Abdominal cocoon,the idiopathic form of sclerosing encapsulating peritonitis,is a rare condition of unknown etiology that results in an intestinal obstruction due to total or partial encapsulation of ...the small bowel by a f ibrocollagenous membrane.Preoperative diagnosis requires a high index of clinical suspicion.The early clinical features are nonspecif ic,are often not recognized and it is diff icult to make a def inite pre-operative diagnosis.Clinical suspicion may be generated by the recurrent episodes of small intestinal obstruction combined with relevant imaging f indings and lack of other plausible etiologies.The radiological diagnosis of abdominal cocoon may now be conf idently made on computed tomography scan.Surgery is important in the management of this disease.Careful dissection and excision of the thick sac with the release of the small intestine leads to complete recovery in the vast majority of cases.
ATLAS, LHC, quark b, quark top, étiquetage des jets issus de quark b, calibration des algorithmes d'étiquetage des jets issus de quark b, quarks top-antitop, section efficace, section efficace ...différentielle des paires top-antitop, masse du top, rapidité du top, nouvelle physique.
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 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.
This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4.7 fb^-1 of proton-proton collision data recorded with the ATLAS detector at the Large ...Hadron Collider at sqrt(s) = 7 TeV. Final states containing one or two isolated leptons (electrons or muons) and jets are considered. Two measurements of alpha_l P, the product of the leptonic spin-analyzing power and the top quark polarization, are performed assuming that the polarization is introduced by either a CP conserving (CPC) or a CP violating (CPV) production process. The measurements obtained, alpha_l P_CPC = -0.035 +/- 0.014 (stat) +/- 0.037 (syst) and alpha_l P_CPV = 0.020 +/- 0.016 (stat) +0.013 -0.017 (syst), are in good agreement with the Standard Model prediction of negligible top quark polarization.
The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 7 TeV has been studied with the ATLAS detector at the LHC using an integrated luminosity of 37 pb-1. ...Measurements of isolated-photon plus jet bin-averaged cross sections are presented as functions of photon transverse energy, jet transverse momentum and jet rapidity. In addition, the bin-averaged cross sections as functions of the difference between the azimuthal angles of the photon and the jet, the photon--jet invariant mass and the scattering angle in the photon--jet centre-of-mass frame have been measured. Next-to-leading-order QCD calculations are compared to the measurements and provide a good description of the data, except for the case of the azimuthal opening angle.
The results of a search for pair production of supersymmetric partners of the Standard Model third-generation quarks are reported. This search uses 20.1 fb-1 of pp collisions at sqrt{s}=8 TeV ...collected by the ATLAS experiment at the Large Hadron Collider. The lightest bottom and top squarks (b1 and t1 respectively) are searched for in a final state with large missing transverse momentum and two jets identified as originating from b-quarks. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the visible cross section for processes beyond the Standard Model. Exclusion limits at the 95% confidence level on the masses of the third-generation squarks are derived in phenomenological supersymmetric R-parity-conserving models in which either the bottom or the top squark is the lightest squark. The b1 is assumed to decay via b1->b chi0 and the t via t1->b chipm, with undetectable products of the subsequent decay of the chipm due to the small mass splitting between the chipm and the chi0.
A measurement of the top quark electric charge is carried out in the ATLAS experiment at the Large Hadron Collider using 2.05 fb-1 of data at a centre-of-mass energy of 7 TeV. In units of the ...elementary electric charge, the top quark charge is determined to be 0.64 +- 0.02 (stat.) +- 0.08 (syst.) from the charges of the top quark decay products in single lepton ttbar candidate events. This excludes models that propose a heavy quark of electric charge --4/3, instead of the Standard Model top quark, with a significance of more than 8 sigma.
The inclusive top quark pair production cross-section has been measured in proton-proton collisions at sqrt(s)=7 TeV and sqrt(s)=8 TeV with the ATLAS experiment at the LHC, using ttbar events with an ...opposite-charge e-mu pair in the final state. The measurement was performed with the 2011 7 TeV dataset corresponding to an integrated luminosity of 4.6 fb-1 and the 2012 8 TeV dataset of 20.3 fb-1. The numbers of events with exactly one and exactly two b-tagged jets were counted and used to simultaneously determine sigma(ttbar) and the efficiency to reconstruct and b-tag a b-jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section was measured to be: sigma(ttbar)=$182.9\pm3.1\pm4.2\pm3.6\pm3.3$ pb (7 TeV) and sigma(ttbar)=$242.4\pm1.7\pm5.5\pm7.5\pm4.2$ pb (8 TeV), where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the knowledge of the integrated luminosity and of the LHC beam energy. The results are consistent with recent theoretical QCD calculations at NNLO. Fiducial measurements corresponding to the experimental acceptance of the leptons are also reported, together with the ratio of cross-sections measured at the two centre-of-mass energies. The inclusive cross-section results were used to determine the top quark pole mass via the dependence of the theoretically-predicted cross-section on $m_t^{pole}$, giving a result of $m_t^{pole}=172.9^{+2.5}_{-2.6}$ GeV. By looking for an excess of ttbar production with respect to the QCD prediction, the results were also used to place limits on the pair-production of supersymmetric top squarks with masses close to the top quark mass decaying to predominantly right-handed top quarks and a light neutralino, the lightest supersymmetric particle. Top squarks with masses between the top quark mass and 177 GeV are excluded at the 95% confidence level.
A measurement of the ZZ production cross section in proton-proton collisions at sqrt(s) = 7 TeV using data recorded by the ATLAS experiment at the Large Hadron Collider is presented. In a data sample ...corresponding to an integrated luminosity of 4.6 fb-1 collected in 2011, events are selected that are consistent either with two Z bosons decaying to electrons or muons or with one Z boson decaying to electrons or muons and a second Z boson decaying to neutrinos. The ZZ*->llll and ZZ->llnunu cross sections are measured in restricted phase-space regions. These results are then used to derive the total cross section for ZZ events produced with both Z bosons in the mass range 66 to 116 GeV, sigmaZZtot = 6.7 +-0.7 +0.4-0.3 +-0.3 pb, which is consistent with the Standard Model prediction of 5.89+0.22-0.18 pb calculated at next-to-leading order in QCD. The normalized differential cross sections in bins of various kinematic variables are presented. Finally, the differential event yield as a function of the transverse momentum of the leading Z boson is used to set limits on anomalous neutral triple gauge boson couplings in ZZ production.
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