Preprint FZJ-2017-06364

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Importance of d-wave contributions in the charge symmetry breaking reaction $dd \to {}^4\text{He}\pi^0$

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2017

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Abstract: 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.


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Contributing Institute(s):
  1. Experimentelle Hadrondynamik (IKP-2)
  2. Zentralinstitut für Elektronik (ZEA-2)
  3. Experimentelle Hadronstruktur (IKP-1)
  4. Theorie der Starken Wechselwirkung (IAS-4)
  5. Theorie der starken Wechselwirkung (IKP-3)
  6. Kernphysikalische Großgeräte (IKP-4)
  7. IKP- Technische und Administrative Infrastruktur (IKP-TA)
Research Program(s):
  1. 612 - Cosmic Matter in the Laboratory (POF3-612) (POF3-612)
  2. 631 - Accelerator R & D (POF3-631) (POF3-631)
Experiment(s):
  1. WASA (Wide Angle Shower Apparatus) at COSY

Appears in the scientific report 2017
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 Record created 2017-09-05, last modified 2025-01-29