932 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.+
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
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
Measurement of the eta->pi+pi-e+e- decay branching ratio
The reaction pd->3He eta at threshold was used to provide a clean source of
eta mesons for decay studies with the WASA detector at CELSIUS. The branching
ratio of the decay eta->pi+pi-e+e- is measured to be (4.3+/-1.3+/-0.4)x10^-4.Comment: 10 pages,6 figures revised versio
Measurement of the Slope Parameter for the eta->3pi0 Decay in the pp->pp eta Reaction
The CELSIUS/WASA setup is used to measure the 3pi0 decay of eta mesons
produced in pp interactions with beam kinetic energies of 1.36 and 1.45 GeV.
The efficiency-corrected Dalitz plot and density distributions for this decay
are shown, together with a fit of the quadratic slope parameter alpha yielding
alpha = -0.026 +/- 0.010(stat) +/- 0.010(syst). This value is compared to
recent experimental results and theoretical predictions.Comment: 4 pages, 7 Postscript figures, uses revtex4.st
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
Polarisation of the omega meson in the pd-->3He+omega reaction at 1360 and 1450 MeV
The tensor polarisation of omega mesons produced in the pd-->3He+omega
reaction has been studied at two energies near threshold. The 3He nuclei were
detected in coincidence with the pi0pi+pi- or pi0gamma decay products of the
omega. In contrast to the case of phi meson production, the omega mesons are
found to be unpolarised. This brings into question the applicability of the
Okubo-Zweig-Iizuka rule when comparing the production of vector mesons in low
energy hadronic reactions.Comment: 11 pages, 4 figure
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