36993625
ADIABATIC INVARIANTS FOR SPIN-ORBIT MOTION
It has been predicted and found experimentally that the polarization direction of particles on the closed orbit can be manipulated, without a noticeable reduction of polarization, by 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. We report here on a proof that relates this property to an adiabatic invariant of spin motion. The proof is relatively simple since only two frequencies, the spin rotation frequency and the particle’s rotation frequency on the closed orbit, are involved. The invariant spin field describes a periodic polarization state of a beam’s phase space distribution. This invariant spin field leads to a very useful parametrization of coupled spin and orbit dynamics. We also report on a proof showing that the invariant spin field gives rise to an adiabatic invariant of spin-orbit motion. The proof is now much more complicated since the orbital frequencies are involved. Due to this adiabatic invariance, the spin field of a polarized beam follows slow changes of the accelerator’s invariant spin field that can occur during a slow acceleration cycle. This feature is essential when high-order spin orbit resonances are crossed since it allows a reduced degree of polarization at the resonance condition to recover, to a large degree, after the resonance has been crossed.
39490210
Equilibrium fluctuations in an N-particle coasting beam: Schottky noise effects
We discuss the longitudinal dynamics of an unbunched beam with a collective effect due to the vacuum chamber and with the discreteness of an N-particle beam (Schottky noise) included. We start with the 2N equations of motion (in angle and energy) with random initial conditions. The 2D phase space density (Klimontovich density) for the N particles is a sum of delta functions and satisfies the Klimontovich equation and the Vlasov equation. An arbitrary function of the energy also satisfies the Vlasov equation and we linearize about a convenient equilibrium density taking the initial conditions to be independent, identically distributed random variables with the equilibrium distribution. The linearized equations can be solved using a Laplace transform in time and a Fourier series in angle. The resultant stochastic process for the phase space density is analyzed and compared with a known result. Work is in progress to study the full nonlinear problem.
122076282
Deflection of GeV particle beams by channeling in bent crystal planes of constant curvature
2396816
Progress on a Vlasov Treatment of Coherent Synchrotron Radiation from Arbitrary Planar Orbits
We report on our progress in the development of a fully self-consistent Vlasov treatment of coherent synchrotron radiation (CSR) effects on particle bunches traveling on arbitrary planar orbits. First we outline our Vlasov approach and the approximation we are currently studying. Then we discuss recent numerical results for a benchmark model studied extensively with codes by several authors.
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
15693839
Self-consistent computation of electromagnetic fields and phase space densities for particles on curved planar orbits
We discuss our progress on the self-consistent calculation of the 4D phase space density (PSD) and electromagnetic fields in a Vlasov-Maxwell formulation. We emphasize coherent synchrotron radiation (CSR) from arbitrary curved planar orbits, with shielding from the vacuum chamber, but space charge forces are naturally included. Our focus on the Vlasov equation will provide simulations with lower numerical/statistical noise than standard PIC methods, and will allow the study of issues such as emittance degradation and microbunching due to space charge and CSR in bunch compressors. The fields excited by the bunch are computed in the lab frame from a new double integral formula. The field formula is derived from retarded potentials by changes of variables. It is singularity-free and requires no computation of retarded times. Ultimately, the Vlasov equation will be integrated in beam frame coordinates using our method of local characteristics. As an important intermediate step, we have developed a "self-consistent Monte Carlo algorithm", and a corresponding parallel code. This gives an accurate representation of the source and will help in understanding the PSD support. In addition we have (1) studied carefully a 2D phase space Vlasov analogue and (2) derived an improved expression of the field of a 1D charge/current distribution which accounts for the interference of different bends and other effects usually neglected. Bunch compressors will be emphasized.
125856023
Simulation of a silicon vertex detector in the D0 experiment
The simulation of a silicon microstrip detector at the center of the DO detector at the Fermilab Tevatron collider is described. The efficiency of a silicon vertex detector for identifying b-quark jets in a ``non-magnetic`` detector such as D0 is investigated. For a position resolution of 10 {mu}m the gluon/b-jet rejection factor is estimated to be 28 for a b-jet efficiency of 25%. The detection of top quarks in the presence of background from high p{sub T} W boson production is studied.
17092028
CP Violation Results from D0
We present results on CP violation from approximately 2.8 fb^{-1} of data collected by the D0 Experiment at the Fermilab Tevatron. The results presented are: (i) an improved measurement of the B_s^0 CP-violating phase from a flavor-tagged analysis of B_s^0 --> J/\psi \phi decays; (ii) a search for direct CP violation in B^{+-} --> J/\psi K^{+-} (\pi^{+-}) decays from a measurement of the charge asymmetry A_{CP}(B^{+-} --> J/\psi K^{+-}); and (iii) a search for indirect CP violation from searches for anomalous charge asymmetries in semileptonic B_s^0 decays.
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.
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. >
118930627
TOP QUARK PHYSICS RESULTS FROM DØ
We describe recent measurements of the ttbar production cross section and the mass of the top quark from the D0 Collaboration.