ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 09(9), 015–51pp.
Abstract: The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1 fb(-1) of proton-proton collision data at = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via or , where denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fully-hadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of . For a branching fraction of 100%, top squark masses in the range 270-645 GeV are excluded for masses below 30 GeV. For a branching fraction of 50% to either or , and assuming the mass to be twice the mass, top squark masses in the range 250-550 GeV are excluded for masses below 60 GeV.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Dalitz plot analysis of B-s(0) -> (D)over-bar(0)K(-)pi(+) decays. Phys. Rev. D, 90(7), 072003–29pp.
Abstract: The resonant substructure of B-s(0) -> (D) over bar K-0(-)pi(+) decays is studied with the Dalitz plot analysis technique. The study is based on a data sample corresponding to an integrated luminosity of 3.0 fb(-1) of pp collision data recorded by LHCb. A structure at m((D) over bar K-0(-)) approximate to 2.86 GeV/c(2) is found to be an admixture of spin-1 and spin-3 resonances. The masses and widths of these states and of the D-s2*(2573)(-) meson are measured, as are the complex amplitudes and fit fractions for all the (D) over bar K-0(-) and K-pi(-) components included in the amplitude model. In addition, the D-s2*(2573)(-) resonance is confirmed to be spin 2.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Observation of Overlapping Spin-1 and Spin-3 (D)over-bar(0) K(-) Resonances at Mass 2.86 GeV/c(2). Phys. Rev. Lett., 113(16), 162001–9pp.
Abstract: The resonant substructure of B-s(0) -> (D) over bar K-0(-)pi(+) decays is studied using a data sample corresponding to an integrated luminosity of 3.0 fb(-1) of pp collision data recorded by the LHCb detector. An excess at m((D) over bar K-0(-)) approximate to 2.86 GeV/c(2) is found to be an admixture of spin-1 and spin-3 resonances. Therefore, the D-sJ*(2860)(-) state previously observed in inclusive e(+)e(-) -> (D) over bar (K-X)-K-0 and pp -> (D) over bar (K-X)-K-0 processes consists of at least two particles. This is the first observation of a heavy flavored spin-3 resonance, and the first time that any spin-3 particle has been seen to be produced in B decays. The masses and widths of the new states and of the D-s2*(2573)(-) meson are measured, giving the most precise determinations to date.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of the resonant and CP components in (B)over-bar(0) -> J/psi pi(+)pi(-) decays. Phys. Rev. D, 90(1), 012003–21pp.
Abstract: The resonant structure of the reaction (B) over bar (0) --> J/psi pi(+)pi(-) is studied using data from 3 fb(-1) of integrated luminosity collected by the LHCb experiment, one third at 7 TeV center-of-mass energy and the remainder at 8 TeV. The invariant mass of the pi(+)pi(-) pair and three decay angular distributions are used to determine the fractions of the resonant and nonresonant components. Six interfering pi(+)pi(-) states, rho(770), f(0)(500), f(2)(1270), rho(1450), omega(782) and rho(1700), are required to give a good description of invariant mass spectra and decay angular distributions. The positive and negative charge parity fractions of each of the resonant final states are determined. The f(0)(980) meson is not seen and the upper limit on its presence, compared with the observed f(0)(500) rate, is inconsistent with a model where these scalar mesons are formed from two quarks and two antiquarks (tetraquarks) at the eight standard deviation level. In the q (q) over bar model, the absolute value of the mixing angle between the f(0)(980) and the f(0)(500) scalar mesons is limited to be less than 17 degrees at 90% confidence level.
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Marchi, T. et al, & Gadea, A. (2014). Quadrupole Transition Strength in the Ni-74 Nucleus and Core Polarization Effects in the Neutron-Rich Ni Isotopes. Phys. Rev. Lett., 113(18), 182501–5pp.
Abstract: The reduced transition probability B(E2;0(+) -> 2(+)) has been measured for the neutron-rich nucleus Ni-74 in an intermediate energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory at Michigan State University. The obtained B(E2;0(+) -> 2(+)) = 642(-226)(+216) e(2) fm(4) value defines a trend which is unexpectedly small if referred to Ni-70 and to a previous indirect determination of the transition strength in Ni-74. This indicates a reduced polarization of the Z = 28 core by the valence neutrons. Calculations in the pfgd model space reproduce well the experimental result indicating that the B(E2) strength predominantly corresponds to neutron excitations. The ratio of the neutron and proton multipole matrix elements supports such an interpretation.
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