Search for new phenomena in events with same-charge leptons and b-jets in p p collisions at √ s = 13 TeV with the ATLAS detectorThe ATLAS Collaboration A search for new phenomena in events with two same-charge leptons or three leptons and jets identified as originating from b-quarks in a data sample of 36.1 fb −1 of pp collisions at √ s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider is reported. No significant excess is found and limits are set on vector-like quark, four-top-quark, and samesign top-quark pair production. The observed (expected) 95% CL mass limits for a vector-like Tand B-quark singlet are m T > 0.98 (0.99) TeV and m B > 1.00 (1.01) TeV respectively. Limits on the production of the vector-like T 5/3 -quark are also derived considering both pair and single production; in the former case the lower limit on the mass of the T 5/3 -quark is (expected to be) 1.19 (1.21) TeV. The Standard Model four-top-quark production cross-section upper limit is (expected to be) 69 (29) fb. Constraints are also set on exotic four-top-quark production models. Finally, limits are set on same-sign top-quark pair production. The upper limit on uu → tt production is (expected to be) 89 (59) fb for a mediator mass of 1 TeV, and a dark-matter interpretation is also derived, excluding a mediator of 3 TeV with a dark-sector coupling of 1.0 and a coupling to ordinary matter above 0.31. Signals considered 2.1 Vector-like T , B, and T 5/3 quarksVector-like quarks are fractionally charged, coloured fermions whose right-and left-handed components transform identically under weak isospin. Their existence is predicted in many BSM models that address the Higgs boson mass fine-tuning problem [7][8][9][10][11][12][13][14][15][16]. VLQ may come in several varieties, including the ATLAS detectorThe ATLAS detector [29] at the LHC covers nearly the entire solid angle around the collision point.3 It consists of an inner tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroidal magnets. The inner-detector system is immersed in a 2 T axial magnetic field and provides charged-particle tracking in the range |η| < 2.5.A high-granularity silicon pixel detector covers the vertex region and typically provides four threedimensional measurements per track, the innermost being in the insertable B-layer [30]. It is followed by a silicon microstrip tracker, which provides four two-dimensional measurement points per track. These silicon detectors are complemented by a transition radiation tracker, which enables radially extended track reconstruction up to |η| = 2.0. The transition radiation tracker also provides electron identification information based on the fraction of hits (typically 30 in total) above a higher energy-deposit threshold corresponding to transition radiation.The calorimeter system covers the pseudorapidity range |η| < 4.9. Within the region |η| < 3.2, electromagnetic calorimetry is provided ...

A measurement of fiducial and differential crosssections for W + W − production in proton-proton collisions at √ s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 36.1 fb −1 is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as W W → e ± νμ ∓ ν. To suppress topquark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory.

Measurement of the Higgs boson mass in theH → Z Z * → 4 and H → γγ channels with √ s = 13 TeV p p collisions using the ATLAS detector The ATLAS Collaboration The mass of the Higgs boson is measured in the H → Z Z * → 4 and in the H → γγ decay channels with 36.1 fb −1 of proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector in 2015 and 2016. The measured value in the H → Z Z * → 4 channel is m Z Z * H = 124.79 ± 0.37 GeV, while the measured value in the H → γγ channel is m γγ H = 124.93 ± 0.40 GeV. Combining these results with the ATLAS measurement based on 7 and 8 TeV proton-proton collision data yields a Higgs boson mass of m H = 124.97 ± 0.24 GeV.

Search for WW/W Z resonance production in νqq final states in pp collisions at √ s = 13 TeV with the ATLAS detectorThe ATLAS Collaboration A search is conducted for new resonances decaying into a WW or WZ boson pair, where one W boson decays leptonically and the other W or Z boson decays hadronically. It is based on proton-proton collision data with an integrated luminosity of 36.1 fb −1 collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of √ s = 13 TeV in 2015 and 2016. The search is sensitive to diboson resonance production via vectorboson fusion as well as quark-antiquark annihilation and gluon-gluon fusion mechanisms. No significant excess of events is observed with respect to the Standard Model backgrounds. Several benchmark models are used to interpret the results. Limits on the production cross section are set for a new narrow scalar resonance, a new heavy vector-boson and a spin-2 Kaluza-Klein graviton.The ATLAS detector [22] is a general-purpose particle detector used to investigate a broad range of physics processes. It includes an inner detector (ID) surrounded by a superconducting solenoid, electromagnetic (EM) and hadronic calorimeters and a muon spectrometer (MS) inside a system of toroidal magnets. The ID consists of a silicon pixel detector including a newly installed innermost layer called the insertable B-layer [23], a silicon microstrip detector and a straw-tube tracker. It is immersed in a 2 T axial 2 magnetic field and provides precision tracking of charged particles with pseudorapidity 1 |η| < 2.5. The straw-tube tracker also provides transition radiation measurements for electron identification. The calorimeter system comprises finely segmented sampling calorimeters using lead/liquid-argon for the detection of EM showers up to |η| = 3.2, and (copper or tungsten)/liquid-argon for hadronic showers for 1.5 < |η| < 4.9. In the central region (|η| < 1.7), a steel/scintillator hadronic calorimeter is used. Outside the calorimeters, the muon system incorporates multiple layers of trigger and tracking chambers in a magnetic field produced by a system of superconducting toroids, enabling an independent precise measurement of muon track momenta for |η| < 2.7. The ATLAS detector has a two-level trigger system that is based on custom hardware followed by a software trigger to reduce the selected event rate to approximately 1 kHz for offline analysis [24]. Signal and background simulationSamples of simulated signal and background events are used to optimize the event selection and to estimate the background contribution from various SM processes. For all the signal samples, the νqq final state is imposed at the generator level.The heavy neutral Higgs boson signal was generated using Powheg-Box v1 [25,26] with the next-toleading-order (NLO) gg_H [27] and VBF_H [28] modules and the CT10 [29] parton density functions (PDF). The Powheg-Box event generator was interfaced to Pythia 8.186 [30] for parton showering, underlying event and hadronization using the AZNLO set o...

So far dark matter direct detection experiments have indicated any dark matter particle to have feeble interactions with nucleons, while the dark relic matter density favors it to take part in weak interactions. We point out that the neutralino dark matter in the Minimal Supersymmetric Standard Model (MSSM) and the Next-to-Minimal Supersymmetric Standard Model (NMSSM) fails to process these two seemingly contradictory features in their most natural parameter space due to the limited theoretical structure. By contrast, the seesaw extension of the NMSSM, which was originally proposed to solve neutrino mass problem, enables the lightest sneutrino as a new viable DM candidate to readily have the features, and thus satisfies the constraints of the DM measurements in its broad parameter space. Compared with the Type-I seesaw extension, the dark matter physics in the inverse seesaw extension is more flexible to be consistent with current dark matter and collider experimental results. We conclude that the weakly interacting massive particles in supersymmetric theory is still a promising dark matter candidate.