A search for excited states of the Bc(±) meson is performed using 4.9  fb(-1) of 7 TeV and 19.2  fb(-1) of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay Bc(±)→J/ψπ(±). The state appears in the m(Bc(±)π(+)π(-))-m(Bc(±))-2m(π(±)) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842±4±5  MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the Bc(±) meson, Bc(±)(2S).

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This paper reviews and extends searches for the direct pair production of the scalar supersymmetric partners of the top and bottom quarks in proton–proton collisions collected by the ATLAS collaboration during the LHC Run 1. Most of the analyses use 20 of collisions at a centre-of-mass energy of TeV, although in some case an additional of collision data at TeV are used. New analyses are introduced to improve the sensitivity to specific regions of the model parameter space. Since no evidence of third-generation squarks is found, exclusion limits are derived by combining several analyses and are presented in both a simplified model framework, assuming simple decay chains, as well as within the context of more elaborate phenomenological supersymmetric models.

Searches for heavy long-lived charged particles are performed using a data sample of 19.1 fb −1 from proton-proton collisions at a centre-of-mass energy of √ s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for tan β between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. R-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer.

A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb −1 of √ s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark,t, which decays promptly into two quarks through Rparity-violating couplings. Top squarks with masses in the range 100 GeV < mt < 410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV < mt < 470 GeV and 480 GeV < mt < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances. IntroductionMassive coloured particles decaying into quarks and gluons are predicted in several extensions of the Standard Model (SM). At hadron colliders, the search for new phenomena in fully hadronic final states, without missing transverse momentum, is experimentally challenging due to the very large SM multijet production cross-section. This paper describes a search for pair-produced particles each decaying into two jets using 36.7 fb −1 of √ s = 13 TeV proton-proton ( pp) collision data recorded in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider (LHC).Supersymmetry (SUSY) [1][2][3][4][5][6][7] is a generalisation of the Poincaré symmetry group that relates fermionic and bosonic degrees of freedom. In the generic superpotential, Yukawa couplings can lead to baryon-and lepton-number violation:where i, j, and k are quark and lepton generation indices. The L i and Q i represent the lepton and quark SU(2) L doublet superfields and H u the Higgs superfield that couples to e-mail: atlas.publications@cern.ch up-type quarks. TheĒ i ,D i , andŪ i are the lepton, downtype quark and up-type quark SU(2) L singlet superfields, respectively. For each term the couplings are λ, λ , λ , as well as κ which is a dimensional mass parameter. The λ and λ couplings are antisymmetric in the exchange of i → j and j → k, respectively. While these terms in many scenarios are removed by imposing an additional Z 2 symmetry (R-parity) [8], the possibility that at least some of these Rparity-violating (RPV) couplings are not zero is not ruled out experimentally [9,10]. This family of models leads to unique collider signatures which can escape conventional searches for R-parity-conserving SUSY.Naturalness arguments [11,12] suggest that higgsinos and top squarks 1 (stops) should be light, with masses below a TeV [13,14]. Third-generation squarks in R-parityconserving scenarios, and top squarks in particular, have been the subject of a thorough programme of searches at the LHC [15][16][17][18][19][20][21][22].If the top squark decays through RPV couplings, however, the existing bounds on its mass can be significantly relaxed [23][24][25][26]. Indirect experimental constrain...