The NA62 experiment reports the branching ratio measurement $$ \mathrm{BR}\left({K}^{+}\to {\pi}^{+}\nu \overline{\nu}\right)=\left({10.6}_{-3.4}^{+4.0}\left|{}_{\mathrm{stat}}\right.\pm {0.9}_{\mathrm{syst}}\right)\times {10}^{-11} $$ BR K + → π + ν ν ¯ = 10.6 − 3.4 + 4.0 stat ± 0.9 syst × 10 − 11 at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016–2018. This provides evidence for the very rare K+→$$ {\pi}^{+}\nu \overline{\nu} $$ π + ν ν ¯ decay, observed with a significance of 3.4σ. The experiment achieves a single event sensitivity of (0.839 ± 0.054) × 10−11, corresponding to 10.0 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. This measurement is also used to set limits on BR(K+→ π+X), where X is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample.

Rubropunctatin (1), monascorubrin (2), monascin (3) and ankaflavin (4) were purified from the mycelium of Monascus purpureus by flash chromatography on silica gel or reversed phase. Their embryotoxicity towards chicken embryos decreased in the order 2 > 1 > 3 > 4. The lower homologues 1 and 3 exhibited teratogenic effects on these organisms. Significant antibiotic activities against Bacillus subtilis and Candida pseudotropicalis were found with compounds 1 and 2. Immunosuppressive activity on mouse T-splenocytes was most pronounced with compounds 3 and 4. None of the compounds showed significant cytotoxic activity towards rat hepatocytes in vitro. Incubation of resting cells of M. purpureus with glycine afforded the dark-red compounds 5 and 6 where the pyran moiety of 1 and 2 changed into the N-substituted dihydropyridine moiety by replacement of the O-atom by the amino group of glycine. Compounds 5 and 6 were less biologically active than the major pigments 1-4.

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Search for production of an invisible dark photon in π 0 decays The NA62 collaboration

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The NA62 experiment reports an investigation of the $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ K + → π + ν ν ¯ mode from a sample of K+ decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0.389 ± 0.024) × 10−10, corresponding to 2.2 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of 1.78 × 10−10 for the $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ K + → π + ν ν ¯ branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of ($$ {0.48}_{-0.48}^{+0.72} $$ 0.48 − 0.48 + 0.72 ) × 10−10, are currently the most precise results worldwide, and are able to constrain some New Physics models that predict large enhancements still allowed by previous measurements.