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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 dark matter in events with a hadronically decaying vector boson and missing transverse momentum in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 10(10), 180–58pp.
Abstract: A search for dark matter (DM) particles produced in association with a hadronically decaying vector boson is performed using pp collision data at a centre-of-mass energy of TeV corresponding to an integrated luminosity of 36.1 fb(-1), recorded by the ATLAS detector at the Large Hadron Collider. This analysis improves on previous searches for processes with hadronic decays of W and Z bosons in association with large missing transverse momentum (mono-W/Z searches) due to the larger dataset and further optimization of the event selection and signal region definitions. In addition to the mono-W/Z search, the as yet unexplored hypothesis of a new vector boson Z produced in association with dark matter is considered (mono-Z search). No significant excess over the Standard Model prediction is observed. The results of the mono-W/Z search are interpreted in terms of limits on invisible Higgs boson decays into dark matter particles, constraints on the parameter space of the simplified vector-mediator model and generic upper limits on the visible cross sections for W/Z+DM production. The results of the mono-Z search are shown in the framework of several simplified-model scenarios involving DM production in association with the Z boson.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Search for new high-mass phenomena in the dilepton final state using 36 fb(-1) of proton-proton collision data at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 10(10), 182–61pp.
Abstract: A search is conducted for new resonant and non-resonant high-mass phenomena in dielectron and dimuon fi nal states. The search uses 36 : 1 fb(-1) of proton-proton collision data, collected at root s = 13TeV by the ATLAS experiment at the LHC in 2015 and 2016. No signi fi cant deviation from the Standard Model prediction is observed. Upper limits at 95% credibility level are set on the cross-section times branching ratio for resonances decaying into dileptons, which are converted to lower limits on the resonance mass, up to 4.1 TeV for the E-6 -motivated Z(X)'. Lower limits on the qqll contact interaction scale are set between 2.4 TeV and 40 TeV, depending on the model.
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NA62 Collaboration(Cortina Gil, E. et al), & Husek, T. (2019). Search for production of an invisible dark photon in (0) decays. J. High Energy Phys., 05(5), 182–20pp.
Abstract: The results of a search for (0) decays to a photon and an invisible massive dark photon at the NA62 experiment at the CERN SPS are reported. From a total of 4.12 x 10(8) tagged (0) mesons, no signal is observed. Assuming a kinetic-mixing interaction, limits are set on the dark photon coupling to the ordinary photon as a function of the dark photon mass, improving on previous searches in the mass range 60-110 MeV/c(2). The present results are interpreted in terms of an upper limit of the branching ratio of the electro-weak decay 0improving the current limit by more than three orders of magnitude.
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Barducci, D., Bertuzzo, E., Caputo, A., & Hernandez, P. (2020). Minimal flavor violation in the see-saw portal. J. High Energy Phys., 06(6), 185–28pp.
Abstract: We consider an extension of the Standard Model with two singlet leptons, with masses in the electroweak range, that induce neutrino masses via the see-saw mechanism, plus a generic new physics sector at a higher scale, A. We apply the minimal flavor violation (MFV) principle to the corresponding Effective Field Theory (nu SMEFT) valid at energy scales E << A. We identify the irreducible sources of lepton flavor and lepton number violation at the renormalizable level, and apply the MFV ansatz to derive the scaling of the Wilson coefficients of the nu SMEFT operators up to dimension six. We highlight the most important phenomenological consequences of this hypothesis in the rates for exotic Higgs decays, the decay length of the heavy neutrinos, and their production modes at present and future colliders. We also comment on possible astrophysical implications.
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Escudero, M., Witte, S. J., & Rius, N. (2018). The dispirited case of gauged U(1)(B-L) dark matter. J. High Energy Phys., 08(8), 190–30pp.
Abstract: We explore the constraints and phenomenology of possibly the simplest scenario that could account at the same time for the active neutrino masses and the dark matter in the Universe within a gauged U(1)(B-L) symmetry, namely right-handed neutrino dark matter. We find that null searches from lepton and hadron colliders require dark matter with a mass below 900 GeV to annihilate through a resonance. Additionally, the very strong constraints from high-energy dilepton searches fully exclude the model for 150 GeV < m(z') < 3 TeV. We further explore the phenomenology in the high mass region (i.e. masses greater than or similar to O(1) TeV) and highlight theoretical arguments, related to the appearance of a Landau pole or an instability of the scalar potential, disfavoring large portions of this parameter space. Collectively, these considerations illustrate that a minimal extension of the Standard Model via a local U(1)(B-L) symmetry with a viable thermal dark matter candidate is difficult to achieve without fine-tuning. We conclude by discussing possible extensions of the model that relieve tension with collider constraints by reducing the gauge coupling required to produce the correct relic abundance.
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