The BABAR Collaboration BABAR, the detector for the SLAC PEP-II asymmetric e + e − B Factory operating at the Υ (4S) resonance, was designed to allow comprehensive studies of CP -violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagnetic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by dE/dx measurements in the tracking detectors and in a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems , VME-and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented.

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D20 is a medium to high resolution two-axis diffractometer capable of producing a neutron flux of 108 s−1 cm−2 at the sample position. The 1536 detection cells of its curved linear position sensitive detector (PSD) cover a continuous 2θ range of 153.6° over a total solid angle of 0.27 sr. This combination of a high incident neutron flux and a large detector solid angle provides D20 with the fastest counting rate, at a given resolution, of any reactor-based neutron diffractometer. Different monochromators and take-off angles, plus optional Soller collimators and secondary slits, permit a wide choice in the Q-space range, wavelength, resolution and flux. A high-resolution configuration offers Δd/d ∼ 2 × 10−3. Fast modern counting electronics allow in situ time-resolved experiments at the timescale of a few tens of milliseconds. In addition, a variety of sample environments, including an optional radial oscillating collimator for suppressing parasitic scattering, contribute to a rich scientific programme.

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