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We search for $J/psi$ radiative decays into a weakly interacting neutral particle, namely an invisible particle, using the $J/psi$ produced through the process $psi(3686)topi^+pi^-J/psi$ in a data sample of $(448.1pm2.9)times 10^6$ $psi(3686)$ decays collected by the BESIII detector at BEPCII. No significant signal is observed. Using a modified frequentist method, upper limits on the branching fractions are set under different assumptions of invisible particle masses up to 1.2 $mathrm{ Gekern -0.1em V}/c^2$. The upper limit corresponding to an invisible particle with zero mass is 7.0$times 10^{-7}$ at the 90% confidence level.
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Using a sample of $1.31times10^{9} ~J/psi$ events collected with the BESIII detector, we perform a study of $J/psitogamma Kbar{K}eta$. The $X(2370)$ is observed in the $Kbar{K}eta$ invariant-mass distribution with a statistical significance of 8.3$sigma$. Its resonance parameters are measured to be $M = 2341.6 pm 6.5text{(stat.)} pm 5.7text{(syst.)}$~MeV/$c^{2}$ and $Gamma = 117 pm 10 text{(stat.)} pm 8 text{(syst.)}$~MeV. The product branching fractions for $J/psito gamma X(2370), X(2370) to K^{+} K^{-}eta$ and $J/psito gamma X(2370), X(2370) to K_{S}^{0} K_{S}^{0}eta$ are determined to be $(1.79 pm 0.23 text{(stat.)} pm 0.65 text{(syst.)}) times 10^{-5}$ and $(1.18 pm 0.32 text{(stat.)} pm 0.39 text{(syst.)}) times 10^{-5}$, respectively. No evident signal for the $X(2120)$ is observed in the $Kbar{K}eta$ invariant-mass distribution. The upper limits for the product branching fractions of $mathcal{B}(J/psi to gamma X(2120)togamma K^{+} K^{-} eta)$ and $mathcal{B}(J/psitogamma X(2120)togamma K_{S}^{0} K_{S}^{0} eta)$ are determined to be $1.49times10^{-5}$ and $6.38times10^{-6}$ at the 90% confidence level, respectively.
We propose an experiment to search for invisible decays of orthopositronium (o-Ps) with a 90% confidence sensitivity in the branching ratio as low as $10^{-8}$. Evidence for this decay mode would unambigously signal new physics: either the existence of extra--dimensions or fractionally charged particles or new light gauge bosons. The experimental approach and the detector components of the proposed experiment are described.
The existence of dark matter has been established in astrophysics. However, there is no candidate for DM in the Stand Model (SM). In SM, the Higgs boson can only decay invisibly via $Hrightarrow ZZ^ast rightarrow ubar{ u} ubar{ u}$ or DM, so any evidence of invisible Higgs decay that exceeds BR (H$rightarrow$inv.) will immediately point to a phenomenon that is beyond the standard model (BSM). In this paper, we report on the upper limit of BR (H$rightarrow$invisible) estimated for three channels, including two leptonic channels and one hadronic channel, under the assumption predicted by SM. With the SM ZH production rate, the upper limit of BR (H$rightarrow$inv.) could reach 0.24% at the 95% confidence level.
Using a sample of $(225.3pm 2.8)times 10^{6}$ $J/psi$ decays collected with the BESIII detector at BEPCII, searches for invisible decays of $eta$ and $eta^prime$ in $J/psitophieta$ and $phieta^prime$ are performed. Decays of $phi to K^{+}K^{-}$ are used to tag the $eta$ and $eta^prime$ decays. No signals above background are found for the invisible decays, and upper limits at the 90% confidence level are determined to be $2.58times10^{-4}$ for the ratio $frac{mathcal{B}(etatorm{invisible})}{mathcal{B}(etatogammagamma)}$ and $2.39times10^{-2}$ for $frac{mathcal{B}(eta^primetorm{invisible})}{mathcal{B}(eta^prime togammagamma)}$.
This paper reports results from a search for nucleon decay through invisible modes, where no visible energy is directly deposited during the decay itself, during the initial water phase of SNO+. However, such decays within the oxygen nucleus would produce an excited daughter that would subsequently de-excite, often emitting detectable gamma rays. A search for such gamma rays yields limits of $2.5 times 10^{29}$ y at 90% Bayesian credibility level (with a prior uniform in rate) for the partial lifetime of the neutron, and $3.6 times 10^{29}$ y for the partial lifetime of the proton, the latter a 70% improvement on the previous limit from SNO. We also present partial lifetime limits for invisible dinucleon modes of $1.3times 10^{28}$ y for $nn$, $2.6times 10^{28}$ y for $pn$ and $4.7times 10^{28}$ y for $pp$, an improvement over existing limits by close to three orders of magnitude for the latter two.
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