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.
A measurement of the Formula omitted decay parameters using Formula omitted of integrated luminosity collected with the ATLAS detector from 13 Formula omitted proton-proton collisions at the LHC is ...presented. The measured parameters include the CP-violating phase Formula omitted, the width difference Formula omitted between the Formula omitted meson mass eigenstates and the average decay width Formula omitted. The values measured for the physical parameters are combined with those from Formula omitted of 7 and 8 Formula omitted data, leading to the following: phis=-0.087±0.036(stat.)±0.021(syst.)radDELTAGAMMAs=0.0657±0.0043(stat.)±0.0037(syst.)ps-1GAMMAs=0.6703±0.0014(stat.)±0.0018(syst.)ps-1Results for Formula omitted and Formula omitted are also presented as 68% confidence level contours in the Formula omitted- Formula omitted plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. Formula omitted and Formula omitted measurements are in agreement with the Standard Model predictions.
A measurement of observables sensitive to spin correlations in Formula omitted production is presented, using 36.1 Formula omitted of pp collision data at Formula omitted TeV recorded with the ATLAS ...detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the Formula omitted system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.
Measurements of Formula omitted and Formula omitted production in Formula omitted final states have been performed. They are based on a data sample with integrated luminosity of 4.6 Formula omitted ...from proton-proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the ATLAS detector at the Large Hadron Collider. Neutral strange particles are separated into three classes, depending on whether they are contained in a jet, with or without a b-tag, or not associated with a selected jet. The aim is to look for differences in their main kinematic distributions. A comparison of data with several Monte Carlo simulations using different hadronisation and fragmentation schemes, colour reconnection models and different tunes for the underlying event has been made. The production of neutral strange particles in Formula omitted dileptonic events is found to be well described by current Monte Carlo models for Formula omitted and Formula omitted production within jets, but not for those produced outside jets.
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.
PDF