38 research outputs found
The ABC Effect in Double-Pionic Nuclear Fusion and a pn Resonance as its Possible Origin
The ABC effect -- a long-standing puzzle in double-pionic fusion -- has been
reexamined by the first exclusive and kinematically complete measurements of
solid statistics for the fusion reactions , He and He using the WASA detector, first at
CELSIUS and recently at COSY -- the latter with a statistics increased by
another two orders of magnitude. In all cases we observe a huge low-mass
enhancement in the -invariant mass accompanied by a pronounced
excitation. For the most basic fusion reaction, the reaction, we observe in addition a very pronounced resonance-like
energy dependence in the total cross section with a maximum 90 MeV below the
mass and a width of only 50 MeV, which is five times smaller
than expected from a conventional -channel excitation. This
reveals the ABC effect to be the consequence of a s-channel resonance with the
formfactor of this dibaryonic state being reflected in the low-mass enhancement
of the -invariant mass. From the fusion reactions to He and He
we learn that this resonance is robust enough to survive even in nuclei.Comment: conference proceedings PANIC 0
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
Experimental and theoretical evidences for an intermediate -dressed dibaryon in the NN interaction
Numerous theoretical and experimental arguments are presented in favor of the
generation of intermediate -dressed dibaryon in interaction at
intermediate and short distances. We argue that this intermediate dibaryon can
be responsible for the strong intermediate-range attraction and the short-range
repulsion in the interaction, and also for the short-range correlations in
nuclei. The suggested mechanism for the -dressing of the dibaryon is
identical to that which explains the Roper resonance structure, its dominant
decay modes and its extraordinary low mass. A similar transformation mechanism
from the glue to the scalar field was discovered in decays. The new
experimental data on 2-production in the scalar-isoscalar channel produced
in - and -collisions and in particular the very recent data on
correlations in C and C scattering in the GeV region seems
to corroborate the existence of the -dressed dibaryon in two- and three
nucleon interactions.Comment: 14 pages,4 figure