A polarization amplitude A$_{{{\mathit D}_{{{2}}}}}$ is a parameter that depends on the initial polarization of the ${{\mathit D}_{{{2}}}}$. For ${{\mathit D}_{{{2}}}}$ decays the helicity angle, ${{\mathit \theta}_{{{H}}}}$, distribution varies like 1 + A$_{{{\mathit D}_{{{2}}}}}$ cos $^2{{\mathit \theta}_{{{H}}}}$, where ${{\mathit \theta}_{{{H}}}}$ is the angle in the ${{\mathit D}^{*}}$ rest frame between the two pions emitted by the ${{\mathit D}_{{{2}}}}$ $\rightarrow$ ${{\mathit D}^{*}}{{\mathit \pi}}$ and ${{\mathit D}^{*}}$ $\rightarrow$ ${{\mathit D}}{{\mathit \pi}}$.

VALUE EVTS DOCUMENT ID TECN  COMMENT • • We do not use the following data for averages, fits, limits, etc. • • $-1.16$ $\pm0.35$ 2.3k 1 ABRAMOWICZ 2013 ZEUS ${{\mathit e}^{\pm}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit D}^{(*)+}}{{\mathit \pi}^{-}}{{\mathit X}}$ $\text{consistent with -1}$ 243k DEL-AMO-SANCH.. 2010 P BABR ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit D}^{+}}{{\mathit \pi}^{-}}{{\mathit X}}$ $-0.74$ ${}^{+0.49}_{-0.38}$ 2 AVERY 1994 C CLE2 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit D}^{*+}}{{\mathit \pi}^{-}}{{\mathit X}}$ 1  From the combined fit of the ${{\mathit M}}({{\mathit D}^{+}}{{\mathit \pi}^{-}}$) and ${{\mathit M}}({{\mathit D}^{*+}}{{\mathit \pi}^{-}}$) distributions. 2  Systematic uncertainties not estimated.

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