Measurements of transverse energy-energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to $\sqrt{s} = 8$ TeV proton-proton collisions with an integrated luminosity of 20.2 fb$^{-1}$. The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of $\alpha_s(\mu)$ predicted in QCD up to scales over 1 TeV. A global fit to the transverse energy-energy correlation distributions yields $\alpha_s(m_Z) = 0.1162 \pm 0.0011 \mbox{ (exp.)}^{+0.0084}_{-0.0070} \mbox{ (theo.)}$, while a global fit to the asymmetry distributions yields a value of $\alpha_s(m_Z) = 0.1196 \pm 0.0013 \mbox{ (exp.)}^{+0.0075}_{-0.0045} \mbox{ (theo.)}$.
TEEC function for 800 GeV < HT2 < 850 GeV
ATEEC function for 800 GeV < HT2 < 850 GeV
TEEC function for 850 GeV < HT2 < 900 GeV
A search for heavy neutral Higgs bosons and $Z^{\prime}$ bosons is performed using a data sample corresponding to an integrated luminosity of 36.1 fb$^{-1}$ from proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded by the ATLAS detector at the LHC during 2015 and 2016. The heavy resonance is assumed to decay to $\tau^+\tau^-$ with at least one tau lepton decaying to final states with hadrons and a neutrino. The search is performed in the mass range of 0.2-2.25 TeV for Higgs bosons and 0.2-4.0 TeV for $Z^{\prime}$ bosons. The data are in good agreement with the background predicted by the Standard Model. The results are interpreted in benchmark scenarios. In the context of the hMSSM scenario, the data exclude $\tan\beta > 1.0$ for $m_A$ = 0.25 TeV and $\tan\beta > 42$ for $m_A$ = 1.5 TeV at the 95% confidence level. For the Sequential Standard Model, $Z^{\prime}_\mathrm{SSM}$ with $m_{Z^{\prime}} < 2.42$ TeV is excluded at 95% confidence level, while $Z^{\prime}_\mathrm{NU}$ with $m_{Z^{\prime}} < 2.25$ TeV is excluded for the non-universal $G(221)$ model that exhibits enhanced couplings to third-generation fermions.
Two dimensional likelihood scan of the gluon-gluon fusion cross section times braching fraction, $\sigma(gg\phi)\times B(\phi\to\tau\tau)$, vs the b-associated production times branching fraction, $\sigma(bb\phi)\times B(\phi\to\tau\tau)$ for the Higgs boson mass ($m_\phi$) indicated in the table. For each mass, 10000 points are scanned. At each point $\Delta(\mathrm{NLL})$ is calculated, defined as the negative-log-likelihood (NLL) of the conditional fit with $\sigma(gg\phi)$ and $\sigma(bb\phi)$ fixed to their values at the point and with the minimum NLL value at any point subtracted. Vaules are provided for the fit to the observed data and to the expected data, which is the sum of Standard Model contributions not including the SM Higgs boson. The best-fit point and the preferred 68% and 95% boundaries are found at $2\Delta(\mathrm{NLL})$ values of 0.0, 2.30 and 5.90, respectively.
This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb$^{-1}$. The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: $|\eta^\gamma|<1.37$ and $1.56<|\eta^\gamma|<2.37$. The measurement covers photon transverse energies $25 < E_\textrm{T}^\gamma<400$ GeV and $25 < E_\textrm{T}^\gamma<350$ GeV respectively for the two $|\eta^\gamma|$ regions. For each jet flavour, the ratio of the cross sections in the two $|\eta^\gamma|$ regions is also measured. The measurement is corrected for detector effects and compared to leading-order and next-to-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central $\gamma+b$ measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions.
Signed shifts of the individual systematic uncertainties on the $\gamma+b$ cross section for $|\eta^\gamma|<1.37$. The numbers after the name of the uncertainty source refer to the individual component in that uncertainty. Each bin of the MC statistical uncertainty is independent of any other bin. The first four components of the photon energy scale uncertainty are specific to this $|\eta^\gamma|$ region and are independent of the components in the other region. The region is indicated as part of their name to indicate the independence between the $|\eta^\gamma|$ regions. The uncertainties on the prompt photon modelling, non-perturbative QCD models and particle-level migration effects are only varied once and not up and down by their nature, but are symmetrised for the final results. Only uncertainties which have at least a 1% variation in at least one bin of the $\gamma+b$ and $\gamma+c$ cross section measurements, including the ratios, are listed. The others are summed in quadrature and listed as a single entry.
Signed shifts of the individual systematic uncertainties on the $\gamma+b$ cross section for $1.56<|\eta^\gamma|<2.37$. The numbers after the name of the uncertainty source refer to the individual component in that uncertainty. Each bin of the MC statistical uncertainty is independent of any other bin. The first four components of the photon energy scale uncertainty are specific to this $|\eta^\gamma|$ region and are independent of the components in the other region. The region is indicated as part of their name to indicate the independence between the $|\eta^\gamma|$ regions. The uncertainties on the prompt photon modelling, non-perturbative QCD models and particle-level migration effects are only varied once and not up and down by their nature, but are symmetrised for the final results. Only uncertainties which have at least a 1% variation in at least one bin of the $\gamma+b$ and $\gamma+c$ cross section measurements, including the ratios, are listed. The others are summed in quadrature and listed as a single entry.
Signed shifts of the individual systematic uncertainties on the $\gamma+c$ cross section for $|\eta^\gamma|<1.37$. The numbers after the name of the uncertainty source refer to the individual component in that uncertainty. Each bin of the MC statistical uncertainty is independent of any other bin. The first four components of the photon energy scale uncertainty are specific to this $|\eta^\gamma|$ region and are independent of the components in the other region. The region is indicated as part of their name to indicate the independence between the $|\eta^\gamma|$ regions. The uncertainties on the prompt photon modelling, non-perturbative QCD models and particle-level migration effects are only varied once and not up and down by their nature, but are symmetrised for the final results. Only uncertainties which have at least a 1% variation in at least one bin of the $\gamma+b$ and $\gamma+c$ cross section measurements, including the ratios, are listed. The others are summed in quadrature and listed as a single entry.
Searches for new phenomena in high-mass diphoton final states with the ATLAS experiment at the LHC are presented. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 36.7 fb$^{-1}$ at a centre-of-mass energy $\sqrt{s}=13$ TeV recorded in 2015 and 2016. Searches are performed for resonances with spin 0, as predicted by theories with an extended Higgs sector, and for resonances with spin 2, using a warped extra-dimension model as a benchmark model, as well as for non-resonant signals, assuming a large extra-dimension scenario. No significant deviation from the Standard Model is observed. Upper limits are placed on the production cross section times branching ratio to two photons as a function of the resonance mass. In addition, lower limits are set on the ultraviolet cutoff scale in the large extra-dimensions model.
Upper limits on the fiducial cross section times branching ratio to two photons at centre-of-mass energy of 13 TeV of a narrow-width (Γ_X = 4 MeV) spin-0 resonance as a function of its mass m_X.
Upper limits on the fiducial cross section times branching ratio to two photons at centre-of-mass energy of 13 TeV of a spin-0 resonance as a function of its mass m_X. The decay width of the resonance equals to 2% of m_X.
Upper limits on the fiducial cross section times branching ratio to two photons at centre-of-mass energy of 13 TeV of a spin-0 resonance as a function of its mass m_X. The decay width of the resonance equals to 6% of m_X.
A search for long-lived, massive particles predicted by many theories beyond the Standard Model is presented. The search targets final states with large missing transverse momentum and at least one high-mass displaced vertex with five or more tracks, and uses 32.8 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV $pp$ collision data collected by the ATLAS detector at the LHC. The observed yield is consistent with the expected background. The results are used to extract 95\% CL exclusion limits on the production of long-lived gluinos with masses up to 2.37 TeV and lifetimes of $\mathcal{O}(10^{-2})$-$\mathcal{O}(10)$ ns in a simplified model inspired by Split Supersymmetry.
Parameterized event selection efficiencies as a function of truth MET for events which have all truth decay vertices occurring before the start of the ATLAS calorimeter. Event-level efficiencies are evaluated for events that have truth MET $> 200$ GeV, pass the trackless jet requirement, and have at least one displaced truth decay within the fiducial volume. To satisfy the event-level efficiency, events must then pass the full event selection.
Parameterized vertex level efficiencies as a function of number of particles associated to a truth decay vertex, and the vertex invariant mass for truth decays with $4$ mm $< R_{\mathrm{decay}} < 22$ mm. Selected particles are required to have nonzero electric charge, $p_{T}(|Q|=1) > 1$ GeV, and $d_0 > 2$ mm. The per-vertex efficiency is evaluated only for truth vertices that have at least 5 associated tracks, an invariant mass $> 10$ GeV, and are in the region $4$ mm $< R_{\mathrm{decay}} < 300$ mm, and $|Z_{\mathrm{decay}}| < 300$ mm. A truth vertex satisfies the vertex level efficiency if it can be matched to a reconstructed DV which passes the final vertex selection.
Parameterized vertex level efficiencies as a function of number of particles associated to a truth decay vertex, and the vertex invariant mass for truth decays with $4$ mm $< R_{\mathrm{decay}} < 22$ mm. Selected particles are required to have nonzero electric charge, $p_{T}(|Q|=1) > 1$ GeV, and $d_0 > 2$ mm. The per-vertex efficiency is evaluated only for truth vertices that have at least 5 associated tracks, an invariant mass $> 10$ GeV, and are in the region $4$ mm $< R_{\mathrm{decay}} < 300$ mm, and $|Z_{\mathrm{decay}}| < 300$ mm. A truth vertex satisfies the vertex level efficiency if it can be matched to a reconstructed DV which passes the final vertex selection.
A search is presented for particles that decay producing a large jet multiplicity and invisible particles. The event selection applies a veto on the presence of isolated electrons or muons and additional requirements on the number of b-tagged jets and the scalar sum of masses of large-radius jets. Having explored the full ATLAS 2015-2016 dataset of LHC proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$, which corresponds to 36.1 fb$^{-1}$ of integrated luminosity, no evidence is found for physics beyond the Standard Model. The results are interpreted in the context of simplified models inspired by R-parity-conserving and R-parity-violating supersymmetry, where gluinos are pair-produced. More generic models within the phenomenological minimal supersymmetric Standard Model are also considered.
Number of signal events expected for 36.1 fb$^{-1}$ at different stages of the event selection for the signal region SR-11j50-0b in a pMSSM inspired model where m($\tilde{g}$) = 1400 GeV and m($\tilde{\chi}_{0}^{1}$) = 200 GeV.
Number of signal events expected for 36.1 fb$^{-1}$ at different stages of the event selection for the signal region SR-11j50-0b in a pMSSM inspired model where m($\tilde{g}$) = 1400 GeV and m($\tilde{\chi}_{0}^{1}$) = 200 GeV.
$E_{\mathrm{T}}^{\mathrm{miss}} / \sqrt{H_{\mathrm{T}}}$ distribution in signal region SR-8j50-0b-MJ340. Two benchmark signal models are overlaid on the plot for comparison. Labelled `pMSSM' and `2-step', they show signal distributions from the example SUSY models (as described in the paper): a pMSSM slice model with ($m \tilde{g}$, $m \tilde{\chi_{1}^{\pm}}$) = (1300, 200) GeV and a cascade decay model with ($m \tilde{g}$, $m \tilde{\chi_{1}^{0}}$) = (1300, 200) GeV.
Measurements of $ZZ$ production in the $\ell^{+}\ell^{-}\ell^{\prime +}\ell^{\prime -}$ channel in proton-proton collisions at 13 TeV center-of-mass energy at the Large Hadron Collider are presented. The data correspond to 36.1 $\mathrm{fb}^{-1}$ of collisions collected by the ATLAS experiment in 2015 and 2016. Here $\ell$ and $\ell'$ stand for electrons or muons. Integrated and differential $ZZ \to \ell^{+}\ell^{-}\ell^{\prime +}\ell^{\prime -}$ cross sections with $Z \to \ell^+\ell^-$ candidate masses in the range of 66 GeV to 116 GeV are measured in a fiducial phase space corresponding to the detector acceptance and corrected for detector effects. The differential cross sections are presented in bins of twenty observables, including several that describe the jet activity. The integrated cross section is also extrapolated to a total phase space and to all Standard-Model decays of $Z$ bosons with mass between 66 GeV and 116 GeV, resulting in a value of $17.3 \pm 0.9$ [$\pm 0.6$ (stat.) $\pm 0.5$ (syst.) $\pm 0.6$ (lumi.)] pb. The measurements are found to be in good agreement with the Standard-Model predictions. A search for neutral triple gauge couplings is performed using the transverse momentum distribution of the leading $Z$-boson candidate. No evidence for such couplings is found and exclusion limits are set on their parameters.
Observed data events as function of the transverse momentum of the 1. lepton.
A search is presented for photonic signatures, motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of proton-proton collision data at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$ recorded by the ATLAS detector at the LHC, and it explores models dominated by both strong and electroweak production of supersymmetric partner states. Experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon or additional jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Standard Model prediction, and 95% confidence-level upper limits of between 0.083 fb and 0.32 fb are set on the visible cross section of contributions from physics beyond the Standard Model. These results are interpreted in terms of lower limits on the masses of gluinos, squarks, and gauginos in the context of generalized models of gauge-mediated supersymmetry, which reach as high as 2.3 TeV for strongly produced and 1.3 TeV for weakly produced supersymmetric partner pairs.
Distribution of the total visible transverse energy $H_{\mathrm{T}}$ for selected diphoton events, after requiring $\Delta\phi_{\mathrm{min}} (\mathrm{jet}, E_{\mathrm{T}}^{\mathrm{miss}}) > 0.5$ but before application of a requirement on $E_{\mathrm{T}}^{\mathrm{miss}}$ and $\Delta\phi_{\mathrm{min}} (\gamma, E_{\mathrm{T}}^{\mathrm{miss}})$ ($\gamma\gamma$ pre-selection). Also shown are the expected $H_{\mathrm{T}}$ distributions of contributing SM processes as well as those for two points each in the parameter spaces of the gluino-bino and wino-bino GGM models (mass values in GeV). Events outside the range of the displayed region are included in the highest-value bin.
Derived exclusion limits for the squark-bino GGM model explored by the diphoton analysis. For each point in the squark-bino parameter space, the SR ($\mathrm{SR}^{\gamma\gamma}_{S-L}$ or $\mathrm{SR}^{\gamma\gamma}_{S-H}$) that provides the best expected sensitivity is used to estimate the exclusion likelihood. The labels indicate the best-expected signal region for each point, where SL and SH mean $\mathrm{SR}^{\gamma\gamma}_{S-L}$ and $\mathrm{SR}^{\gamma\gamma}_{S-H}$, respectively.
Properties of the Higgs boson are measured in the two-photon final state using 36.1 fb$^{-1}$ of proton-proton collision data recorded at $\sqrt{s} = 13$ TeV by the ATLAS experiment at the Large Hadron Collider. Cross-section measurements for the production of a Higgs boson through gluon-gluon fusion, vector-boson fusion, and in association with a vector bosonor a top-quark pair are reported. The signal strength, defined as the ratio of the observed to the expected signal yield, is measured for each of these production processes as well as inclusively. The global signal strength measurement of $0.99 \pm 0.14$ improves on the precision of the ATLAS measurement at $\sqrt{s} = 7$ and 8 TeV by a factor of two. Measurements of gluon-gluon fusion and vector-boson fusion productions yield signal strengths compatible with the Standard Model prediction. Measurements of simplified template cross sections, designed to quantify the different Higgs boson production processes in specific regions of phase space, are reported. The cross section for the production of the Higgs boson decaying to two isolated photons in a fiducial region closely matching the experimental selection of the photons is measured to be $55 \pm 10$ fb, which is in good agreement with the Standard Model prediction of $64 \pm 2$ fb. Furthermore, cross sections in fiducial regions enriched in Higgs boson production in vector-boson fusion or in association with large missing transverse momentum, leptons or top-quark pairs are reported. Differential and double-differential measurements are performed for several variables related to the diphoton kinematics as well as the kinematics and multiplicity of the jets produced in association with a Higgs boson. No significant deviations from a wide array of Standard Model predictions are observed.
Measured differential cross section with associated uncertainties as a function of PT(2GAMMA) [NJET=1,PT>30 GEV]. Each systematic uncertainty sources is fully uncorrelated with the other sources and fully correlated across bins, except for the background modelling systematics for which an uncorrelated treatment across bins is more appropriate.
A search for the supersymmetric partners of the Standard Model bottom and top quarks is presented. The search uses 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV collected by the ATLAS experiment at the Large Hadron Collider. Direct production of pairs of bottom and top squarks ($\tilde{b}_{1}$ and $\tilde{t}_{1}$) is searched for in final states with $b$-tagged jets and missing transverse momentum. Distinctive selections are defined with either no charged leptons (electrons or muons) in the final state, or one charged lepton. The zero-lepton selection targets models in which the $\tilde{b}_{1}$ is the lightest squark and decays via $\tilde{b}_{1} \rightarrow b \tilde{\chi}^{0}_{1}$, where $\tilde{\chi}^{0}_{1}$ is the lightest neutralino. The one-lepton final state targets models where bottom or top squarks are produced and can decay into multiple channels, $\tilde{b}_{1} \rightarrow b \tilde{\chi}^{0}_{1}$ and $\tilde{b}_{1} \rightarrow t \tilde{\chi}^{\pm}_{1}$, or $\tilde{t}_{1} \rightarrow t \tilde{\chi}^{0}_{1}$ and $\tilde{t}_{1} \rightarrow b \tilde{\chi}^{\pm}_{1}$, where $\tilde{\chi}^{\pm}_{1}$ is the lightest chargino and the mass difference $m_{\tilde{\chi}^{\pm}_{1}}- m_{\tilde{\chi}^{0}_{1}}$ is set to 1 GeV. No excess above the expected Standard Model background is observed. Exclusion limits at 95\% confidence level on the mass of third-generation squarks are derived in various supersymmetry-inspired simplified models.
Observed exclusion limit for b1L-SRA300-2j for sbottom pair production with asymmetric decay into a bottom quark and a neutralino or a top quark and a chargino.
Observed exclusion limit for b1L-SRA300-2j for sbottom pair production with asymmetric decay into a bottom quark and a neutralino or a top quark and a chargino.
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