A search for non-resonant new phenomena, originating from either contact interactions or large extra spatial dimensions, has been carried out using events with two isolated electrons or muons. These events, produced at the LHC in proton-proton collisions at sqrt(s) = 7 TeV, were recorded by the ATLAS detector. The data sample, collected throughout 2011, corresponds to an integrated luminosity of 4.9 and 5.0 fb-1 in the e+e- and mu+mu- channels, respectively. No significant deviations from the Standard Model expectation are observed. Using a Bayesian approach, 95% confidence limit lower limits ranging from 9.0 to 13.9 TeV are placed on the energy scale of llqq contact interactions in the left-left isoscalar model. Lower limits ranging from 2.4 to 3.9 TeV are also set on the string scale in large extra dimension models. After combination of these limits with results from a similar search in the diphoton channel, slightly more stringent limits are obtained.
Expected and observed numbers of events in the dielectron channel for the contact interactions search region. The yields are normalized to the Z peak control region and include predictions for SM backgrounds as well as for SM+CI with different CI scales for constructive (LAMBDA-) and destructive (LAMBDA+) interference. The errors quoted originate from both systematic uncertainties and limited MC statistics.
Expected and observed numbers of events in the dimuon channel for the contact interactions search region. The yields are normalized to the Z peak control region and include predictions for SM backgrounds as well as for SM+CI with different CI scales for constructive (LAMBDA-) and destructive (LAMBDA+) interference. The errors quoted originate from both systematic uncertainties and limited MC statistics.
Expected and observed 95% C.L. lower limits on the contact interaction energy scale LAMBDA for the dielectron and dimuon channels, as well as for the combination of those channels. Results are provided for constructive and destruc- tive interference as well as different choices of flat priors.
Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton-proton collisions at sqrt(s)= 7 TeV corresponding to an integrated luminosity of 4.4 fb-1 collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios. No events in the signal region are observed and limits are set on the production cross section for supersymmetric particles, multiplied by the square of the branching ratio for a neutralino to decay to charged hadrons and a muon, as a function of the neutralino lifetime. To allow these limits to be used in a variety of models, they are presented for a range of squark and neutralino masses.
Efficiency-vs-radial-vertex-position without re-tracking The efficiency for reconstructing a displaced vertex passing all cuts, as a function of radial distance from the z-axis to the vertex positon. The retrack and noretrack suffixes refer to whether or not the procedure known as re-tracking, where the tracking algorithm is re-run with looser cuts, on the leftover hits from standard tracking, was used to select the tracks that were input to the vertexing algorithm.
Efficiency-vs-radial-vertex-position with re-tracking The efficiency for reconstructing a displaced vertex passing all cuts, as a function of radial distance from the z-axis to the vertex positon. The retrack and noretrack suffixes refer to whether or not the procedure known as re-tracking, where the tracking algorithm is re-run with looser cuts, on the leftover hits from standard tracking, was used to select the tracks that were input to the vertexing algorithm.
Event selection efficiency vs mean proper decay length The MH, HH, ML suffix used for overlaying the graphs refers to the combinations of squark and neutralino masses in the signal MC sample: MH is 700GeV squarks and 494GeV neutralinos, HH is 1.5TeV squarks and 494GeV neutralinos, and ML is 700GeV squarks and 108GeV neutralinos. The tables show the efficiency for reconstructing a signal event, where at least one vertex candidate passes all selection requirements, as a function of the proper decay length c*tau of the neutralino.
Using 1.8 fb-1 of pp collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the Large Hadron Collider, we present measurements of the production cross sections of Upsilon(1S,2S,3S) mesons. Upsilon mesons are reconstructed using the di-muon decay mode. Total production cross sections for p_T<70 GeV and in the rapidity interval |Upsilon|<2.25 are measured to be 8.01+-0.02+-0.36+-0.31 nb, 2.05+-0.01+-0.12+-0.08 nb, 0.92+-0.01+-0.07+-0.04 nb respectively, with uncertainties separated into statistical, systematic, and luminosity measurement effects. In addition, differential cross section times di-muon branching fractions for Upsilon(1S), Upsilon(2S), and Upsilon(3S) as a function of Upsilon transverse momentum p_T and rapidity are presented. These cross sections are obtained assuming unpolarized production. If the production polarization is fully transverse or longitudinal with no azimuthal dependence in the helicity frame the cross section may vary by approximately +-20%. If a non-trivial azimuthal dependence is considered, integrated cross sections may be significantly enhanced by a factor of two or more. We compare our results to several theoretical models of Upsilon meson production, finding that none provide an accurate description of our data over the full range of Upsilon transverse momenta accessible with this dataset.
Corrected cross-section measurements in the isotopic spin-alignment scenario. The second (sys) error is the uncertainty in the luminosity.
Fiducial Upsilon(1S) production cross-section, where pT>4 GeV and |eta|<2.3 for both muons, as a function of Upsilon(1S) pT in the Upsilon(1S) rapidity (|y|) bins 0-1.2 and 1.2-2.25. The first uncertainty is statistical, the second is systematic.
Fiducial Upsilon(2S) production cross-section, where pT>4 GeV and |eta|<2.3 for both muons, as a function of Upsilon(2S) pT in the Upsilon(2S) rapidity (|y|) bins 0-1.2 and 1.2-2.25. The first uncertainty is statistical, the second is systematic.
The results of a search for direct pair production of heavy top-quark partners in 4.7 fb-1 of integrated luminosity from pp collisions at sqrt(s) = 7 TeV collected by the ATLAS detector at the LHC are reported. Heavy top-quark partners decaying into a top quark and a neutral non-interacting particle are searched for in events with two leptons in the final state. No excess above the Standard Model expectation is observed. Limits are placed on the mass of a supersymmetric scalar top and of a spin-1/2 top-quark partner. A spin-1/2 top-quark partner with a mass between 300 GeV and 480 GeV, decaying to a top quark and a neutral non-interacting particle lighter than 100 GeV, is excluded at 95% confidence level.
(1) Number of generated MC events for the scalar top signal grid (2) Relative Cross section uncertainties for the scalar top signal grid.
(1) Acceptance of the same flavour selection for the scalar top signal grid (2) Selection efficiency of the same flavour selection for the scalar top signal grid (3) Product of the acceptance and efficiency of the same flavour selection for the scalar top signal grid (4) Relative experimental uncertainties on the acceptance times efficiency of the same flavour selection for the scalar top signal grid.
(1) Acceptance of the different flavour selection for the scalar top signal grid (2) Selection efficiency of the different flavour selection for the scalar top signal grid (3) Product of the acceptance and efficiency of the different flavour selection for the scalar top signal grid (4) Relative experimental uncertainties on the acceptance times efficiency of the different flavour selection for the scalar top signal grid.
A study of WZ production in proton-proton collisions at sqrt(s) = 7 TeV is presented using data corresponding to an integrated luminosity of 4.6 fb^-1 collected with the ATLAS detector at the Large Hadron Collider in 2011. In total, 317 candidates, with a background expectation of 68+/-10 events, are observed in double-leptonic decay final states with electrons, muons and missing transverse momentum. The total cross-section is determined to be sigma_WZ(tot) = 19.0+1.4/-1.3(stat.)+/-0.9(syst.)+/-0.4(lumi.) pb, consistent with the Standard Model expectation of 17.6+1.1/-1.0 pb. Limits on anomalous triple gauge boson couplings are derived using the transverse momentum spectrum of Z bosons in the selected events. The cross section is also presented as a function of Z boson transverse momentum and diboson invariant mass.
The measured fiducial cross section.
The measured total cross section.
Normalised fiducial cross section in bins of the PT of the Z0.
This letter reports the results of a search for top and bottom squarks from gluino pair production in 4.7 fb^-1 of pp collisions at sqrt(s) = 7 TeV using the ATLAS detector at the LHC. The search is performed in events with large missing transverse momentum and at least three jets identified as originating from a b-quark. Exclusion limits are presented for a variety of gluino-mediated models with gluino masses up to 1 TeV excluded.
Figure 2-a. Observed limit +1sigma-th.
Figure 2-a. Observed limit.
Figure 2-a. Observed limit -1sigma-th.
The prompt and non-prompt production cross-sections for the chi_c1 and chi_c2 charmonium states are measured in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector at the LHC using 4.5 fb^-1 of integrated luminosity. The chi_c states are reconstructed through the radiative decay chi_c -> J/psi gamma (with J/psi -> mu+mu-) where photons are reconstructed from gamma -> e+e- conversions. The production rate of the chi_c2 state relative to the chi_c1 state is measured for prompt and non-prompt chi_c as a function of J/psi transverse momentum. The prompt chi_c cross-sections are combined with existing measurements of prompt J/psi production to derive the fraction of prompt J/psi produced in feed-down from chi_c decays. The fractions of chi_c1 and chi_c2 produced in b-hadron decays are also measured.
Differential cross-section for prompt chi_c1 production, measured in bins of J/psi pT, assuming unpolarised chi_c production. The measurements are not corrected for the branching fractions of the decays chi_c --> J/psi + gamma and J/psi --> mu+ mu-. The uncertainty envelope associated with the unknown chi_c spin alignment is also shown.
Differential cross-section for prompt chi_c2 production, measured in bins of J/psi pT, assuming unpolarised chi_c production. The measurements are not corrected for the branching fractions of the decays chi_c --> J/psi + gamma and J/psi --> mu+ mu-. The uncertainty envelope associated with the unknown chi_c spin alignment is also shown.
Differential cross-section for non-prompt chi_c1 production, measured in bins of J/psi pT, assuming unpolarised chi_c production. The measurements are not corrected for the branching fractions of the decays chi_c --> J/psi + gamma and J/psi --> mu+ mu-. The uncertainty envelope associated with the unknown chi_c spin alignment is also shown.
A search is presented for direct top-squark pair production in final states with two leptons (electrons or muons) of opposite charge using 20.3fb-1 of pp collision data at sqrt(s)=8TeV, collected by the ATLAS experiment at the Large Hadron Collider in 2012. No excess over the Standard Model expectation is found. The results are interpreted under the separate assumptions (i) that the top squark decays to a b-quark in addition to an on-shell chargino whose decay occurs via a real or virtual W boson, or (ii) that the top squark decays to a t-quark and the lightest neutralino. A top squark with a mass between 150 GeV and 445 GeV decaying to a b-quark and an on-shell chargino is excluded at 95% confidence level for a top squark mass equal to the chargino mass plus 10 GeV, in the case of a 1 GeV lightest neutralino. Top squarks with masses between 215 (90) GeV and 530 (170) GeV decaying to an on-shell (off-shell) t-quark and a neutralino are excluded at 95% confidence level for a 1 GeV neutralino.
Distribution of mT2 for events passing all the signal candidate selection requirements, except that on mT2 of the L90 and L120 selections, for SF events.
Distribution of mT2 for events passing all the signal candidate selection requirements, except that on mT2 of the L90 and L120 selections, for DF events.
Distribution of mT2 for events passing all the signal candidate selection requirements, except that on mT2 of the L100 selection, for SF events.
The production of W bosons in association with two jets in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$=7 TeV has been analysed for the presence of double-parton interactions using data corresponding to an integrated luminosity of 36/pb, collected with the ATLAS detector at the LHC. The fraction of events arising from double-parton interactions, $f_{DP}^{(D)}$ has been measured through the momentum balance between the two jets and amounts to $f_{DP}^{(D)} = 0.08 \pm 0.01 (stat.) \pm 0.02 (sys.)$ for jets with transverse momentum PT > 20 GeV and rapidity |y|<2.8. This corresponds to a measurement of the effective area parameter for hard double-parton interactions of $\sigma_{eff} = 15 \pm 3 (stat.)^{+5}_{-3}$ (sys.) mb.
Distribution of Delta(jets,normalised), defined in Eq. (11) of the paper as the transverse momentum of the dijet system normalised by the sum of the individual transverse momenta, in the data after unfolding to hadron level. The errors on the data represent the quadrature sum of the statistical and systematic uncertainties. Data have been normalised to unity.
Distribution of Delta(jets), defined in Eq. (10) of the paper as the transverse momentum of the dijet system, in the data after unfolding to hadron level. The errors on the data represent the quadrature sum of the statistical and systematic uncertainties. Data have been normalised to unity.
A measurement is presented of the phi to K+K- production cross section at sqrt(s) = 7 TeV using pp collision data corresponding to an integrated luminosity of 383 mub-1, collected with the ATLAS experiment at the LHC. Selection of phi(1020) mesons is based on the identification of charged kaons by their energy loss in the pixel detector. The differential cross section is measured as a function of the transverse momentum, pTphi, and rapidity, |yphi|, of the phi(1020) meson in the fiducial region 500 < pTphi< 1200 MeV, |yphi| < 0.8, kaon pTK> 230 MeV and kaon momentum pK< 800 MeV.The integrated phi(1020)-meson production cross section in this fiducial range is measured to be s(phi K+K-) = 570 pm 8 (stat) pm 66 (syst) pm 20 (lumi) mub.
The differential PHI(1020) meson production cross section measured in the fiducial region as a function of the PHI(1020) transverse momentum.
The differential PHI(1020) meson production cross section measured in the fiducial region as a function of the PHI(1020) rapidity.
The integrated PHI(1020) meson production cross section in the fiducial region.
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