203 research outputs found
Energy Dependence of the Delta Resonance: Chiral Dynamics in Action
There is an important connection between the low energy theorems of QCD and
the energy dependence of the Delta resonance in pi-N scattering, as well as the
closely related gamma^{*} N -> pi N reaction. The resonance shape is due not
only to the strong pi-N interaction in the p wave but the small interaction in
the s wave; the latter is due to spontaneous chiral symmetry breaking in QCD
(i.e. the Nambu-Goldstone nature of the pion). A brief overview of experimental
tests of chiral perturbation theory and chiral based models is presentedComment: 11 pages, 6 figures, Festschrift for S.N. yan
Farmers’ knowledge of the banana (Musa Sp.) agroforestry systems in Kiboga District, Central Uganda
Banana is a major food and cash crop in Uganda, particularly in the central and southwestern regions. However, production is still below attainable yields and at the same time declining due to a number of reasons, with low soil fertility being paramount. Few farmers use inorganic fertilizers, with majority of them relying mainly on organic supplements including integration of trees/shrubs. However, trees and shrubs exist on banana farms in undefined numbers and composition, with no spacing and canopy management recommendations. Also, there is limited information on farmers’ knowledge on these systems. A survey was, therefore, conducted on 70 randomly selected farms in Kiboga district, central Uganda to assess farmers’ knowledge of, as well as identify trees and shrubs species and banana cultivars in their agro-ecologies. A total of 1,558 trees and shrubs belonging to 40 species and 21 families were recorded in the study area (52 trees/shrubs per banana plantation). These were dominated by Jackfruit, Artocarpus heterophyllus (15%), Natal fig, Ficus natalensis (10%), Albizia, Albizia coriaria (10%) and mango, Mangifera indica (9%). Further, 1,779 banana mats belonging to nine (9) cultivars and three (3) genome groups were observed growing underneath these four commonest tree species (2.6 banana mats per tree). The highest number of banana mats was observed growing underneath F. natalensis (54%) and A. coriaria (42%). Most (87%) observed banana cultivars belonged to the cooking East African Highland Banana (Musa AAA-EAHB) and dominated by Ndibwabalangira (21%). Farmers reported 25 benefits they derive from banana-trees/shrubs integration; with shade and firewood (38%), as well as income and timber (35%) being the main benefits reported. They also reported that the highest percentage of benefits was derived from F. natalensis (44%) and A. coriaria (32%). Of the four (4) most prevalent tree species, A. coriaria (100%) and F. natalensis (96%) were reported as good companion plant to bananas, whereas, A. heterophyllus (99%) and M. indica (97%) were regarded as bad companion plants. Farmers preferred a tree that allows light penetration (96%), is compatible with bananas and other crops (87%) and has easily decomposable leaves (83%). Therefore, F. natalensis and A. coriaria should be integrated in banana agrosystems for soil fertility improvement whereas; A. heterophyllus and M. indica be planted on farm boundaries. However, the best-bet spacing and pruning regimes for these trees should be determined to minimize the negative attributes as much as possible.Keywords: Albizia coriaria, Artocarpus heterophyllus, banana cultivars, benefits, companions, Ficus natalensis, Mangifera indica, tree-specie
New Measurement of Compton Scattering from the Deuteron and an Improved Extraction of the Neutron Electromagnetic Polarizabilities
The electromagnetic polarizabilities of the nucleon are fundamental
properties that describe its response to external electric and magnetic fields.
They can be extracted from Compton-scattering data --- and have been, with good
accuracy, in the case of the proton. In contradistinction, information for the
neutron requires the use of Compton scattering from nuclear targets. Here we
report a new measurement of elastic photon scattering from deuterium using
quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden.
These first new data in more than a decade effectively double the world
dataset. Their energy range overlaps with previous experiments and extends it
by 20 MeV to higher energies. An analysis using Chiral Effective Field Theory
with dynamical \Delta(1232) degrees of freedom shows the data are consistent
with and within the world dataset. After demonstrating that the fit is
consistent with the Baldin sum rule, extracting values for the isoscalar
nucleon polarizabilities and combining them with a recent result for the
proton, we obtain the neutron polarizabilities as \alpha_n = [11.55 +/-
1.25(stat) +/- 0.2(BSR) +/- 0.8(th)] X 10^{-4} fm^3 and \beta_n = [3.65 -/+
1.25(stat) +/- 0.2(BSR) -/+ 0.8(th)] X 10^{-4} fm3, with \chi^2 = 45.2 for 44
degrees of freedom.Comment: 6 pages, 3 figures, comments from Physical Review Letters Referees
addresse
Investigation of the conjectured nucleon deformation at low momentum transfer
We report new precise H measurements at the
resonance at (GeV/c) using the MIT/Bates
out-of-plane scattering (OOPS) facility. The data reported here are
particularly sensitive to the transverse electric amplitude () of the
transition. Analyzed together with previous data yield
precise quadrupole to dipole amplitude ratios and and
for . They give credence to the conjecture of
deformation in hadronic systems favoring, at low , the dominance of
mesonic effects.Comment: 4 pages, 1figur
Measurements of the \gamma * p --> \Delta(1232) reaction at low Q2
We report new p measurements in the
resonance at the low momentum transfer region utilizing the
magnetic spectrometers of the A1 Collaboration at MAMI. The mesonic cloud
dynamics are predicted to be dominant and appreciably changing in this region
while the momentum transfer is sufficiently low to be able to test chiral
effective calculations. The results disagree with predictions of constituent
quark models and are in reasonable agreement with dynamical calculations with
pion cloud effects, chiral effective field theory and lattice calculations. The
reported measurements suggest that improvement is required to the theoretical
calculations and provide valuable input that will allow their refinements
Measurement of the Partial Cross Sections s(TT), s(LT) and [s(T)+epsilon*s(L)] of the p(e,e' pi+)n Reaction in the Delta(1232) Resonance
We report new precision p(e,e' pi+})n measurements in the Delta(1232)
resonance at Q2 = 0.127(GeV/c)2 obtained at the MIT-Bates Out-Of-Plane
scattering facility. These are the lowest, but non-zero, Q2 measurements in the
pi+ channel. The data offer new tests of the theoretical calculations,
particularly of the background amplitude contributions. The chiral effective
field theory and Sato-Lee model calculations are not in agreement with this
experiment
Two-body Photodisintegration of 3He Between 7 and 16 MeV
A comprehensive data set is reported for the two-body photodisintegration cross section of 3He using mono-energetic photon beams at eleven energies between 7.0 and 16.0 MeV. A 3He + Xe high-pressure gas scintillator served as target and detector. Although our data are in much better agreement with our state-of-the-art theoretical calculations than the majority of the previous data, these calculations underpredict the new data by about 10%. This disagreement suggests an incomplete understanding of the dynamics of the three-nucleon system and its response to electromagnetic probes
Unambiguous Identification of the Second 2+ State in 12C and the Structure of the Hoyle State
The second 2+ state of 12C, predicted over fifty years ago as an excitation
of the Hoyle state, has been unambiguously identified using the 12C(g,a_0)8Be
reaction. The alpha particles produced by the photodisintegration of 12C were
detected using an Optical Time Projection Chamber (O-TPC). Data were collected
at beam energies between 9.1 and 10.7 MeV using the intense nearly
mono-energetic gamma-ray beams at the HIgS facility. The measured angular
distributions determine the cross section and the E1-E2 relative phases as a
function of energy leading to an unambiguous identification of the second 2+
state in 12C at 10.03(11) MeV, with a total width of 800(130) keV and a ground
state gamma-decay width of 60(10) meV; B(E2: 2+ ---> gs) = 0.73(13) e2fm4 [or
0.45(8) W.u.]. The Hoyle state and its rotational 2+ state that are more
extended than the ground state of 12C presents a challenge and constraints for
models attempting to reveal the nature of three alpha particle states in 12C.
Specifically it challenges the ab-initio Lattice Effective Field Theory (L-EFT)
calculations that predict similar r.m.s. radii for the ground state and the
Hoyle state.Comment: Accepted for Publication in the Physical Review Lette
An Optical Readout TPC (O-TPC) for Studies in Nuclear Astrophysics With Gamma-Ray Beams at HIgS
We report on the construction, tests, calibrations and commissioning of an
Optical Readout Time Projection Chamber (O-TPC) detector operating with a
CO2(80%) + N2(20%) gas mixture at 100 and 150 Torr. It was designed to measure
the cross sections of several key nuclear reactions involved in stellar
evolution. In particular, a study of the rate of formation of oxygen and carbon
during the process of helium burning will be performed by exposing the chamber
gas to intense nearly mono-energetic gamma-ray beams at the High Intensity
Gamma Source (HIgS) facility. The O-TPC has a sensitive target-drift volume of
30x30x21 cm^3. Ionization electrons drift towards a double parallel grid
avalanche multiplier, yielding charge multiplication and light emission.
Avalanche induced photons from N2 emission are collected, intensified and
recorded with a Charge Coupled Device (CCD) camera, providing two-dimensional
track images. The event's time projection (third coordinate) and the deposited
energy are recorded by photomultipliers and by the TPC charge-signal,
respectively. A dedicated VME-based data acquisition system and associated data
analysis tools were developed to record and analyze these data. The O-TPC has
been tested and calibrated with 3.183 MeV alpha-particles emitted by a 148Gd
source placed within its volume with a measured energy resolution of 3.0%.
Tracks of alpha and 12C particles from the dissociation of 16O and of three
alpha-particles from the dissociation of 12C have been measured during initial
in-beam test experiments performed at the HIgS facility at Duke University. The
full detection system and its performance are described and the results of the
preliminary in-beam test experiments are reported.Comment: Supported by the Richard F. Goodman Yale-Weizmann Exchange Program,
ACWIS, NY, and USDOE grant Numbers: DE-FG02-94ER40870 and DE-FG02-97ER4103
- …