Agarwalla, S. K., Li, T., & Rubbia, A. (2012). An incremental approach to unravel the neutrino mass hierarchy and CP violation with a long-baseline superbeam for large theta(13). J. High Energy Phys., 05(5), 154–32pp.
Abstract: Recent data from long-baseline neutrino oscillation experiments have provided new information on theta(13), hinting that 0.01 less than or similar to sin(2) 2 theta(13) less than or similar to 0.1 at 2 sigma confidence level. In the near future, further confirmation of this result with high significance will have a crucial impact on the optimization of the future long-baseline neutrino oscillation experiments designed to probe the neutrino mass ordering and leptonic CP violation. In this context, we expound in detail the physics reach of an experimental setup where neutrinos produced in a conventional wide-band beam facility at CERN are observed in a proposed Giant Liquid Argon detector at the Pyhasalmi mine, at a distance of 2290 km. Due to the strong matter effects and the high detection efficiency at both the first and second oscillation maxima, this particular setup would have unprecedented sensitivity to the neutrino mass ordering and leptonic CP violation in the light of the emerging hints of large theta(13). With a 10 to 20 kt 'pilot' detector and just a few years of neutrino beam running, the neutrino mass hierarchy could be determined, irrespective of the true values of delta(CP) and the mass hierarchy, at 3 sigma (5 sigma) confidence level if sin(2) 2 theta(13)(true) = 0.05 (0.1). With the same exposure, we start to have 3 sigma sensitivity to CP violation if sin(2) 2 theta(13)(true) > 0.05, in particular testing maximally CP-violating scenarios at a high confidence level. After optimizing the neutrino and anti-neutrino running fractions, we study the performance of the setup as a function of the exposure, identifying three milestones to have roughly 30%, 50% and 70% coverage in delta(CP) (true) for 3 sigma CP violation discovery. For comparison, we also study the CERN to Slanic baseline of 1540 km. This work nicely demonstrates that an incremental program, staged in terms of the exposure, can achieve the desired physics goals within a realistically feasible timescale, and produce significant new results at each stage.
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del Aguila, F., Aparici, A., Bhattacharya, S., Santamaria, A., & Wudka, J. (2012). A realistic model of neutrino masses with a large neutrinoless double beta decay rate. J. High Energy Phys., 05(5), 133–30pp.
Abstract: The minimal Standard Model extension with the Weinberg operator does accommodate the observed neutrino masses and mixing, but predicts a neutrinoless double beta (0 nu beta beta) decay rate proportional to the effective electron neutrino mass, which can be then arbitrarily small within present experimental limits. However, in general 0 nu beta beta decay can have an independent origin and be near its present experimental bound; whereas neutrino masses are generated radiatively, contributing negligibly to 0 nu beta beta decay. We provide a realization of this scenario in a simple, well defined and testable model, with potential LHC effects and calculable neutrino masses, whose two-loop expression we derive exactly. We also discuss the connection of this model to others that have appeared in the literature, and remark on the significant differences that result from various choices of quantum number assignments and symmetry assumptions. In this type of models lepton flavor violating rates are also preferred to be relatively large, at the reach of foreseen experiments. Interestingly enough, in our model this stands for a large third mixing angle, sin(2) theta(13) greater than or similar to 0.008, when μ-> eee is required to lie below its present experimental limit.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2012). Measurement of the cross section for top-quark pair production in pp collisions at root s=7 TeV with the ATLAS detector using final states with two high-p(T) leptons. J. High Energy Phys., 05(5), 059–35pp.
Abstract: A measurement is reported of the production cross section of top-quark pairs (t (t) over bar) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the LHC. Candidate events have a signature consistent with containing two isolated leptons, large missing transverse momentum, and at least two jets. Using a data sample corresponding to an integrated luminosity of 0.70 fb(-1), a t (t) over bar production cross section sigma(t (t) over bar) = 176 +/- 5(stat.)(-11)(+14)(syst.) +/- 8(lum.) pb is measured for an assumed top-quark mass of m(t) = 172.5 GeV. This measurement is in good agreement with Standard Model predictions.
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Li, X. Q., Li, Y. M., Lu, G. R., & Su, F. (2012). B-s(0)-(B)over-bar(s)(0) mixing in a family non-universal Z ' model revisited. J. High Energy Phys., 05(5), 049–27pp.
Abstract: Motivated by the very recent measurements performed at the LHCb and the Tevatron of the B-s(0) – (B) over bar (0)(s) mixing, in this paper we revisit it in a family non-universal Z' model, to check if a simultaneous explanation for all the mixing observables, especially for the like-sign dimuon charge asymmetry observed by the D0 collaboration, could be made in such a specific model. In the first scenario where the Z' boson contributes only to the off-diagonal element M-12(s), it is found that, once the combined constraints from Delta M-s, phi(s) and Delta Gamma(s) are imposed, the model could not explain the measured flavour-specific CP asymmetry a(fs)(s), at least within its 1 sigma ranges. In the second scenario where the NP contributes also to the absorptive part Gamma(s)(12) via tree-level Z'-induced b -> c (c) over bars operators, we find that, with the constraints from Delta M-s, phi(s) and the indirect CP asymmetry in (B) over bar (d) -> J/psi K-S taken into account, the present measured 1 sigma experimental ranges for a(fs)(s) could not be reproduced too. Thus, such a specific Z' model with our specific assumptions could not simultaneously reconcile all the present data on B-s(0) – B-s(0) mixing. Future improved measurements from the LHCb and the proposed superB experiments, especially of the flavour-specific CP asymmetries, are expected to shed light on the issue.
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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. (2012). Measurement of the W boson polarization in top quark decays with the ATLAS detector. J. High Energy Phys., 06(6), 088–46pp.
Abstract: This paper presents measurements of the polarization of W bosons in top quark decays, derived from t (t) over bar events with missing transverse momentum, one charged lepton and at least four jets, or two charged leptons and at least two jets. Data from pp collisions at a centre-of-mass energy of 7 TeV were collected with the ATLAS experiment at the LHC and correspond to an integrated luminosity of 1.04 fb(-1). The measured fractions of longitudinally, left-and right-handed polarization are F-0 = 0.67 +/- 0.07, F-L = 0.32 +/- 0.04 and F-R = 0.01 +/- 0.05, in agreement with the Standard Model predictions. As the polarization of the W bosons in top quark decays is sensitive to the Wtb vertex Lorentz structure and couplings, the measurements were used to set limits on anomalous contributions to the Wtb couplings.
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