The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton-proton data produced at a ...centre-of-mass energy of 8 TeV with an integrated luminosity of Formula omitted. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti- Formula omitted algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton-proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in Formula omitted + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum Formula omitted 1500 GeV, and the relative energy resolution is Formula omitted for Formula omitted and Formula omitted for Formula omitted. The calibration scheme for jets with radius parameter Formula omitted, for which jets receive a dedicated calibration of the jet mass, is also discussed.
Results are presented from the measurement by ATLAS of long-range ( Formula omitted) dihadron angular correlations in Formula omitted and 13 TeV pp collisions containing a Z boson. The analysis is ...performed using 19.4 Formula omitted of Formula omitted TeV data recorded during Run 1 of the LHC and 36.1 Formula omitted of Formula omitted TeV data recorded during Run 2. Two-particle correlation functions are measured as a function of relative azimuthal angle over the relative pseudorapidity range Formula omitted for different intervals of charged-particle multiplicity and transverse momentum. The measurements are corrected for the presence of background charged particles generated by collisions that occur during one passage of two colliding proton bunches in the LHC. Contributions to the two-particle correlation functions from hard processes are removed using a template-fitting procedure. Sinusoidal modulation in the correlation functions is observed and quantified by the second Fourier coefficient of the correlation function, Formula omitted, which in turn is used to obtain the single-particle anisotropy coefficient Formula omitted. The Formula omitted values in the Z-tagged events, integrated over Formula omitted GeV, are found to be independent of multiplicity and Formula omitted, and consistent within uncertainties with previous measurements in inclusive pp collisions. As a function of charged-particle Formula omitted, the Z-tagged and inclusive Formula omitted values are consistent within uncertainties for Formula omitted GeV.
The inclusive and fiducial Formula omitted production cross-sections are measured in the lepton+jets channel using Formula omitted of proton-proton collision data at a centre-of-mass energy of 8 TeV ...recorded with the ATLAS detector at the LHC. Major systematic uncertainties due to the modelling of the jet energy scale and b-tagging efficiency are constrained by separating selected events into three disjoint regions. In order to reduce systematic uncertainties in the most important background, the Formula omitted process is modelled using Formula omitted+ jets events in a data-driven approach. The inclusive Formula omitted cross-section is measured with a precision of 5.7% to be Formula omitted, assuming a top-quark mass of 172.5 GeV. The result is in agreement with the Standard Model prediction. The cross-section is also measured in a phase space close to that of the selected data. The fiducial cross-section is Formula omitted with a precision of 4.5%.
The results of a search for new heavy Formula omitted bosons decaying to an electron or muon and a neutrino using proton-proton collision data at a centre-of-mass energy of Formula omitted TeV are ...presented. The dataset was collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1 Formula omitted. As no excess of events above the Standard Model prediction is observed, the results are used to set upper limits on the Formula omitted boson cross-section times branching ratio to an electron or muon and a neutrino as a function of the Formula omitted mass. Assuming a Formula omitted boson with the same couplings as the Standard Model W boson, Formula omitted masses below 5.1 TeV are excluded at the 95% confidence level.
A search for heavy resonances decaying into a pair of Formula omitted bosons leading to Formula omitted and Formula omitted final states, where Formula omitted stands for either an electron or a ...muon, is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 Formula omitted corresponding to an integrated luminosity of 36.1 Formula omitted collected with the ATLAS detector during 2015 and 2016 at the Large Hadron Collider. Different mass ranges for the hypothetical resonances are considered, depending on the final state and model. The different ranges span between 200 and 2000 Formula omitted. The results are interpreted as upper limits on the production cross section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are translated to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models, while those for the spin-2 resonance are used to constrain the Randall-Sundrum model with an extra dimension giving rise to spin-2 graviton excitations.
A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb Formula omitted of Formula omitted = 13 TeV pp collision data recorded ...by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, Formula omitted, which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range Formula omitted Formula omitted are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges Formula omitted Formula omitted and Formula omitted Formula omitted. Additional limits are set on the pair-production of massive colour-octet resonances.
A search for doubly charged Higgs bosons with pairs of prompt, isolated, highly energetic leptons with the same electric charge is presented. The search uses a proton-proton collision data sample at ...a centre-of-mass energy of 13 TeV corresponding to 36.1 Formula omitted of integrated luminosity recorded in 2015 and 2016 by the ATLAS detector at the LHC. This analysis focuses on the decays Formula omitted, Formula omitted and Formula omitted, fitting the dilepton mass spectra in several exclusive signal regions. No significant evidence of a signal is observed and corresponding limits on the production cross-section and consequently a lower limit on Formula omitted are derived at 95% confidence level. With Formula omitted, the observed lower limit on the mass of a doubly charged Higgs boson only coupling to left-handed leptons varies from 770 to 870 GeV (850 GeV expected) for Formula omitted and both the expected and observed mass limits are above 450 GeV for Formula omitted and any combination of partial branching ratios.
The differential cross-section for the production of a W boson in association with a top quark is measured for several particle-level observables. The measurements are performed using Formula omitted ...of pp collision data collected with the ATLAS detector at the LHC in 2015 and 2016. Differential cross-sections are measured in a fiducial phase space defined by the presence of two charged leptons and exactly one jet matched to a b-hadron, and are normalised with the fiducial cross-section. Results are found to be in good agreement with predictions from several Monte Carlo event generators.
The modification of the production of Formula omitted, Formula omitted, and Formula omitted ( Formula omitted) in p+Pb collisions with respect to their production in pp collisions has been studied. ...The p+Pb and pp datasets used in this paper correspond to integrated luminosities of Formula omitted and Formula omitted respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of Formula omitted and Formula omitted are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor, Formula omitted for Formula omitted and Formula omitted. No significant modification of the Formula omitted production is observed while Formula omitted production is found to be suppressed at low transverse momentum in p+Pb collisions relative to pp collisions. The production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central p+Pb collisions.
This paper presents a measurement of the polarisation of Formula omitted leptons produced in Formula omitted decays which is performed with a dataset of proton-proton collisions at Formula omitted ...TeV, corresponding to an integrated luminosity of 20.2 fb Formula omitted recorded with the ATLAS detector at the LHC in 2012. The Formula omitted decays are reconstructed from a hadronically decaying Formula omitted lepton with a single charged particle in the final state, accompanied by a Formula omitted lepton that decays leptonically. The Formula omitted polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic Formula omitted decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The Formula omitted polarisation extracted over the full phase space within the Formula omitted mass range of 66 Formula omitted 116 GeV is found to be Formula omitted. It is in agreement with the Standard Model prediction of Formula omitted, which is obtained from the ALPGEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA Formula omitted decay library.
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