Search for high-mass dilepton resonances using139 fb −1 of p p collision data collected at √ s = 13 TeV with the ATLAS detectorThe ATLAS Collaboration A search for high-mass dielectron and dimuon resonances in the mass range of 250 GeV to 6 TeV is presented. The data were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of √ s = 13 TeV during Run 2 of the Large Hadron Collider and correspond to an integrated luminosity of 139 fb −1 . A functional form is fitted to the dilepton invariant-mass distribution to model the contribution from background processes, and a generic signal shape is used to determine the significance of observed deviations from this background estimate. No significant deviation is observed and upper limits are placed at the 95% confidence level on the fiducial cross-section times branching ratio for various resonance width hypotheses. The derived limits are shown to be applicable to spin-0, spin-1 and spin-2 signal hypotheses. For a set of benchmark models, the limits are converted into lower limits on the resonance mass and reach 4.5 TeV for the E 6 -motivated Z ψ boson. Also presented are limits on Heavy Vector Triplet model couplings.ATLAS [14-16] is a multipurpose detector with a forward-backward symmetric cylindrical geometry with respect to the LHC beam axis.1 The innermost layers consist of tracking detectors in the pseudorapidity range |η| < 2.5. This inner detector (ID) is surrounded by a thin superconducting solenoid that provides a 1 ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the centre of the detector and the z-axis along the beam pipe. The x-axis points from the IP to the centre of the LHC ring, and the y-axis points upwards. Cylindrical coordinates (r, φ) are used in the transverse plane, φ being the azimuthal angle around the z-axis. The pseudorapidity is defined in terms of the polar angle θ as η = − ln tan(θ/2). Angular distance is measured in units of ∆R ≡ (∆η) 2 + (∆φ) 2 .

The ATLAS CollaborationResults of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses proton-proton collision data corresponding to an integrated luminosity of 36.1 fb −1 at a centre-of-mass energy of 13 TeV collected in 2015 and 2016 with the ATLAS detector at the Large Hadron Collider. Events are required to have at least one jet with a transverse momentum above 250 GeV and no leptons (e or µ). Several signal regions are considered with increasing requirements on the missing transverse momentum above 250 GeV. Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits in models with pair-produced weakly interacting dark-matter candidates, large extra spatial dimensions, and supersymmetric particles in several compressed scenarios.

A measurement of the mass of the W boson is presented based on proton-proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb −1 of integrated luminosity. The selected data sample consists of 7.8 × 10 6 candidates in the W → μν channel and 5.9 × 10 6 candidates in the W → eν channel. The W -boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yieldingwhere the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. A measurement of the mass difference between the W + and W − bosons yields m W + − m W − = − 29 ± 28 MeV.

A search for the decay of the Standard Model Higgs boson into a bb pair when produced in association with a W or Z boson is performed with the ATLAS detector. The analysed data, corresponding to an integrated luminosity of 36.1 fb −1 , were collected in proton-proton collisions in Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Final states containing zero, one and two charged leptons (electrons or muons) are considered, targeting the decays Z → νν, W → ν and Z → . For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 3.5 standard deviations, compared to an expectation of 3.0 standard deviations. This excess provides evidence for the Higgs boson decay into b-quarks and for its production in association with a vector boson. The combination of this result with that of the Run 1 analysis yields a ratio of the measured signal events to the Standard Model expectation equal to 0. [7]. The properties of the discovered particle have been measured using the Run 1 dataset, collected at centre-of-mass energies of 7 TeV and 8 TeV, and were found to be compatible with those predicted by the Standard Model (SM) within uncertainties, typically of the order of ±20% [8-11]. The Run 2 dataset at an energy of 13 TeV provides an opportunity to increase the precision of such measurements, and to challenge theory predictions further. While analyses of Higgs bosons decaying into vector bosons are entering an era of detailed differential measurements, direct evidence for the coupling of the Higgs boson to fermions was established only via the observation of the decay into τ -leptons through the combination of ATLAS and CMS Run 1 results [11], and, more recently, through the combination of CMS Run 1 and Run 2 results [12]. Although the gluon-gluon fusion production mode provides indirect evidence for the coupling of the Higgs boson to top quarks, there is currently no direct observation of the coupling of the Higgs boson to quarks. The decay of the SM Higgs boson into pairs of b-quarks is expected to have a branching ratio of 58% for m H = 125 GeV [13], the largest among all decay modes. Accessing H → bb decays is therefore crucial for constraining, under fairly general assumptions [14,15], the overall Higgs boson decay width. At the LHC, the very large backgrounds arising from multi-jet production make an inclusive search extremely challenging. The most sensitive production modes for probing H → bb decays are those where the Higgs boson is produced in association with a W or Z boson [16]; their leptonic decay modes lead to clean signatures that can be efficiently triggered on, while rejecting most of the multi-jet backgrounds.Searches for a Higgs boson in the bb decay mode were conducted at the Tevatron by the CDF and D0 Collaborations. They reported an excess of events in V H associated production (where V is used to denote W or Z) in the mass range of 120 GeV to 135 GeV, with a global signifi...

A search for doubly charged Higgs bosons with pairs of prompt, isolated, highly energetic leptons with the same electric charge is presented. The search uses a protonproton collision data sample at a centre-of-mass energy of 13 TeV corresponding to 36.1 fb −1 of integrated luminosity recorded in 2015 and 2016 by the ATLAS detector at the LHC. This analysis focuses on the decays H ±± → e ± e ± , H ±± → e ± μ ± and H ±± → μ ± μ ± , fitting the dilepton mass spectra in several exclusive signal regions. No significant evidence of a signal is observed and corresponding limits on the production cross-section and consequently a lower limit on m(H ±± ) are derived at 95% confidence level. With ± ± = e ± e ± /μ ± μ ± /e ± μ ± , the observed lower limit on the mass of a doubly charged Higgs boson only coupling to left-handed leptons varies from 770 to 870 GeV (850 GeV expected) for B(H ±± → ± ± ) = 100% and both the expected and observed mass limits are above 450 GeV for B(H ±± → ± ± ) = 10% and any combination of partial branching ratios. IntroductionEvents with two prompt, isolated, highly energetic leptons with the same electric charge (same-charge leptons) are produced very rarely in a proton-proton collision according to the predictions of the standard model (SM), but may occur with higher rate in various theories beyond the standard model (BSM). This analysis focuses on BSM theories that contain a doubly charged Higgs particle H ±± using the observed invariant mass of same-charge lepton pairs. In the absence of evidence for a signal, lower limits on the mass of the H ±± particle are set at the 95% confidence level.Doubly charged Higgs bosons can arise in a large variety of BSM theories, namely in left-right symmetric (LRS) e-mail: atlas.publications@cern.ch models [1][2][3][4][5], Higgs triplet models [6,7], the little Higgs model [8], type-II see-saw models [9][10][11][12][13], the GeorgiMachacek model [14], scalar singlet dark matter [15], and the Zee-Babu neutrino mass model [16][17][18]. Theoretical studies [19][20][21] [22]. Besides the leptonic decay, the H ±± particle can decay into a pair of W bosons as well. For low values of the Higgs triplet vacuum expectation value v , it decays almost exclusively to leptons while for high values of v the decay is mostly to a pair of W bosons [9,12]. In this analysis, the coupling to W bosons is assumed to be negligible and only pair production via the Drell-Yan process is considered. The Feynman diagram of the production mechanism is presented in Fig. 1.The analysis targets only decays of the H ±± particle into electrons and muons, denoted by . Other final states X that are not directly selected in this analysis are taken into account by reducing the lepton multiplicity of the final state. These states X would include, for instance, τ leptons or W bosons, as well as particles which escape detection. The total assumed branching ratio of H ±± is therefore B(Moreover, the decay width is assumed to be negligible compared to the detector resolution, which is compa...