ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). A search for resonances decaying into a Higgs boson and a new particle X in the XH -> qqbb final state with the ATLAS detector. Phys. Lett. B, 779, 24–45.
Abstract: A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1 fb(-1) of proton-proton collision data at root s = 13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle Xis assumed to decay to a pair of light quarks, and the fully hadronic final state XH -> q (q) over bar 'b (b) over bar is analysed. The search considers the regime of high XH resonance masses, where the X and H bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XH mass versus X mass is scanned for evidence of a signal, over a range of XH resonance mass values between 1 TeV and 4 TeV, and for X particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XH and X masses, on the production cross-section of the XH -> q (q) over bar 'b (b) over bar resonance.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Measurement of the cross section of high transverse momentum Z -> b(b)over-bar production in proton-proton collisions at root s=8 TeV with the ATLAS detector. Phys. Lett. B, 738, 25–43.
Abstract: This Letter reports the observation of a high transverse momentum Z -> b (b) over bar signal in proton-proton collisions at root s = 8TeVand the measurement of its production cross section. The data analysed were collected in 2012 with the ATLAS detector at the LHC and correspond to an integrated luminosity of 19.5 fb(-1). The Z -> b (b) over bar decay is reconstructed from a pair of b-tagged jets, clustered with the anti- k(t) jet algorithm with R = 0.4, that have low angular separation and form a dijet with p(T) > 200 GeV. The signal yield is extracted from a fit to the dijet invariant mass distribution, with the dominant, multi-jet background mass shape estimated by employing a fully data-driven technique that reduces the dependence of the analysis on simulation. The fiducial cross section is determined to be sigma(fid)(Z -> b (b) over bar) = 2.02 +/- 0.20 (stat.) +/- 0.25 (syst.) +/- 0.06 (lumi.) pb = 2.02 +/- 0.33 pb, in good agreement with next-to-leading-order theoretical predictions.
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Yamagata-Sekihara, J., Garcia-Recio, C., Nieves, J., Salcedo, L. L., & Tolos, L. (2016). Formation spectra of charmed meson-nucleus systems using an antiproton beam. Phys. Lett. B, 754, 26–32.
Abstract: We investigate the structure and formation of charmed meson--nucleus systems, with the aim of understanding the charmed meson-nucleon interactions and the properties of the charmed mesons in the nuclear medium. The (D) over bar mesic nuclei are of special interest, since they have tiny decay widths due to the absence of strong decays for the (D) over barN pair. Employing an effective model for the (D) over barN and DN interactions and solving the Klein-Gordon equation for (D) over bar and D in finite nuclei, we find that the D0-11B system has 1s and 2p mesic nuclear states and that the D0-11B system binds in a 1s state. In view of the forthcoming experiments by the PANDA and CBM Collaborations at the future FAIR facility and the J-PARC upgrade, we calculate the formation spectra of the [(D) over bar B--11] and [D-0-B-11] mesic nuclei for an antiproton beam on a C-12 target. Our results suggest that it is possible to observe the 2p D- mesic nuclear state with an appropriate experimental setup.
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Centelles Chulia, S., Srivastava, R., & Valle, J. W. F. (2017). Generalized bottom-tau unification, neutrino oscillations and dark matter: Predictions from a lepton quarticity flavor approach. Phys. Lett. B, 773, 26–33.
Abstract: We propose an A(4) extension of the Standard Model with a Lepton Quarticity symmetry correlating dark matter stability with the Dirac nature of neutrinos. The flavor symmetry predicts (i) a generalized bottom-tau mass relation involving all families, (ii) small neutrino masses are induced a la seesaw, (iii) CP must be significantly violated in neutrino oscillations, (iv) the atmospheric angle theta(23) lies in the second octant, and (v) only the normal neutrino mass ordering is realized.
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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). Search for a heavy Standard Model Higgs boson in the channel H -> ZZ -> l(+)l(-) q(q)over-bar using the ATLAS detector. Phys. Lett. B, 707(1), 27–45.
Abstract: A search for a heavy Standard Model Higgs boson decaying via H -> ZZ -> l(+)l(-)q (q) over bar, where l = e, mu, is presented. The search is performed using a data set of pp collisions at root s = 7 TeV, corresponding to an integrated luminosity of 1.04 fb(-1) collected in 2011 by the ATLAS detector at the CERN LHC collider. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section (relative to that expected from the Standard Model) of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. Within this mass range, there is at present insufficient sensitivity to exclude a Standard Model Higgs boson. For a Higgs boson with a mass of 360 GeV, where the sensitivity is maximal, the observed and expected cross section upper limits are factors of 1.7 and 2.7, respectively, larger than the Standard Model prediction.
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