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Lepton family number violation is tested by searching for $mu^+to e^+X^0$ decays among the 5.8$times 10^8$ positive muon decay events analyzed by the TWIST collaboration. Limits are set on the production of both massless and massive $X^0$ bosons. The large angular acceptance of this experiment allows limits to be placed on anisotropic $mu^+to e^+X^0$ decays, which can arise from interactions violating both lepton flavor and parity conservation. Branching ratio limits of order $10^{-5}$ are obtained for bosons with masses of 13 - 80 MeV/c$^2$ and with different decay asymmetries. For bosons with masses less than 13 MeV/c$^{2}$ the asymmetry dependence is much stronger and the 90% limit on the branching ratio varies up to $5.8 times 10^{-5}$. This is the first study that explicitly evaluates the limits for anisotropic two body muon decays.
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Charged lepton flavor violating muon decay ${mu}^+{rightarrow}e^+X_H$, where $X_H$ is a massive neutral boson, was sought by searching for extra peaks in the muon decay ${mu}^+{rightarrow}e^+{ u}bar{ u}$ energy spectrum in the $m_{X_H}$ mass region $47.8-95.1$ MeV/$c^2$. No signal was found and 90% confidence level upper limits were set on the branching ratio ${Gamma}({mu}^+{rightarrow}e^+X_H)/{Gamma}({mu}^+{rightarrow}e^+{ u}bar{ u})$ at the level of $10^{-5}$ for this region.
We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, $mu^+ to mathrm{e}^+mathrm{X}, mathrm{X} to gammagamma$. This search uses a dataset resulting from $7.5times 10^{14}$ stopped muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009--2013. No significant excess is found in the mass region 20--45 MeV/c$^2$ for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20--40 MeV/c$^2$, down to $mathcal{O}(10^{-11})$ at 90% confidence level.
A search for the rare two-body charmless baryonic decay $B^+ to p barLambda$ is performed with $pp$ collision data, corresponding to an integrated luminosity of $3,mbox{fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of $B^+ to p barLambda$ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the $B^+ to K^0_{mathrm S} pi^+$ decay for normalisation, is begin{eqnarray} mathcal{B}(B^+ to p barLambda) & = & ( 2.4 ,^{+1.0}_{-0.8} pm 0.3 ) times 10^{-7} ,, onumber end{eqnarray} where the first uncertainty is statistical and the second systematic.
We present results from a search for solar axions with the COSINE-100 experiment. We find no evidence of solar axion events from a data-set of 6,303.9 kg$cdot$days exposure and set a 90,% confidence level upper limit on the axion-electron coupling, $g_{ae}$, at 1.70~$times$~$10^{-11}$ for an axion mass less than 1,keV/c$^2$. This limit excludes QCD axions heavier than 0.59,eV/c$^2$ in the DFSZ model and 168.1,eV/c$^2$ in the KSVZ model.
We have searched for proton into muon plus neutral kaon using data from a 91.7 kiloton-year exposure of Super-Kamiokande-I, a 49.2 kiloton-year exposure of Super-Kamiokande-II, and a 31.9 kiloton-year exposure of Super-Kamiokande-III. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation and no evidence for proton decay in this mode was found. We set a partial lifetime lower limit of 1.6x10^33 years at the 90% confidence level.
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