This title appears in the Scientific Report : 2017

##### Importance of d-wave contributions in the charge symmetry breaking reaction $dd \to {}^4\text{He}\pi^0$
Personal Name(s): Adlarson, P. / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / Zurek, Maria (Corresponding author) IKP- Technische und Administrative Infrastruktur; IKP-TA Kernphysikalische Großgeräte; IKP-4 Theorie der starken Wechselwirkung; IKP-3 Theorie der Starken Wechselwirkung; IAS-4 Experimentelle Hadronstruktur; IKP-1 Zentralinstitut für Elektronik; ZEA-2 Experimentelle Hadrondynamik; IKP-2 2017 Preprint Accelerator R & D Cosmic Matter in the Laboratory Get full text OpenAccess OpenAccess Publikationsportal JuSER
Please use the identifier: http://hdl.handle.net/2128/15257 in citations.
 This letter reports the first measurement of the contribution of higher partial waves in the charge symmetry breaking reaction $dd \to {}^4\text{He}\pi^0$ using the WASA-at-COSY detector setup at an excess energy of $Q = 60$ MeV. The determined differential cross section can be parametrized as $\text{d}\sigma/\text{d}\Omega = a + b\cos^{2}\theta^*$, where $\theta^*$ is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are $a = \left(1.55 \pm 0.46 (\text{stat}) ^{+0.32}_{-0.8} (\text{syst}) \right) \text{pb/sr}$ and $b = \left(13.1 \pm 2.1 (\text{stat}) ^{+1.0}_{-2.7} (\text{syst})\right) \text{pb/sr}$. The data are compatible with vanishing $p$-waves and a sizable $d$-wave contribution. This finding should strongly constrain the contribution of the $\Delta$ isobar to the $dd \to {}^4\text{He}\pi^0$ reaction and is therefore crucial for a quantitative understanding of quark mass effects in nuclear production reactions.