208 research outputs found
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Data acquisition and experiment control system for a large area neutron detector
The system consists of a data input subsystem, a display subsystem and a spectrometer control subsystem. The data input subsystem consists of a two-dimensional analog-to-digital converter with the analog section remote from the rest of the system. The analog-to-digital converter clock runs at 100 MHz. There can be up to 1024 channels in each dimension for a maximum array size of approx. 1 million words. Arrays of this size may be easily handled by a multiport memory with 6.71 x 10/sup 7/ words of address space. The read/increment/write time for data in this array is 2.5 ..mu..sec per event. The display and neutron spectrometer subsystem are also briefly described
Parity nonconserving observables in thermal neutron capture on a proton
We calculate parity nonconserving observables in the processes where a
neutron is captured on a proton at the threshold energy radiating a photon.
Various potential models such as Paris, Bonn and Argonne are used for the
strong interactions, and the meson-exchange description is employed for the
weak interactions between hadrons. The photon polarization in the
unpolarized neutron capture process and photon asymmetry in the
polarized neutron capture process are obtained in terms of the weak
meson-nucleon coupling constants. turns out to be basically
insensitive to the employed strong interaction models and thus can be uniquely
determined in terms of the weak coupling constants, but depends
significantly on the strong interaction models.Comment: 13 pages, 11 eps figure
Diffractive Dissociation in Deep Inelastic Scattering at HERA
The diffraction dissociation of virtual photons is considered in the
framework of conventional Regge theory. It is shown that the recent HERA data
on large rapidity gap events can be successfully described in terms of the
Pomeron structure function. Using Regge factorization, the latter can be
related to the deuteron structure function. The parameters which relate these
two structure functions are determined from soft hadronic diffraction data. The
size of the shadowing corrections at low x and large Q**2 is also obtained.Comment: 17 pages, TEX, preprint LPTHE Orsay 94-4
An Effective Field Theory Calculation of the Parity Violating Asymmetry in n+p -> d+gamma
Weak interactions are expected to induce a parity violating pion-nucleon
coupling, h_{\pi NN}^{(1)}. This coupling should be measurable in a proposed
experiment to study the parity violating asymmetry A_\gamma in the process \vec
n + p \to d+\gamma. We compute the leading dependence of A_\gamma on the
coupling h_{\pi NN}^{(1)} using recently developed effective field theory
techniques and find an asymmetry of A_\gamma = +0.17 h_{\pi NN}^{(1)} at
leading order. This asymmetry has the opposite sign to that given by
Desplanques, Donoghue and Holstein.Comment: 7 pages, 2 figures from 3 eps files, late
Fabrication of GaNxAs1-x Quantum Structures by Focused Ion Beam Patterning
A novel approach to the fabrication of GaNxAs1-x quantum dots and wires via
ion beam patterning is presented. Photomodulated reflectance spectra confirm
that N can be released from the As sublattice of an MBE-grown GaNxAs1-x film by
amorphization through ion implantation followed by regrowth upon rapid thermal
annealing (RTA). Amorphization may be achieved with a focused ion beam (FIB),
which is used to implant Ga ions in patterned lines such that annealing
produces GaAs regions within a GaNxAs1-x film. The profiles of these amorphized
lines are dependent upon the dose implanted, and the film reaches a damage
threshold during RTA due to excess Ga. By altering the FIB implantation
pattern, quantum dots or wires may be fabricated.Comment: To appear in the proceedings of the 27th International Conference on
the Physics of Semiconductors (ICPS-27, Flagstaff, AZ, July 26-30, 2004
Elastic Nd scattering at intermediate energies as a tool for probing the short-range deuteron structure
A calculation of the deuteron polarization observables , ,
, and the differential cross-section for elastic
nucleon-deuteron scattering at incident deuteron energies 270 and 880 MeV in
lab is presented. A comparison of the calculations with two different deuteron
wave-functions derived from the Bonn-CD -potential model and the dressed
bag quark model is carried out. A model-independent approach, based on an
optical potential framework, is used in which a nucleon-nucleon -matrix is
assumed to be local and taken on the energy shell, but still depends on the
internal nucleon momentum in a deuteron.Comment: 15 pages, 4 figure
The Onset of Color Transparency in Reactions on Nuclei
Quantum filtering of the ejectile wave packet from hard scattering on
bound nucleons puts stringent constraints on the onset of color transparency in
reactions in nuclei at moderate energies. Based on
multiple-scattering theory, we derive a novel formula for nuclear transparency
and discuss its energy dependence in terms of a color transparency sum rule.Comment: 14 pages (LATEX), 3 figures (not included, available from the
authors), KFA-IKP(TH)-1992-1
Strangeness-Conserving Hadronic Parity Violation at Low Energies
The parity-violating nucleon-nucleon interaction is the key to understanding
the strangeness-conserving hadronic weak interaction at low energies. In this
brief talk, I review the past accomplishments in and current status of this
subject, and outline a new joint effort between experiment and theory that
tries to address the potential problems in the past by focusing on parity
violation in few-nucleon systems and using the language of effective field
theory.Comment: 8 pages, to appear in the proceedings of the Second Meeting of the
APS Topical Group on Hadronic Physics, Nashville, TN, USA, Oct. 22-24, 200
Evidence for Color Fluctuations in Hadrons from Coherent Nuclear Diffraction}
A QCD-based treatment of projectile size fluctuations is used to compute
inelastic diffractive cross sections for coherent
hadron-nuclear processes. We find that fluctuations near the average size give
the major contribution to the cross section with contribution
from small size configurations.
The computed values of are consistent with the limited
available data. The importance of coherent diffraction studies for a wide range
of projectiles for high energy Fermilab fixed target experiments is emphasized.
The implications of these significant color fluctuations for relativistic heavy
ion collisions are discussed.Comment: Report number DOE/ER 40427-13-N93 11 pages, 3 figures available from
author Mille
Reggeon and pion contributions in semi-exclusive diffractive processes at HERA
A detailed analysis of semi-exclusive diffractive processes in e-p DIS at
HERA, with the diffractive final states in the forward direction is presented.
The contributions of the subleading f_2, \omega, a_2, \rho reggeons and the
pion exchanges to the diffractive structure function with the forward proton or
neutron are estimated. It is found that the (a_2,\rho) reggeons are entirely
responsible for the forward neutron production at x_P < 10^{-3}. The \pi N
production in the forward region is estimated using the Deck mechanism. The
significance of this reaction for the processes measured at HERA, especially
with the leading neutron, is discussed.Comment: Strongly revised version accepted for publication in Phys.Rev.D.
Latex, 14 pages with 5 eps figures include
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