Abstract
The charge symmetry breaking reaction dd → 4 Heπ0 has been measured with the WASA-at-COSY experimental setup at a beam momentum of pd = 1.2 GeV/c (Q = 60 MeV). For the first time a signal for this reaction has been observed at an excess energy well above threshold. The determined preliminary total cross section is σ tot prel = (120±20stat. ) pb.
Highlights
In the framework of the Standard Model, isospin symmetry is broken by the mass and charge difference of quarks [1, 2]
From isospin symmetry breaking observables it is difficult to access these individual terms, because on the hadronic level, isospin symmetry breaking is dominated by the pion mass difference (∆π), which is almost a pure electromagnetic effect
The reactions, where these two sources of isospin symmetry breaking can be disentangled, open an experimental window to probe the u and d quark mass difference effects in hadronic processes [3]. This can be achieved by using charge symmetry breaking (CSB) observables where ∆π does not contribute
Summary
In the framework of the Standard Model, isospin symmetry is broken by the mass and charge difference of quarks [1, 2]. The reactions, where these two sources of isospin symmetry breaking can be disentangled, open an experimental window to probe the u and d quark mass difference effects in hadronic processes [3]. This can be achieved by using charge symmetry breaking (CSB) observables where ∆π does not contribute. A consistent theoretical analysis of both measurements is currently in progress [8,9,10,11,12,13] It is shown within a plane wave calculation, that when all parameters are fixed the p-waves in the dd −−→ 4Heπ0 reaction may be predicted parameter free to leading and nextto-leading order [11]. Experimental input of p-wave contributions at higher excess energies is needed
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