Abstract
Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd→He4π0 have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of pd=1.2 GeV/c using the WASA-at-COSY facility. The total cross section amounts to σtot=(118±18stat±13sys±8ext) pb and first data on the differential cross section are consistent with s-wave pion production.
Highlights
Within the Standard Model there are two sources of isospin violation,8 namely the electro-magnetic interaction and the differences in the masses of the lightest quarks [1,2]
In this letter results were presented for a measurement of the charge symmetry breaking reaction dd → 4Heπ 0 at an excess energy of 60 MeV
The energy dependence of the square of the production amplitude might indicate the on-set of higher partial waves or some unusual energy dependence of the s-wave amplitude — given the current statistical error, no conclusion on the strength of the higher partial waves is possible from the differential cross section
Summary
Within the Standard Model there are two sources of isospin violation, namely the electro-magnetic interaction and the differences in the masses of the lightest quarks [1,2]. An example is charge symmetry breaking (CSB) observables — charge symmetry is an isospin rotation by 180 degrees that exchanges up and down quarks — as the pion mass term is invariant under this rotation For this case, the impact of soft photons has been studied systematically [7,8,9,10,11] and can be controlled. Future theoretical CSB studies for dd → 4Heπ 0 can be based on recent developments in effective field theories for few-nucleon systems [28] as well as for the reaction N N → N Nπ [29,30,31], promising a model-independent analysis of the data.
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