A search for the direct production of charginos and neutralinos in final states with three leptons and missing transverse momentum is presented. The analysis is based on 20.3 fb-1 of sqrt(s) = 8 TeV proton--proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations and limits are set in R-parity-conserving phenomenological Minimal Supersymmetric Standard Models and in simplified supersymmetric models, significantly extending previous results. For simplified supersymmetric models of direct chargino ($\tilde\chi^\pm_1$) and next-to-lightest neutralino ($\tilde{\chi}_2^0$) production with decays to lightest neutralino ($\tilde{\chi}_1^0$) via either all three generations of sleptons, staus only, gauge bosons, or Higgs bosons, $\tilde\chi^\pm_1$ and $\tilde{\chi}_2^0$ masses are excluded up to 700 GeV, 380 GeV, 345 GeV, or 148 GeV respectively, for a massless $\tilde{\chi}_1^0$.
Number of expected and observed events in the validation region VR0taub.
For events in the low-ETmiss validation region, the MT distribution in VR0taunoZa.
For events in the low-ETmiss validation region, the MT distribution in VR0tauZa.
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.
The production of a W boson in association with a single charm quark is studied using 4.6 fb^-1 of pp collision data at sqrt(s)=7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96 +0.26 -0.30 at Q^2=1.9 GeV^2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio sigma(W^+ + bar{c})/sigma(W^- + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-bar{s} quark asymmetry.
Measured integrated cross sections of the production of a W boson with a single c-jet, a D meson or a D* meson times the branching ratio W -> l nu in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. Jets are not required for the W+D/D* cross sections. The cross sections are defined for OS-SS events.
Measured integrated cross section ratios of the production of W+ and W- bosons associated with a single c-jet, a D meson or a D* meson in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. Jets are not required for the W+D/D* cross sections. The cross sections are defined for OS-SS events.
Measured differential cross sections as function of the lepton pseudo-rapidity of the production of a W boson with a single c-jet times the branching ratio W -> l nu in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. The cross sections are defined for OS-SS events.
We report on the first measurement of the azimuthal anisotropy ($v_2$) of dielectrons ($e^{+}e^{-}$ pairs) at mid-rapidity from $\sqrt{s_{_{NN}}} = 200$ GeV Au+Au collisions with the STAR detector at RHIC, presented as a function of transverse momentum ($p_T$) for different invariant-mass regions. In the mass region $M_{ee}\!<1.1$ GeV/$c^2$ the dielectron $v_2$ measurements are found to be consistent with expectations from $\pi^{0}$, $\eta$, $\omega$ and $\phi$ decay contributions. In the mass region $1.1\!<M_{ee}\!<2.9$ GeV/$c^2$, the measured dielectron $v_2$ is consistent, within experimental uncertainties, with that from the $c\bar{c}$ contributions.
The dielectron $v_2$ in the $\pi^0$ Dalitz decay region as a function of $p_T$ in different centralities from Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Expected dielectron $v_2$ from $\pi^0$ Dalitz decay as a function of $p_T$ in different centralities from Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
The dielectron $v_2$ as a function of $p_T$ in minimum-bias Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for the $\pi^0$ mass region.
We report the first measurements of the moments -- mean ($M$), variance ($\sigma^{2}$), skewness ($S$) and kurtosis ($\kappa$) -- of the net-charge multiplicity distributions at mid-rapidity in Au+Au collisions at seven energies, ranging from $\sqrt {{s_{\rm NN}}}$= 7.7 to 200 GeV, as a part of the Beam Energy Scan program at RHIC. The moments are related to the thermodynamic susceptibilities of net-charge, and are sensitive to the proximity of the QCD critical point. We compare the products of the moments, $\sigma^{2}/M$, $S\sigma$ and $\kappa\sigma^{2}$ with the expectations from Poisson and negative binomial distributions (NBD). The $S\sigma$ values deviate from Poisson and are close to NBD baseline, while the $\kappa\sigma^{2}$ values tend to lie between the two. Within the present uncertainties, our data do not show non-monotonic behavior as a function of collision energy. These measurements provide a distinct way of determining the freeze-out parameters in heavy-ion collisions by comparing with theoretical models.
The efficiency and centrality bin width corrected mean (M) of the net-charge multiplicity distributions as a function of number of participating nucleons $N_{part}$ for Au+Au collisions at 7.7 GeV. The dotted lines represent calculations from the central limit theorem. The error bars are statisticaland systematic errors.
The efficiency and centrality bin width corrected mean (M) of the net-charge multiplicity distributions as a function of number of participating nucleons $N_{part}$ for Au+Au collisions at 11.5 GeV. The dotted lines represent calculations from the central limit theorem. The error bars are statisticaland systematic errors.
The efficiency and centrality bin width corrected mean (M) of the net-charge multiplicity distributions as a function of number of participating nucleons $N_{part}$ for Au+Au collisions at 19.6 GeV. The dotted lines represent calculations from the central limit theorem. The error bars are statisticaland systematic errors.
Measurements of fiducial cross sections for the electroweak production of two jets in association with a Z-boson are presented. The measurements are performed using 20.3 inverse femtobarns of proton-proton collision data collected at a centre-of-mass energy of sqrt(s)=8 TeV by the ATLAS experiment at the Large Hadron Collider. The electroweak component is extracted by a fit to the dijet invariant mass distribution in a fiducial region chosen to enhance the electroweak contribution over the dominant background in which the jets are produced via the strong interaction. The electroweak cross sections measured in two fiducial regions are in good agreement with the Standard Model expectations and the background-only hypothesis is rejected with significance above the 5 sigma level. The electroweak process includes the vector boson fusion production of a Z-boson and the data are used to place limits on anomalous triple gauge boson couplings. In addition, measurements of cross sections and differential distributions for inclusive Z-boson-plus-dijet production are performed in five fiducial regions, each with different sensitivity to the electroweak contribution. The results are corrected for detector effects and compared to predictions from the SHERPA and POWHEG event generators.
Unfolded normalised differential Z+2j cross section as a function of dijet invariant mass in the baseline region.
Unfolded normalised differential Z+2j cross section as a function of dijet invariant mass in the search region.
Unfolded normalised differential Z+2j cross section as a function of the rapidity separation between the leading jets in the baseline region.
The process pp--> W + J/psi provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.5 fb-1 of sqrt{s} = 7 TeV pp collisions at the LHC, the first observation is made of the production of W + prompt J/psi events in hadronic collisions, using W-->mu+nu and J/psi-->mu+mu. A yield of 27.4+7.5-6.5 W + prompt J/psi events is observed, with a statistical significance of 5.1 sigma. The production rate as a ratio to the inclusive W boson production rate is measured, and the double parton scattering contribution to the cross section is estimated.
The W + prompt J/psi to inclusive W production cross-section ratio (times 10^6) in the J/psi fiducial region (Fiducial), after correction for J/psi acceptance (Inclusive), and after subtraction of the double parton scattering component (DPS-subtracted). The first uncertainty is statistical, the second is systematic, and the third/fourth (where applicable) is the uncertainty up/down due to spin-alignment.
The inclusive (SPS+DPS) cross-section ratio (times 10^6) as a function of J/psi transverse momentum, along with the estimate of the DPS contribution. For the inclusive result, the first uncertainty is statistical, second uncertainty is systematic, and the third uncertainty is the possible variation due to spin-alignment.
The inclusive (SPS+DPS) cross-section ratio (times 10^6) as a function of J/psi transverse momentum under the LONGITUDINAL spin-alignment hypothesis. The first uncertainty is statistical and the second uncertainty is systematic.
Rapidity-odd directed flow($v_1$) measurements for charged pions, protons and antiprotons near mid-rapidity ($y=0$) are reported in $\sqrt{s_{NN}} =$ 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV Au + Au collisions as recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). At intermediate impact parameters, the proton and net-proton slope parameter $dv_1/dy|_{y=0}$ shows a minimum between 11.5 and 19.6 GeV. In addition, the net-proton $dv_1/dy|_{y=0}$ changes sign twice between 7.7 and 39 GeV. The proton and net-proton results qualitatively resemble predictions of a hydrodynamic model with a first-order phase transition from hadronic matter to deconfined matter, and differ from hadronic transport calculations.
Directed flow for protons versus rapidity for central (0-10$\%$), intermediate-centrality (10-40$\%$) and peripheral (40-80$\%$) Au+Au collisions at $\sqrt{s_{NN}}$ = 39, 27, 19.6, 11.5 and 7.7 GeV. Errors are statistical only.
Directed flow for $\pi^{-}$ versus rapidity for central (0-10$\%$), intermediate-centrality (10-40$\%$) and peripheral (40-80$\%$) Au+Au collisions at $\sqrt{s_{NN}}$ = 39, 27, 19.6, 11.5 and 7.7 GeV. Errors are statistical only.
Directed flow for protons and anti-protons versus rapidity for intermediate-centrality (10-40$\%$) Au+Au collisions at $\sqrt{s_{NN}}$ = 200, 62.4, 39, 27, 19.6, 11.5 and 7.7 GeV. Errors are statistical only.
We report the STAR measurements of dielectron ($e^+e^-$) production at midrapidity ($|y_{ee}|<$1) in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200\,GeV. The measurements are evaluated in different invariant mass regions with a focus on 0.30-0.76 ($\rho$-like), 0.76-0.80 ($\omega$-like), and 0.98-1.05 ($\phi$-like) GeV/$c^{2}$. The spectrum in the $\omega$-like and $\phi$-like regions can be well described by the hadronic cocktail simulation. In the $\rho$-like region, however, the vacuum $\rho$ spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of 1.77$\pm$0.11(stat.)$\pm$0.24(sys.)$\pm$0.33(cocktail) is determined with respect to the hadronic cocktail simulation that excludes the $\rho$ meson. The excess yield in the $\rho$-like region increases with the number of collision participants faster than the $\omega$ and $\phi$ yields. Theoretical models with broadened $\rho$ contributions through interactions with constituents in the hot QCD medium provide a consistent description of the dilepton mass spectra for the measurement presented here and the earlier data at the Super Proton Synchrotron energies.
Uncorrected Distributions of e+ e- invariant mass, the reconstructed background, and the signal pairs in 200 GeV Au+Au minimum bias collisions.
The ratio of signal to background in Au + Au collisions at $\sqrt{s_{{NN}}}$ = 200 GeV (Minimum Bias).
The ratio of signal to background in Au + Au collisions at $\sqrt{s_{{NN}}}$ = 200 GeV (Central).
The neutral current e+/-p cross section has been measured up to values of Bjorken x of approximately 1 with the ZEUS detector at HERA using an integrated luminosity of 187 inv. pb of e-p and 142 inv. pb of e+p collisions at sqrt(s) = 318GeV. Differential cross sections in x and Q2, the exchanged boson virtuality, are presented for Q2 geq 725GeV2. An improved reconstruction method and greatly increased amount of data allows a finer binning in the high-x region of the neutral current cross section and leads to a measurement with much improved precision compared to a similar earlier analysis. The measurements are compared to Standard Model expectations based on a variety of recent parton distribution functions.
Double differential cross section for Q^2=725 GeV^2.
Double differential cross section for Q^2=875 GeV^2.
Double differential cross section for Q^2=1025 GeV^2.
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