126030076
Measurement of B_s Oscillations and CP Violation Results from D0
We present a measurement of the B{sub s}{sup 0} - B{sub s}{sup 0} oscillation frequency, {Delta}m{sub s}, using a combination of semi-leptonic and hadronic B{sub s} decay candidates selected from data collected by the D0 Experiment at the Fermilab Tevatron. We also present several results on CP violation, including an improved measurement of the B{sub s} CP-violating phase from a flavor-tagged analysis of B{sub s}{sup 0} {yields} J/{psi} + {phi} decays.
122654690
Silicon microstrip wedge detectors for the DØ silicon tracker
Abstract The silicon tracking system proposed for the DO upgrade is discussed. The design of “wedge” modules for the forward disk section of the tracker is described. The wedge detectors are double-sided with a stereo angle of ± 15° and a strip pitch of 50 μm. Each strip includes an integrated ac-coupling capacitor and polysilicon bias resistor. First results from recently fabricated prototype wedge detectors are presented.
120475830
Physics capabilities of the DO upgrade detector
The D0 detector at Fermilab is being upgraded to meet the demands imposed by high luminosity Tevatron running planned to begin in 1998. The central tracking detectors will be replaced with silicon and scintillating fiber tracking systems inside a solenoidal magnetic field and a preshower detector will be added to aid in electron identification. The design and performance of these systems are described and detailed simulations of the physics capabilities of the upgraded detector are presented. In particular the authors focus on the study of electroweak boson properties and top quark physics and briefly describe the b-physics capabilities.
122003047
Silicon drift photodiodes
Abstract Low capacitance photodiodes based on the principle of the solid state drift chamber have been constructred and tested. The devices are based on a cellular design with an anode at the centre of each of five cells allowing electrons liberated by ionisation to drift up to 1 mm to the readout strip. Results on the performance of the detectors, including leakage current, capacitance and drift properties, are presented and compared with simulations. A second series drift photodiodes have been processed which incorporate improvements based on results acquired from the first design. They have leakage currents of a few nA and shorter drift times at the periphery of the drift cells. We present measurements showing the performance of the new devices.
110084127
A silicon drift photodiode
A low-capacitance photodiode based on the principle of the solid-state drift chamber has been constructed and tested. The device is based on a cellular design with an anode at the center of each of five cells, allowing electrons liberated by ionization to drift up to 1 mm to the readout strip. Two designs were produced with p/sup +/ implant widths of 75 mu m and 85 mu m, respectively, using n-type material of 3.5-k Omega -cm resistivity. The opposite surface is a uniform p-type implant, features matching those of the other surface, and is unmetallized to ensure good photosensitivity. Results on the performance of the detector, including leakage current, capacitance, and drift properties, are presented and compared with simulation results. >
110541630
Punch-through currents and floating strip potentials in silicon detectors
Punch-through currents flowing between adjacent p/sup +/ strips on the surface of silicon microstrip drift detectors have been observed. Measurements of the floating strip potential have shown that a p/sup +/ strip acquires a voltage such that the punch-through current and the leakage current are equal and opposite. The factors influencing the threshold for the punch-through effect have been compared with a simple computer model, and the predicted variation with the interstrip gap is found to be in reasonable agreement with measured values for a variety of detectors. >
117418480
Reliability of numerical solutions of a diffusion equation modeling rf noise-induced dilution in particle beams
The dilution process in particle beams caused by noise in the rf accelerating system has been modeled using a diffusion equation. Particle tracking can also be undertaken to determine the effects of rf noise, through it is much more computationally extensive than integrating the diffusion equation. In this paper we present the integration results using the Method of Lines (MOL) for certain important classes of noise. We will describe the numerical algorithms in detail, including those that are made to remove anomalous solutions. Reliability of the numerical results will be checked using both finite-difference and finite-element (Galerkin) methods in discretization and applying the same algorithms to the cases of linear and quadratic diffusion coefficients where exact solutions are known.
56450130
Impedance description of coherent synchrotron radiation with account of bunch deformation
We are concerned with coherent longitudinal motion in a storage ring, especially with situations in which coherent synchrotron radiation (CSR) can in∞uence stability of the beam. The collective force from CSR is usually described by an impedance or a wake function in such a way that the force depends only on the charge distribution at the present time. This description is exact only for a rigid bunch, since causality demands that the force depend on the prior history of the bunch. We show how to treat a deforming bunch by applying the \complete impedance" Z(n;!), a function of wave number and frequency. We derive this impedance and study its analytic properties for a special model: radiation from circular orbits shielded by parallel plates representing the metallic vacuum chamber. We analyze the corresponding collective force, obtaining the usual formula as a flrst approximation, plus easily computed corrections that depend on present and prior values of the time derivative of the charge density. In related papers we have applied these results in numerical simulations of instabilities induced by CSR. PACS numbers: Valid PACS appear here
59440178
Adiabatic invariance of spin-orbit motion in accelerators
It has been predicted and found experimentally that the polarization direction of particles on the closed orbit of a circular accelerator can be manipulated, without a noticeable reduction of polarization, by means of a slow variation of magnetic fields. This feature has been used to avoid imperfection resonances where the spin precession frequency is close to a multiple of the circulation frequency. As a first step we show that this property is related to an adiabatic invariant of spin motion. The proof is relatively simple since it involves only two frequencies, the spin-rotation frequency and the particle’s rotation frequency on the closed orbit. The invariant spin field (ISF) describes a periodic polarization state of a beam’s phasespace distribution. This ISF leads to a very useful parametrization of coupled spin and orbit dynamics. We prove that this ISF gives rise to an adiabatic invariant of spin-orbit motion. This proof is much more complicated since the orbital frequencies are involved. Because of this adiabatic invariance, a beam’s spin field follows slow changes of the accelerator’s ISF that can occur during a slow acceleration cycle. This feature is essential when high-order spin-orbit resonances are crossed, since it allows polarization that has been reduced at the resonance condition to be recovered, to a large degree, after the resonances have been crossed.
110696864
Rf noise tolerances at the SSC
We apply the diffusion in action theory developed by Dome, Krinsky, and Wang to the determination of SSC rf noise tolerances using the emittance-doubling time as a criterion. We present results for white amplitude and white phase noise, noise measured from a HP synthesizer and from a SLAC PEP klystron. We also derive a scaling law for white amplitude and phase noise that allows one to understand the dependence of the diffusion process on the rf frequency. Lastly we qualitatively discuss the implementation of feedback loops to reduce rf noise.
15671309
Construction of Large Period Symplectic Maps by Interpolative Methods
The goal is to construct a symplectic evolution map for a large section of an accelerator, say a full turn of a large ring or a long wiggler. We start with an accurate tracking algorithm for single particles, which is allowed to be slightly non-symplectic. By tracking many particles for a distance S one acquires sufficient data to construct the mixed-variable generator of a symplectic map for evolution over S, given in terms of interpolatory functions. Two ways to find the generator are considered: (1) Find its gradient from tracking data, then the generator itself as a line integral. (2) Compute the action integral on many orbits. A test of method (1) has been made in a difficult example: a full turn map for an electron ring with strong nonlinearity near the dynamic aperture. The method succeeds at fairly large amplitudes, but there are technical difficulties near the dynamic aperture due to oddly shaped interpolation domains. For a generally applicable algorithm we propose method (2), realized with meshless interpolation methods.