Cottin, G., Helo, J. C., & Hirsch, M. (2018). Displaced vertices as probes of sterile neutrino mixing at the LHC. Phys. Rev. D, 98(3), 035012–6pp.
Abstract: We investigate the reach at the LHC to probe light sterile neutrinos with displaced vertices. We focus on sterile neutrinos N with masses m(N) similar to (5-30) GeV that are produced in rare decays of the standard model gauge bosons and decay inside the inner trackers of the LHC detectors. With a strategy that triggers on the prompt lepton accompanying the N displaced vertex and considers charged tracks associated with it, we show that the 13 TeV LHC with 3000/fb is able to probe active-sterile neutrino mixings down to vertical bar V-lN vertical bar(2) approximate to 10(-9), with l = e, mu, which is an improvement of up to 4 orders of magnitude when comparing with current experimental limits from trileptons and proposed lepton-jets searches. In the case when tau mixing is present, mixing angles as low as vertical bar V-tau N vertical bar(2) approximate to 10(-8) can be accessed.
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Centelles Chulia, S., Srivastava, R., & Valle, J. W. F. (2018). Seesaw Dirac neutrino mass through dimension-six operators. Phys. Rev. D, 98(3), 035009–18pp.
Abstract: In this paper, a follow-up of [S. C. Chulia, R. Srivastava, and J. W. F. Valle, Phys. Lett. B 781, 122 (2018)], we describe the many pathways to generate Dirac neutrino mass through dimension-six operators. By using only the standard model Higgs doublet in the external legs, one gets a unique operator 1/Lambda(2) (L) over bar (Phi) over bar (Phi) over bar Phi nu(R). In contrast, the presence of new scalars implies new possible field contractions, which greatly increase the number of possibilities. Here, we study in detail the simplest ones, involving SU(2)(L) singlets, doublets, and triplets. The extra symmetries needed to ensure the Dirac nature of neutrinos can also be responsible for stabilizing dark matter.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., Castillo, F. L., et al. (2018). Search for flavor-changing neutral currents in top quark decays t -> Hc and t -> Hu in multilepton final states in proton-proton collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 98(3), 032002–25pp.
Abstract: Flavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo-Kobayashi-Maskawa matrix; the corresponding rates for top quark decay processes are experimentally unobservable. Extensions of the Standard Model can generate new flavor-changing neutral current processes, leading to signals which, if observed, would be unambiguous evidence of new interactions. A data set conesponding to an integrated luminosity of 36.1 fb(-1) of pp collisions at a center-of-mass energy of root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider is used to search for top quarks decaying to up or charm quarks with the emission of a Higgs boson, with subsequent Higgs boson decay to final states with at least one electron or muon. No signal is observed and limits on the branching fractions B(t -> Hc) < 0.16% and B(t -> Hu) < 0.19% at 95% confidence level are obtained (with expected limits of 0.15% in both cases).
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Dai, L. R., Zhang, X., & Oset, E. (2018). Semileptonic decays of B-(*), D-(*) into vl and pseudoscalar or vector mesons. Phys. Rev. D, 98(3), 036004–16pp.
Abstract: We perform a study of the B-(*), D-(*) scmileptonic decays, using a differcnt mcthod than in conventional approaches, where the matrix elements of the weak operators are evaluated and a detailed spin-angular momentum algebra is performed to obtain very simple expressions at the end for the different decay modes. Using only one experimental decay rate in the B or D sectors, the rates for the rest of decay modes are predicted and thcy arc in good agrcement with experiment. Somc discrepancies arc observed in the tau dccay mode for which we find an explanation. We perform evaluations for B and D' decay rates that can be used in future measurements, now possible in the LHCb Collaboration.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Izmaylov, A., & Novella, P. (2018). Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K. Phys. Rev. D, 98(3), 032003–46pp.
Abstract: This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C8H8) target. The data were taken between years 2010 and 2013, corresponding to approximately 6 x 10(20) protons on target. Thanks to their exploration of the proton kinematics and of imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measurements. These results are compared to many neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space. In case of events without a proton above a detection threshold in the final state, a fully consistent implementation of the local Fermi gas model with multinucleon interactions gives the best description of the data. In the case of at least one proton in the final state, the spectral function model agrees well with the data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane transverse to the incoming neutrino. Within the models considered, only the existence of multinucleon interactions are able to describe the extracted cross section within regions of high transverse kinematic imbalance. The effect of final-state interactions is also discussed.
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