41 research outputs found

    Standard-model predictions for CP violation in B<sup>0</sup>-meson decay

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    We examine the present set of constraints on the parameters of the standard model and use the unitarity triangle to present their allowed range. We give the implications of this for CP violation in the B-meson system as a function of top-quark mass, emphasizing what luminosity of an electronpositron collider is needed to guarantee a statistically significant asymmetry in one or more B decay channels.</p

    Search for sterile neutrinos decaying into pions at the LHC

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    We study the possibility to observe sterile neutrinos with masses in the range between 5 GeV and 20 GeV at the LHC, using the exclusive semileptonic modes involving pions, namely W to lepton + N to n pions + lepton+lepton (n = 1, 2, 3). The two pion and three pion modes require extrapolations of form factors to large time-like q2q^2, which we do using vector dominance models as well as light front holographic QCD, with remarkable agreement. This mass region is difficult to explore with inclusive dilepton+dijet modes or trilepton modes and impossible to explore in rare meson decays. While particle identification is a real challenge in these modes, vertex displacement due to the long living neutrino in the above mass range can greatly help reduce backgrounds. Assuming a sample of 10910^9 W bosons at the end of the LHC Run 2, these modes could discover a sterile neutrino in the above mass range or improve the current bounds on the heavy-to-light lepton mixings by an order of magnitude, UlN22×106U_{l N}^2 \sim 2 \times 10^{-6}. Moreover, by studying the equal sign and opposite sign dileptons, the Majorana or Dirac character of the sterile neutrino may be revealed.Comment: 18 pages, 4 double figure

    Search for heavy sterile neutrinos in trileptons at the LHC

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    We present a search strategy for both Dirac and Majorana sterile neutrinos from the purely leptonic decays of W± → e± e± μ^\mp ν\nu and μ± μ± emnplus ν\nu at the 14 TeV LHC. The discovery and exclusion limits for sterile neutrinos are shown using both the Cut-and-Count (CC) and Multi-Variate Analysis (MVA) methods. We also discriminate between Dirac and Majorana sterile neutrinos by exploiting a set of kinematic observables which differ between the Dirac and Majorana cases. We find that the MVA method, compared to the more common CC method, can greatly enhance the discovery and discrimination limits. Two benchmark points with sterile neutrino mass mNm_N = 20 GeV and 50 GeV are tested. For an integrated luminosity of 3000 fb1^{−1}, sterile neutrinos can be found with 5σ significance if heavy-to-light neutrino mixings |UNe2_{Ne} |^2 ~ |UNμ2_{Nμ}|^2~ 106^{−6}, while Majorana vs. Dirac discrimination can be reached if at least one of the mixings is of order 1015^{−15}

    Search for Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC

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    Heavy sterile neutrinos with masses below MWM_W can induce trilepton events at the 14 TeV LHC through purely leptonic WW decays of W±e±e±μνW^\pm \to e^\pm e^\pm \mu^\mp \nu and μ±μ±eν\mu^\pm \mu^\pm e^\mp \nu where the heavy neutrino will be in an intermediate state on its mass shell. Discovery and exclusion limits for the heavy neutrinos are found using both Cut-and-Count (CC) and a Multi-Variate Analysis (MVA) methods in this study. We also show that it is possible to discriminate between a Dirac and a Majorana heavy neutrino, even when lepton number conservation cannot be directly tested due to unobservability of the final state neutrino. This discrimination is done by exploiting a combined set of kinematic observables that differ between the Majorana vs. Dirac cases. We find that the MVA method can greatly enhance the discovering and discrimination limits in comparison with the CC method. With an integrated luminosity of 3000 fb1{\rm fb}^{-1}, sterile neutrinos can be found with 5σ\sigma significance if heavy-to-light neutrino mixings UNe2UNμ2106|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-6}, while the Majorana vs. Dirac type can be distinguished if UNe2UNμ2105|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-5} or even UN2106|U_{N\ell}|^2\sim 10^{-6} if one of mixing elements can be at least one order of magnitude smaller than the other

    Signatures of Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC

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    Heavy sterile neutrinos with masses below MWM_W can induce trilepton events at the 14 TeV LHC through purely leptonic WW decays of W±e±e±μνW^\pm \to e^\pm e^\pm \mu^\mp \nu and μ±μ±eν\mu^\pm \mu^\pm e^\mp \nu where the heavy neutrino will be in an intermediate state on its mass shell. Discovery and exclusion limits for the heavy neutrinos are found using both Cut-and-Count (CC) and a Multi-Variate Analysis (MVA) methods in this study. We also show that it is possible to discriminate between a Dirac and a Majorana heavy neutrino, even when lepton number conservation cannot be directly tested due to unobservability of the final state neutrino. This discrimination is done by exploiting a combined set of kinematic observables that differ between the Majorana vs. Dirac cases. We find that the MVA method can greatly enhance the discovering and discrimination limits in comparison with the CC method. For a 14-TeV pppp collider with integrated luminosity of 3000 fb1{\rm fb}^{-1}, sterile neutrinos can be found with 5σ\sigma significance if heavy-to-light neutrino mixings UNe2UNμ2106|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-6}, while the Majorana vs. Dirac type can be distinguished if UNe2UNμ2105|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-5} or even UN2106|U_{N\ell}|^2\sim 10^{-6} if one of the mixing elements is at least an order of magnitude smaller than the other.Comment: 10 pages, 12 figure

    Search for Heavy Sterile Neutrinos in Trileptons at the LHC

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    We present a search strategy for both Dirac and Majorana sterile neutrinos from the purely leptonic decays of W±e±e±μνW^\pm \to e^\pm e^\pm \mu^\mp \nu and μ±μ±eν\mu^\pm \mu^\pm e^\mp \nu at the 14 TeV LHC. The discovery and exclusion limits for sterile neutrinos are shown using both the Cut-and-Count (CC) and Multi-Variate Analysis (MVA) methods. We also discriminate between Dirac and Majorana sterile neutrinos by exploiting a set of kinematic observables which differ between the Dirac and Majorana cases. We find that the MVA method, compared to the more common CC method, can greatly enhance the discovery and discrimination limits. Two benchmark points with sterile neutrino mass mN=20m_N = 20 GeV and 50 GeV are tested. For an integrated luminosity of 3000 fb1{\rm fb}^{-1}, sterile neutrinos can be found with 5σ5 \sigma significance if heavy-to-light neutrino mixings UNe2UNμ2106|U_{Ne}|^2 \sim |U_{N\mu}|^2\sim 10^{-6}, while Majorana vs. Dirac discrimination can be reached if at least one of the mixings is of order 10510^{-5}.Comment: 4 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1703.0193
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