1058703
Combination of measurements of the top-quark pair production cross section from the Tevatron Collider
We combine six measurements of the inclusive top-quark pair (t(sic)) production cross section (sigma(t)(sic)) from data collected with the CDF and D0 detectors at the Fermilab Tevatron with proton-antiproton collisions at root s = 1.96 TeV. The data correspond to integrated luminosities of up to 8.8 fb(-1). We obtain a value of sigma tt = 7.60 +/- 0.41 pb for a top-quark mass of m(t) = 172.5 GeV. The contributions to the uncertainty are 0.20 pb from statistical sources, 0.29 pb from systematic sources, and 0.21 pb from the uncertainty on the integrated luminosity. The result is in good agreement with the standard model expectation of 7.35(-0.33)(+0.28) pb at next-to-next-to-leading order and next-to-next-to leading logarithms in perturbative QCD.
12834301
Jet energy scale determination in the D0 experiment
The calibration of jet energy measured in the DO detector is presented, based on p (p) over bar collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider, jet energies are measured using a sampling calorimeter composed of uranium and liquid argon as the passive and active media, respectively. This paper describes the energy calibration of jets performed with gamma+jet, Z+jet and dilet events, with jet transverse momentum p(T) > 6 GeV and pseudorapidity range vertical bar eta vertical bar < 3.6, The corrections are measured separately for data and simulation, achieving a precision of 1.4-1.8% for jets in the central part of the calorimeter ancl up to 3.5% for the jets with pseudorapidity vertical bar eta vertical bar = 3.0. Specific corrections are extracted to enhance the description of jet energy in simulation and in particular of the effects due to the flavor of the parton originating the jet, correcting biases up to 3-4% in jets with low PT originating from gluons and up to 6-8% in jets from b quarks. Published by Elsevier B.V.
15350493
Search for long-lived particles decaying into electron or photon pairs with the D0 detector.
In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, such as hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.
12420090
Observation and properties of the orbitally excited B_(s2)(*) meson.
We report the direct observation of the excited L=1 state B_(s2)(*) in fully reconstructed decays to B+K-. The mass of the B_(s2)(*) meson is measured to be 5839.6+/-1.1(stat)+/-0.7(syst) MeV/c(2), and its production rate relative to the B+ meson is measured to be [1.15+/-0.23(stat)+/-0.13(syst)]%.
195944
Precision measurement of the top quark mass in lepton + jets final States.
We measure the mass of the top quark in lepton+jets final states using the full sample of pp collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at sqrt[s] = 1.96 TeV, corresponding to 9.7 fb(-1) of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from tt production or background. The overall jet energy scale is constrained in situ by the mass of the W boson. We measure m(t) = 174.98 ± 0.76 GeV. This constitutes the most precise single measurement of the top-quark mass.
208869198
Measurement of angular correlations of jets at s=1.96 TeV and determination of the strong coupling at high momentum transfers
We present a measurement of the average value of a new observable at hadron colliders that is sensitive to QCD dynamics and to the strong coupling constant, while being only weakly sensitive to parton distribution functions. The observable measures the angular correlations of jets and is defined as the number of neighboring jets above a given transverse momentum threshold which accompany a given jet within a given distance Delta-R in the plane of rapidity and azimuthal angle. The ensemble average over all jets in an inclusive jet sample is measured and the results are presented as a function of transverse momentum of the inclusive jets, in different regions of Delta-R and for different transverse momentum requirements for the neighboring jets. The measurement is based on a data set corresponding to an integrated luminosity of 0.7 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider in pp-bar collisions at sqrt(s)=1.96 The results are well described by a perturbative QCD calculation in next-to-leading order in the strong coupling constant, corrected for non-perturbative effects. From these results, we extract the strong coupling and test the QCD predictions for its running over a range of momentum transfers of 50-400 GeV.
116993797
Reductions of a Lax pair for selfduality equations of the Yang-Mills model
16541392
Closed N=2 strings: Picture changing, hidden symmetries and SDG hierarchy
We study the action of picture-changing and spectral flow operators on a ground ring of ghost number zero operators in the chiral BRST cohomology of the closed N=2 string and describe an infinite set of symmetry charges acting on physical states. The transformations of physical string states are compared with symmetries of self-dual gravity which is the effective field theory of the closed N=2 string. We derive all infinitesimal symmetries of the self-dual gravity equations in (2+2)-dimensional space–time and introduce an infinite hierarchy of commuting flows on the moduli space of self-dual metrics. The dependence on moduli parameters can be recovered by solving the equations of the SDG hierarchy associated with an infinite set of Abelian symmetries generated recursively from translations. These nonlocal Abelian symmetries are shown to coincide with the hidden Abelian string symmetries responsible for the vanishing of most scattering amplitudes. Therefore, N=2 string theory "predicts" not only self-dual ...
14478899
Sigma models with N=8 supersymmetries in 2+1 and 1+1 dimensions
Abstract We introduce an N = 8 supersymmetric extension of the Bogomolny-type model for Yang–Mills–Higgs fields in 2 + 1 dimensions related with twistor string theory. It is shown that this model is equivalent to an N = 8 supersymmetric U ( n ) chiral model in 2 + 1 dimensions with a Wess–Zumino–Witten-type term. Further reduction to 1 + 1 dimensions yields N = ( 8 , 8 ) supersymmetric extensions of the standard U ( n ) chiral model and Grassmannian sigma models.
119253503
Integrable vortex-type equations on the two-sphere
We consider the Yang-Mills instanton equations on the four-dimensional manifold ${S}^{2}\ifmmode\times\else\texttimes\fi{}\ensuremath{\Sigma}$, where $\ensuremath{\Sigma}$ is a compact Riemann surface of genus $gg1$ or its covering space ${H}^{2}=\mathrm{SU}(1,1)/\mathrm{U}(1)$. Introducing a natural ansatz for the gauge potential, we reduce the instanton equations on ${S}^{2}\ifmmode\times\else\texttimes\fi{}\ensuremath{\Sigma}$ to vortex-type equations on the sphere ${S}^{2}$. It is shown that when the scalar curvature of the manifold ${S}^{2}\ifmmode\times\else\texttimes\fi{}\ensuremath{\Sigma}$ vanishes, the vortex-type equations are integrable, i.e., can be obtained as compatibility conditions of two linear equations (Lax pair), which are written down explicitly. Thus, the standard methods of integrable systems can be applied for constructing their solutions. However, even if the scalar curvature of ${S}^{2}\ifmmode\times\else\texttimes\fi{}\ensuremath{\Sigma}$ does not vanish, the vortex equations are well defined and have solutions for any values of the topological charge $N$. We show that any solution to the vortex equations on ${S}^{2}$ with a fixed topological charge $N$ corresponds to a Yang-Mills instanton on ${S}^{2}\ifmmode\times\else\texttimes\fi{}\ensuremath{\Sigma}$ of charge $(g\ensuremath{-}1)N$.
16752674
Non-Abelian Vortices, Super Yang–Mills Theory and Spin(7)-Instantons
We consider a complex vector bundle $${\mathcal{E}}$$ endowed with a connection $${\mathcal{A}}$$ over the eight-dimensional manifold $${\mathbb{R}^2\times G/H}$$, where G/H = SU(3)/U(1) × U(1) is a homogeneous space provided with a never-integrable almost-complex structure and a family of SU(3)-structures. We establish an equivalence between G-invariant solutions $${\mathcal{A}}$$ of the Spin(7)-instanton equations on $${\mathbb{R}^2\times G/H}$$ and general solutions of non-Abelian coupled vortex equations on $${\mathbb{R}^2}$$. These vortices are BPS solitons in a d = 4 gauge theory obtained from $${\mathcal{N} =1}$$ supersymmetric Yang–Mills theory in ten dimensions compactified on the coset space G/H with an SU(3)-structure. The novelty of the obtained vortex equations lies in the fact that Higgs fields, defining morphisms of vector bundles over $${\mathbb{R}^2}$$, are not holomorphic in the generic case. Finally, we introduce BPS vortex equations in $${\mathcal{N} =4}$$ super Yang–Mills theory and show that they have the same feature.