We present precise tests of CP and CPT symmetry based on the full dataset of K to pipi decays collected by the KTeV experiment at Fermi National Accelerator Laboratory during 1996, 1997, and 1999. ...This dataset contains 16 million K to 2pi0 and 69 million K to pi+pi- decays. We measure the direct CP violation parameter Re(epsilon'/epsilon) = (19.2 pm 2.1)x10-4. We find the KL-KS mass difference Deltam = (5270 pm 12)x10^6 hbar/s and the KS lifetime tauS = (89.62 pm 0.05)x10-12 s. We also measure several parameters that test CPT invariance. We find the difference between the phase of the indirect CP violation parameter, epsilon, and the superweak phase, phi_epsilon - phi_SW = (0.40 pm 0.56) degrees. We measure the difference of the relative phases between the CP violating and CP conserving decay amplitudes for K to pi+pi- (phi+-) and for K to 2pi0 (phi00), Delta phi = (0.30 pm 0.35) degrees. From these phase measurements, we place a limit on the mass difference between K0 and K0bar, DeltaM < 4.8 x 10-19 GeV/c^2 at 95% C.L. These results are consistent with those of other experiments, our own earlier measurements, and CPT symmetry.
We consider an alternative explanation for the deficit of nu sub(e) in Ga solar neutrino calibration experiments and of the nu sub(e) in short-baseline reactor experiments by a model where neutrinos ...can oscillate into sterile Kaluza-Klein modes that can propagate in compactified submicrometer flat extra dimensions. We have analyzed the results of the gallium radioactive source experiments and 19 reactor experiments with baseline shorter than 100 m, and showed that these data can be fit into this scenario. The values of the lightest neutrino mass and of the size of the largest extra dimension that are compatible with these experiments are mostly not excluded by other neutrino oscillation experiments.
We report the first observation of two Cabibbo-suppressed decay modes, Ξc+→Σ+π−π+ and Ξc+→Σ−π+π+. We observe 59±14 over a background of 87, and 22±8 over a background of 13 events, respectively, for ...the signals. The data were accumulated using the SELEX spectrometer during the 1996–1997 fixed target run at Fermilab, chiefly from a 600GeV/cΣ− beam. The branching ratios of the decays relative to the Cabibbo-favored Ξc+→Ξ−π+π+ are measured to be B(Ξc+→Σ+π−π+)/B(Ξc+→Ξ−π+π+)=0.48±0.20, and B(Ξc+→Σ−π+π+)/B(Ξc+→Ξ−π+π+)=0.18±0.09, respectively. We also report branching ratios for the same decay modes of the Λc+ relative to Λc+→pK−π+.
We present a measurement of \(B(\pi^0 \rightarrow e^+e^- \gamma)/B(\pi^0 \rightarrow \gamma\gamma)\), the Dalitz branching ratio, using data taken in 1999 by the E832 KTeV experiment at Fermi ...National Accelerator Laboratory. We use neutral pions from fully reconstructed \(K_L\) decays in flight; the measurement is based on about 60 thousand \(K_L \rightarrow \pi^0\pi^0\pi^0 \rightarrow \gamma\gamma~\gamma\gamma~e^+e^-\gamma\) decays. We normalize to \(K_L \rightarrow \pi^0\pi^0\pi^0 \rightarrow 6\gamma\) decays. We find \(B(\pi^0 \rightarrow e^+e^- \gamma)/B(\pi^0 \rightarrow \gamma\gamma)\) \((m_{e^+e^-}\) > 15 MeV/\(c^2)\) = \(3.920 \pm 0.016(stat) \pm 0.036 (syst) \times 10^{-3}\). Using the Mikaelian and Smith prediction for the \(e^+e^-\) mass spectrum, we correct the result to the full \(e^+e^-\) mass range. The corrected result is \(B(\pi^0 \rightarrow e^+e^- \gamma)/B(\pi^0 \rightarrow \gamma\gamma) = 1.1559 \pm 0.0047(stat) \pm 0.0106 (syst)\)%. This result is consistent with previous measurements and the uncertainty is a factor of three smaller than any previous measurement.
The KTeV E799 experiment has conducted a search for the rare decay \(K_{L}\to\pi^{0}\pi^{0}\gamma\) via the topology \(K_{L}\to\pi^{0}\pi^{0}_D\gamma\) (where \(\pi^0_D\to\gamma e^+e^-\)). Due to ...Bose statistics of the \(\pi^0\) pair and the real nature of the photon, the \(K_{L}\to\pi^{0}\pi^{0}\gamma\) decay is restricted to proceed at lowest order by the CP conserving direct emission (DE) of an E2 electric quadrupole photon. The rate of this decay is interesting theoretically since chiral perturbation theory predicts that this process vanishes at level \(O(p^4)\). Therefore, this mode probes chiral perturbation theory at \(O(p^6)\). In this paper we report a determination of an upper limit of \(2.43\times 10^{-7}\) (90% CL) for \(K_{L}\to\pi^{0}\pi^{0}\gamma\). This is approximately a factor of 20 lower than previous results.
We report on a new measurement of the branching ratio B(KL->pi0 gamma gamma)using the KTeV detector. We reconstruct 1982 events with an estimated background of 608, that results in B(KL -> pi0 gamma ...gamma) = (1.29 +/- 0.03(stat) +/- 0.05(syst)) x 10**-6. We also measure the parameter, aV, which characterizes the strength of vector meson exchange terms in this decay. We find aV = -0.31 +/- 0.05(stat) +/- 0.07(syst). These results utilize the full KTeV data set collected from 1997 to 2000 and supersede earlier KTeV measurements of the branching ratio and aV.
We present a new determination of the parity of the neutral pion via the double Dalitz decay pi^0 -> e+ e- e+ e-. Our sample, which consists of 30511 candidate decays, was collected from K_L -> pi0 ...pi0 pi0 decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative pi^0 parity, and place a limit on scalar contributions to the pi^0 -> e+ e- e+ e- decay amplitude of less than 3.3% assuming CPT conservation. The pi^0 gamma* gamma* form factor is well described by a momentum-dependent model with a slope parameter fit to the final state phase space distribution. Additionally, we have measured the branching ratio of this mode to be B(pi^0 -> e+ e- e+ e-) = (3.26 +- 0.18) x 10^(-5).
We report on a new measurement of the branching ratio B(KL -> pi0 e+ e- gamma) using the KTeV detector. This analysis uses the full KTeV data set collected from 1997 to 2000. We reconstruct 139 ...events over a background of 14, which results in B(KL -> pi0 e+ e- gamma) = (1.62 +/- 0.14 (stat) +/- 0.09 (syst)) x 10^{-8}. This result supersedes the earlier KTeV measurement of this branching ratio.
Coherent Λπ− production on Pb of 600 GeV Σ− hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width ...ΓΣ(1385)−→Σ−γ<9.5 keV, and estimate the cross section for γΣ−→Λπ− at s≈1.385 GeV to be 56±16 μb.
We study the constraints that electroweak precision data can impose, after the discovery of the Higgs boson by the LHC, on neutrinophilic two-Higgs-doublet models which comprise one extra ...\(SU(2)\times U(1)\) doublet and a new symmetry, namely a spontaneously broken \(\mathbb{Z}_2\) or a softly broken global \(U(1)\). In these models the extra Higgs doublet, via its very small vacuum expectation value, is the sole responsible for neutrino masses. We find that the model with a \(\mathbb{Z}_2\) symmetry is basically ruled out by electroweak precision data, even if the model is slightly extended to include extra right-handed neutrinos, due to the presence of a very light scalar. While the other model is still perfectly viable, the parameter space is considerably constrained by current data, specially by the \(T\) parameter. In particular, the new charged and neutral scalars must have very similar masses.
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