ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Search for flavour-changing neutral current top-quark decays to q Z in pp collision data collected with the ATLAS detector at root s=8 TeV. Eur. Phys. J. C, 76(1), 12–24pp.
Abstract: A search for the flavour-changing neutral-current decay is presented. Data collected by the ATLAS detector during 2012 from proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of root s = 8 TeV, corresponding to an integrated luminosity of 20.3 fb(-1), are analysed. Top-quark pair-production events with one top quark decaying through the t -> qZ (q = u,c) channel and the other through the dominant Standard Model mode t -> bW are considered as signal. Only the decays of the Z boson to charged leptons and leptonic W boson decays are used. No evidence for a signal is found and an observed (expected) upper limit on the t -> qZ branching ratio of 7 x 10(-4) (8 x 10(-4)) is set at the 95 % confidence level.
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Vijande, J., Valcarce, A., Richard, J. M., & Sorba, P. (2016). Search for doubly-heavy dibaryons in a quark model. Phys. Rev. D, 94(3), 034038–6pp.
Abstract: We study the stability of hexaquark systems containing two heavy quarks and four light quarks within a simple quark model. No bound or metastable state is found. The reason stems from a delicate interplay between chromoelectric and chromomagnetic effects. Our calculation also provides information about anticharmed pentaquarks that are seemingly unbound in simple quark models.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Search for direct top squark pair production in final states with two tau leptons in pp collisions at root s=8 TeV with the ATLAS detector. Eur. Phys. J. C, 76(2), 81–30pp.
Abstract: A search for direct pair production of the supersymmetric partner of the top quark, decaying via a scalar tau to a nearly massless gravitino, has been performed using 20 fb(-1) of proton-proton collision data at root s = 8 TeV. The data were collected by the ATLAS experiment at the LHC in 2012. Top squark candidates are searched for in events with either two hadronically decaying tau leptons, one hadronically decaying tau and one light lepton, or two light leptons. No significant excess over the Standard Model expectation is found. Exclusion limits at 95 % confidence level are set as a function of the top squark and scalar tau masses. Depending on the scalar tau mass, ranging from the 87 GeV LEP limit to the top squark mass, lower limits between 490 and 650 GeV are placed on the top squark mass within the model considered.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., Costa, M. J., et al. (2016). Search for dark matter produced in association with a Higgs boson decaying to two bottom quarks in pp collisions at root s=8 TeV with the ATLAS detector. Phys. Rev. D, 93(7), 072007–33pp.
Abstract: This article reports on a search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb(-1) of pp collisions at a center-of-mass energy of 8 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum b (b) over bar system with either a pair of small-radius jets, or a single large-radius jet with substructure. The observed data are found to be consistent with the expected Standard Model backgrounds. Model-independent upper limits are placed on the visible cross sections for events with a Higgs boson decaying into b (b) over bar and large missing transverse momentum with thresholds ranging from 150 to 400 GeV. Results are interpreted using a simplified model with a Z' gauge boson decaying into different Higgs bosons predicted in a two-Higgs-doublet model, of which the heavy pseudoscalar Higgs decays into a pair of dark matter particles. Exclusion limits are also presented for the mass scales of various effective field theory operators that describe the interaction between dark matter particles and the Higgs 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. (2016). Search for dark matter produced in association with a hadronically decaying vector boson in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 763, 251–268.
Abstract: A search is presented for dark matter produced in association with a hadronically decaying W or Z boson using 3.2 fb(-1) of ppcollisions at root s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Events with a hadronic jet compatible with a Wor Z boson and with large missing transverse momentum are analysed. The data are consistent with the Standard Model predictions and are interpreted in terms of both an effective field theory and a simplified model containing dark matter.
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