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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2014). Evidence for the baryonic decay (B)over-bar(0) -> D-0 Lambda(Lambda)over-bar. Phys. Rev. D, 89(11), 112002–9pp.
Abstract: Evidence is presented for the baryonic B meson decay (B) over bar (0) -> (B) over bar (0)Lambda(Lambda) over bar based on a data sample of 471 x 10(6) B (B) over bar pairs collected with the BABAR detector at the PEP-II asymmetric e(+)e(-) collider located at the SLAC National Accelerator Laboratory. The branching fraction is determined to be B((B) over bar (0) -> (B) over bar (0)Lambda(Lambda) over bar) = (9.8(-2.6)(+2.9) +/- 1.9) x 10(-6), corresponding to a significance of 3.4 standard deviations including additive systematic uncertainties. A search for the related baryonic B meson decay (B) over bar (0) -> D-0 Sigma(0)(Lambda) over bar (0) with Sigma(0) -> Lambda gamma is performed and an upper limit B((B)over bar>(0) -> D-0 Sigma(0)(Lambda) over bar + (B)over bar>(0) -> D-0 Lambda(Sigma) over bar (0)) < 3.1 x 10(-5) is determined at 90% confidence level.
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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). Flavor tagged time-dependent angular analysis of the B-s(0) -> J/psi phi decay and extraction of Delta Gamma(s) and the weak phase phi(s) in ATLAS. Phys. Rev. D, 90(5), 052007–26pp.
Abstract: A measurement of the B-s(0) -> J/psi phi decay parameters, updated to include flavor tagging is reported using 4.9 fb(-1) of integrated luminosity collected by the ATLAS detector from root s = 7 TeV pp collisions recorded in 2011 at the LHC. The values measured for the physical parameters are phi(s) = 0.12 +/- 0.25(stat) +/- 0.05(syst) rad Delta Gamma(s) = 0.053 +/- 0.021(stat) +/- 0.010(syst) ps(-1) Gamma(s) = 0.677 +/- 0.007(stat) +/- 0.004(syst) ps(-1) vertical bar A(parallel to)(0)vertical bar(2) = 0.220 +/- 0.008(stat) +/- 0.009(syst) vertical bar A(0)(0)vertical bar(2) = 0.529 +/- 0.006(stat) +/- 0.012(syst) delta(perpendicular to) = 3.89 +/- 0.47(stat) +/- 0.11(syst) rad where the parameter Delta Gamma(s) is constrained to be positive. The S-wave contribution was measured and found to be compatible with zero. Results for phi(s) and Delta Gamma(s) are also presented as 68% and 95% likelihood contours, which show agreement with the Standard Model expectations.
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Aguilar, A. C., Binosi, D., Ibañez, D., & Papavassiliou, J. (2014). New method for determining the quark-gluon vertex. Phys. Rev. D, 90(6), 065027–26pp.
Abstract: We present a novel nonperturbative approach for calculating the form factors of the quark-gluon vertex in terms of an unknown three-point function, in the Landau gauge. The key ingredient of this method is the exact all-order relation connecting the conventional quark-gluon vertex with the corresponding vertex of the background field method, which is Abelian-like. When this latter relation is combined with the standard gauge technique, supplemented by a crucial set of transverse Ward identities, it allows the approximate determination of the nonperturbative behavior of all 12 form factors comprising the quark-gluon vertex, for arbitrary values of the momenta. The actual implementation of this procedure is carried out in the Landau gauge, in order to make contact with the results of lattice simulations performed in this particular gauge. The most demanding technical aspect involves the approximate calculation of the components of the aforementioned (fully dressed) three-point function, using lattice data as input for the gluon propagators appearing in its diagrammatic expansion. The numerical evaluation of the relevant form factors in three special kinematical configurations (soft-gluon and quark symmetric limit, zero quark momentum) is carried out in detail, finding qualitative agreement with the available lattice data. Most notably, a concrete mechanism is proposed for explaining the puzzling divergence of one of these form factors observed in lattice simulations.
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Barranco, L., Boubekeur, L., & Mena, O. (2014). Model-independent fit to Planck and BICEP2 data. Phys. Rev. D, 90(6), 063007–7pp.
Abstract: Inflation is the leading theory to describe elegantly the initial conditions that led to structure formation in our Universe. In this paper, we present a novel phenomenological fit to the Planck, WMAP polarization (WP) and the BICEP2 data sets using an alternative parametrization. Instead of starting from inflationary potentials and computing the inflationary observables, we use a phenomenological parametrization due to Mukhanov, describing inflation by an effective equation of state, in terms of the number of e-folds and two phenomenological parameters alpha and beta. Within such a parametrization, which captures the different inflationary models in a model-independent way, the values of the scalar spectral index n(s), its running and the tensor-to-scalar ratio r are predicted, given a set of parameters (alpha, beta). We perform a Markov Chain Monte Carlo analysis of these parameters, and we show that the combined analysis of Planck and WP data favors the Starobinsky and Higgs inflation scenarios. Assuming that the BICEP2 signal is not entirely due to foregrounds, the addition of this last data set prefers instead the phi(2) chaotic models. The constraint we get from Planck and WP data alone on the derived tensor-to-scalar ratio is r < 0.18 at 95% C.L., value which is consistent with the one quoted from the BICEP2 Collaboration analysis, r = 0.16(-0.05)(+0-06), after foreground subtraction. This is not necessarily at odds with the 2 sigma tension found between Planck and BICEP2 measurements when analyzing data in terms of the usual n(s) and r parameters, given that the parametrization used here, for the preferred value n(s) similar or equal to 0.96, allows only for a restricted parameter space in the usual (n(s), r) plane.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Search for pair-produced third-generation squarks decaying via charm quarks or in compressed supersymmetric scenarios in pp collisions at root s = 8 TeV with the ATLAS detector. Phys. Rev. D, 90(5), 052008–36pp.
Abstract: Results of a search for supersymmetry via direct production of third-generation squarks are reported, using 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV recorded by the ATLAS experiment at the LHC in 2012. Two different analysis strategies based on monojetlike and c-tagged event selections are carried out to optimize the sensitivity for direct top squark-pair production in the decay channel to a charm quark and the lightest neutralino ((t) over tilde (1) -> c + (chi) over tilde (0)(1)) across the top squark-neutralino mass parameter space. No excess above the Standard Model background expectation is observed. The results are interpreted in the context of direct pair production of top squarks and presented in terms of exclusion limits in the (m((t) over tilde1), m((chi) over tilde 10)) parameter space. A top squark of mass up to about 240 GeV is excluded at 95% confidence level for arbitrary neutralino masses, within the kinematic boundaries. Top squark masses up to 270 GeV are excluded for a neutralino mass of 200 GeV. In a scenario where the top squark and the lightest neutralino are nearly degenerate in mass, top squark masses up to 260 GeV are excluded. The results from the monojetlike analysis are also interpreted in terms of compressed scenarios for top squark-pair production in the decay channel (t) over tilde (1) -> b + ff' + (chi) over tilde (0)(1) and sbottom pair production with (b) over tilde -> b + (chi) over tilde (0)(1), leading to a similar exclusion for nearly mass-degenerate third-generation squarks and the lightest neutralino. The results in this paper significantly extend previous results at colliders.
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Boucenna, M. S., Morisi, S., Shafi, Q., & Valle, J. W. F. (2014). Inflation and majoron dark matter in the neutrino seesaw mechanism. Phys. Rev. D, 90(5), 055023–6pp.
Abstract: We propose that inflation and dark matter have a common origin, connected to the neutrino mass generation scheme. As a model we consider spontaneous breaking of global lepton number within the seesaw mechanism. We show that it provides an acceptable inflationary scenario consistent with the recent cosmic microwave background B-mode observation by the BICEP2 experiment. The scheme may also account for the baryon asymmetry of the Universe through leptogenesis for reasonable parameter choices.
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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 high-mass dilepton resonances in pp collisions at root s = 8 TeV with the ATLAS detector. Phys. Rev. D, 90(5), 052005–30pp.
Abstract: The ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to dielectron or dimuon final states. Results are presented from an analysis of proton-proton (pp) collisions at a center-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb(-1) in the dimuon channel. A narrow resonance with Standard Model Z couplings to fermions is excluded at 95% confidence level for masses less than 2.79 TeV in the dielectron channel, 2.53 TeV in the dimuon channel, and 2.90 TeV in the two channels combined. Limits on other model interpretations are also presented, including a grand-unification model based on the E-6 gauge group, Z* bosons, minimal Z' models, a spin-2 graviton excitation from Randall-Sundrum models, quantum black holes, and a minimal walking technicolor model with a composite Higgs boson.
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Ruiz-Femenia, P. (2014). First estimate of the NNLO nonresonant corrections to top-antitop threshold production at lepton colliders. Phys. Rev. D, 89(9), 097501–4pp.
Abstract: We compute the dominant term in the expansion in rho = 1 – M-w/m(t) of the unknown next-to-next-to-leading order nonresonant contributions to the e+ e(-) -> W+ W- b (b) over bar total cross section at energies close to the top-antitop threshold. Our analytic result disagrees with a previous calculation by other authors [A. A. Penin and J. H. Piclum, J. High Energy Phys. 01 (2012) 034]. We show that our determination has the correct infrared structure needed to cancel the divergences proportional to the top width arising in the resonant production of the same final state, and we point to a missing contribution in the computation of Penin and Piclum to explain the discrepancy.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of CP violation in B-s(0) ->Phi Phi decays. Phys. Rev. D, 90(5), 052011–17pp.
Abstract: A measurement of the decay time-dependent CP-violating asymmetry in B-s(0) -> phi phi decays is presented, along with measurements of the T-odd triple-product asymmetries. In this decay channel, the CP-violating weak phase arises from the interference between B-s(0) -(B) over bar (0)(s) mixing and the loop-induced decay amplitude. Using a sample of proton-proton collision data corresponding to an integrated luminosity of 3.0 fb(-1) collected with the LHCb detector, a signal yield of approximately 4000 B-s(0) -> phi phi decays is obtained. The CP-violating phase is measured to be phi(s) = -0.17 +/- 0.15(stat) +/- 0.03(syst) rad. The triple-product asymmetries are measured to be A(U) = -0.003 +/- 0.017(stat) +/- 0.006(syst) and A(V) = -0.017 +/- 0.017(stat) +/- 0.006(syst). Results are consistent with the hypothesis of CP conservation.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2014). Measurement of the inclusive nu(mu) charged current cross section on iron and hydrocarbon in the T2K on-axis neutrino beam. Phys. Rev. D, 90(5), 052010–15pp.
Abstract: We report a measurement of the nu(mu) inclusive charged current cross sections on iron and hydrocarbon in the Tokai-to-Kamioka (T2K) on-axis neutrino beam. The measured inclusive charged current cross sections on iron and hydrocarbon averaged over the T2K on-axis flux with a mean neutrino energy of 1.51 GeVare (1.444 +/- 0.002(stat)(-0.157)(+0.189)- (syst)) x 10(-38) cm(2)/ nucleon and (1.379 +/- 0.009(stat)(-0.147)(+0.178) (syst)) x 10(-38) 38 cm(2)/ nucleon, respectively, and their cross-section ratio is 1.047 +/- 0.007(stat) +/- 0.035(syst). These results agree well with the predictions of the neutrino interaction model, and thus we checked the correct treatment of the nuclear effect for iron and hydrocarbon targets in the model within the measurement precisions.
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