, V. Kuchinskiy, N. Leonetti, F. Li, W. Malyshev, V. Matsushita, A. Meucci, M. Mihara, S. Molzon, W. Mori, T. Nicolò, D. Nishiguchi, H. Ochi, A. Ootani, W. Oya, A. Palo, D. Panareo, M. Papa, A. Pettinacci, V. Popov, A. Renga, F. Ritt, S. Rossella, M. Scarpellini, A. Rozhdestvensky. S. Schwendimann, P. Signorelli, G. Takahashi, M. Uchiyama, Y. Venturini, A. Vitali, B. Voena, C. Yamamoto, K. Yokota, R. Yonemoto, T.
contents	The observation of a resonance structure in the opening angle of the electron-positron pairs in the $^{7}$Li(p,\ee) $^{8}$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 $^{4}$He and $^{12}$C nuclei with the same experimental technique. The MEG II apparatus at PSI, designed to search for the $μ^+ \rightarrow \mathrm{e}^+ γ$ 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 $γ$ and the e$^{+}$e$^{-}$ pair emerging from the $^8\mathrm{Be}^*$ 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 \SI{17.6}{\mega\electronvolt} and \SI{18.1}{\mega\electronvolt}. No significant signal was found, and limits at \SI{90}{\percent} C.L. on the branching ratios (relative to the $γ$ emission) of the two resonances to X17 were set, $R_{17.6} < 1.8 \times 10^{-6} $ and $R_{18.1} < 1.2 \times 10^{-5} $.
format	Preprint
id	arxiv_https___arxiv_org_abs_2411_07994
institution	arXiv
publishDate	2024
record_format	arxiv
spellingShingle	Search for the X17 particle in $^{7}\mathrm{Li}(\mathrm{p},\mathrm{e}^+ \mathrm{e}^{-}) ^{8}\mathrm{Be}$ processes with the MEG II detector The MEG II collaboration Afanaciev, K. Baldini, A. M. Ban, S. Benmansour, H. Boca, G. Cattaneo, P. W. Cavoto, G. Cei, F. Chiappini, M. Corvaglia, A. Maso, G. Dal De Bari, A. De Gerone, M. Barusso, L. Ferrari Francesconi, M. Galli, L. Gallucci, G. Gatti, F. Gerritzen, L. Grancagnolo, F. Grandoni, E. G. Grassi, M. Grigoriev, D. N. Hildebrandt, M. Ignatov, F. Ikeda, F. Iwamoto, T. Karpov, S. Kettle, P. -R. Khomutov, N. Kolesnikov, A. Kravchuk, N. Krylov, V. Kuchinskiy, N. Leonetti, F. Li, W. Malyshev, V. Matsushita, A. Meucci, M. Mihara, S. Molzon, W. Mori, T. Nicolò, D. Nishiguchi, H. Ochi, A. Ootani, W. Oya, A. Palo, D. Panareo, M. Papa, A. Pettinacci, V. Popov, A. Renga, F. Ritt, S. Rossella, M. Scarpellini, A. Rozhdestvensky. S. Schwendimann, P. Signorelli, G. Takahashi, M. Uchiyama, Y. Venturini, A. Vitali, B. Voena, C. Yamamoto, K. Yokota, R. Yonemoto, T. Nuclear Experiment High Energy Physics - Experiment The observation of a resonance structure in the opening angle of the electron-positron pairs in the $^{7}$Li(p,\ee) $^{8}$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 $^{4}$He and $^{12}$C nuclei with the same experimental technique. The MEG II apparatus at PSI, designed to search for the $μ^+ \rightarrow \mathrm{e}^+ γ$ 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 $γ$ and the e$^{+}$e$^{-}$ pair emerging from the $^8\mathrm{Be}^*$ 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 \SI{17.6}{\mega\electronvolt} and \SI{18.1}{\mega\electronvolt}. No significant signal was found, and limits at \SI{90}{\percent} C.L. on the branching ratios (relative to the $γ$ emission) of the two resonances to X17 were set, $R_{17.6} < 1.8 \times 10^{-6} $ and $R_{18.1} < 1.2 \times 10^{-5} $.
title	Search for the X17 particle in $^{7}\mathrm{Li}(\mathrm{p},\mathrm{e}^+ \mathrm{e}^{-}) ^{8}\mathrm{Be}$ processes with the MEG II detector
topic	Nuclear Experiment High Energy Physics - Experiment
url	https://arxiv.org/abs/2411.07994