Beam energy dependence of charged pion ratio in $^{28}$Si + In reactions

TL;DR

This study measures the energy-dependent ratio of charged pions produced in silicon-indium reactions at various energies, revealing discrepancies with existing models and highlighting the need for improved theoretical understanding of nuclear symmetry energy.

Contribution

The paper provides new experimental data on pion production ratios at multiple energies, challenging current transport model predictions and emphasizing the necessity for advanced theoretical approaches.

Findings

Pions are emitted isotropically from a single source.

The $ ext{π}^-/ ext{π}^+$ ratio varies with pion energy.

Standard models do not accurately predict the observed ratios.

Abstract

The double differential cross sections for $^{nat}$In($^{28}$Si, $\pi ^{\pm}$) reactions are measured at 400, 600, and 800 MeV/nucleon. Both $\pi^+$ and $\pi^-$ are found to be emitted isotropically from a single moving source. The $\pi^- / \pi^+$ yield ratio is determined as a function of the charged pion energy between 25 and 100 MeV. The experimental results significantly differ from the prediction of the standard transport model calculation using the code PHITS. This discrepancy suggests that more theoretical works are required to deduce firm information on the nuclear symmetry energy from the $\pi^- / \pi^+$ yield ratio.