148 research outputs found
Resonant behaviour in double charge exchange reaction of \pi^+ mesons on the nuclear photoemulsion
The invariant mass spectra of the and systems produced in the
double charge exchange (DCX) of positively charged pions on photoemulsion are
analysed. A pronounced peak is observed in the invariant mass
spectrum, while the spectrum exhibits a strong Migdal-Watson effect of
the proton-proton final state interaction. These findings are in favor of the
-decoupled pseudoscalar resonance with T=0 called .Comment: 13 pages, 5 figures, revised versio
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Magnets for the national spallation neutron source accumulator ring
The National Spallation Neutron Source Accumulator Ring will require large aperture dipole magnets, strong focusing quadrupole magnets, and smaller low field dipole, quadrupole, and sextupole correcting magnets. All of the magnets will provide a fixed magnetic field throughout the accumulator`s fill/storage/extraction cycle. Similar fixed field magnets will also be provided for the beam transport systems. Because of the high intensity in the accumulator, the magnets must be designed with high tolerances for optimum field quality and for the high radiation environment which may be present at the injection/extraction areas, near the collimators, and near the target area. Field specifications and field plots are presented as well as planned fabrication methods and procedures, cooling system design, support, and installation
Two-pion production in deuteron-deuteron collisions at low energies
The cross section for the dd -> 4He pi pi reaction is estimated near
threshold in a two-step model where a pion created in a first interaction
produces a second pion in a subsequent interaction. This approach, which
describes well the rates of 2pi and eta production in the pd -> 3He pi pi and
dd -> 4He eta reactions, leads to predictions that are much too low compared to
experiment. Alternatives to this and the double-Delta model will have to be
sought to explain these data.Comment: 5 pages with 4 postscript figure
Study of the p p -> p p pi+ pi- Reaction in the Low-Energy Tail of the Roper Resonance
Exclusive measurements of the p p -> p p pi+ pi- reaction have been carried
out at Tp = 775 MeV at CELSIUS using the PROMICE/WASA setup. Together with data
obtained at lower energy they point to a dominance of the Roper excitation in
this process. From the observed interference of its decay routes N* -> N sigma
and N* -> Delta pi -> N sigma their energy-dependent relative branching ratio
is determined
Three-body decay of the d* dibaryon
Under certain circumstances, a three-body decay width can be approximated by
an integral involving a product of two off-shell two-body decay widths. This
``angle-average'' approximation is used to calculate the decay width
of the dibaryon in a simple model for the most
important Feynman diagrams describing pion emissions with baryon-baryon recoil
and meson retardation. The decay width is found to be about 0.006 (0.07, 0.5)
MeV at the mass of 2065 (2100, 2150) MeV for input dynamics derived from
the Full Bonn potential. The smallness of this width is qualitatively
understood as the result of the three-body decay being ``third forbidden''. The
concept of forbiddenness and the threshold behavior of a three-body
decay are further studied in connection with the decay of the dibaryon
where the idea of unfavorness has to be introduced.
The implications of these results are briefly discussed.Comment: 15 pages, RevTeX, two-column journal style, six figure
The d' dibaryon in the quark-delocalization, color-screening model
We study the questions of the existence and mass of the proposed dibaryon in the quark-delocalization, color-screening model
(QDCSM). The transformation between physical and symmetry bases has been
extended to the cases beyond the SU(2) orbital symmetry. Using parameters fixed
by baryon properties and scattering, we find a mild attraction in the
channel, but it is not strong enough to form a deeply bound state
as proposed for the state. Nor does the (isospin) I=2 N
configuration have a deeply bound state. These results show that if a narrow
dibaryon state does exist, it must have a more complicated structure.Comment: 12 pp. latex, no figs., 2 tables, additional refs., Report-no was
adde
Low-lying S-wave and P-wave Dibaryons in a Nodal Structure Analysis
The dibaryon states as six-quark clusters of exotic QCD states are
investigated in this paper. With the inherent nodal surface structure analysis,
the wave functions of the six-quark clusters (in another word, the dibaryons)
are classified. The contribution of the hidden color channels are discussed.
The quantum numbers of the low-lying dibaryon states are obtained. The States
, ,
, and the
hidden color channel states with the same quantum numbers are proposed to be
the candidates of dibaryons, which may be observed in experiments.Comment: 29 pages, 2 figure
Kariesprävalenz von Schülern in 16 Zürcher Landgemeinden in den Jahren 1992 bis 2000
Standardized dental examinations of schoolchildren were regularly carried out since 1964 in 16 rural communities of the Canton of Zurich. In 1964, there were no 14-year-old schoolchildren free from caries; in the Nineties about half of the 14-year-olds had a caries-free permanent dentition (DMFT = 0). From the year 1992 to 2000, the caries prevalence (DMFT) of 14-year-olds decreased once again, by 31%. The pit and fissure caries prevalence (DFS) of 12- and 14-year-olds decreased by 28% and 37%, respectively. In 2000, the mean DMFT-value of the 12- and 14-year-old schoolchildren was 0.90 and 1.27 respectively. In 1964, only few 7-year-old schoolchildren were caries-free; in the Nineties about half of the 7-year-olds had a primary dentition without caries. From the year 1992 to 2000, caries prevalence (dmft) in 7-, 8- and 9-year-olds increased by 64%, 22% and 31%. In 2000, the mean dmft-value of all 7-year-old schoolchildren was 2.45. The Swiss schoolchildren had 1.79 dmft; the schoolchildren from former Yugoslavia and from Albania had 6.89 dmft and those of other nations had 3.37 dmft. Possible reasons for the continuous caries decrease in the permanent dentition and the increase in the primary dentition are discussed. Additional measures in order to improve the situation in the primary dentition are proposed
Observation of strong final-state effects in pi+ production in pp collisions at 400 MeV
Differential cross sections of the reactions and have been measured at MeV by detecting the charged
ejectiles in the angular range . The
deduced total cross sections agree well with those published previously for
neighbouring energies. The invariant mass spectra are observed to be strongly
affected by production and final-state interaction. The data are
well described by Monte Carlo simulations including both these effects. The
ratio of and cross sections also compares
favourably to a recent theoretical prediction which suggests a dominance of
-production in the relative -state.Comment: 17 pages, 5 figure
Higher Partial Waves in p+p->p+p+eta near Threshold
Exclusive measurements of the production of eta mesons in the p+p->p+p+eta
reaction have been carried out at excess energies of 16 and 37 MeV above
threshold. The deviations from phase space are dominated by the proton-proton
final state interaction and this influences particularly the energy
distribution of the eta meson. However, evidence is also presented at the
higher energy for the existence of an anisotropy in the angular distributions
of the eta meson and also of the final proton-proton pair, probably to be
associated with D-waves in this system interfering with the dominant S-wave
term. The sign of the eta angular anisotropy suggests that rho-exchange is
important for this reaction.Comment: 16 pages, LaTeX2e, 3 EPS Figures, Updated version, Accepted for
publication in Phys. Lett.
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