Carrasco, N., Ciuchini, M., Dimopoulos, P., Frezzotti, R., Gimenez, V., Herdoiza, G., et al. (2014). B-physics from N-f=2 tmQCD: the Standard Model and beyond. J. High Energy Phys., 03(3), 016–52pp.
Abstract: We present a lattice QCD computation of the b-quark mass, the B and B-s decay constants, the B-mixing bag parameters for the full four-fermion operator basis as well as determinations for xi and f(Bq) root B-i((q)) extrapolated to the continuum limit and to the physical pion mass. We used N-f = 2 twisted mass Wilson fermions at four values of the lattice spacing with pion masses ranging from 280 to 500 MeV. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out on ratios of physical quantities computed at nearby quark masses, exploiting the fact that they have an exactly known infinite mass limit. Our results are m(b)(m(b), (MS) over bar) = 4.29(12) GeV, f(Bs) = 228(8) MeV, f(B) = 189(8) MeV and f(Bs)/f(B) = 1.206(24). Moreover with our results for the bag-parameters we find xi = 1.225(31), B-1((s))/B-1((d)) = 1.01(2), f (Bd) root(B) over cap ((d))(1) = 216(10) MeV and integral Bs root(B) over cap ((s))(1) = 262(10) MeV. We also computed the bag parameters for the complete basis of the four-fermion operators which are required in beyond the SM theories. By using these results for the bag parameters we are able to provide a refined Unitarity Triangle analysis in the presence of New Physics, improving the bounds coming from B-(s) -(B) over bar ((s)) mixing.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Search for charged Higgs bosons decaying via H-+/- -> tau(+/-)nu in fully hadronic final states using pp collision data at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 03(3), 088–45pp.
Abstract: The results of a search for charged Higgs bosons decaying to a T lepton and a neutrino. H-+/- -> T-+/-nu, are presented. The analysis is based on 19.5 fb(-1) of proton-proton collision data at root s = 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. Charged Higgs bosons are searched for in events consistent with top-quark pair production or in associated production with a top quark, depending on the considered H-+/- mass. The final state is characterised by the presence of a hadronic T decay, missing transverse momentum, b-tagged jets, a hadronically decaying W boson, and the absence of any isolated electrons or unions with high transverse momenta. The data are consistent with the expected background from Standard Model processes. A statistical analysis leads to 95% confidence-level upper limits on the product of branching ratios B(t -> bH(+/-)) x B(H-+/- -> T-+/-nu), between 0.23% and 1.3% for charged Higgs boson masses in the range 80 160 GeV. lit also leads to 95% confidence-level upper limits on the production cross section times branching ratio, sigma(pp -> tH(+/-) + X) x B(H-+/--> T(+/-)v), between 0.76 pb and 4.5 fb, for charged Higgs boson masses ranging from 180 GeV to 1000 GeV. In the context of different scenarios of the Minimal Supersymnietric Standard Model, these results exclude nearly all values of tan beta above one for charged Higgs boson masses between 80 GeV and 160 GeV, and exclude a region of parameter space with high tan beta for H-+/- masses between 200 GeV and 250 GeV.
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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 anomalous production of prompt same-sign lepton pairs and pair-produced doubly charged Higgs bosons with root s=8 TeV pp collisions using the ATLAS detector. J. High Energy Phys., 03(3), 041–48pp.
Abstract: A low-background inclusive search for new physics in events with same-sign dileptons is presented. The search uses proton-proton collisions corresponding to 20.3 fb(-1) of integrated luminosity taken in 2012 at a centre-of-mass energy of 8TeV with the ATLAS detector at the LHC. Pairs of isolated leptons with the same electric charge and large transverse momenta of the type e(+/-) e(+/-), e(+/-) mu(+/-), and mu(+/-) mu(+/-) are selected and their invariant mass distribution is examined. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the cross-sections for processes beyond the Standard Model. Limits are placed as a function of the dilepton invariant mass within a fiducial region corresponding to the signal event selection criteria. Exclusion limits are also derived for a specific model of doubly charged Higgs boson production.
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Aristizabal Sierra, D., Degee, A., Dorame, L., & Hirsch, M. (2015). Systematic classification of two-loop realizations of the Weinberg operator. J. High Energy Phys., 03(3), 040–41pp.
Abstract: We systematically analyze the d = 5 Weinberg operator at 2-loop order. Using a diagrammatic approach, we identify two different interesting categories of neutrino mass models: (i) Genuine 2-loop models for which both, tree-level and 1-loop contributions, are guaranteed to be absent. And (ii) finite 2-loop diagrams, which correspond to the 1-loop generation of some particular vertex appearing in a given 1-loop neutrino mass model, thus being effectively 2-loop. From the large list of all possible 2-loop diagrams, the vast majority are infinite corrections to lower order neutrino mass models and only a moderately small number of diagrams fall into these two interesting classes. Moreover, all diagrams in class (i) are just variations of three basic diagrams, with examples discussed in the literature before. Similarly, we also show that class (ii) diagrams consists of only variations of these three plus two more basic diagrams. Finally, we show how our results can be consistently and readily used in order to construct two-loop neutrino mass models.
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Ilisie, V. (2015). New Barr-Zee contributions to (g-2)(mu) in two-Higgs-doublet models. J. High Energy Phys., 04(4), 077–27pp.
Abstract: We study the contribution of new sets of two-loop Barr-Zee type diagrams to the anomalous magnetic moment of the muon within the two-Higgs-doublet model framework. We show that some of these contributions can be quite sizeable for a large region of the parameter space and can significantly reduce, and in some cases even explain, the discrepancy between the theoretical prediction and the experimentally measured value of this observable. Analytical expressions are given for all the calculations performed in this work.
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