Observation of single top-quark production.
We report observation of the electroweak production of single top quarks in pp[over ] collisions at sqrt[s]=1.96 TeV based on 2.3 fb(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(pp[over ]--> tb + X, tqb + X) = 3.94 + or - 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10(-7), corresponding to a 5.0 standard deviation significance for the observation.

title: Jet energy scale determination in the D0 experiment
abstract: 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.

title: Observation and properties of the orbitally excited B_(s2)(*) meson.
abstract: 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)]%.

title: Search for long-lived particles decaying into electron or photon pairs with the D0 detector.
abstract: 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.

title: Measurement of angular correlations of jets at s=1.96 TeV and determination of the strong coupling at high momentum transfers
abstract: 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.

title: Precision measurement of the top quark mass in lepton + jets final States.
abstract: 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.

title: On Explicit point multimonopoles in SU(2) gauge theory
abstract: It is well known that the Dirac monopole solution with the U(1) gauge group embedded into the group SU(2) is equivalent to the SU(2) Wu–Yang point monopole solution having no Dirac string singularity. We consider a multicenter configuration of m Dirac monopoles and n antimonopoles and its embedding into SU(2) gauge theory. Using geometric methods, we construct an explicit solution of the SU(2) Yang–Mills equations which generalizes the Wu–Yang solution to the case of m monopoles and n antimonopoles located at arbitrary points in R3.

title: Fundamental chiral strings
abstract: The problem of the non-uniqueness of the string theory in the space Rd-1,1 with d ≤ 10 and the procedure of the compactification and the deompactification are discussed. We consider a compact bosonic string defined as a closed string moving in the Lorentizian torus T25,1 and introduce fundamental chiral bosonic string (FCBS) as a universal cover of a compact string. It is shown that the Fock spaces of any standard strings are embedded into the Fock space of FCBS.

title: Integrability of vortex equations on Riemann surfaces
abstract: The Abelian Higgs model on a compact Riemann surface Σ of genus g is considered. We show that for g>1 the Bogomolny equations for multi-vortices at critical coupling can be obtained as compatibility conditions of two linear equations (Lax pair) which are written down explicitly. These vortices correspond precisely to SO(3)-symmetric Yang–Mills instantons on the (conformal) gravitational instanton Σ×S2 with a scalar-flat Kahler metric. Thus, the standard methods of constructing solutions and studying their properties by using Lax pairs (twistor approach, dressing method, etc.) can be applied to the vortex equations on Σ. In the twistor description, solutions of the integrable vortex equations correspond to rank-2 holomorphic vector bundles over the complex 3-dimensional twistor space of Σ×S2. We show that in the general (nonintegrable) case there is a bijection between the moduli spaces of solutions to vortex equations on Σ and of pseudo-holomorphic bundles over the almost complex twistor space.

title: Quiver gauge theory of non-Abelian vortices and noncommutative instantons in higher dimensions
abstract: We construct explicit Bogomolnyi, Prasad, Sommerfeld (BPS) and non-BPS solutions of the Yang-Mills equations on the noncommutative space Rθ2n×S2 which have manifest spherical symmetry. Using SU(2)-equivariant dimensional reduction techniques, we show that the solutions imply an equivalence between instantons on Rθ2n×S2 and non-Abelian vortices on Rθ2n, which can be interpreted as a blowing-up of a chain of D0-branes on Rθ2n into a chain of spherical D2-branes on Rθ2n×S2. The low-energy dynamics of these configurations is described by a quiver gauge theory which can be formulated in terms of new geometrical objects generalizing superconnections. This formalism enables the explicit assignment of D0-brane charges in equivariant K-theory to the instanton solutions.

title: Rank two quiver gauge theory, graded connections and noncommutative vortices
abstract: We consider equivariant dimensional reduction of Yang-Mills theory on K?hler manifolds of the form M ? P1 ? P1. This induces a rank two quiver gauge theory on M which can be formulated as a Yang-Mills theory of graded connections on M. The reduction of the Yang-Mills equations on M ? P1 ? P1 induces quiver gauge theory equations on M and quiver vortex equations in the BPS sector. When M is the noncommutative space ?2n both BPS and non-BPS solutions are obtained, and interpreted as states of D-branes. Using the graded connection formalism, we assign D0-brane charges in equivariant K-theory to the quiver vortex configurations. Some categorical properties of these quiver brane configurations are also described in terms of the corresponding quiver representations.