ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2018). Search for Higgs bosons produced via vector-boson fusion and decaying into bottom quark pairs in root s=13 TeV pp collisions with the ATLAS detector. Phys. Rev. D, 98(5), 052003–29pp.
Abstract: A search for the b (b) over bar decay of the Standard Model Higgs boson produced through vector-boson fusion is presented. Three mutually exclusive channels are considered: two all-hadronic channels and a photon-associated channel. Results are reported from the analysis of up to 30.6 fb(-1) of pp data at root s = 13 TeV collected with the ATLAS detector at the LHC. The measured signal strength relative to the Standard Model prediction from the combined analysis is 2.5(-1.3)(+1.4) for inclusive Higgs boson production and 3.0(-1.6)(+1.7) for vector-boson fusion production only.
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Fileviez Perez, P., & Murgui, C. (2018). Dark matter and the seesaw scale. Phys. Rev. D, 98(5), 055008–9pp.
Abstract: We discuss the possibility of finding an upper hound on the seesaw scale using the cosmological bound on the cold dark matter relic density. We investigate a simple relation between the origin of neutrino masses and the properties of a dark matter candidate in a simple theory where the new symmetry breaking scale defines the seesaw scale. Imposing the cosmological hounds, we find an upper bound of order multi-TeV on the lepton number violation scale. We investigate the predictions for direct and indirect detection dark matter experiments and the possible signatures at the Large Hadron Collider.
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Hiller Blin, A. N., Sun, Z. F., & Vicente Vacas, M. J. (2018). Electromagnetic form factors of spin-1/2 doubly charmed baryons. Phys. Rev. D, 98(5), 054025–13pp.
Abstract: We study the electromagnetic form factors of the doubly charmed baryons, using covariant chiral perturbation theory within the extended on-mass-shell scheme. Vector-meson contributions are also taken into account. We present results for the baryon magnetic moments, charge, and magnetic radii. While some of the chiral Lagrangian parameters could be set to values determined in previous works, the available lattice results for Xi(+)(CC) and Omega(+)(CC) only allow for robust constraints on the low-energy constant combination, c(89) (= -1/3 c(8) + 4c(9)). The couplings of the doubly charmed baryons to the vector mesons have been estimated assuming the Okubo-Zweig-Iizuka rule. We also give the expressions for the form factors of the double-beauty baryons considering the masses predicted in the framework of quark models. A comparison of our results with those obtained in heavy baryon chiral perturbation theory at the same chiral order is made.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2018). Combination of searches for heavy resonances decaying into bosonic and leptonic final states using 36 fb(-1) of proton-proton collision data at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 98(5), 052008–32pp.
Abstract: Searches for new heavy resonances decaying into different pairings of W, Z, or Higgs bosons, as well as directly into leptons, are presented using a data sample corresponding to 36.1 fb(-1) of pp collisions at root s = 13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting bosonic decay modes in the qqqq, vvqq, evqq, eeqq, evev, eevv, evee, eeee, qqbb, vvbb, evbb, and eebb final states are combined, searching for a narrow-width resonance. Likewise, analyses selecting the leptonic ev and ee final states are also combined. These two sets of analyses are then further combined. No significant deviation from the Standard Model predictions is observed. Three benchmark models are tested: a model predicting the existence of a new heavy scalar singlet, a simplified model predicting a heavy vector-boson triplet, and a bulk Randall-Sundrum model with a heavy spin-2 Kaluza-Klein excitation of the graviton. Cross section limits are set at the 95% confidence level using an asymptotic approximation and are compared with predictions for the benchmark models. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The data exclude a heavy vector-boson triplet with mass below 5.5 TeV in a weakly coupled scenario and 4.5 TeV in a strongly coupled scenario, as well as a Kaluza-Klein graviton with mass below 2.3 TeV.
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Lara, I., Lopez-Fogliani, D. E., Muñoz, C., Nagata, N., Otono, H., & Ruiz de Austri, R. (2018). Looking for the left sneutrino LSP with displaced-vertex searches. Phys. Rev. D, 98(7), 075004–17pp.
Abstract: We analyze a displaced dilepton signal expected at the LHC for a tau left sneutrino as the lightest supersymmetric particle with a mass in the range 45-100 GeV. The sneutrinos are pair produced via a virtual W, Z or gamma in the s channel and, given the large value of the tau Yukawa coupling, their decays into two dileptons or a dilepton plus missing transverse energy from neutrinos can be significant. The discussion is carried out in the framework of the μnu SSM, where the presence of R-parity violating couplings involving right-handed neutrinos solves the μproblem and can reproduce the neutrino data. To probe the tau left sneutrinos we compare the predictions of this scenario with the ATLAS search for long-lived particles using displaced lepton pairs in pp collisions at root s = 8 TeV, allowing us to constrain the parameter space of the model. We also consider an optimization of the trigger requirements used in existing displaced-vertex searches by means of a high level trigger that exploits tracker information. This optimization is generically useful for a light metastable particle decaying into soft charged leptons. The constraints on the sneutrino turn out to be more stringent. We finally discuss the prospects for the 13 TeV LHC searches as well as further potential optimizations.
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