Browsing by Author "Alexeev, G.D."

We present a measurement of direct photon pair production cross sections using 4.2 fb−14.2 fb−1 of data collected with the D0 detector at the Fermilab Tevatron View the MathML sourcepp¯ Collider. We measure single differential cross sections as a function of the diphoton mass, the transverse momentum of the diphoton system, the azimuthal angle between the photons, and the polar scattering angle of the photons. In addition, we measure double differential cross sections considering the last three kinematic variables in three diphoton mass bins. The results are compared with different perturbative QCD predictions and event generators

We present a measurement of the correlation between the spins of t and View the MathML source quarks produced in proton–antiproton collisions at the Tevatron Collider at a center-of-mass energy of 1.96 TeV. We apply a matrix element technique to dilepton and single-lepton+jets final states in data accumulated with the D0 detector that correspond to an integrated luminosity of 9.7 fb−1. The measured value of the correlation coefficient in the off-diagonal basis, View the MathML source, is in agreement with the standard model prediction, and represents evidence for a top–antitop quark spin correlation difference from zero at a level of 4.2 standard deviations.

We present the first combined measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations, using the recently proposed quantity R φ. The variable R φ measures the fraction of the inclusive dijet events in which the azimuthal separation of the two jets with the highest transverse momenta is less than a specified value of the parameter φmax. The quantity R φ is measured in p¯p collisions at √ s = 1.96 TeV, as a function of the dijet rapidity interval, the total scalar transverse momentum, and φmax. The measurement uses an event sample corresponding to an integrated luminosity of 0.7 fb−1 collected with the D0 detector at the Fermilab Tevatron Collider. The results are compared to predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for non-perturbative effects. The theory predictions describe the data well, except in the kinematic region of large dijet rapidity intervals and small φmax.