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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2014). Observation of Electron Neutrino Appearance in a Muon Neutrino Beam. Phys. Rev. Lett., 112(6), 061802–8pp.
Abstract: The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, corresponding to a significance of 7.3 sigma when compared to 4.92 +/- 0.55 expected background events. In the Pontecorvo-Maki-Nakagawa-Sakata mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles theta(12), theta(23), theta(13), a mass difference vertical bar Delta m(32)(2)vertical bar and a CP violating phase delta(CP). In this neutrino oscillation scenario, assuming vertical bar Delta m(32)(2)vertical bar = 2.4 x 10(-3) eV(2), sin theta(2)(23) = 0.5, and vertical bar Delta m(32)(2)vertical bar > 0 (vertical bar Delta m(32)(2)vertical bar < 0), a best- fit value of sin2 theta(2)(13) = 0.140(- 0.032)(+0.038) (0.170(-0.037)(+0.045)) is obtained at delta(CP) = 0. When combining the result with the current best knowledge of oscillation parameters including the world average value of theta(13) from reactor experiments, some values of delta(CP) are disfavored at the 90% C. L.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Search for Quantum Black Hole Production in High-Invariant-Mass Lepton plus Jet Final States Using pp Collisions at root s=8 TeV and the ATLAS Detector. Phys. Rev. Lett., 112(9), 091804–18pp.
Abstract: This Letter presents a search for quantum black-hole production using 20.3 fb(-1) of data collected with the ATLAS detector in pp collisions at the LHC at root s = 8 TeV. The quantum black holes are assumed to decay into a final state characterized by a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton + jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black holes with threshold mass above 3.5 TeV is 0.18 fb. This limit constrains the threshold quantum black-hole mass to be above 5.3 TeV in the model considered.
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Fujita, Y. et al, Algora, A., Estevez-Aguado, E., Molina, F., & Rubio, B. (2014). Observation of Low- and High-Energy Gamow-Teller Phonon Excitations in Nuclei. Phys. Rev. Lett., 112(11), 112502–5pp.
Abstract: Gamow-Teller (GT) transitions in atomic nuclei are sensitive to both nuclear shell structure and effective residual interactions. The nuclear GT excitations were studied for the mass number A = 42, 46, 50, and 54 “f-shell” nuclei in (He-3, t) charge-exchange reactions. In the Ca-42 -> Sc-42 reaction, most of the GT strength is concentrated in the lowest excited state at 0.6 MeV, suggesting the existence of a low-energy GT phonon excitation. As A increases, a high-energy GT phonon excitation develops in the 6-11 MeV region. In the Fe-54 -> Co-54 reaction, the high-energy GT phonon excitation mainly carries the GT strength. The existence of these two GT phonon excitations are attributed to the 2 fermionic degrees of freedom in nuclei.
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Taprogge, J. et al, Gadea, A., & Montaner-Piza, A. (2014). 1p(3/2) Proton-Hole State in Sn-132 and the Shell Structure Along N=82. Phys. Rev. Lett., 112(13), 132501–6pp.
Abstract: A low-lying state in In-131(82), the one-proton hole nucleus with respect to double magic Sn-132, was observed by its gamma decay to the I-pi 1/2(-) beta-emitting isomer. We identify the new state at an excitation energy of E-x = 1353 keV, which was populated both in the beta decay of Cd-131(83) and after beta-delayed neutron emission from Cd-132(84), as the previously unknown pi p(3/2) single-hole state with respect to the Sn-132 core. Exploiting this crucial new experimental information, shell-model calculations were performed to study the structure of experimentally inaccessible N = 82 isotones below Sn-132. The results evidence a surprising absence of proton subshell closures along the chain of N = 82 isotones. The consequences of this finding for the evolution of the N = 82 shell gap along the r-process path are discussed.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Study of Beauty Hadron Decays into Pairs of Charm Hadrons. Phys. Rev. Lett., 112(20), 202001–9pp.
Abstract: First observations of the decays A(b)(0) -> A(c)(+)D((s))(-) are reported using data corresponding to an integrated luminosity of 3 fb(-1) collected at 7 and 8 TeV center-of- ass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction B(B-s(0) -> D+Ds-) is made and a search is performed for the decays B-0((s)) -> A(c)(+)A(c)(-). The results obtained are B(A(b)(0) -> A(c)(+)D(-))/B(A(b)(0) -> A(c)(+)D(s)(-)) = 0.042 +/- 0.003 (stat) +/- 0.003 (syst), [B(A(b)(0) -> A(c)(+)D(s)(-))/B((B) over bar (0) -> D+Ds-)]/[B(A(b)(0) -> A(c)(+)pi(-))/B((B) over bar (0) -> D+pi(-))] = 0.96 +/- 0.02 (stat) +/- 0.06 (syst), B(B-s(0) -> D+Ds-)/B((B) over bar (0) -> D+Ds-) = 0.038 +/- 0.004 (stat) +/- (syst), B((B) over bar (0) -> A(c)(+)A(c)(-))/B((B) over bar (0) -> D+Ds-) < 0.0022[95% C.L.], B(B-s(0) -> A(c)(+)A(c)(-)) /B(B-s(0) -> D+Ds-) < 0.30[95% C.L.]. Measurement of the mass of the A(b)(0) baryon relative to the (B) over bar (0) meson gives M(A(b)(0)) – M((B) over bar (0)) = 339.72 +/- 0.24 (stat) +/- 0.18 (syst) MeV/c(2). This result provides the most precise measurement of the mass of the A(b)(0) baryon to date.
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