Miguel A. Furman

Weak interactions of ultra heavy fermions

Abstract We study the weak interactions of ultra heavy fermions, their scattering at high energies and the renormalization corrections they induce at low energies.

Weak interactions of ultra heavy fermions (II)

Abstract We discuss the weak interactions of ultra heavy fermions at low and high energy in the SU(2)L × U(1) gauge theory. Using partial-wave unitarity at high energy we establish critical fermion mass values beyond which strong couplings occur in the theory and the perturbation expansion fails. The critical masses are ( 500 √N ) GeV for quarks and ( 1.0 √N ) TeV for leptons, where N is the number of nearly degenerate SU(2)L doublets of quarks and leptons respectively. At low energies, far below their production threshold, we show that ultra heavy fermions would induce large, observable one-loop radiative corrections. One of these corrections (obtained also by Veltman) implies, using present experimental data, an upper limit of ∼700 GeV for a heavy lepton in an SU(2)L doublet with a massless neutrino.

The axial current in dimensional regularization

Abstract We show that a fully anticommuting γ 5 is a correct and natural prescription for the dimensional regularization of one fermion loop graphs in spontaneously broken gauge theories. Other prescriptions introduce spurious anomalies into Ward identities which are actually anomly free. Our prescription is correct even though no such γ 5 exists: it cannot exist precisely because of the familiar chiral anomaly.

LARGE CORRECTIONS TO HIGH pT HADRON-HADRON SCATTERING IN QCD

Abstract We have computed the first non-trivial QCD corrections to the quark-quark scattering process which contributes to the production of hadrons at large p T in hadron-hadron collisions. Using quark distribution functions defined in deep inelastic scattering and fragmentation functions defined in one particle inclusive e + e − annihilation, we find that the corrections are large. This implies that QCD perturbation theory may not be reliable for large- p T haron physics.

Critical Exponents for the Reggeon Quantum Spin Model

Abstract The Reggeon quantum spin (RQS) model on the transverse lattice in D dimensional impact parameter space has been conjectured to have the same critical behaviour as the Reggeon field theory (RFT). Thus from a high “temperature” series of ten ( D = 2) and twenty ( D = 1) terms for the RQS model we extrapolate to the critical temperature T = T c by Pade approximants to obtain the exponents η =0.238±0.008, z =1.16±0.01, v =1.271±0.007 for D =2 and η =0.317±0.002, z =1.272±0.007, v =1.736±0.001, λ =0.57±0.03 for D =1. These exponents naturally interpolate between the D =0 and D =4− e results for RFT as expected on the basis of the universality conjecture.

Initial experimental studies of electron accumulation in a heavy-ion beam

Accelerators for heavy-ion inertial fusion energy (HIF) have an economic incentive to fit beam tubes tightly to beams, putting them at risk from electron clouds produced by emission of electrons and gas from walls. Theory and PIC simulations suggest that the electrons will be radially trapped in the /spl ges/1 kV ion-beam potential. We are beginning studies on the High-Current Experiment (HCX) with unique capabilities to characterize electron production and trapping, the effects on ion beams, and mitigation techniques. We are measuring the flux of electrons and gas evolved from a target, whose angle to the beam can be varied between 78/spl deg/ and 88/spl deg/ from normal incidence. Quadrupole magnets are operating with a variety of internal charged particle diagnostics to measure the beam halo loss, net charge, electron ionization rate, and gas density.

Simulating relativistic beam and plasma systems using an optimal boosted frame

It was shown recently that it may be computationally advantageous to perform computer simulations in a Lorentz boosted frame for a certain class of systems. However, even if the computer model relies on a covariant set of equations, it was pointed out that algorithmic difficulties related to discretization errors may have to be overcome in order to take full advantage of the potential speedup. In this paper, we summarize the findings, the difficulties and their solutions, and review the applications of the technique that have been performed to date.

Filling in the Roadmap for Self-Consistent Electron Cloud and Gas Modeling

Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-laboratory effort to understand the underlying physics via the combined application of experiment, theory, and simulation is underway. We present here the status of the simulation capability development, based on a merge of the three-dimensional parallel Particle-In-Cell (PIC) accelerator code WARP and the electron cloud code POSINST, with additional functionalities. The development of the new capability follows a “roadmap” describing the different functional modules, and their inter-relationships, that are ultimately needed to reach self-consistency. Newly developed functionalities include a novel particle mover bridging the time scales between electron and ion motion, a module to generate neutrals desorbed by beam ion impacts at the wall, and a module to track impact ionization of the gas by beam ions or electrons. Example applications of the new capability to the modeling of electron effects in the High Current Experiment (HCX) are given.

Simulation and analysis of microwave transmission through an electron cloud, a comparison of results

Simulation studies for transmission of microwaves through electron clouds show good agreement with analytic results. The electron cloud produces a shift in phase of the microwave. Experimental observation of this phenomena would lead to a useful diagnostic tool for accessing the local density of electron clouds in an accelerator. These experiments are being carried out at the CERN SPS and the PEP-II LER at SLAC and is proposed to be done at the Fermilab main injector. In this study, a brief analysis of the phase shift is provided and the results are compared with that obtained from simulations.

Electron-cloud measurements and simulations for the APS

We compare experimental results with simulations of the electron cloud effect induced by a positron beam at the APS synchrotron light source at ANL, where the electron cloud effect has been observed and measured with dedicated probes. We find good agreement between simulations and measurements for reasonable values of certain secondary electron yield (SEY) parameters, most of which were extracted from recent bench measurements at SLAC.