1,164 research outputs found
Electromagnetic proton form factors in large QCD
The electromagnetic form factors of the proton are obtained using a
particular realization of QCD in the large limit (),
which sums up the infinite number of zero-width resonances to yield an Euler's
Beta function (Dual-). The form factors and
, as well as agree very well with reanalyzed space-like
data in the whole range of momentum transfer. In addition, the predicted ratio
is in good agreement with recent polarization transfer
measurements at Jefferson Lab.Comment: 10 page
The Inclusive-Exclusive Connection and the Neutron Negative Central Charge Density
We find an interpretation of the recent finding that the central charge
density of the neutron is negative by using models of generalized parton
distributions at zero skewness to relate the behavior of deep inelastic
scattering quark distributions, evaluated at large values of Bjorken x, to the
transverse charge density evaluated at small distances. The key physical input
of these models is the Drell-Yan-West relation We find that the d quarks
dominate the neutron structure function for large values of Bjorken x, where
the large longitudinal momentum of the struck quark has a significant impact on
determining the center-of-momentum of the system, and thus the "center" of the
nucleon in the transverse position plane.Comment: 17 pages, 8 figures. Text of an invited talk presented by G. A.
Miller at the 2008 Division of Nuclear Physics Meeting in Oakland. Prepared
for Int. Journ. Mod. Phys.
The ratio of scattering cross sections predicted from the global fit of elastic data
We present predictions for the value of the cross section ratio , determined from our fit of the elastic
cross section and polarization data. In this fit we took into account the
phenomenological two-photon exchange dispersive correction.
The cross section ratios which are expected to be measured by the VEPP-3
experiment are computed. The kinematical region which will be covered by the
E04-116 JLab experiment is also considered. It is shown that for both
experiments the predicted cross section ratios deviate from unity within more
than .Comment: 7 pages, 4 figure
Final Report for the Success of African American Students (SAAS) in Independent Schools project
The Success of African American Students (SAAS) in Independent Schools was a collaborative, longitudinal, mixed-method research project focused on investigating and understanding the variety of social, emotional, and institutional factors that were thought to influence how Black students navigate the independent school environment. SAAS involved researchers from the University of Pennsylvania (Penn) Graduate School of Education working with faculty and staff from several Philadelphia area independent schools. The SAAS project was supported by five years of funding from the National Institute of Mental Health (NIMH). Finally, SAAS utilized qualitative methods such as focus groups and semi-structured interviews as well as quantitative methods such as questionnaire surveys and behavioral observations
Improvements to the Total Temperature Calibration of the NASA Glenn Icing Research Tunnel
The ability to accurately set repeatable total temperature conditions is critical for collecting quality icing condition data, particularly near freezing conditions. As part of efforts to continually improve data quality in the NASA Glenn Icing Research Tunnel (IRT), new facility instrumentation and new calibration hardware for total temperature measurement were installed and new operational techniques were developed and implemented. This paper focuses on the improvements made in the calibration of total temperature in the IRT
Effect of configuration modification on the hypersonic aerodynamic characteristics of a blended delta wing-body entry vehicle
The longitudinal, lateral, and directional aerodynamic characteristics of a delta-wing configuration were obtained experimentally at Mach 20 in helium with Reynolds numbers, based on model length, of 1.5 million and 2.9 million and at a Mach number of 6 in air with a Reynolds number, based on model length, of 4.8 million. The angles of attack varied from 0 deg to 55 deg for two sideslip angles. The effects of the addition of dorsal fins, the removal of wing tip fins, an increase in elevon span, and changes in elevon hinge-line sweep angle are discussed. The unmodified vehicle had a maximum lift-drag ratio of 2.1 at Mach 19 and of 2.4 at Mach 6 with about the same lateral and directional stability level at both Mach numbers. As the Mach number increased from 6 to 20, the longitudinal center of pressure moved forward and more positive elevon deflection was therefore required to maintain a given trim angle. The removal of wing tip fins increased the maximum lift-drag ratio and had a negligible effect on longitudinal stability, but caused directional instability that was not corrected by the dorsal fins examined. The shape of the wing and elevon hinge-line sweep had a large influence on the induced yawing moment due to roll control
A description of the ratio between electric and magnetic proton form factors by using space-like, time-like data and dispersion relations
We use the available information on the ratio between the electric and
magnetic proton form factors coming from recently published space-like data and
from the few available time-like data. We apply a dispersive procedure on these
data to evaluate the behaviour of this ratio, as a complex function, for all
values of q^2.Comment: 12 pages, 7 Encapsulated Postscript figures, uses epsfig, rotating,
exscale, amsmath, cite, latexsym, graphics, color packages, added reference
Wroclaw neutrino event generator
A neutrino event generator developed by the Wroclaw Neutrino Group is
described. The physical models included in the generator are discussed and
illustrated with the results of simulations. The considered processes are
quasi-elastic scattering and pion production modelled by combining the
resonance excitation and deep inelastic scattering.Comment: Talk given at 2nd Scandanavian Neutrino Workshop (SNOW 2006),
Stockholm, Sweden, 2-6 May 2006. 3 pages, 6 figure
Nucleon Form Factors - A Jefferson Lab Perspective
The charge and magnetization distributions of the proton and neutron are
encoded in their elastic electromagnetic form factors, which can be measured in
elastic electron--nucleon scattering. By measuring the form factors, we probe
the spatial distribution of the proton charge and magnetization, providing the
most direct connection to the spatial distribution of quarks inside the proton.
For decades, the form factors were probed through measurements of unpolarized
elastic electron scattering, but by the 1980s, progress slowed dramatically due
to the intrinsic limitations of the unpolarized measurements. Early
measurements at several laboratories demonstrated the feasibility and power of
measurements using polarization degrees of freedom to probe the spatial
structure of the nucleon. A program of polarization measurements at Jefferson
Lab led to a renaissance in the field of study, and significant new insight
into the structure of matter.Comment: 20 pages, 9 figures; Chapter in the book "A decade of Physics at
Jefferson Lab", to be published in Journal of Physics: Conference Serie
Momentum Transfer Dependence of Nuclear Transparency from the Quasielastic ^(12)C(e, e'p) Reaction
The cross section for quasielastic ^(12)C(e,e’p) scattering has been measured at momentum transfer Q^2=1, 3, 5, and 6.8 (GeV/c)^2. The results are consistent with scattering from a single nucleon as the dominant process. The nuclear transparency is obtained and compared with theoretical calculations that incorporate color transparency effects. No significant rise of the transparency with Q^2 is observed
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