Электронный каталог

Статья

Afanaciev, K.
Search for the X17 Particle in *7Li(p, e*+e*-)*8Be Processes with the MEG II Detector / K.Afanaciev, N.Khomutov, A.Kolesnikov, N.Kravchuk, V.Krylov, N.Kuchinskiy, V.Malyshev, A.Popov, A.Rozhdestvensky, [a.o.]. – Text : electronic // The European Physical Journal C. – 2025. – Vol. 85, No. 7. – P. 763. – URL: https://doi.org/10.1140/epjc/s10052-025-14345-0. – Bibliogr.: 32.

The observation of a resonance structure in the opening angle of the electron-positron pairs in the *7Li(p,e*+e*-)*8Be 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 *4He and *1*2C nuclei with the same experimental technique. The MEG II apparatus at PSI, designed to search for the 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 γ and the e*+e*- pair emerging from the *8Be&sup(* ) 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 γ emission) of the two resonances to X17 were set, R&sub(17.6) < 1.8 × 10&sup(−6) and R&sub(18.1) < 1.2 × 10&sup(−5) in the mass range between 16.5 MeV/c*2 and 17.1 MeV/c*2 .



ОИЯИ = ОИЯИ (JINR)2025
Спец.(статьи,препринты) = С 332.3 - Образование электронно-позитронных пар. Позитрон, позитроний. Взаимодействие позитрона с веществом
Спец.(статьи,препринты) = С 343 в - Взаимодействие протонов с ядрами (Z>2). Изобарно- аналоговые состояния
Бюллетени = 39/025