Inhaltszusammenfassung:
Two-pion production in elementary nucleon-nucleon (NN) collisions
offers a variety of aspects concerning the dynamics of the total
system as well as that of its subsystems pi pi, NN, pi N, pi pi N
and pi NN.
Exclusive high-statistics measurements of
the pp->pp pi^+ pi^- reaction have been carried out
at the CELSIUS storage ring using the PROMICE/WASA detector
setup with the cluster-jet H_2 target.
The obtained values for integral cross sections have turned
out to be an order of magnitude lower than expected from previous
bubble-chamber measurements. Differential cross sections at
T_p=750 MeV and 775 MeV offer a new opportunity for studying the
mechanisms of this reaction.
Close to threshold this reaction is expected to be dominated by the
excitation of the N^*(1440) resonance in one of the participating
nucleons, since
single delta excitation leads to the emission of a single pion
only.
Indeed, for the first time the measured differential cross sections
show clear signs of the N^*(1440) excitation as well as of the
interference of its decay channels into the N pi pi system.
The data also demonstrate that sigma-exchange between the colliding
nucleons is the dominant interaction process.
In recent years the CELSIUS/WASA detector in Uppsala has been upgraded.
As part of the work presented here, a thin trigger hodoscope
(FWC) was developed. Its purpose is to have cleaner trigger
conditions in the experiments.
First test measurements were taken under simple conditions to check
the performance of the sensitive detector components and of the new
trigger electronics. This upgrade was done in order to
measure rare decays of the light neutral mesons (pi^0, eta).
In the future it will be also used again for exclusive measurements of charged
two-pion production. In addition it will create the opportunity to exclusively
measure the neutral reaction channels e.g. pp->pp pi^0 pi^0.
Abstract:
Two-pion production in elementary nucleon-nucleon (NN) collisions
offers a variety of aspects concerning the dynamics of the total
system as well as that of its subsystems pi pi, NN, pi N, pi pi N
and pi NN.
Exclusive high-statistics measurements of
the pp->pp pi^+ pi^- reaction have been carried out
at the CELSIUS storage ring using the PROMICE/WASA detector
setup with the cluster-jet H_2 target.
The obtained values for integral cross sections have turned
out to be an order of magnitude lower than expected from previous
bubble-chamber measurements. Differential cross sections at
T_p=750 MeV and 775 MeV offer a new opportunity for studying the
mechanisms of this reaction.
Close to threshold this reaction is expected to be dominated by the
excitation of the N^*(1440) resonance in one of the participating
nucleons, since
single delta excitation leads to the emission of a single pion
only.
Indeed, for the first time the measured differential cross sections
show clear signs of the N^*(1440) excitation as well as of the
interference of its decay channels into the N pi pi system.
The data also demonstrate that sigma-exchange between the colliding
nucleons is the dominant interaction process.
In recent years the CELSIUS/WASA detector in Uppsala has been upgraded.
As part of the work presented here, a thin trigger hodoscope
(FWC) was developed. Its purpose is to have cleaner trigger
conditions in the experiments.
First test measurements were taken under simple conditions to check
the performance of the sensitive detector components and of the new
trigger electronics. This upgrade was done in order to
measure rare decays of the light neutral mesons (pi^0, eta).
In the future it will be also used again for exclusive measurements of charged
two-pion production. In addition it will create the opportunity to exclusively
measure the neutral reaction channels e.g. pp->pp pi^0 pi^0.
N*-1440-Resonance , PROMICE/WASA-Detector , two-pion production
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