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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Observation and Properties of the X(3872) Decaying to J/ψ π + π − in pp Collisions at √ s= 1.96 TeV

This Letter describes the search for a new heavy charged gauge boson W ′ decaying into an electron and a neutrino. The data were collected with the D0 detector at the Fermilab Tevatron pp Collider at √ s = 1.96 TeV, and correspond to an integrated luminosity of about 1 fb −1 . Lacking any significant excess in the data in comparison with known processes, an upper limit is set on σ W ′ × B(W ′ → eν),