A search has been performed for the experimental signature of an isolated photon with high transverse momentum, at least one jet identified as originating from a bottom quark, and high missing transverse momentum. Such a final state may originate from supersymmetric models with gauge-mediated supersymmetry breaking in events in which one of a pair of higgsino-like neutralinos decays into a photon and a gravitino while the other decays into a Higgs boson and a gravitino. The search is performed using the full dataset of 7 TeV proton-proton collisions recorded with the ATLAS detector at the LHC in 2011, corresponding to an integrated luminosity of 4.7 fb-1. A total of 7 candidate events are observed while 7.5 pm 2.2 events are expected from the Standard Model background. The results of the search are interpreted in the context of general gauge mediation to exclude certain regions of a benchmark plane for higgsino-like neutralino production.
Missing ET distribution.
Signal Point Information: (1) Number of Monte Carlo events generated (2) Total signal cross section (pb) (3) Signal acceptance (4) Relative uncertainty on acceptance (5) CLs expected (6) CLs observed.
The observed limit contour in the GLUINO-NEUTRALINO plane.
We report a study of final states containing a W boson and hadronic jets, produced in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected with the ATLAS detector at the CERN LHC and comprise the full 2010 data sample of 36 pb^-1. Cross sections are determined using both the electron and muon decay modes of the W boson and are presented as a function of inclusive jet multiplicity, N_jet, for up to five jets. At each multiplicity, cross sections are presented as a function of jet transverse momentum, the scalar sum of the transverse momenta of the charged lepton, missing transverse momentum, and all jets, the invariant mass spectra of jets, and the rapidity distributions of various combinations of leptons and final-state jets. The results, corrected for all detector effects and for all backgrounds such as diboson and top quark pair production, are compared with particle-level predictions from perturbative QCD. Leading-order multiparton event generators, normalized to the NNLO total cross section for inclusive W-boson production, describe the data reasonably well for all measured inclusive jet multiplicities. Next-to-leading-order calculations from MCFM, studied here for N_jet >= 2, and BlackHat-Sherpa, studied here for N_jet >= 4, are found to be mostly in good agreement with the data.
The measured W+jets cross section as a function of the jet multiplicity for jet PT > 30 GeV shown for "Born" leptons and for QED corrected "dressed" leptons.
The measured W+jets cross section ratio as a function of jet multiplicity for jet PT > 30 GeV.
The measured W+jets cross section as a function of the pT of the first jet in the event for jet multiplicities >= 1 and jet PT > 30 GeV shown for "Born" leptons and for QED corrected "dressed" leptons.
We present the first measurement of the correlation between the $Z^0$ spin and the three-jet plane orientation in polarized $Z^0$ decays into three jets in the SLD experiment at SLAC utilizing a longitudinally polarized electron beam. The CP-even and T-odd triple product $\vec{S_Z}\cdot(\vec{k_1}\times \vec{k_2})$ formed from the two fastest jet momenta, $\vec{k_1}$ and $\vec{k_2}$, and the $Z^0$ polarization vector $\vec{S_Z}$, is sensitive to physics beyond the Standard Model. We measure the expectation value of this quantity to be consistent with zero and set 95\% C.L. limits of $-0.022 < \beta < 0.039$ on the correlation between the $Z^0$-spin and the three-jet plane orientation.
Asymmetry extracted from formula: (1/SIG(Q=3JET))*D(SIG)/D(COS(OMEGA)) = 9/16*[(1-1/3*(COS(OMEGA))**2) + ASYM*Az*(1-2*Pmis(ABS(COS(OMEGA))))*COS(OMEGA)], where OMEGA is polar angle of [k1,k2] vector (jet-plane normal), Pmis is the p robability of misassignment of of jet-plane normal, Az is beam polarization. Jets were reconstructed using the 'Durham' jet algorithm with a jet-resol ution parameter Yc = 0.005.
We have searched for signatures of polarization in hadronic jets from $Z~0 \rightarrow q \bar{q}$ decays using the ``jet handedness'' method. The polar angle asymmetry induced by the high SLC electron-beam polarization was used to separate quark jets from antiquark jets, expected to be left- and right-polarized, respectively. We find no evidence for jet handedness in our global sample or in a sample of light quark jets and we set upper limits at the 95\% C.L. of 0.063 and 0.099 respectively on the magnitude of the analyzing power of the method proposed by Efremov {\it et al.}
Polarized E- beam. Events were classified as being of light or heavy flavors based on impact parameters of charged tracks measured in the vertex detector. Jet handedness are measured for helicity-based and chirality-based analysis (seetext). C=95PCT CL indicates the upper limits at the 95 PCT C.L. on the magnitudes.
We have determined the strong coupling αs from measurements of jet rates in hadronic decays of Z0 bosons collected by the SLD experiment at SLAC. Using six collinear and infrared safe jet algorithms we compared our data with the predictions of QCD calculated up to second order in perturbation theory, and also with resummed calculations. We find αs(MZ2)=0.118±0.002(stat)±0.003(syst)±0.010(theory), where the dominant uncertainty is from uncalculated higher order contributions.
The second systematic error comes from the theoretical uncertainties.
We present improved measurements of the differential production rates of stable charged particles in hadronic Z0 decays, and of charged pions, kaons and protons identified over a wide momentum range using the SLD Cherenkov Ring Imaging Detector. In addition to flavor-inclusive Z0 decays, measurements are made for Z0 decays into light (u, d, s), c and b primary flavors, selected using the upgraded Vertex Detector. Large differences between the flavors are observed that are qualitatively consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results are used to test the predictions of QCD in the Modified Leading Logarithm Approximation, with the ansatz of Local Parton-Hadron Duality, and the predictions of three models of the hadronization process. The light-flavor results provide improved tests of these predictions, as they do not include the contribution of heavy-hadron production and decay; the heavy-flavor results provide complementary model tests. In addition we have compared hadron and antihadron production in light quark (as opposed to antiquark) jets. Differences are observed at high momentum for all three charged hadron species, providing direct probes of leading particle effects, and stringent constraints on models.
Production rates of all stable charged particles. The statistical and systematic errors are shown separately for the momentum distribution. They are combined in quadrature for the other two distributions. The first DSYS error is due tothe uncertainty in the track finding efficiency and the second DSYS error is th e rest of the systematic error.
The charged pion fraction and differential production rate per hadronic Z0 decay.
The charged kaon fraction and differential production rate per hadronic Z0 decay.
The $t\bar{t}$ production cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton--proton collisions at a centre-of-mass energy of 7 TeV in the single-lepton channel. The data were collected with the ATLAS detector at the CERN Large Hadron Collider and comprise the full 2011 data sample corresponding to an integrated luminosity of 4.6 fb$^{-1}$. Differential cross-sections are presented as a function of the jet multiplicity for up to eight jets using jet transverse momentum thresholds of 25, 40, 60, and 80 GeV, and as a function of jet transverse momentum up to the fifth jet. The results are shown after background subtraction and corrections for all detector effects, within a kinematic range closely matched to the experimental acceptance. Several QCD-based Monte Carlo models are compared with the results. Sensitivity to the parton shower modelling is found at the higher jet multiplicities, at high transverse momentum of the leading jet and in the transverse momentum spectrum of the fifth leading jet. The MC@NLO+HERWIG MC is found to predict too few events at higher jet multiplicities.
Measurement of the $t\overline{t}$ cross-section as a function of the jet multiplicity for jets with $p_{\mathrm{T}}$ larger than 25 GeV. The uncertainties given correspond to the individual contributions of each source of systematic uncertainty as described in the paper.
Measurement of the $t\overline{t}$ cross-section as a function of the jet multiplicity for jets with $p_{\mathrm{T}}$ larger than 40 GeV. The uncertainties given correspond to the individual contributions of each source of systematic uncertainty as described in the paper.
Measurement of the $t\overline{t}$ cross-section as a function of the jet multiplicity for jets with $p_{\mathrm{T}}$ larger than 60 GeV. The uncertainties given correspond to the individual contributions of each source of systematic uncertainty as described in the paper.
Differential cross sections for the production of at least four jets have been measured in proton-proton collisions at $\sqrt{s} = 8$ TeV at the Large Hadron Collider using the ATLAS detector. Events are selected if the four anti-$k_{t}$ R=0.4 jets with the largest transverse momentum ($p_{T}$) within the rapidity range $|y|<2.8$ are well separated ($dR^{\rm min}_{4j}>0.65$), all have $p_{T}>64$ GeV, and include at least one jet with $p_{T} >100$ GeV. The dataset corresponds to an integrated luminosity of 20.3 $fb^{-1}$. The cross sections, corrected for detector effects, are compared to leading-order and next-to-leading-order calculations as a function of the jet momenta, invariant masses, minimum and maximum opening angles and other kinematic variables.
Measured differential four-jet cross section for R=0.4 jets, in bins of pT1, along with the uncertainties in the measurement. The events are selected using the inclusive analysis cuts. All uncertainties are given in %. The first uncertainty quoted is due to the number of data events. DSYS:mcstat is the statistical uncertainty due to the number of MC simulation events. The other columns, denoted with DSYS, correspond to the experimental systematic uncertainties arising from JES, JER, unfolding and luminosity, respectively.
Measured differential four-jet cross section for R=0.4 jets, in bins of pT2, along with the uncertainties in the measurement. The events are selected using the inclusive analysis cuts. All other details are as for pT1.
Measured differential four-jet cross section for R=0.4 jets, in bins of pT3, along with the uncertainties in the measurement. The events are selected using the inclusive analysis cuts. All other details are as for pT1.
A measurement of the jet activity in ttbar events produced in proton-proton collisions at a centre-of-mass energy of 7 TeV is presented, using 2.05 fb^-1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The ttbar events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also performed, in which events are vetoed if the scalar transverse momentum sum of the additional jets in each rapidity interval is above a threshold. In both measurements, the data are corrected for detector effects and compared to the theoretical models implemented in MC@NLO, POWHEG, ALPGEN and SHERPA. The experimental uncertainties are often smaller than the spread of theoretical predictions, allowing deviations between data and theory to be observed in some regions of phase space.
The measured fraction of events, the gap fraction, surviving the veto cut of having no additional jets in the |rapidity| interval < 0.8 having a transverse momentum greater than Q, as a function of Q.
The measured fraction of events, the gap fraction, surviving the veto cut of having no additional jets in the |rapidity| interval 0.8-1.5 having a transverse momentum greater than Q, as a function of Q.
The measured fraction of events, the gap fraction, surviving the veto cut of having no additional jets in the |rapidity| interval 1.5-2.1 having a transverse momentum greater than Q, as a function of Q.
A search for squarks and gluinos in final states containing jets, missing transverse momentum and no high-pT electrons or muons is presented. The data represent the complete sample recorded in 2011 by the ATLAS experiment in 7 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 4.7 fb^-1. No excess above the Standard Model background expectation is observed. Gluino masses below 860 GeV and squark masses below 1320 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino, for squark or gluino masses below 2 TeV, respectively. Squarks and gluinos with equal masses below 1410 GeV are excluded. In MSUGRA/CMSSM models with tan beta = 10, A_0 = 0 and mu > 0, squarks and gluinos of equal mass are excluded for masses below 1360 GeV. Constraints are also placed on the parameter space of SUSY models with compressed spectra. These limits considerably extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.
The meff_incl distribution in Signal Region A.
The meff_incl distribution in Signal Region Ap.
The meff_incl distribution in Signal Region B.
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