We present a novel formalism to calculate the total and the differential cross sections for heavy unstable top-quark pair production near threshold. Within the context of the nonrelativistic quark model, we introduce the running toponium width To( E , p ) in the Schrodinger equation for the three-point Green's function that governs the ti contribution to the e ' e annihilation process. The effect of the running of the width is found to be significant in two aspects: (i) it takes account of the phase-space volume for the decay process t T -b w i b w and provides a consistent framework for calculating the differential cross sections; and (ii) it reduces the widths of the low-lying resonances to considerably less than 2T,(m:). Furthermore, the running of the width causes the total cross section to decrease significantly at c.m. energies below the first "resonance" enhancement, whereas it makes the "peak" cross section more distinct than is obtained in the fixed toponium width approximation. We use the two-loop-improved QCD potential in our calculation, and the a , ( m , l= dependences of the total and differential cross sections are studied quantitatively, where MS denotes the modified minimal subtraction scheme. We find that the correlations in the a, and m , measurements are opposite in the total and differential cross sections, and the simultaneous measurements would lead to an accurate determination of both parameters.

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The linacs proposed for the Next Linear Collider (NLC) and Japanese Linear Collider (JLC) would contain several thousand X-Band accelerator structures that would operate at a loaded gradient of 50 MV/m. An extensive experimental and theoretical program is underway at SLAC, FNAL and KEK to develop structures that reliably operate at this gradient. The development of standing wave structures is a part of this program. The properties of standing wave structures allow them to operate at the loaded gradient in contrast to traveling wave structures that need conditioning to the unloaded gradient (65 MV/m for NLC/JLC). The gradients in the standing structures tested thus far have been limited by input coupler breakdowns. The behavior of these breakdowns is consistent with a model of pulsed heating due to high magnetic fields. New input couplers have been designed to reduce maximum magnetic fields. This paper discusses design considerations related to high power performance, wakefield suppression and results of high power tests of prototype standing wave structures.

During the 1997 98 luminosity run of the Stanford Linear Collider SLC, two n o v el RF-based detectors were brought i n to operation, in order to monitor the interaction-point IP bunch lengths and uctuations in the relative arrival time of the two colliding beams. Both bunch length and timing can strongly a ect the SLC luminosity and had not been monitored in previous years. The two new detectors utilize a broad-band microwave signal, which i s excited by the beam through a ceramic gap in the nal-focus beam pipe and transported outside of the beamline vault by a 160-ft long X-Band waveguide. We describe the estimated luminosity reduction due to bunch-length drift and IP timing uctuation, the monitor layout, the expected responses and signal levels, calibration measurements, and beam observations.