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.
The inclusive $t\bar{t}$ production charge asymmetry, $A_C$, with statistical and systematic uncertainties combined.
Measured charge asymmetry, $A_C$, values for the electron and muon channels combined after unfolding as a function of the $t\bar{t}$ invariant mass, $m_{t\bar{t}}$. The quoted uncertainties include statistical and systematic components after the marginalisation.
Measured charge asymmetry, $A_C$, values for the electron and muon channels combined after unfolding as a function of the $t\bar{t}$ velocity along the z-axis, $\beta_{z,t\bar{t}}$. The quoted uncertainties include statistical and systematic components after the marginalisation.
Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states $X(3872)$ and $\psi(2S)$, in the decay mode $J/\psi \pi^+\pi^-$, measured using 11.4 fb$^{-1}$ of $pp$ collisions at $\sqrt{s} = 8$ TeV by the ATLAS detector at the LHC. The ratio of cross-sections $X(3872)/\psi(2S)$ is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of $X(3872)$ and $\psi(2S)$. Assuming independent single effective lifetimes for non-prompt $X(3872)$ and $\psi(2S)$ production gives $R_B = \frac{\mathcal{B}(B \rightarrow X(3872)\textrm{ + any}) \mathcal{B}(X(3872 \rightarrow J/\psi\pi^+\pi^-)}{\mathcal{B}(B \rightarrow \psi(2S)\textrm{ + any}) \mathcal{B}(\psi(2S) \rightarrow J/\psi\pi^+\pi^-)} = (3.95 \pm 0.32 \mathrm{(stat)} \pm 0.08\mathrm{(sys)}) \times 10^{-2}$, while separating short- and long-lived contributions, assuming that the short-lived component is due to $B_c$ decays, gives $R_B = (3.57 \pm 0.33\mathrm{(stat)} \pm 0.11\mathrm{(sys)}) \times 10^{-2}$, with the fraction of non-prompt $X(3872)$ produced via $B_c$ decays for $p_\mathrm{T}(X(3872)) > 10$ GeV being $(25 \pm 13\mathrm{(stat)} \pm 2\mathrm{(sys)} \pm 5\mathrm{(spin)})\%$. The distributions of the dipion invariant mass in the $X(3872)$ and $\psi(2S)$ decays are also measured and compared to theoretical predictions.
Measured effective pseudo-proper lifetime for non-prompt $\psi(2S)$ production.
Measured effective pseudo-proper lifetime for non-prompt $X(3872)$ production.
Measured non-prompt $X(3872) / \psi(2S)$ production ratio using the single-lifetime fit model.
This paper describes a measurement of fiducial and differential cross sections of gluon-fusion Higgs boson production in the $H{\rightarrow\,}WW^{\ast}{\rightarrow\,}e\nu\mu\nu$ channel, using 20.3 fb$^{-1}$ of proton-proton collision data. The data were produced at a centre-of-mass energy of $\sqrt{s} = 8$ TeV at the CERN Large Hadron Collider and recorded by the ATLAS detector in 2012. Cross sections are measured from the observed $H{\rightarrow\,}WW^{\ast}{\rightarrow\,}e\nu\mu\nu$ signal yield in categories distinguished by the number of associated jets. The total cross section is measured in a fiducial region defined by the kinematic properties of the charged leptons and neutrinos. Differential cross sections are reported as a function of the number of jets, the Higgs boson transverse momentum, the dilepton rapidity, and the transverse momentum of the leading jet. The jet-veto efficiency, or fraction of events with no jets above a given transverse momentum threshold, is also reported. All measurements are compared to QCD predictions from Monte Carlo generators and fixed-order calculations, and are in agreement with the Standard Model predictions.
Measured total fiducial cross section in fb.
Measured fiducial cross section in fb as a function of Njet. Jet PT>25 GeV for |eta|<2.4 and PT>30 GeV for 2.4<|eta|<4.5.
Measured fiducial cross section in fb/GeV as a function of pTH.
The production of two prompt $J/\psi$ mesons, each with transverse momenta $p_{\mathrm{T}}>8.5$ GeV and rapidity $|y| < 2.1$, is studied using a sample of proton-proton collisions at $\sqrt{s} = 8$ TeV, corresponding to an integrated luminosity of 11.4 fb$^{-1}$ collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised $J/\psi$ production, is measured as a function of the transverse momentum of the lower-$p_{\mathrm{T}}$ $J/\psi$ meson, di-$J/\psi$ $p_{\mathrm{T}}$ and mass, the difference in rapidity between the two $J/\psi$ mesons, and the azimuthal angle between the two $J/\psi$ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two $J/\psi$ mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be $\sigma_{\mathrm{eff}} = 6.3 \pm 1.6 \mathrm{(stat)} \pm 1.0 \mathrm{(syst)}$ mb.
The cross-section in bins of the sub-leading $J/\psi$ transverse momentum in the central rapidity region, assuming unpolarised $J/\psi$ mesons and excluding the $J/\psi$ spin-alignment systematic uncertainty. The branching fraction and luminosity uncertainties are not included in the systematic uncertainty as they are constant at 1.1$\%$ and 1.9$\%$ respectively.
The cross-section in bins of the sub-leading $J/\psi$ transverse momentum in the forward rapidity region, assuming unpolarised $J/\psi$ mesons and excluding the $J/\psi$ spin-alignment systematic uncertainty. The branching fraction and luminosity uncertainties are not included in the systematic uncertainty as they are constant at 1.1$\%$ and 1.9$\%$ respectively.
The cross-section in bins of the di-$J/\psi$ transverse momentum in the central rapidity region, assuming unpolarised $J/\psi$ mesons and excluding the $J/\psi$ spin-alignment systematic uncertainty. The branching fraction and luminosity uncertainties are not included in the systematic uncertainty as they are constant at 1.1$\%$ and 1.9$\%$ respectively.
A measurement of the correlations between the polar angles of leptons from the decay of pair-produced $t$ and $\bar{t}$ quarks in the helicity basis is reported, using proton-proton collision data collected by the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 4.6fb$^{-1}$ at a center-of-mass energy of $\sqrt{s}=7$TeV collected during 2011. Candidate events are selected in the dilepton topology with large missing transverse momentum and at least two jets. The angles $\theta_1$ and $\theta_2$ between the charged leptons and the direction of motion of the parent quarks in the $t\bar{t}$ rest frame are sensitive to the spin information, and the distribution of {\mbox{$\cos\theta_1\cdot\cos\theta_2$}} is sensitive to the spin correlation between the $t$ and $\bar{t}$ quarks. The distribution is unfolded to parton level and compared to the next-to-leading order prediction. A good agreement is observed.
The numerical summary of the unfolded $\cos\theta_1\cdot\cos\theta_2$ distribution, with statistical and systematic uncertainties.
The correlation factors for the statistical uncertainties between any two bins of the unfolded distribution.
A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an $R$-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a $b$-jet. The dataset corresponds to an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a $b$-quark.
Signal acceptance (in %) in the (BRe,BRtau) plane for a 800 GeV stop, for the SR800 signal region.
Expected exclusion limit contour in the (BRe,BRtau) plane for a 600 GeV stop. All limits are computed at 95% CL.
Expected exclusion limit contour in the (BRe,BRtau) plane for a 600 GeV stop. All limits are computed at 95% CL.
A search is conducted for new resonances decaying into a $W$ or $Z$ boson and a 125 GeV Higgs boson in the $\nu\bar{\nu}b\bar{b}$, $\ell^{\pm}{\nu}b\bar{b}$, and $\ell^+\ell^-b\bar{b}$ final states, where $\ell ^{\pm}= e^{\pm}$ or $\mu^{\pm}$, in $pp$ collisions at $\sqrt s = 13$ TeV. The data used correspond to a total integrated luminosity of 36.1 fb$^{-1}$ collected with the ATLAS detector at the Large Hadron Collider during the 2015 and 2016 data-taking periods. The search is conducted by examining the reconstructed invariant or transverse mass distributions of $Wh$ and $Zh$ candidates for evidence of a localised excess in the mass range of 220 GeV up to 5 TeV. No significant excess is observed and the results are interpreted in terms of constraints on the production cross-section times branching fraction of heavy $W^\prime$ and $Z^\prime$ resonances in heavy-vector-triplet models and the CP-odd scalar boson $A$ in two-Higgs-doublet models. Upper limits are placed at the 95 % confidence level and range between $9.0\times 10^{-4}$ pb and $8.1\times 10^{-1}$ pb depending on the model and mass of the resonance.
Upper limits on Zprime to Z h production cross section x branching fraction in pb
Upper limits on Zprime to Z h production cross section x branching fraction in pb
Upper limits on Wprime to W h production cross section x branching fraction in pb
A search for supersymmetry in events with large missing transverse momentum, jets, and at least one hadronically decaying tau lepton has been performed using 3.2 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the Large Hadron Collider in 2015. Two exclusive final states are considered, with either exactly one or at least two tau leptons. No excess over the Standard Model prediction is observed in the data. Results are interpreted in the context of gauge-mediated supersymmetry breaking and a simplified model of gluino pair production with tau-rich cascade decays, substantially improving on previous limits. In the GMSB model considered, supersymmetry-breaking scale ($\Lambda$) values below 92 TeV are excluded at the 95% confidence level, corresponding to gluino masses below 2000 GeV. For large values of $\tan\beta$, values of $\Lambda$ up to 107 TeV and gluino masses up to 2300 GeV are excluded. In the simplified model, gluino masses are excluded up to 1570 GeV for neutralino masses around 100 GeV. Neutralino masses up to 700 GeV are excluded for all gluino masses between 800 GeV and 1500 GeV, while the strongest exclusion of 750 GeV is achieved for gluino masses around 1400 GeV.
mTtau distributions for "extended SR selections" of the 1 tau channel, for the Compressed SR selection without the mTtau > 80 GeV requirement. The last bin includes overflow events. Uncertainties are statistical only. Signal predictions are overlaid for several benchmark models, normalised to their predicted cross sections. For the simplified model, "LM" refers to a low mass splitting, or compressed scenario, with m(gluino)=665 GeV and m(neutralino)=585 GeV; "MM" stands for a medium mass splitting, with m(gluino)=1145 GeV and m(neutralino)=265 GeV; "HM" denotes a high mass splitting scenario, with m(gluino)=1305 GeV and m(neutralino)=105 GeV.
mTtau distributions for "extended SR selections" of the 1 tau channel, for the Medium Mass SR selection without the mTtau > 200 GeV requirement. The last bin includes overflow events. Uncertainties are statistical only. Signal predictions are overlaid for several benchmark models, normalised to their predicted cross sections. For the simplified model, "LM" refers to a low mass splitting, or compressed scenario, with m(gluino)=665 GeV and m(neutralino)=585 GeV; "MM" stands for a medium mass splitting, with m(gluino)=1145 GeV and m(neutralino)=265 GeV; "HM" denotes a high mass splitting scenario, with m(gluino)=1305 GeV and m(neutralino)=105 GeV.
mTtau distributions for "extended SR selections" of the 1 tau channel, for the High Mass SR selection without the mTtau > 200 GeV requirement. The last bin includes overflow events. Uncertainties are statistical only. Signal predictions are overlaid for several benchmark models, normalised to their predicted cross sections. For the simplified model, "LM" refers to a low mass splitting, or compressed scenario, with m(gluino)=665 GeV and m(neutralino)=585 GeV; "MM" stands for a medium mass splitting, with m(gluino)=1145 GeV and m(neutralino)=265 GeV; "HM" denotes a high mass splitting scenario, with m(gluino)=1305 GeV and m(neutralino)=105 GeV.
Measurements of the per-event charged-particle yield as a function of the charged-particle transverse momentum and rapidity are performed using $p+$Pb collision data collected by the ATLAS experiment at the LHC at a centre-of-mass energy of $\sqrt{s_{NN}}=5.02$ TeV. Charged particles are reconstructed over pseudorapidity $|\eta|<2.3$ and transverse momentum between $0.1$ GeV and $22$ GeV in a dataset corresponding to an integrated luminosity of $1$ $\mu b^{-1}$. The results are presented in the form of charged-particle nuclear modification factors, where the $p+$Pb charged-particle multiplicities are compared between central and peripheral $p+$Pb collisions as well as to charged-particle cross sections measured in pp collisions. The $p+$Pb collision centrality is characterized by the total transverse energy measured in $-4.9<\eta<-3.1$, which is in the direction of the outgoing lead beam. Three different estimations of the number of nucleons participating in the $p+$Pb collision are carried out using the Glauber model and two Glauber-Gribov colour-fluctuation extensions to the Glauber model. The values of the nuclear modification factors are found to vary significantly as a function of rapidity and transverse momentum. A broad peak is observed for all centralities and rapidities in the nuclear modification factors for charged-particle transverse momentum values around $3$ GeV. The magnitude of the peak increases for more central collisions as well as rapidity ranges closer to the direction of the outgoing lead nucleus.
Invariant differential $p_{T}$ spectra of charged particles which are produced in p+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV shown in six $\eta$ intervals, for the 0--90% centrality interval. The individual spectra are scaled by constant factors (indicated in the legend) for visibility. The statistical uncertainties are indicated with vertical lines and the systematic uncertainties are indicated with boxes, but are generally much smaller than the size of the symbols.
Invariant differential $p_{T}$ spectra of charged particles which are produced in p+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV shown in six y* intervals, for the 0--90% centrality interval. The individual spectra are scaled by constant factors (indicated in the legend) for visibility. The statistical uncertainties are indicated with vertical lines and the systematic uncertainties are indicated with boxes, but are generally much smaller than the size of the symbols.
The invariant differential y* spectra of charged particles produced in p+Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV are shown in five centrality intervals for $p_{T}>0.1$ GeV. The statistical uncertainties are indicated with vertical lines and the systematic uncertainties are indicated with boxes.
Ratios of top-quark pair to $Z$-boson cross sections measured from proton--proton collisions at the LHC centre-of-mass energies of $\sqrt s=13$TeV, 8TeV, and 7TeV are presented by the ATLAS Collaboration. Single ratios, at a given $\sqrt s$ for the two processes and at different $\sqrt s$ for each process, as well as double ratios of the two processes at different $\sqrt s$, are evaluated. The ratios are constructed using previously published ATLAS measurements of the $t\overline{t}$ and $Z$-boson production cross sections, corrected to a common phase space where required, and a new analysis of $Z \rightarrow \ell^+ \ell^-$ where $\ell=e,\mu$ at $\sqrt s=13$TeV performed with data collected in 2015 with an integrated luminosity of $3.2$fb$^{-1}$. Correlations of systematic uncertainties are taken into account when evaluating the uncertainties in the ratios. The correlation model is also used to evaluate the combined cross section of the $Z\rightarrow e^+e^-$ and the $Z\rightarrow \mu^+ \mu^-$ channels for each $\sqrt s$ value. The results are compared to calculations performed at next-to-next-to-leading-order accuracy using recent sets of parton distribution functions. The data demonstrate significant power to constrain the gluon distribution function for the Bjorken-$x$ values near 0.1 and the light-quark sea for $x<0.02$.
Measured fiducial cross section times leptonic branching ratio for Z/gamma* production in the Z/gamma* -> e+e- final state at 13TeV.
Measured fiducial cross section times leptonic branching ratio for Z/gamma* production in the Z/gamma* -> mu+ mu- final state at 13TeV.
Breakdown of systematic uncertainties in percent for the measured fiducial cross section times leptonic branching ratio for Z/gamma* production in the Z/gamma* -> e+e- final state at 13TeV.
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