Tain, J. L. et al, Valencia, E., Algora, A., Agramunt, J., Rubio, B., Estevez, E., et al. (2015). Enhanced gamma-Ray Emission from Neutron Unbound States Populated in beta Decay. Phys. Rev. Lett., 115(6), 062502–5pp.
Abstract: Total absorption spectroscopy is used to investigate the beta-decay intensity to states above the neutron separation energy followed by gamma-ray emission in Br-87,Br-88 and Rb-94. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large. intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The gamma branching as a function of excitation energy is compared to Hauser-Feshbach model calculations. For Br-87 and Br-88 the gamma branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daughter can only decay through the emission of a large orbital angular momentum neutron with a strongly reduced barrier penetrability. In the case of neutron-rich Rb-94 the observed 4.5% branching is much larger than the calculations performed with standard nuclear statistical model parameters, even after proper correction for fluctuation effects on individual transition widths. The difference can be reconciled by introducing an enhancement of 1 order of magnitude in the photon strength to neutron strength ratio. An increase in the photon strength function of such magnitude for very neutron-rich nuclei, if it proves to be correct, leads to a similar increase in the (n, gamma) cross section that would have an impact on r process abundance calculations.
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Garcia Soto, A., Zhelnin, P., Safa, I., & Arguelles, C. A. (2022). Tau Appearance from High-Energy Neutrino Interactions. Phys. Rev. Lett., 128(17), 171101–7pp.
Abstract: High-energy muon and electron neutrinos yield a non-negligible flux of tau neutrinos as they propagate through Earth. In this Letter, we address the impact of this additional component in the PeV and EeV energy regimes for the first time. Above 300 TeV, this contribution is predicted to be significantly larger than the atmospheric background, and it alters current and future neutrino telescopes' capabilities to discover a cosmic tau-neutrino flux. Further, we demonstrate that Earth-skimming neutrino experiments, designed to observe tau neutrinos, will be sensitive to cosmogenic neutrinos even in extreme scenarios without a primary tau-neutrino component.
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Simpson, G. S. et al, & Montaner-Piza, A. (2014). Yrast 6(+) Seniority Isomers of Sn-136,Sn-138. Phys. Rev. Lett., 113(13), 132502–6pp.
Abstract: Delayed gamma-ray cascades, originating from the decay of (6(+)) isomeric states, in the very neutron-rich, semimagic isotopes Sn-136,Sn-138 have been observed following the projectile fission of a U-238 beam at RIBF, RIKEN. The wave functions of these isomeric states are proposed to be predominantly a fully aligned pair of f(7/2) neutrons. Shell-model calculations, performed using a realistic effective interaction, reproduce well the energies of the excited states of these nuclei and the measured transition rates, with the exception of the B(E2; 6(+) -> 4(+)) rate of Sn-136, which deviates from a simple seniority scheme. Empirically reducing the nu f(7/2)(2) orbit matrix elements produces a 4(1)(+) state with almost equal seniority 2 and 4 components, correctly reproducing the experimental B(E2; 6(+) -> 4(+)) rate of Sn-136. These data provide a key benchmark for shell-model interactions far from stability.
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BABAR Collaboration(del Amo Sanchez, P. et al), Lopez-March, N., Martinez-Vidal, F., & Oyanguren, A. (2011). Search for Production of Invisible Final States in Single-Photon Decays of Gamma(1S). Phys. Rev. Lett., 107(2), 021804–7pp.
Abstract: We search for single-photon decays of the Gamma(1S) resonance, Gamma -> gamma + invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson A(0), or a pair of dark matter particles, chi(chi) over bar. Both A(0) and chi are assumed to have zero spin. We tag Gamma(1S) decays with a dipion transition Gamma(1S) -> pi(+)pi(-)Y(1S) and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range m(A0) <= 9.2 GeV and m(chi) <= 4.5 GeV in the sample of 98 x 10(6) Gamma(2S) decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states.
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BABAR Collaboration(del Amo Sanchez, P. et al), Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2011). Observation of the Decay B- -> D_s(*) K- l- nu(bar). Phys. Rev. Lett., 107(4), 041804–8pp.
Abstract: We report the observation of the decay B(-) -> D(s)(()*()+)K(-)l(-)(nu) over bar (l) based on 342 fb(-1) of data collected at the Y(4S) resonance with the BABAR detector at the PEP-II e(+)e(-) storage rings at SLAC. A simultaneous fit to three D(s)(+) decay chains is performed to extract the signal yield from measurements of the squared missing mass in the B meson decay. We observe the decay B(-) -> D(s)(()*()+)K(-)l(-)(nu) over bar (l) with a significance greater than 5 standard deviations (including systematic uncertainties) and measure its branching fraction to be B(B(-) -> D(s)(()*())K(-)l(-)(nu) over bar (l) = [6.13(-1.03)(+1.04)(stat) +/- 0.43(syst) +/- 0.51 (B(D(s)))] X 10(-4), where the last error reflects the limited knowledge of the D(s) branching fractions.
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