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If new physics is found at the LHC (and the ILC) the reconstruction of the underlying theory should not be biased by assumptions about high-scale models. For the mapping of many measurements onto high-dimensional parameter spaces we introduce SFitter with its new weighted Markov chain technique. SFitter constructs an exclusive likelihood map, determines the best-fitting parameter point and produces a ranked list of the most likely parameter points. Using the example of the TeV-scale supersymmetric Lagrangian we show how a high-dimensional likelihood map will generally include degeneracies and strong correlations. SFitter allows us to study such model-parameter spaces employing Bayesian as well as frequentist constructions. We illustrate in detail how it should be possible to analyze high-dimensional new-physics parameter spaces like the TeV-scale MSSM at the LHC. A combination of LHC and ILC measurements might well be able to completely cover highly complex TeV-scale parameter spaces.

If supersymmetry is observed at the LHC its model parameters can be measured at the electroweak scale. We discuss the expected precision on the parameter determination, including a proper treatment of experimental and theoretical errors. Particular attention is paid to degenerate solutions. Using the SFitter framework we perform a bottom–up reconstruction of the unified parameters at the high scale, including a full error propagation.

High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e + e- linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.

A measurement of the $ZZ$ production in the $\\ell^{-}\\ell^{+}\\ell^{\\prime -}\\ell^{\\prime +}$ and $\\ell^{-}\\ell^{+}\\nu\\bar{\\nu}$ channels $(\\ell = e, \\mu)$ in proton--proton collisions at $\\sqrt{s} = 8$ TeV at the Large Hadron Collider at CERN, using data corresponding to an integrated luminosity of 20.3 fb$^{-1}$ collected by the ATLAS experiment in 2012 is presented. The fiducial cross sections for $ZZ\\to\\ell^{-}\\ell^{+}\\ell^{\\prime -}\\ell^{\\prime +}$ and $ZZ\\to \\ell^{-}\\ell^{+}\\nu\\bar{\\nu}$ are measured in selected phase-space regions. The total cross section for $ZZ$ events produced with both $Z$ bosons in the mass range 66 to 116 GeV is measured from the combination of the two channels to be $7.3\\pm0.4\\textrm{(stat)}\\pm0.3\\textrm{(syst)}\\pm0.2\\textrm{(lumi)}$ pb, which is consistent with the Standard Model prediction of $6.6^{+0.7}_{-0.6}$ pb. The differential cross sections in bins of various kinematic variables are presented. The differential event yield as a function of the transverse momentum of the leading $Z$ boson is used to set limits on anomalous neutral triple gauge boson couplings in $ZZ$ production.

Two searches for new phenomena in final states containing a same-flavour opposite-lepton (electron or muon) pair, jets, and large missing transverse momentum are presented. These searches make use of proton--proton collision data, collected during 2015 and 2016 at a centre-of-mass energy $\\sqrt{s}=13$ TeV by the ATLAS detector at the Large Hadron Collider, which correspond to an integrated luminosity of 14.7 fb$^{-1}$. Both searches target the pair production of supersymmetric particles, squarks or gluinos, which decay to final states containing a same-flavour opposite-sign lepton pair via one of two mechanisms: a leptonically decaying Z boson in the final state, leading to a peak in the dilepton invariant-mass distribution around the Z boson mass; and decays of neutralinos (e.g. $\\tilde{\\chi}_2^0 \\rightarrow \\ell^+\\ell^- \\tilde{\\chi}_1^0$), yielding a kinematic endpoint in the dilepton invariant-mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted in simplified models of gluino-pair (squark-pair) production, and provide sensitivity to gluinos (squarks) with masses as large as 1.70 TeV (980 GeV).

Differential cross sections for the production of at least four jets have been measured in proton--proton collisions at $\\sqrt{s} = 8$ TeV at the Large Hadron Collider using the ATLAS detector. The dataset corresponds to an integrated luminosity of 20.3 $fb^{-1}$. The cross sections, corrected for detector effects, are compared to leading-order and next-to-leading-order calculations as a function of the jet momenta, invariant masses, minimum and maximum opening angles and other kinematic variables.

This paper reports inclusive and differential measurements of the $t\\bar{t}$ charge asymmetry $A_{\\textrm{C}}$ in 20.3 fb$^{-1}$ of $\\sqrt{s} = 8$ TeV $pp$ collisions recorded by the ATLAS experiment at the Large Hadron Collider at CERN. Three differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the $t\\bar{t}$ system. The $t\\bar{t}$ pairs are selected in the single-lepton channels ($e$ or $\\mu$) with at least four jets, and a likelihood fit is used to reconstruct the $t\\bar{t}$ event kinematics. A Bayesian unfolding procedure is performed to infer the asymmetry at parton level from the observed data distribution. The inclusive $t\\bar{t}$ charge asymmetry is measured to be $A_{\\textrm{C}} = 0.009 \\pm 0.005$ (stat.$+$syst.). The inclusive and differential measurements are compatible with the values predicted by the Standard Model.

A study of the decays B0→μ+μ− and B0s→μ+μ− has been performed using data corresponding to an integrated luminosity of 25 fb−1 of 7 TeV and 8 TeV proton--proton collisions collected with the ATLAS detector during the LHC Run 1. For B0, an upper limit on the branching fraction is set at B(B0→μ+μ−)<4.2×10−10 at 95% confidence level. For B0s, the branching fraction B(B0s→μ+μ−)=(0.9+1.1−0.8)×10−9 is measured. The results are consistent with the Standard Model expectation with a p-value of 4.8%, corresponding to 2.0 standard deviations.

A search is performed for an excited muon in the channel pp→μμ∗→μμ jet jet, assuming both the production and decay occur via a contact interaction. The analysis is based on 20.3 fb−1 of pp collision data at a centre-of-mass energy of s√ = 8 TeV taken with the ATLAS detector at the Large Hadron Collider. No evidence of excited muons is found, and limits are set at the 95% confidence level on the cross section times branching ratio as a function of the excited-muon mass mμ∗. For mμ∗ between 1.3 TeV and 3.0 TeV, the upper limit on σB(μ∗→μqq¯) is between 0.6 and 1 fb. Limits on σB are converted to lower bounds on the compositeness scale Λ. In the limiting case Λ=mμ∗, excited muons with a mass below 2.8 TeV are excluded. With the same model assumptions, these limits at larger μ∗ masses improve upon previous limits from searches based on the decay μ∗→μγ.