Charged pion production in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>2</mml:mn><mml:mi>A</mml:mi></mml:mrow></mml:math>to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>8</mml:mn><mml:mi>A</mml:mi><mml:mspace width="0.3em"/><mml:mtext>GeV</mml:mtext></mml:mrow></mml:math>central<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mtext>Au</mml:mtext><mml:mo>+</mml:mo><mml:mtext>Au</mml:mtext></mml:mrow></mml:math>Collisions

Momentum spectra of charged pions over nearly full rapidity coverage from target to beam rapidity have been extracted from $0\ensuremath{-}5%$ most central $\text{Au}+\text{Au}$ collisions in the beam energy range from $2A$ to $8A\phantom{\rule{0.3em}{0ex}}\text{GeV}$ by the E895 experiment. Using a thermal parametrization to fit the transverse mass spectra, rapidity density distributions are extracted. The observed spectra are compared with predictions from the RQMD version 2.3 cascade model and also to a thermal model including longitudinal flow. The total $4\ensuremath{\pi}$ yields of the charged pions are used to infer an initial-state entropy produced in the collisions.