9813062
Space-charge-dominated phenomena in the UMER source region
For space-charge-dominated beams, details of the beam distribution as it emerges from the source region can strongly influence beam evolution well downstream. This occurs because collective space-charge modes, excited as the beam is born, can remain undamped for many focusing periods. Nevertheless, traditional studies of the source region in particle beam systems have emphasized the behavior of averaged beam characteristics such as total current, rms beam size, or emittance, rather than the details of the full beam distribution function that are necessary to predict the excitation of any collective space-charge modes. Simulations of the source region using the particle-in-cell WARP code along with detailed comparisons to experimental measurements of the beam in the University of Maryland Electron Ring (UMER) are therefore being employed to understand the complex behavior that has been observed in the source region, including a surprising sensitivity of the beam evolution to details of the transverse velocity distribution.
120340582
Edge imaging in intense beams
The appearance of rings of charge observed near the edge of beams from high-perveance guns is described with a simple ray tracing technique inspired by the particle-core model. We illustrate the technique, which has no analog in light optics, with examples from experiments employing solenoid focusing of an electron beam. The rings of charge result from the combined effects of external focusing and space-charge forces acting on paraxial fringe particles with relatively large initial transverse velocities. The model is independent of the physical mechanisms responsible for the fringe particles. Furthermore, the focal length for edge imaging in a uniform focusing channel is derived using a linearized trajectory equation for the motion of fringe particles. Counterintuitively, the focal length decreases as the beam current increases.
29456018
Electromagnetic excitation of the delta resonance in nuclei.
Inclusive cross sections for the proton and nuclear targets of A = 4, 9, 12, and 16 were measured for 537 and 730 MeV electrons scattered at 37.1 deg. Systematic features of the continuum scattering data are compared with other electron scattering data and with photoabsorption measurements. A model calculation based on the isobar-hole formalism is compared with the data in the delta resonance region.
119115234
Z Boson Asymmetry Measurements at the Tevatron
We present measurements of the forward-backward asymmetry (A_fb) in dilepton pair decays of Z bosons produced in ppbar collisions using the full Tevatron dataset. The CDF experiment extracts a value for the effective weak mixing angle parameter sin^{2}\theta^{l}_{eff} of 0.2315 +/- 0.0010 from the A_fb distribution of dimuon events in 9.2 fb^{-1} of integrated luminosity. From dielectron events in 9.7 fb^{-1} of data, the D0 experiment finds sin^{2}\theta^{l}_{eff} = 0.23106 +/- 0.00053, the world's most precise measurement of sin^{2}\theta^{l}_{eff} from hadron colliders and with light quark couplings.
108516447
Carbon fiber grounding in the D0 Run IIb silicon detector design
Abstract Carbon fiber support structures have become common elements of silicon detector designs. While the use of carbon fiber solves a variety of mechanical problems, it presents a challenging set of electrical concerns. Well-designed coupling and grounding schemes are essential for producing low-noise environments within the detectors. General principles involved in grounding systems with carbon fiber structures are described, as well as specific applications to the D0 Run IIb silicon detector.