118459011
Fermion-dimer scattering using an impurity lattice Monte Carlo approach and the adiabatic projection method
We present lattice Monte Carlo calculations of fermion-dimer scattering in the limit of zero-range interactions using the adiabatic projection method. The adiabatic projection method uses a set of initial cluster states and Euclidean time projection to give a systematically improvable description of the low-lying scattering cluster states in a finite volume. We use L\"uscher's finite-volume relations to determine the s-wave, p-wave, and d-wave phase shifts. For comparison, we also compute exact lattice results using Lanczos iteration and continuum results using the Skorniakov-Ter-Martirosian equation. For our Monte Carlo calculations we use a new lattice algorithm called impurity lattice Monte Carlo. This algorithm can be viewed as a hybrid technique which incorporates elements of both worldline and auxiliary-field Monte Carlo simulations.
119868800
Ab initio lattice results for Fermi polarons in two and three dimensions
We investigate the attractive Fermi polaron problem in two and three dimensions using non-perturbative Monte Carlo simulations. We introduce a new Monte Carlo algorithm called the impurity lattice Monte Carlo method. This algorithm samples the path integral in a computationally efficient manner and has only small sign oscillations for systems with a single impurity. To benchmark the method, we calculate the universal polaron energy in three dimensions in the scale-invariant unitarity limit and find agreement with published results. We then present the first fully non-perturbative calculations of the polaron energy in two dimensions in the limit of zero range interactions. We find evidence for a smooth crossover transition from a fermionic quasiparticle to a molecular state as a function of interaction strength with significant mixing between the two descriptions in the crossover region.
15307965
The role of Monte Carlo within a diagonalization/Monte Carlo scheme
Abstract We review the method of stochastic error correction which eliminates the truncation error associated with any subspace diagonalization. Monte Carlo sampling is used to compute the contribution of the remaining basis vectors not included in the initial diagonalization. The method is part of a new approach to computational quantum physics which combines both diagonalization and Monte Carlo techniques.
125749692
Nuclear lattice simulations
We review recent progress on nuclear lattice simulations using chiral effective field theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-to- leading order, isospin-breaking and Coulomb effects, and the binding energy of light nuclei.
118374917
Lattice calculations for A = 3 , 4, 6, 12 nuclei using chiral effective field theory
Abstract.We present lattice calculations for the ground-state energies of tritium, helium-3, helium-4, lithium-6, and carbon-12 nuclei. Our results were previously summarized in a letter publication. This paper provides full details of the calculations. We include isospin-breaking, Coulomb effects, and interactions up to next-to-next-to-leading order in chiral effective field theory.
13972554
A non-perturbative analysis of symmetry breaking in two-dimensional φ4 theory using periodic field methods
Abstract We describe the generalization of spherical field theory to other modal expansion methods. The main approach remains the same, to reduce a d -dimensional field theory into a set of coupled one-dimensional systems. The method we discuss here uses an expansion with respect to periodic-box modes. We apply the method to φ 4 theory in two dimensions and compute the critical coupling and critical exponents. We compare with lattice results and predictions via universality and the two-dimensional Ising model.
120849057
Design and performance of an 8 cm thick intrinsic germanium detector telescope
Abstract A detector telescope consisting of eight 1 cm thick intrinsic Ge diodes is described. The diodes have thin dead layer Li junctions (∼15 ωm ) and are mounted in interchangeable holders. Designs of the holders and the mounting assembly are presented. The major problem in using stopping detectors at medium energies is the tail of low pulse height events produced by nuclear reactions and scattering out. A technique for rejecting these events is described and the results obtained with deuterons from p-d elastic scattering of 800 MeV protons are presented. Analysis of the nuclear reaction tail for 120, 220, and 250 MeV deutrons yields an average total reaction cross section for deuterons on Ge of σ R = (1490±130) mb.
123008932
The response of drift tubes to variations in wire diameter and gas filling
Abstract A systematic study of the response of single-wire drift tubes to variations in the wire diameter and gas fillings has been conducted. Gas gain as a function of applied voltage and pulse-shape characteristics were measured for both the proportional and streamer modes. Argon gas fillings with mixtures of ethane, methane, isobutane, and carbon dioxide were studied. Ethanol and isopropyl alcohol admixtures were added to determine effects on stability. Additional studies were conducted on nonstandard gas mixtures such as Freon and neon fillings, and “magic gas”. Wire diameters included in the study were 20, 25, 50, and 100 μm. The results demonstrate that streamer operation can be achieved with most gases and wire diameters. However, in most cases, admixtures of alcohol were necessary to obtain adequate streamer mode plateaus for the smaller diameter wires.
118591353
A prediction of the neutron and charged particle backgrounds in the L detector
Monte Carlo calculations have been made of the neutron flux and activation in the forward and barrel calorimeters in the L* detector and of the neutron flux in the central detector volume. In addition estimates of the charged particle and neutron background rates in the vicinity of the muon chambers has been determined. The Los Alamos National Laboratory code system LAHET and CINDER, 90 along with ISAJET and GEANT were used in these studies. The results indicate that neutron fluences as low as 2 {times} 10{sup 12} per SSC year can be achieved in the central volume. 6 refs., 3 figs., 2 tabs.
111344904
Beam test of prototype 18 cm silicon-strip detectors with high speed electronics
A prototype silicon microstrip detector for the GEM general purpose detector proposed for the Super Collider was assembled and tested in the laboratory with radioactive sources and an IR-laser, and at SLAC in a 25 GeV electron beam. The system was designed for performance in the GEM environment: 60 MHz bunch crossing at 10/sup 33/ luminosity with inner barrel occupancies of 0.16%. Signals from the strips were amplified by custom designed high-speed, low-power, low-noise, low-mass, integrated microelectronics The mechanical design of the GEM tracker motivated the selection of long (18 cm) strip lengths (achieved by wire-bonding three 6 cm long detectors). Evaluation of the test beam and laboratory results demonstrate the feasibility of this approach.
30885576
Wide Dynamic Range Beam Profile Monitor
An economical harp multiplexer system has been developed to achieve a wide dynamic range. The harp system incorporates a pneumatically actuated harp detector with ceramic boards and carbon wires; a high-sensitivity multiplexer packaged in a double-wide NIM module; and flat, shielded ribbon cable consisting of individual twisted pairs. The system multiplexes 30 wires in each of the x and y planes simultaneously and operates with or without computer control. The system has operated in beams of 100 nA to 1 mA, 1-to 120-Hz repetition rate, with a signal-to-noise ratio of greater than 10/1.