ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2015). Search for s-channel single top-quark production in proton-proton collisions at root s=8 TeV with the ATLAS detector. Phys. Lett. B, 740, 118–136.
Abstract: This Letter presents a search at the LHC for s-channel single top-quark production in proton-proton collisions at a centre-of-mass energy of 8 TeV. The analyzed data set was recorded by the ATLAS detector and corresponds to an integrated luminosity of 20.3 fb(-1). Selected events contain one charged lepton, large missing transverse momentum and exactly two b-tagged jets. A multivariate event classifier based on boosted decision trees is developed to discriminate s-channel single top-quark events from the main background contributions. The signal extraction is based on a binned maximum-likelihood fit of the output classifier distribution. The analysis leads to an upper limit on the s-channel single topquark production cross-section of 14.6 pb at the 95% confidence level. The fit gives a cross-section of sigma(s) = 5.0 +/- 4.3 pb, consistent with the Standard Model expectation.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Search for CP violation in D-0 -> pi(-)pi(+)pi(0) decays with the energy test. Phys. Lett. B, 740, 158–167.
Abstract: A search for time-integrated CP violation in the Cabibbo-suppressed decay D-0 -> pi(-)pi(+)pi(0) ir is performed using for the first time an unbinned model-independent technique known as the energy test. Using proton-proton collision data, corresponding to an integrated luminosity of 2.0 fb(-1) collected by the LHCb detector at a centre-of-mass energy of root s = 8 TeV, the world's best sensitivity to CP violation in this decay is obtained. The data are found to be consistent with the hypothesis of CP symmetry with a p-value of (2.6 +/- 0.5)%.
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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. (2015). Search for the X-b and other hidden-beauty states in the pi(+)pi(-)gamma(1S) channel at ATLAS. Phys. Lett. B, 740, 199–217.
Abstract: This Letter presents a search for a hidden-beauty counterpart of the X(3872) in the mass ranges of 10.05-10.31 GeV and 10.40-11.00 GeV, in the channel X-b -> pi(+)pi(-)gamma(1S)(-> mu(+)mu(-)), using 16.2 fb(-1) of root s = 8 TeV pp collision data collected by the ATLAS detector at the LHC. No evidence for new narrow states is found, and upper limits are set on the product of the Xb cross section and branching fraction, relative to those of the gamma(25), at the 95% confidence level using the CLs approach. These limits range from 0.8% to 4.0%, depending on mass. For masses above 10.1 GeV, the expected upper limits from this analysis are the most restrictive to date. Searches for production of the gamma(1(3)D(J)), gamma(10860), and gamma(11 020) states also reveal no significant signals.
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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. (2015). Search for H -> gamma gamma produced in association with top quarks and constraints on the Yukawa coupling between the top quark and the Higgs boson using data taken at 7 TeV and 8 TeV with the ATLAS detector. Phys. Lett. B, 740, 222–242.
Abstract: A search is performed for Higgs bosons produced in association with top quarks using the diphoton decay mode of the Higgs boson. Selection requirements are optimized separately for leptonic and fully hadronic final states from the top quark decays. The dataset used corresponds to an integrated luminosity of 4.5 fb(-1) of proton-proton collisions at a center-of-mass energy of 7 TeV and 20.3 fb(-1) at 8 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess over the background prediction is observed and upper limits are set on the ttH production cross section. The observed exclusion upper limit at 95% confidence level is 6.7 times the predicted Standard Model cross section value. In addition, limits are set on the strength of the Yukawa coupling between the top quark and the Higgs boson, taking into account the dependence of the ttH and tH cross sections as well as the H -> gamma gamma branching fraction on the Yukawa coupling. Lower and upper limits at 95% confidence level are set at 1.3 and +8.0 times the Yukawa coupling strength in the Standard Model.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Determination of gamma and-2 beta(s) from charmless two-body decays of beauty mesons. Phys. Lett. B, 741, 1–11.
Abstract: Using the latest LHCb measurements of time-dependent CP violation in the B-s(0) -> K+K- decay, a U-spin relation between the decay amplitudes of B-s(0) -> K+K- and B-0 -> p(+)p(-) decay processes allows constraints to be placed on the angle gamma of the unitarity triangle and on the B-s(0) mixing phase -2 beta(s). Results from an extended approach, which uses additional inputs on B-0 -> pi(0)pi(0) and B+ -> pi(+)pi(0) decays from other experiments and exploits isospin symmetry, are also presented. The dependence of the results on the maximum allowed amount of U-spin breaking is studied. At 68% probability, the value gamma =( 63.5(-6.7)(+7.2))degrees modulo 180 degrees is determined. In an alternative analysis, the value -2 beta(s)= – 0.12(-0.16)(+ 0.14) rad is found. In both measurements, the uncertainties due to U-spin breaking effects up to 50% are included.
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Celis, A., Fuentes-Martin, J., & Serodio, H. (2015). An invisible axion model with controlled FCNCs at tree level. Phys. Lett. B, 741, 117–123.
Abstract: We derive the necessary conditions to build a class of invisible axion models with Flavor Changing Neutral Currents at tree-level controlled by the fermion mixing matrices and present an explicit model implementation. A horizontal Peccei-Quinn symmetry provides a solution to the strong CP problem via the Peccei-Quinn mechanism and predicts a cold dark mater candidate, the invisible axion or familon. The smallness of active neutrino masses can be explained via a type I seesaw mechanism, providing a dynamical origin for the heavy seesaw scale. The possibility to avoid the domain wall problem stands as one of the most interesting features of the type of models considered. Experimental limits relying on the axion-photon coupling, astrophysical considerations and familon searches in rare kaon and muon decays are discussed.
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Barenboim, G., & Park, W. I. (2015). Spiral inflation. Phys. Lett. B, 741, 252–255.
Abstract: We propose a novel scenario of primordial inflation in which the inflaton goes through a spiral motion starting from around the top of a symmetry breaking potential. We show that, even though inflation takes place for a field value much smaller than Planck scale, it is possible to obtain relatively large tensor-to-scalar ratio (r similar to 0.1) without fine tuning. The inflationary observables perfectly match Planck data.
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NA48/2 Collaboration(Batley, J. R. et al), & Fiorini, L. (2015). Search for the dark photon in pi(0) decays. Phys. Lett. B, 746, 178–185.
Abstract: A sample of 1.69 x 10(7) fully reconstructed pi(0) -> gamma e(+)e(-) decay candidates collected by the NA48/2 experiment at CERN in 2003-2004 is analyzed to search for the dark photon (A') production in the pi(0) -> gamma A' decay followed by the prompt A' -> e(+)e(-) decay. No signal is observed, and an exclusion region in the plane of the dark photon mass m(A') and mixing parameter epsilon(2) is established. The obtained upper limits on epsilon(2) are more stringent than the previous limits in the mass range 9 MeV/c(2) < m(A') < 70 MeV/c(2). The NA48/2 sensitivity to the dark photon production in the K-+/- -> pi(+/-)A' decay is also evaluated.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the lifetime of the B-c(+) cmeson using the B-c(+) -> J/psi pi(+) decay mode. Phys. Lett. B, 742, 29–37.
Abstract: The difference in total widths between the B-c(+) and B+ mesons is measured using a data sample corresponding to an integrated luminosity of 3.0 fb(-1) collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton-proton collisions at the LHC. Through the study of the time evolution of B-c(+) -> J/psi pi(+) and B+ -> J/psi K+ decays, the width difference is measured to be Delta Gamma = Gamma(Bc+) – Gamma(Bc+) = 4.46 +/- 0.14 +/- 0.07 mm(-1) c, where the first uncertainty is statistical and the second systematic. The known lifetime of the B+ meson is used to convert this to a precise measurement of the B-c(+) clifetime, tau(Bc+) = 513.4 +/- 11.0 +/- 5.7 fs, where the first uncertainty is statistical and the second is systematic.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the CP-violating phase beta in B-0 -> J/psi pi(+)pi(-) decays and limits on penguin effects. Phys. Lett. B, 742, 38–49.
Abstract: Time-dependent CP violation is measured in the (B-0) over bar -> J/psi pi(+)pi(-) p-channel for each pi(+)pi(-) resonant final state using data collected with an integrated luminosity of 3.0 fb(-1) in pp collisions using the LHCb detector. The final state with the largest rate, J/psi rho(0)(770), is used to measure the CP-violating angle 2 beta(eff) to be (41.7 +/- 9.6(-6.3)(+2.8)).. This result can be used to limit the size of penguin amplitude contributions to CPviolation measurements in, for example, (B-0) over bar -> J/psi pi(+)pi(-) decays. Assuming approximate SU(3) flavour symmetry and neglecting higher order diagrams, the shift in the CP-violating phase phi(s) limited to be within the interval [-1.05 degrees, + 1.18 degrees] at 95% confidence level. Changes to the limit due to SU(3) symmetry breaking effects are also discussed.
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