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 phenomena with large jet multiplicities and missing transverse momentum using large-radius jets and flavour-tagging at ATLAS in 13 TeV pp collisions. J. High Energy Phys., 12(12), 034–52pp.
Abstract: A search is presented for particles that decay producing a large jet multiplicity and invisible particles. The event selection applies a veto on the presence of isolated electrons or muons and additional requirements on the number of b-tagged jets and the scalar sum of masses of large-radius jets. Having explored the full ATLAS 2015-2016 dataset of LHC proton-proton collisions at root s = 13 TeV, which corresponds to 36.1 fb(-1) of integrated luminosity, no evidence is found for physics beyond the Standard Model. The results are interpreted in the context of simplified models inspired by R-parity-conserving and R-parity-violating supersymmetry, where gluinos are pair-produced. More generic models within the phenomenological minimal supersymmetric Standard Model are also considered.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., et al. (2018). Search for pair production of up-type vector-like quarks and for four-top-quark events in final states with multiple b-jets with the ATLAS detector. J. High Energy Phys., 07(7), 089–68pp.
Abstract: A search for pair production of up-type vector-like quarks (T) with a significant branching ratio into a top quark and either a Standard Model Higgs boson or a Z boson is presented. The same analysis is also used to search for four-top-quark production in several new physics scenarios. The search is based on a dataset of pp collisions at root s = 13TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb(-1). Data are analysed in the lepton+jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets, as well as the jets+E-T(miss) final state, characterised by multiple jets and large missing transverse momentum. The search exploits the high multiplicity of jets identified as originating from b-quarks, and the presence of boosted, hadronically decaying top quarks and Higgs bosons reconstructed as large-radius jets, characteristic of signal events. No significant excess above the Standard Model expectation is observed, and 95% CL upper limits are set on the production cross sections for the different signal processes considered. These cross-section limits are used to derive lower limits on the mass of a vector-like T quark under several branching ratio hypotheses assuming contributions from T -> Wb, Zt, Ht decays. The 95% CL observed lower limits on the T quark mass range between 0.99TeV and 1.43TeV for all possible values of the branching ratios into the three decay modes considered, significantly extending the reach beyond that of previous searches. Additionally, upper limits on anomalous four-top-quark production are set in the context of an effective field theory model, as well as in an universal extra dimensions model.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2019). Measurement of the branching fractions of the decays D+ -> K-K+K+, D+ -> pi-pi(+) K+ and D-s(+) -> pi-K+K+. J. High Energy Phys., 03(3), 176–24pp.
Abstract: The branching fractions of the doubly Cabibbo-suppressed decays D+ ! K, D+ ! and D+ s ! are measured using the decays D+ ! K and D+ s ! K as normalisation channels. The measurements are performed using proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 8TeV, corresponding to an integrated luminosity of 2.0 fb. The results are B (D+ ! K) B (D+ ! K) = (6 : 541 0 : 025 0 : 042) 10 B (D+ ! ) B (D+ ! K) = (5 : 231 0 : 009 0 : 023) 10 B (D+ s ! ) B (D+ s ! K) = (2 : 372 0 : 024 0 : 025) 10 where the uncertainties are statistical and systematic, respectively. These are the most precise measurements up to date.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). Measurements of the branching fractions of Lambda(+)(c) -> p pi(-)pi(+), Lambda(+)(c) -> pK(-)K(+), and Lambda(+)(c) -> p pi K-(+). J. High Energy Phys., 03(3), 043–23pp.
Abstract: The ratios of the branching fractions of the decays do Lambda(+)(c) -> , p pi(-)pi(+), Lambda(+->)(c) pK(-)K(+), and Lambda(+)(c) -> p pi K--(+) with respect to the Cabibbo-favoured Lambda(+)(c) -> pK(-)pi(+) decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb(-1): B(Lambda(+)(c) -> p pi(-)pi(+))/B(Lambda(+)(c) -> pK(-)pi(+)) = (7.44 +/- 0.08 +/- 0.18)%. B(Lambda(+)(c) -> pK(-)K(+))/B(Lambda(+)(c) -> pK(-)pi(+) = (1.70 +/- 0.03 +/- 0.03)%, B(Lambda(+)(c) -> p pi(-)pi K-+(+))/B(Lambda(+)(c) -> pK(-)pi(+) = (0.165 +/- 0.015 +/- 0.005)%, where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world average value for B(Lambda(+)(c) -> p pi(-)pi(+)), the corresponding branching fractions are B(Lambda(+)(c) -> p pi(-)pi(+) = (4.72 +/- 0.05 +/- 0.11 +/- 0.25) x 10(-3), B(Lambda(+)(c) -> pK(-)K(+)) = (1.08 +/- 0.02 +/- 0.02 +/- 0.06) x 10(-3), B(Lambda(+)(c) -> , p pi K--(+)) = (1.04 +/- 0.09 +/- 0.03 +/- 0.05) x 10(-4), where the final uncertainty is due to B(Lambda(+)(c) -> pK(-)pi(+)).
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). A search for Xi(++)(cc) -> D(+)pK(-)pi(+) decays. J. High Energy Phys., 10(10), 124–21pp.
Abstract: A search for the Xi(++)(cc) baryon through the Xi(++)(cc) -> D(+)pK(-)pi(+) decay is performed with a data sample corresponding to an integrated luminosity of 1.7 fb(-1) recorded by the LHCb experiment in pp collisions at a centre-of-mass energy of 13 TeV. No significant signal is observed in the mass range from the kinematic threshold of the decay to 3800 MeV/c(2). An upper limit is set on the ratio of branching fractions R = B(Xi(++)(cc) -> D(+)pK(-)pi(+))/B(Xi(++)(cc) -> A(c)(+) K- pi(+)pi(+)) with R < 1.7 (2.1) x 10(-2) at the 90% (95%) confidence level at the known mass of the Xi(++)(cc) state.
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