Explore the vast range of titles available.

The MEG II experiment, based at the Paul Scherrer Institut in Switzerland, reports the result of a search for the decay μ + → e + γ from data taken in the first physics run in 2021. No excess of events over the expected background is observed, yielding an upper limit on the branching ratio of B ( μ + → e + γ ) < 7.5 × 10 - 13 (90% CL). The combination of this result and the limit obtained by MEG gives B ( μ + → e + γ ) < 3.1 × 10 - 13 (90% CL), which is the most stringent limit to date. A ten-fold larger sample of data is being collected during the years 2022–2023, and data-taking will continue in the coming years.

This letter reports the result of the search for the decay μ + → e + γ undertaken at the Paul Scherrer Institut in Switzerland with the MEG II experiment using the data collected in the 2021–2022 physics runs. The sensitivity of the branching ratio measurement in this search is 2.2 × 10 - 13 , a factor of 2.4 better than that of the full MEG dataset and obtained in a data taking period of about one fourth that of MEG, thanks to the superior performances of the new detector. The observed data are consistent with the expected background, yielding an upper limit on the branching ratio of B ( μ + → e + γ ) < 1.5 × 10 - 13 (90% C.L.). Additional improvements are expected with the data collected during the years 2023–2024. The data-taking will continue in the coming years.

The observation of a resonance structure in the opening angle of the electron-positron pairs in the 7 Li(p,e + e - ) 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 + → 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 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 γ emission) of the two resonances to X17 were set, R 17.6 < 1.8 × 10 - 6 and R 18.1 < 1.2 × 10 - 5 in the mass range between 16.5 MeV / c 2 and 17.1 MeV / c 2 .

Women with a deleterious germline mutation in BRCA1 or BRCA2 are candidates for bilateral salpingo-oophorectomy (BSO). To address the need for adjustment of the current BSO procedure, we investigated the length and the nature of the fallopian tube epithelium that is not removed by BSO. Fourteen consecutive hysterectomy specimens were collected. Complete cross-sections with a 3-mm interval were made of the tubal lumen from the outside of the uterus at the cutoff point of the current BSO procedure to the uterine cavity and examined for the presence or absence of tubal type (ciliated) epithelium and subepithelial endometrial stroma. The fallopian tube remnant had a median length of 12 mm (range 6–15 mm). Tubal type (ciliated) epithelium was shown to be present in all uteri in the first cross-section containing 100% endometrial stroma, as well as in the uterine cavity of all but two of the hysterectomy specimens. A substantial part of the fallopian tube remains in situ after prophylactic BSO and is covered with tubal type ciliated epithelium. More research is necessary to investigate the role of this remnant part of the tube for BRCA carriers.

This letter reports the result of the search for the decay$${\\upmu ^+ \\rightarrow e^+ \\upgamma }$$μ + → e + γ undertaken at the Paul Scherrer Institut in Switzerland with the MEG II experiment using the data collected in the 2021–2022 physics runs. The sensitivity of the branching ratio measurement in this search is$${2.2 \\times 10^{-13}}$$2.2 × 10 - 13 , a factor of 2.4 better than that of the full MEG dataset and obtained in a data taking period of about one fourth that of MEG, thanks to the superior performances of the new detector. The observed data are consistent with the expected background, yielding an upper limit on the branching ratio of$$\\mathcal{B} ({\\upmu ^+ \\rightarrow \\textrm{e}^+ \\upgamma }) < {1.5 \\times 10^{-13}}$$B ( μ + → e + γ ) < 1.5 × 10 - 13 (90% C.L.). Additional improvements are expected with the data collected during the years 2023–2024. The data-taking will continue in the coming years.

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 two resonances to X17 were set,$$R_{17.6} <{1.8}\\,\\times \\,10^{-6}$$R 17.6 < 1.8 × 10 - 6 and$$R_{18.1} < {1.2}\\,\\times \\,10^{-5}$$R 18.1 < 1.2 × 10 - 5 in the mass range between$${16.5}\\hbox { MeV}/\\hbox {c}^{2}$$16.5 MeV / c 2 and$${17.1}\\hbox { MeV}/\\hbox {c}^{2}$$17.1 MeV / c 2 .