This letter presents a search for new resonances decaying to final states with a vector boson produced in association with a high transverse momentum photon, $V\gamma$, with $V= W(\rightarrow \ell ...\nu)$ or $Z(\rightarrow \ell^{+} \ell^{-})$, where $\ell = e$ or $\mu$. The measurements use 20.3 fb$^{-1}$ of proton-proton collision data at a center-of-mass energy of $\sqrt{s}=8$ TeV recorded with the ATLAS detector. No deviations from the Standard Model expectations are found, and production cross section limits are set at 95% confidence level. Masses of the hypothetical $a_{T}$ and $\omega_{T}$ states of a benchmark Low Scale Technicolor model are excluded in the ranges 275,960 GeV and $200,700\cup750,890$ GeV, respectively. Limits at 95% confidence level on the production cross section of a singlet scalar resonance decaying to $Z\gamma$ final states have also been obtained for masses below 1180 GeV.
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.
A measurement of the mass difference between top and anti-top quarks is presented. In a 4.7 fb-1 data sample of proton--proton collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the ...LHC, events consistent with ttbar production and decay into a single charged lepton final state are reconstructed. For each event, the mass difference between the top and anti-top quark candidate is calculated. A two b-tag requirement is used in order to reduce the background contribution. A maximum likelihood fit to these per-event mass differences yields mt-mtbar = 0.67 +/- 0.61 (stat) +/- 0.41 (syst) GeV, consistent with CPT invariance.
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.
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 $\tilde{\chi}_1^0$.
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.
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 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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In the safety assessment of novel foods produced through biotechnology, careful consideration is given to determining the allergenic potential of newly introduced proteins. IgE serum screening is one ...tool for evaluating whether the protein in question has sequence identity to a known allergen or if the source of the gene encoding the protein is a known allergenic food. A “specific” serum screen involves testing a gene product with sera from patients with documented clinical allergy to a specific allergen to confirm that the gene product of interest is not the same protein to which the patient produces IgE antibodies. A “targeted” serum screen involves testing the gene product of interest with sera from patients sensitive to food or aeroallergens from the same broad group. The concept of a global sera bank with accessible, well-characterized sera for use in such assays is an appealing option. This paper summarizes the consensus elements from a workshop to evaluate the potential utility of an international sera bank for evaluating the allergenicity of novel proteins. Areas of agreement following the workshop included the following: (1) specific sera screens are appropriate for exploring potentially cross-reactive proteins that have been identified through bioinformatics analyses; however, additional validation is needed, particularly for targeted sera screens, (2) practical and ethical considerations may preclude the formation of a global sera bank, and therefore, (3) a regional network of clinicians who could serve as sources of patient sera or be approached to conduct sera studies would be the most practical alternative.
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