610 research outputs found
Anisotropy in the pion angular distribution of the reaction pp -> pp pi0 at 400 MeV
The reaction pp -> pp pi0 was studied with the WASA detector at the CELSIUS
storage ring. The center of mass angular distribution of the pi0 was obtained
by detection of the gamma decay products together with the two outgoing
protons, and found to be anisotropic with a negative second derivative slope,
in agreement with the theoretical predictions from a microscopic calculation.Comment: Revtex 4 style, 5 pages 7 figures, PACS numbers:13.60.Le, 13.75.Cs,
21.45.+v, 25.10.+
Comparative feeding ecology and habitats use of Crenicichla species (Perciformes: Cichlidae) in a Venezuelan floodplain river
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.
Search for Narrow NNpi Resonances in Exclusive p p -> p p pi+ pi- Measurements
Narrow structures in the range of a few MeV have been searched for in p p pi+
and p p pi- invariant mass spectra obtained from exclusive measurements of the
p p -> p p pi+ pi- reaction at Tp = 725, 750 and 775 MeV using the PROMICE/WASA
detector at CELSIUS. The selected reaction is particularily well suited for the
search for NN and / or N Delta decoupled dibaryon resonances. Except for a
possible fluctuation at 2087 MeV/c^2 in Mpppi- no narrow structures could be
identified neither in Mpppi+ nor in Mpppi- on the 3 sigma level of statistical
significance, giving an upper limit (95% C.L.) for dibaryon production in this
reaction of sigma < 20 nb for 2020 MeV/c^2 < m(dibaryon) < 2085 MeV/c^2Comment: 3 pages, 4 figure
Exclusive Measurements of pp -> dpi+pi0: Double-Pionic Fusion without ABC Effect
Exclusive measurements of the reaction pp -> dpi+pi0 have been carried out at
T_p = 1.1 GeV at the CELSIUS storage ring using the WASA detector. The
isovector pi+pi0 channel exhibits no enhancement at low invariant pipi masses,
i. e. no ABC effect. The differential distributions are in agreement with the
conventional t-channel Delta-Delta excitation process, which also accounts for
the observed energy dependence of the total cross section. This is an update of
a previously published version -- see important note at the end of the article
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
Double-Pionic Fusion of Nuclear Systems and the ABCEffect -- Aproaching a Puzzle by Exclusive and Kinematically Complete Measurements
The ABC effect - a puzzling low-mass enhancement in the invariant
mass spectrum - is well-known from inclusive measurements of two-pion
production in nuclear fusion reactions. Here we report on first exclusive and
kinematically complete measurements of the most basic double pionic fusion
reaction at 1.03 and 1.35 GeV. The measurements, which
have been carried out at CELSIUS-WASA, reveal the ABC effect to be a
channel phenomenon associated with both a resonance-like
energy dependence in the integral cross section and the formation of a
system in the intermediate state. A corresponding simple
s-channel resonance ansatz provides a surprisingly good description of the
data
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