Motivated by the recent LHC hints of a Higgs boson around 125 GeV, we assume a SM-like Higgs with the mass 123-127 GeV and study its implication in low energy SUSY by comparing the MSSM and NMSSM. We consider various experimental constraints at 2σ level (including the muon g − 2 and the dark matter relic density) and perform a comprehensive scan over the parameter space of each model. Then in the parameter space which is allowed by current experimental constraints and also predicts a SM-like Higgs in 123-127 GeV, we examine the properties of the sensitive parameters (like the top squark mass and the trilinear coupling A t ) and calculate the rates of the di-photon signal and the V V * (V = W, Z) signals at the LHC. Our typical findings are: (i) In the MSSM the top squark and A t must be large and thus incur some fine-tuning, which can be much ameliorated in the NMSSM; (ii) In the MSSM a light stau is needed to enhance the di-photon rate of the SM-like Higgs to exceed its SM prediction, while in the NMSSM the di-photon rate can be readily enhanced in several ways; (iii) In the MSSM the signal rates of pp → h → V V * at the LHC are never enhanced compared with their SM predictions, while in the NMSSM they may get enhanced significantly; (iv) A large part of the parameter space so far survived will be soon covered by the expected XENON100(2012) sensitivity (especially for the NMSSM).

Results of a search for supersymmetry via direct production of third-generation squarks are reported, using 20.3 fb −1 of proton-proton collision data at ffiffi ffi s p ¼ 8 TeV recorded by the ATLAS experiment at the LHC in 2012. Two different analysis strategies based on monojetlike and c-tagged event selections are carried out to optimize the sensitivity for direct top squark-pair production in the decay channel to a charm quark and the lightest neutralino (t 1 → c þχ 0 1 ) across the top squark-neutralino mass parameter space. No excess above the Standard Model background expectation is observed. The results are interpreted in the context of direct pair production of top squarks and presented in terms of exclusion limits in the (m~t 1 , m~χ0 1 ) parameter space. A top squark of mass up to about 240 GeV is excluded at 95% confidence level for arbitrary neutralino masses, within the kinematic boundaries. Top squark masses up to 270 GeV are excluded for a neutralino mass of 200 GeV. In a scenario where the top squark and the lightest neutralino are nearly degenerate in mass, top squark masses up to 260 GeV are excluded. The results from the monojetlike analysis are also interpreted in terms of compressed scenarios for top squark-pair production in the decay channelt 1 → b þ ff 0 þχ 0 1 and sbottom pair production withb 1 → b þχ 0 1 , leading to a similar exclusion for nearly mass-degenerate third-generation squarks and the lightest neutralino. The results in this paper significantly extend previous results at colliders.

The ATLAS CollaborationDark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H → invisible decays where H is produced according to the Standard Model via vector boson fusion, Z( )H, and W/Z(had)H, all performed with the ATLAS detector using 36.1 fb −1 of pp collisions at a center-of-mass energy of √ s = 13 TeV at the LHC. In combination with the results at √ s = 7 and 8 TeV, an exclusion limit on the H → invisible branching ratio of 0.26 (0.17 +0.07 −0.05 ) at 95% confidence level is observed (expected). 1 ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the center of the detector and the z-axis along the beam pipe. The x-axis points to the center of the LHC ring, and the y-axis points upward. 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). The distance between two objects in η-φ space is ∆R = (∆η) 2 + (∆φ) 2 . Transverse momentum is defined by p T = p sin θ.

A search for a heavy charged-boson resonance decaying into a charged lepton (electron or muon) and a neutrino is reported. A data sample of 139 fb −1 of proton-proton collisions at ffiffi ffi s p ¼ 13 TeV collected with the ATLAS detector at the LHC during 2015-2018 is used in the search. The observed transverse mass distribution computed from the lepton and missing transverse momenta is consistent with the distribution expected from the Standard Model, and upper limits on the cross section for pp → W 0 → lν are extracted (l ¼ e or μ). These vary between 1.3 pb and 0.05 fb depending on the resonance mass in the range between 0.15 and 7.0 TeV at 95% confidence level for the electron and muon channels combined. Gauge bosons with a mass below 6.0 and 5.1 TeV are excluded in the electron and muon channels, respectively, in a model with a resonance that has couplings to fermions identical to those of the Standard Model W boson. Crosssection limits are also provided for resonances with several fixed Γ=m values in the range between 1% and 15%. Model-independent limits are derived in single-bin signal regions defined by a varying minimum transverse mass threshold. The resulting visible cross-section upper limits range between 4.6 (15) pb and 22 (22) ab as the threshold increases from 130 (110) GeV to 5.1 (5.1) TeV in the electron (muon) channel.

Measurement of W ± Z production cross sections and gauge boson polarisation in p p collisions at √ s = 13 TeV with the ATLAS detectorThe ATLAS Collaboration This paper presents measurements of W ± Z production cross sections in pp collisions at a centreof-mass energy of 13 TeV. The data were collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider, and correspond to an integrated luminosity of 36.1 fb −1 . The W ± Z candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The measured inclusive cross section in the detector fiducial region for a single leptonic decay mode is σ fid. W ± Z→ ν = 63.7 ± 1.0 (stat.) ± 2.3 (syst.) ± 1.4 (lumi.) fb, reproduced by the next-to-next-to-leading-order Standard Model prediction of 61.5 +1.4 −1.3 fb. Cross sections for W + Z and W − Z production and their ratio are presented as well as differential cross sections for several kinematic observables. An analysis of angular distributions of leptons from decays of W and Z bosons is performed for the first time in pair-produced events in hadronic collisions, and integrated helicity fractions in the detector fiducial region are measured for the W and Z bosons separately. Of particular interest, the longitudinal helicity fraction of pair-produced vector bosons is also measured.The ATLAS detector [32-34] is a multipurpose particle detector with a cylindrical geometry1 and nearly 4π coverage in solid angle. A set of tracking detectors around the collision point (collectively referred to as the inner detector) is located within a superconducting solenoid providing a 2 T axial magnetic field, and is surrounded by a calorimeter system and a muon spectrometer. The inner detector (ID) consists of a silicon pixel detector and a silicon microstrip tracker, together providing precision tracking in the pseudorapidity range |η| < 2.5, complemented by a straw-tube transition radiation tracker providing tracking and electron identification information for |η| < 2.0. The electromagnetic calorimeter covers the region |η| < 3.2 and is based on a lead/liquid-argon (LAr) sampling technology. The hadronic calorimeter uses a steel/scintillator-tile sampling detector in the region |η| < 1.7 and a copper/LAr detector in the region 1.5 < |η| < 3.2. The most forward region of ATLAS, 3.1 < |η| < 4.9, is equipped with a forward calorimeter, measuring electromagnetic and hadronic energies in copper/LAr and tungsten/LAr modules. The muon spectrometer (MS) comprises separate trigger and high-precision tracking chambers to measure the deflection of muons in a magnetic field generated by three large superconducting toroids with coils arranged with an eightfold azimuthal symmetry around the calorimeters. The high-precision chambers cover the range of |η| < 2.7 with three layers of monitored drift tubes, complemented by cathode strip chambers in the forward region, where the particle flux is highest. The muon trigger system covers the range |η| < 2.4 with resistive-plate chambers in the barrel a...