The DØ experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to DØ.

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The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron pp collider. Using a 0.9 fb −1 dataset, we apply a multivariate analysis to separate signal from background and measure σ(pp → tb + X, tqb + X) = 4.9 ± 1.4 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.035%, corresponding to a 3.4 standard deviation significance. We use the cross section measurement to directly determine the CKM matrix element that describes the W tb coupling and find 0.

We present the results of a search for the effects of large extra spatial dimensions in p p collisions at s p 1:96 TeV in events containing a pair of energetic muons. The data correspond to 246 pb ÿ1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. Good agreement with the expected background was found, yielding no evidence for large extra dimensions. We set 95% C.L. lower limits on the fundamental Planck scale between 0.85 and 1.27 TeV within several formalisms. These are the most stringent limits achieved in the dimuon channel to date.

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The static properties, such as magnetic moment, charge radius, and axial-vector coupling constants, of the quark core of baryons in the nucleon octet have been studied in an independent-quark model based on the Dirac equation with equally mixed scalar-vector potential in harmonic form in the current quark mass limit. The results obtained with the corrections due to center-of-mass motion are in reasonable agreement with experimental values.

We study all possible texture zeros in the Majorana neutrino mass matrix which are allowed from neutrino oscillation as well as cosmology data when the charged lepton mass matrix is assumed to take the diagonal form. In case of one-zero texture, we write down the Majorana phases which are assumed to be equal and the lightest neutrino mass as a function of the Dirac CP phase. In case of two-zero texture, we numerically evaluate all the three CP phases and lightest neutrino mass by solving four real constraint equations. We then constrain texture zero mass matrices from the requirement of producing correct baryon asymmetry through the mechanism of leptogenesis.Adopting a type I seesaw framework, we consider the CP violating out of equilibrium decay of the lightest right handed neutrino as the source of lepton asymmetry. Apart from discriminating between the texture zero mass matrices and light neutrino mass hierarchy, we also constrain the Dirac and Majorana CP phases so that the observed baryon asymmetry can be produced. In two-zero texture, we further constrain the diagonal form of Dirac neutrino mass matrix from the requirement of producing correct baryon asymmetry.

We study a model of neutrino within the framework of minimal extended seesaw (MES), which plays an important role in active and sterile neutrino phenomenology in (3+1) scheme. The A 4 flavor symmetry is augmented by additional Z 4 ×Z 3 symmetry to constraint the Yukawa Lagrangian of the model. We use non-trivial Dirac mass matrix, with broken µ − τ symmetry, as the origin of leptonic mixing. Interestingly, such structure of mixing naturally leads to the non-zero reactor mixing angle θ 13 . Non-degenerate mass structure for right-handed neutrino M R is considered so that we can further extend our study to Leptogenesis. We have also considered three different cases for sterile neutrino mass, M S to check the viability of this model, within the allowed 3σ bound in this MES framework.