A search for excited electrons produced in pp collisions at Formula omitted = 13 Formula omitted via a contact interaction Formula omitted is presented. The search uses 36.1 fb Formula omitted of ...data collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider. Decays of the excited electron into an electron and a pair of quarks ( Formula omitted) are targeted in final states with two electrons and two hadronic jets, and decays via a gauge interaction into a neutrino and a Formula omitted boson ( Formula omitted) are probed in final states with an electron, missing transverse momentum, and a large-radius jet consistent with a hadronically decaying Formula omitted boson. No significant excess is observed over the expected backgrounds. Upper limits are calculated for the Formula omitted and Formula omitted production cross sections as a function of the excited electron mass Formula omitted at 95% confidence level. The limits are translated into lower bounds on the compositeness scale parameter Formula omitted of the model as a function of Formula omitted. For Formula omitted Formula omitted, the lower bound for Formula omitted is 11 Formula omitted. In the special case of Formula omitted, the values of Formula omitted Formula omitted are excluded. The presented limits on Formula omitted are more stringent than those obtained in previous searches.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The production cross-sections for Formula omitted and Z bosons are measured using ATLAS data corresponding to an integrated luminosity of 4.0 pb Formula omitted collected at a centre-of-mass energy ...Formula omitted TeV. The decay channels Formula omitted and Formula omitted are used, where Formula omitted can be an electron or a muon. The cross-sections are presented for a fiducial region defined by the detector acceptance and are also extrapolated to the full phase space for the total inclusive production cross-section. The combined (average) total inclusive cross-sections for the electron and muon channels are: sigmaW+right arrowlνtot=2312±26(stat.)±27(syst.)±72(lumi.)±30(extr.)pb,sigmaW-right arrowlνtot=1399±21(stat.)±17(syst.)±43(lumi.)±21(extr.)pb,sigmaZright arrowlltot=323.4±9.8(stat.)±5.0(syst.)±10.0(lumi.)±5.5(extr.)pb.Measured ratios and asymmetries constructed using these cross-sections are also presented. These observables benefit from full or partial cancellation of many systematic uncertainties that are correlated between the different measurements.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A measurement of fiducial and differential cross-sections for Formula omitted production in proton-proton collisions at Formula omitted TeV with the ATLAS experiment at the Large Hadron Collider ...using data corresponding to an integrated luminosity of 36.1 Formula omitted is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as Formula omitted. To suppress top-quark 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.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Searches for scalar leptoquarks pair-produced in proton-proton collisions at Formula omitted TeV at the Large Hadron Collider are performed by the ATLAS experiment. A data set corresponding to an ...integrated luminosity of 36.1 fb Formula omitted is used. Final states containing two electrons or two muons and two or more jets are studied, as are states with one electron or muon, missing transverse momentum and two or more jets. No statistically significant excess above the Standard Model expectation is observed. The observed and expected lower limits on the leptoquark mass at 95% confidence level extend up to 1.29 TeV and 1.23 TeV for first- and second-generation leptoquarks, respectively, as postulated in the minimal Buchmüller-Rückl-Wyler model, assuming a branching ratio into a charged lepton and a quark of 50%. In addition, measurements of particle-level fiducial and differential cross sections are presented for the Formula omitted, Formula omitted and Formula omitted processes in several regions related to the search control regions. Predictions from a range of generators are compared with the measurements, and good agreement is seen for many of the observables. However, the predictions for the Formula omitted measurements in observables sensitive to jet energies disagree with the data.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, Formula omitted, for proton-proton collision data collected by the ...ATLAS detector at the Large Hadron Collider at a centre-of-mass energy Formula omitted Formula omitted. These decays are reconstructed from calorimeter jets found with the anti- Formula omitted Formula omitted jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of Formula omitted track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb Formula omitted of data collected in 2015 and 2016 using Formula omitted and Formula omitted event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A study of the decays Bs0 → μ+μ− and B0 → μ+μ− has been performed using 26.3 fb−1 of 13 TeV LHC proton-proton collision data collected with the ATLAS detector in 2015 and 2016. Since the detector ...resolution in μ+μ− invariant mass is comparable to the Bs0-B0 mass difference, a single fit determines the signal yields for both decay modes. This results in a measurement of the branching fraction ℬBs0→μ+μ−=3.2−1.0+1.1×10−9\ \mathrm{\mathcal{B}}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\right)=\left({3.2}_{-1.0}^{+1.1}\right)\times {10}^{-9} \ and an upper limit ℬB0→μ+μ−<4.3×10−10\ \mathrm{\mathcal{B}}\left({B}^0\to {\mu}^{+}{\mu}^{-}\right)<4.3\times {10}^{-10} \ at 95% confidence level. The result is combined with the Run 1 ATLAS result, yielding ℬBs0→μ+μ−=2.8−0.7+0.8×10−9\ \mathrm{\mathcal{B}}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\right)=\left({2.8}_{-0.7}^{+0.8}\right)\times {10}^{-9} \ and ℬB0→μ+μ−<2.1×10−10\ \mathrm{\mathcal{B}}\left({B}^0\to {\mu}^{+}{\mu}^{-}\right)<2.1\times {10}^{-10} \ at 95% confidence level. The combined result is consistent with the Standard Model prediction within 2.4 standard deviations in the ℬB0→μ+μ−−ℬBs0→μ+μ−\ \mathrm{\mathcal{B}}\left({B}^0\to {\mu}^{+}{\mu}^{-}\right)-\mathrm{\mathcal{B}}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\right) \ plane.
Algorithms used for the reconstruction and identification of electrons in the central region of the ATLAS detector at the Large Hadron Collider (LHC) are presented in this paper; these algorithms are ...used in ATLAS physics analyses that involve electrons in the final state and which are based on the 2015 and 2016 proton-proton collision data produced by the LHC at Formula omitted = 13 Formula omitted. The performance of the electron reconstruction, identification, isolation, and charge identification algorithms is evaluated in data and in simulated samples using electrons from Formula omitted and Formula omitted decays. Typical examples of combinations of electron reconstruction, identification, and isolation operating points used in ATLAS physics analyses are shown.
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This paper presents measurements of the Formula omitted and Formula omitted cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data ...were collected in proton-proton collisions at a centre-of-mass energy of 8 Formula omitted with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of Formula omitted. The precision of the cross-section measurements varies between 0.8 and 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.
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This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Formula omitted boson decaying into a muon pair. The data ...were obtained using the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of 13 Formula omitted with an integrated luminosity of Formula omitted. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Formula omitted boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This paper presents measurements of \W^{\pm }Z\ production cross sections in pp collisions at a centre-of-mass energy of 13 \\text {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~\hbox {fb}^{-1}\. The \W^{\pm }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 \\sigma _{W^\pm Z \rightarrow \ell ^{'} \nu \ell \ell }^{\text {fid.}} = 63.7 \, \pm ~1.0~\text {(stat.)} \, \pm ~2.3~\text {(syst.)} \, \pm ~1.4~\text {(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.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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