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G. A. Miller

Publications and source records attributed to G. A. Miller.

88 records · Page 5Linked to original sources
arXiv1995

Color Transparency Effects in Electron Deuteron Interactions at Intermediate Q^2

High momentum transfer electrodisintegration of polarized and unpolarized deuterium targets, $d(e,e'p)n$ is studied. We show that the importance of final state interactions-FSI, occuring when a knocked out nucleon interacts with the other nucleon, depends strongly on the momentum of the spectator nucleon. In particular, these FSI occur when the essential contributions to the scattering amplitude arise from internucleon distances $\sim 1.5~fm$. But the absorption of the high momentum $γ^*$ may produce a point like configuration, which evolves with time. In this case, the final state interactions probe the point like configuration at the early stage of its evolution. The result is that significant color transparency effects, which can either enhance or suppress computed cross sections, are predicted to occur for $\sim 4 GeV^2 \ge Q^2\leq~10~(GeV/c)^2$.

nucl-th↗
arXiv1994

Color Transparency and the Vanishing Deuterium Shadow

We find that the final state interactions in the $d(e,e'np)$ amplitude depend strongly on the final momentum of the spectator nucleon. This means that color transparency effects can be studied at rather low four-momentum transfer $Q^2\geq$ 4 (GeV/c)$^2$ using un-polarized and polarized deuteron targets.

nucl-th↗
arXiv1994

Expansion Aspect of Color Transparency on the Lattice

The opportunity to observe color transparency (CT) is determined by how rapidly a small-sized hadronic wave packet expands. Here we use SU(2) lattice gauge theory with Wilson fermions in the quenched approximation to investigate the expansion. The wave packet is modeled by a point hadronic source, often used as an interpolating field in lattice calculations. The procedure is to determine the Euclidean time (t), pion channel, Bethe-Salpeter amplitude $Ψ(r,t)$, and then evaluate $b^2(t)=\int d^3 r Ψ(r,t) r^2 sin^2 θΨ_π(r)$. This quantity represents the soft interaction of a small-sized wave packet with a pion. The time dependence of $b^2(t)$ is fit as a superposition of three states, which is found sufficient to reproduce a reduced size wave packet. Using this superposition allows us to make the analytic continuation required to study the wave packet expansion in real time. We find that the matrix elements of the soft interaction $\hat b^2$ between the excited and ground state decrease rapidly with the energy of the excited state.

hep-lat↗
arXiv1994

A Proposed Test of Charge Symmetry in $Σ$ Decay

The semi-leptonic decays of $Σ^\pm$ offer a vehicle for observing charge symmetry-breaking. The effect is expected to be about 6\%, enhanced due to the replacement of two u quarks by d quarks. We propose that present experimental data be improved to search for this effect.

hep-ph↗
arXiv1994

The Geometrical Color Optics Of Coherent High Energy Processes

CONTENTS. 1.Introduction, 1.1 QCD ideas to be tested; 2. Coherence phenomena in QED, 2.1 Charge transparency, 2.2 Charge filtering, 2.3 Charge opacity; 3. Color transparency in perturbative QCD, 3.1 Coherence length in QCD, 3.2 Bjorken scaling for deep inelastic processes, 3.3 Hard Coherent Diffraction {}From Nucleons and Nuclei; 4. Soft Diffractive Physics and Color Fluctuations, 4.1 Scattering eigenstates formalism; 4.2 Current information on color fluctuations in Hadrons, 4.3 Small Size Configurations in Pions, 4.4 Nuclear inelastic diffraction as evidence for color fluctuations near the average value, 4.5 Inelastic screening corrections to the total cross sections; 5. Color transparency in nuclear quasielastic reactions. 5.1 Is a small system made?, 5.2 Time development, 5.3 Relevant data; 6. Color fluctuations in nucleons and nucleus-nucleus collisions, 6.1 Color opacity effects, 6.2 Color fluctuations and central collisions, 6.3 Leading hadron transparency effects in central collisions.

hep-ph↗
arXiv1994

Charge Independence and Symmetry of Nuclear Forces

Charge independence and symmetry are approximate symmetries of nature. The observations of the small symmetry breaking effects and the consequences of those effects are reviewed. The effects of the mass difference between up and down quarks and the off shell dependence $q^2$ of $ρ^0$-$ω$ mixing are stressed. In particular, I argue that models which predict a strong $q^2$ dependence of $ρ^0$-$ω$ mixing seem also to predict a strong $q^2$ variation for the $ρ^0$-$γ^*$ matrix element, in contradiction with experiment.

nucl-th↗
arXiv1994

Searching for Color Coherent Effects at Intermediate $Q^2$ via Double Scattering Processes

We propose that measuring the $Q^2$ dependence of the number of final-state interactions of the recoil protons in quasi-elastic electron scattering from light nuclei is a new method to investigate Color Coherent effects at {\bf intermediate} values of $Q^2$ ({$\sim$ few $(GeV/c)^2$}). This is instead of measuring events without final-state interactions. Our calculations indicate that such measurements could reveal significant color transparency effects for the highest of the energies initially available at CEBAF. Measurements that detect more than one hadron in the final state, which require the use of large acceptance ($4π$) detectors, are required.

nucl-th↗
arXiv1993

Transverse Quark Distribution in Mesons - QCD Sum Rule Approach -

QCD sum rules are used to compute the first few moments of the mesonic quark momentum. Transverse, longitudinal and mixed transverse-longitudinal components are examined. The transverse size of the pion is shown to be dictated by the gluon condensate, even though the mass and the longitudinal distribution are dominated by the quark condensate. The implications of our results for color transparency physics and finite temperature QCD are discussed.

hep-ph↗
arXiv1993

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 $σ_{diff}$ for coherent hadron-nuclear processes. We find that fluctuations near the average size give the major contribution to the cross section with $ \le few \%$ contribution from small size configurations. The computed values of $σ_{diff}$ 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.

hep-ph↗
arXiv1993

Vector Color Transparency

Color transparency (CT) in high momentum transfer $(e,e' \vec p)$ reactions is explored. The spin of the proton and photon are treated explicitly, hence the name ``Vector CT". The Dirac distorted wave impulse approximation is used as a starting point; then CT effects are embedded. A hadronic basis is used to describe the struck proton as a wavepacket of physical baryon resonances. The effects of the wavepacket expansion on the normal component of the ejectile polarization, which vanishes in the limit of full CT, are investigated. This formalism is also applied to study CT effects in total cross sections, individual separated nuclear response functions, Fermi motion of the initial nucleon, non-zero size of the initial wavepacket and the effects of relativistic lower components. We show that including CT reduces the violations of current conservation (CC), a typical problem in calculations of this kind. The energy dependence of the normal polarization in $(e,e' \vec p)$ reactions is found to be slow. However, a measurement of the normal transverse response in a heavy nucleus, such as $^{208}Pb$ seems to afford the opportunity to see CT at quite low momentum transfers. The effects of Fermi motion are investigated, and choosing the momentum of the struck nucleon to be large leads to significant violations of CC.

nucl-th↗
arXiv1993

Coherent Nuclear Diffractive Production of Minijets - Illuminating Color Transparency

The cross section for coherent nuclear processes in which an incident meson or photon dissociates diffractively into two jets of high relative transverse momentum (between about 1 and 3 GeV/c) is found to be proportional in QCD to $A^2$ in a wide kinematical region. The leading correction to this is a significant positive term $\propto A^{7/3}$ caused by nuclear multiple-scattering. We find also that shadowing of hard diffractive processes reappears as a leading twist effect in the TeV energy range.

hep-ph↗
arXiv1992

Sum Rule Description of Color Transparency

The assumption that a small point-like configuration does not interact with nucleons leads to a new set of sum rules that are interpreted as models of the baryon-nucleon interaction. These models are rendered semi-realistic by requiring consistency with data for cross section fluctuations in proton-proton diffractive collisions.

nucl-th↗
arXiv1992

Multiple-Scattering Series For Color Transparency

Color transparency CT depends on the formation of a wavepacket of small spatial extent. It is useful to interpret experimental searches for CT with a multiple scattering scattering series based on wavepacket-nucleon scattering instead of the standard one using nucleon-nucleon scattering. We develop several new techniques which are valid for differing ranges of energy. These techniques are applied to verify some early approximations; study new forms of the wave-packet-nucleon interaction; examine effects of treating wave packets of non-zero size; and predict the production of $N^*$'s in electron scattering experiments.

hep-ph↗
arXiv1992

Realistic Hadronic Matrix Element Approach to Color Transparency

Color transparency occurs if a small-sized wave packet, formed in a high momentum transfer process, escapes the nucleus before expanding. The time required for the expansion depends on the masses of the baryonic components of the wave packet. Measured proton diffractive dissociation and electron deep inelastic scattering cross sections are used to examine and severely constrain the relevant masses. These constraints allow significant color transparency effects to occur at experimentally accessible momentum transfers.

hep-ph↗