51. 
 Aad, G, et al.
(författare)

Searches for scalar leptoquarks in pp collisions at [Formula: see text] = 8 TeV with the ATLAS detector.
 2016

Ingår i: European Physical Journal C. Particles and Fields.  : Springer.  14346044. ; 76

Tidskriftsartikel (refereegranskat)abstract
 Searches for pairproduced scalar leptoquarks are performed using 20 fb[Formula: see text] of protonproton collision data provided by the LHC and recorded by the ATLAS detector at [Formula: see text] TeV. Events with two electrons (muons) and two or more jets in the final state are used to search for first (second)generation leptoquarks. The results from two previously published ATLAS analyses are interpreted in terms of thirdgeneration leptoquarks decaying to [Formula: see text] and [Formula: see text] final states. No statistically significant excess above the Standard Model expectation is observed in any channel and scalar leptoquarks are excluded at 95 % CL with masses up to [Formula: see text] 1050 GeV for firstgeneration leptoquarks, [Formula: see text] 1000 GeV for secondgeneration leptoquarks, [Formula: see text] 625 GeV for thirdgeneration leptoquarks in the [Formula: see text] channel, and 200 [Formula: see text] 640 GeV in the [Formula: see text] channel.


52. 
 Aad, G, et al.
(författare)

Study of the [Formula: see text] and [Formula: see text] decays with the ATLAS detector.
 2016

Ingår i: European Physical Journal C. Particles and Fields.  : Springer.  14346044. ; 76

Tidskriftsartikel (refereegranskat)abstract
 The decays [Formula: see text] and [Formula: see text] are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb[Formula: see text] of pp collisions collected at centreofmass energies [Formula: see text] TeV and 8 TeV, respectively. Signal candidates are identified through [Formula: see text] and [Formula: see text] decays. With a twodimensional likelihood fit involving the [Formula: see text] reconstructed invariant mass and an angle between the [Formula: see text] and [Formula: see text] candidate momenta in the muon pair rest frame, the yields of [Formula: see text] and [Formula: see text], and the transverse polarisation fraction in [Formula: see text] decay are measured. The transverse polarisation fraction is determined to be [Formula: see text], and the derived ratio of the branching fractions of the two modes is [Formula: see text], where the first error is statistical and the second is systematic. Finally, a sample of [Formula: see text] decays is used to derive the ratios of branching fractions [Formula: see text] and [Formula: see text], where the third error corresponds to the uncertainty of the branching fraction of [Formula: see text] decay. The available theoretical predictions are generally consistent with the measurement.


53. 
 Aad, G, et al.
(författare)

Study of the spin and parity of the Higgs boson in diboson decays with the ATLAS detector.
 2015

Ingår i: European Physical Journal C. Particles and Fields.  : Springer.  14346044 . 14346052. ; 75:10

Tidskriftsartikel (refereegranskat)abstract
 Studies of the spin, parity and tensor couplings of the Higgs boson in the [Formula: see text], [Formula: see text] and [Formula: see text] decay processes at the LHC are presented. The investigations are based on [Formula: see text] of pp collision data collected by the ATLAS experiment at [Formula: see text] TeV and [Formula: see text] TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers [Formula: see text], is tested against several alternative spin scenarios, including nonSM spin0 and spin2 models with universal and nonuniversal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9 % confidence level. Using the [Formula: see text] and [Formula: see text] decays, the tensor structure of the interaction between the spin0 boson and the SM vector bosons is also investigated. The observed distributions of variables sensitive to the nonSM tensor couplings are compatible with the SM predictions and constraints on the nonSM couplings are derived.


54. 
 Aad, G., et al.
(författare)

Summary of the ATLAS experiment's sensitivity to supersymmetry after LHC Run 1interpreted in the phenomenological MSSM
 2015

Ingår i: Journal of High Energy Physics.  : Springer.  10298479 . 11266708. ; :10

Tidskriftsartikel (refereegranskat)abstract
 A summary of the constraints from the ATLAS experiment on Rparityconserving supersymmetry is presented. Results from 22 separate ATLAS searches are considered, each based on analysis of up to 20.3 fb(1) of protonproton collision data at centreofmass energies of root s = 7 and 8TeV at the Large Hadron Collider. The results are interpreted in the context of the 19parameter phenomenological minimal supersymmetric standard model, in which the lightest supersymmetric particle is a neutralino, taking into account constraints from previous precision electroweak and flavour measurements as well as from dark matter related measurements. The results are presented in terms of constraints on supersymmetric particle masses and are compared to limits from simplified models. The impact of ATLAS searches on parameters such as the dark matter relic density, the couplings of the observed Higgs boson, and the degree of electroweak finetuning is also shown. Spectra for surviving supersymmetry model points with low finetunings are presented.


55. 
 Aad, G., et al.
(författare)

Z boson production in p plus Pb collisions at root SNN=5.02 TeV measured with the ATLAS detector
 2015

Ingår i: Physical Review C (Nuclear Physics).  : American Physical Society.  05562813 . 1089490X. ; 92:4

Tidskriftsartikel (refereegranskat)abstract
 The ATLAS Collaboration measures the inclusive production of Z bosons via their decays into electron and muon pairs in p + Pb collisions at root SNN = 5.02 TeV at the Large Hadron Collider. The measurements are made using data corresponding to integrated luminosities of 29.4 and 28.1 nb(1) for Z > ee and Z > mu mu, respectively. The results from the two channels are consistent and combined to obtain a cross section times the Z > ll branching ratio, integrated over the rapidity region vertical bar y(Z)*vertical bar < 3.5, of 139.8 +/ 4.8 (statistical) +/ 6.2 (systematic) +/ 3.8 (luminosity) nb. Differential cross sections are presented as functions of the Z boson rapidity and transverse momentum and compared with models based on parton distributions both with and without nuclear corrections. The centrality dependence of Z boson production in p + Pb collisions is measured and analyzed within the framework of a standard Glauber model and the model's extension for fluctuations of the underlying nucleonnucleon scattering cross section.


56. 
 Aad, G., et al.
(författare)

A search for t(t)overbar resonances using leptonplusjets events in protonproton collisions at root s=8 TeV with the ATLAS detector
 2015

Ingår i: Journal of High Energy Physics.  : Springer.  10298479 . 11266708. ; :8

Tidskriftsartikel (refereegranskat)abstract
 A search for new particles that decay into top quark pairs is reported. The search is performed with the ATLAS experiment at the LHC using an integrated luminosity of 20.3 fb(1) of protonproton collision data collected at a centreofmass energy of root s = 8TeV. The leptonplusjets final state is used, where the top pair decays to W (+) bW()(b) over bar, with one W boson decaying leptonically and the other hadronically. The invariant mass spectrum of top quark pairs is examined for local excesses or deficits that are inconsistent with the Standard Model predictions. No evidence for a top quark pair resonance is found, and 95% confidencelevel limits on the production rate are determined for massive states in benchmark models. The upper limits on the crosssection times branching ratio of a narrow Z' boson decaying to top pairs range from 4.2 pb to 0.03 pb for resonance masses from 0.4 TeV to 3.0 TeV. A narrow leptophobic topcolour Z' boson with mass below 1.8 TeV is excluded. Upper limits are set on the crosssection times branching ratio for a broad colouroctet resonance with Gamma/m = 15% decaying to tt. These range from 4.8 pb to 0.03 pb for masses from 0.4 TeV to 3.0 TeV. A KaluzaKlein excitation of the gluon in a RandallSundrum model is excluded for masses below 2.2 TeV.


57. 
 Aad, G, et al.
(författare)

Determination of spin and parity of the Higgs boson in the [Formula: see text] decay channel with the ATLAS detector.
 2015

Ingår i: European Physical Journal C. Particles and Fields.  : Springer.  14346044. ; 75:5

Tidskriftsartikel (refereegranskat)abstract
 Studies of the spin and parity quantum numbers of the Higgs boson in the [Formula: see text] final state are presented, based on protonproton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb[Formula: see text] at a centreofmass energy of [Formula: see text] TeV. The Standard Model spinparity [Formula: see text] hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the StandardModellike Higgs boson and CPeven ([Formula: see text]) or CPodd ([Formula: see text]) Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.


58. 
 Aad, G, et al.
(författare)

Determination of the Ratio of bQuark Fragmentation Fractions f_{s}/f_{d} in pp Collisions at sqrt[s]=7 TeV with the ATLAS Detector.
 2015

Ingår i: Physical Review Letters.  : American Physical Society.  10797114. ; 115:26

Tidskriftsartikel (refereegranskat)abstract
 With an integrated luminosity of 2.47 fb^{1} recorded by the ATLAS experiment at the LHC, the exclusive decays B_{s}^{0}→J/ψϕ and B_{d}^{0}→J/ψK^{*0} of B mesons produced in pp collisions at sqrt[s]=7 TeV are used to determine the ratio of fragmentation fractions f_{s}/f_{d}. From the observed B_{s}^{0}→J/ψϕ and B_{d}^{0}→J/ψK^{*0} yields, the quantity (f_{s}/f_{d})[B(B_{s}^{0}→J/ψϕ)/B(B_{d}^{0}→J/ψK^{*0})] is measured to be 0.199±0.004(stat)±0.008(syst). Using a recent theory prediction for [B(B_{s}^{0}→J/ψϕ)/B(B_{d}^{0}→J/ψK^{*0})] yields (f_{s}/f_{d})=0.240±0.004(stat)±0.010(syst)±0.017(th). This result is based on a new approach that provides a significant improvement of the world average.


59. 
 Aad, G., et al.
(författare)

Differential topantitop crosssection measurements as a function of observables constructed from finalstate particles using pp collisions at root s=7 TeV in the ATLAS detector
 2015

Ingår i: Journal of High Energy Physics.  : Springer.  10298479 . 11266708. ; :6

Tidskriftsartikel (refereegranskat)abstract
 Various differential crosssections are measured in topquark pair (t (t) over bar) events produced in protonproton collisions at a centreofmass energy of root s = 7 TeV at the LHC with the ATLAS detector. These differential crosssections are presented in a data set corresponding to an integrated luminosity of 4.6 fb(1). The differential crosssections are presented in terms of kinematic variables, such as momentum, rapidity and invariant mass, of a topquark proxy referred to as the pseudotopquark as well as the pseudotopquark pair system. The dependence of the measurement on theoretical models is minimal. The measurements are performed on tt events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a bquark. The hadronic and leptonic pseudotopquarks are defined via the leptonic or hadronic decay mode of the W boson produced by the topquark decay in events with a single charged lepton. Differential crosssection measurements of the pseudotopquark variables are compared with several Monte Carlo models that implement nexttoleading order or leadingorder multileg matrixelement calculations.


60. 
 Aad, G., et al.
(författare)

Measurement of colour flow with the jet pull angle in t(t)overbar events using the ATLAS detector at root s=8 TeV
 2015

Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and HighEnergy Physics.  : Elsevier.  03702693 . 18732445. ; 750, s. 475493

Tidskriftsartikel (refereegranskat)abstract
 The distribution and orientation of energy inside jets is predicted to be an experimental handle on colour connections between the hardscatter quarks and gluons initiating the jets. This Letter presents a measurement of the distribution of one such variable, the jet pull angle. The pull angle is measured for jets produced in t (t) over bar events with one W boson decaying leptonically and the other decaying to jets using 20.3 fb(1) of data recorded with the ATLAS detector at a centreofmass energy of root s = 8 TeV at the LHC. The jet pull angle distribution is corrected for detector resolution and acceptance effects and is compared to various models. (C) 2015 CERN for the benefit of the ATLAS Collaboration. Published by Elsevier B.V.

