114628
Model-independent measurement of the W-boson helicity in top-quark decays at D0.
We present the first model-independent measurement of the helicity of W bosons produced in top quark decays, based on a 1 fb(-1) sample of candidate tt events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron pp Collider. We reconstruct the angle theta(*) between the momenta of the down-type fermion and the top quark in the W boson rest frame for each top quark decay. A fit of the resulting costheta(*) distribution finds that the fraction of longitudinal W bosons f(0)=0.425+/-0.166(stat)+/-0.102(syst) and the fraction of right-handed W bosons f(+)=0.119+/-0.090(stat)+/-0.053(syst), which is consistent at the 30% C.L. with the standard model.
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.
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.
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)]%.
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.
121208022
Some solutions of the Yang–Mills equations in dimension greater than four
The Yang–Mills equations for gauge fields of an arbitrary semisimple Lie group G in Euclidean spaces Rn with dimension n≥4 is considered. For gauge fields Aa we introduce the ansatze which reduce the Yang–Mills equations in Rn to a set of nonlinear differential matrix equations (Rouhani–Ward equations). This permits us to write out the explicit form of cosmological, plane‐wave, and other types of solutions.
119167413
Heterotic compactifications on nearly Kähler manifolds
We consider compactifications of heterotic supergravity on anti-de Sitter space, with a six-dimensional nearly Kähler manifold as the internal space. Completing the model proposed by Frey and Lippert [10] with the particular choice of SU(3)/U(1) × U(1) for the internal manifold, we show that it satisfies not only the supersymmetry constraints but also the equations of motion with string corrections of order α′. Furthermore, we present a nonsupersymmetric model. In both solutions we find confirmed a recent result of Ivanov [18] on the connection used for anomaly cancellation. Interestingly, the volume of the internal space is fixed by the supersymmetry constraints and/or the equations of motion.
14687778
Holomorphic analogs of topological gauge theories
Abstract We introduce a new class of gauge field theories in any complex dimension, based on algebra-valued ( p , q )-forms on complex n -manifolds. These theories are holomorphic analogs of the well-known Chern-Simons and BF topological theories defined on real manifolds. We introduce actions for different special holomorphic BF theories on complex, Kahler and Calabi-Yau manifolds and describe their gauge symmetries. Candidate observables, topological invariants and relations to integrable models are briefly discussed.
119721291
Hidden symmetries of Kaluza-Klein theories
It is shown that the introduction of dynamical torsion in Kaluza-Klein theories makes it possible to increase the number of gauge fields extracted from the Lagrangian without increasing the number of additional dimensions. An example of spontaneous compactification of a studied model is considered.
121020880
Vortices, strings, and pseudoinstantons