$\Delta$ resonances in Ca+Ca, Ni+Ni and Au+Au reactions from 1 AGeV to 2 AGeV: Consistency between yields, mass shifts and decoupling temperatures

Understand

The Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport approach is used to calculate $\Delta$(1232) yields in Ca+Ca, Ni+Ni and Au+Au collisions between 1 AGeV and 2 AGeV.

• We compare and validate two different methods to extract the yields of $\Delta$(1232) resonances in such low energy nuclear collisions: Firstly, the $\pi^-$ spectra at low $p_\mathrm{T}$ are used to infer the $\Delta$(1232) yield in A+A collisions, a method employed by the GSI/FOPI experiment.
• Secondly, we employ the invariant mass method used by the HADES collaboration, which has recently reported data in the $\Delta^{++}\rightarrow\pi^++p$ channel.
• We show that both methods are compatible with each other and with the theoretical calculations, indicating that the new HADES results are compatible with the previous FOPI measurements.