Double-pionic fusion of nuclear systems and the "ABC" effect: approaching a puzzle by exclusive and kinematically complete measurements.
The ABC effect-a puzzling low-mass enhancement in the pipi invariant mass spectrum, first observed by Abashian, Booth, and Crowe-is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn-->dpi;{0}pi;{0} at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (pipi)_{I=L=0} channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a DeltaDelta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.
Bashkanov
M
M
Physikalisches Institut der Universität Tübingen, D-72076 Tübingen, Germany.
Bargholtz
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C
Berłowski
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Bogoslawsky
D
D
Calén
H
H
Clement
H
H
Demiroers
L
L
Doroshkevich
E
E
Duniec
D
D
Ekström
C
C
Fransson
K
K
Geren
L
L
Gustafsson
L
L
Höistad
B
B
Ivanov
G
G
Jacewicz
M
M
Jiganov
E
E
Johansson
T
T
Khakimova
O
O
Keleta
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Koch
I
I
Kren
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F
Kullander
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S
Kupść
A
A
Lindberg
K
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Marciniewski
P
P
Meier
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R
Morosov
B
B
Pauly
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C
Pettersson
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H
Petukhov
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Y
Povtorejko
A
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Pricking
A
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Ruber
R J M Y
RJ
Schönning
K
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Scobel
W
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Shwartz
B
B
Skorodko
T
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Sopov
V
V
Stepaniak
J
J
Tegner
P-E
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Thörngren-Engblom
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P
Tikhomirov
V
V
Turowiecki
A
A
Wagner
G J
GJ
Wolke
M
M
Zabierowski
J
J
Zartova
I
I
Złomanczuk
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J