We discuss the sensitivity of neutrino experiments at the luminosity frontier to generic hidden sectors containing new (sub)-GeV neutral states. The weak interaction of these states with the standard model can be efficiently probed through all of the allowed renormalizable ``portals'' (in the Higgs, vector, and neutrino sectors) at fixed target proton beam facilities, with complementary sensitivity to colliders. We concentrate on the kinetic-mixing vector portal, and show that certain regions of the parameter space for a new $\mathrm{U}(1{)}_{S}$ gauge sector with long-lived sub-GeV mass states decaying to standard model leptons are already severely constrained by the data sets at LSND, MiniBooNE, and NuMI/MINOS. Furthermore, scenarios in which portals allow access to stable neutral particles, such as MeV-scale dark matter, generally predict that the neutrino beam is accompanied by a ``dark matter beam,'' observable through neutral-current-like interactions in the detector. As a consequence, we show that the LSND electron recoil event sample currently provides the most stringent direct constraint on MeV-scale dark matter models.

Exploring portals to a hidden sector through fixed targets

A comprehensive overview of kaon decays is presented The standard model predictions are discussed in detail, covering both the underlying short-distance electroweak dynamics and the important interplay of QCD at long distances Chiral perturbation theory provides a universal framework for treating leptonic, semileptonic, and nonleptonic decays including rare and radiative modes All allowed decay modes with branching ratios of at least ${10}^{\ensuremath{-}11}$ are analyzed Some decays with even smaller rates are also included Decays that are strictly forbidden in the standard model are not considered in this review The present experimental status and the prospects for future improvements are reviewed

Kaon Decays in the Standard Model

We calculate the charm-quark contribution to the decay ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ in next-to-next-to-leading order of QCD. This new contribution reduces the theoretical uncertainty in the relevant parameter ${P}_{c}$ from $\ifmmode\pm\else\textpm\fi{}22%$ down to $\ifmmode\pm\else\textpm\fi{}7%$, corresponding to scale uncertainties of $\ifmmode\pm\else\textpm\fi{}3%$ and $\ifmmode\pm\else\textpm\fi{}6%$ in the short-distance part of the branching ratio and the determination of the Wolfenstein parameter $\overline{\ensuremath{\rho}}$ from ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$. The error in ${P}_{c}=0.115\ifmmode\pm\else\textpm\fi{}0.018$ is now in equal shares due to the combined scale uncertainties and the current uncertainty in the charm-quark mass. We find $\mathcal{B}({K}_{L}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}{)}_{\mathrm{SD}}=(0.79\ifmmode\pm\else\textpm\fi{}0.12)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$, with the present uncertainty in the Cabibbo-Kobayashi-Maskawa element ${V}_{td}$ being the dominant individual source in the quoted error.

Charm-Quark Contribution to K L →μ + μ - at Next-to-Next-to-Leading Order

The KTeV experiment at Fermilab has isolated a total of 132 events from the rare decay K(L)-->e+ e- mu+ mu-, with an estimated background of 0.8 events. The branching ratio of this mode is determined to be [2.69+/-0.24(stat)+/-0.12(syst)]x10(-9), with a radiative cutoff of M(2)(ee mu mu)/M(2)(K)>0.95. The first measurement using this mode of the parameter alpha from the D'Ambrosio-Isidori-Portoles (DIP) model of the K(L)gamma*gamma* vertex yields a result of -1.59+/-0.37, consistent with values obtained from other decay modes. Because of the limited statistics, no sensitivity is found to the DIP parameter beta. We use this decay mode to set limits on CP and lepton violation.

/pdf/measurements-of-the-decay-k-l-e-e-mu-mu-20a30p9l4s.pdf

Measurements of the decay K(L) --> e+ e- mu+ mu-

Losses from the proton and antiproton beams of the Fermilab Tevatron have been shown to produce a halo which contribute to backgrounds to physics signals in the Collider Detector at Fermilab (CDF). To provide a measure of the beam halo and losses, we have installed arrays of scintillation counters on both sides of the CDF detector. We describe here the physical configuration of these counters, their implementation and performance within the Fermilab Accelerator Control Network (ACNET). We show correlations between these new devices and the accelerator operating conditions. We point out that the use of these monitors is leading to improvement in the accelerator operations and reduced backgrounds in CDF.

Beam halo monitoring at CDF

We report on the analysis of the rare decay K{sub L}{yields}{mu}{sup +}{mu}{sup -}{gamma} the 1997 data from the KTeV experiment at Fermilab. A total of 9327 candidate events are observed with 2.4% background, representing a factor of 40 increase in statistics over the current world sample. We find that B(K{sub L}{yields}{mu}{sup +}{mu}{sup -}{gamma})=(3.62{+-}0.04{sub stat}{+-}0.08{sub syst}) x 10{sup -7}. The form factor parameter {alpha}{sub K{sup *}} is measured to be {alpha}{sub K{sup *}}=-0.160{sup +0.026}{sub -0.028}. In addition, we make the first measurement of the parameter {alpha} from the D'Ambrosio-Isidori-Portoles form factor, finding {alpha}=-1.54{+-}0.10. In that model, this {alpha} measurement limits the Cabibbo-Kobayashi-Maskawa parameter {rho}>-0.2.

Measurement of the branching ratio and form factor of K(L)-->mu(+)mu(-)gamma.

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Measurement of the branching ratio and form factor of K(L)-->mu(+)mu(-)gamma.