What limits mechanical cat-state coherence as mass grows?

Mechanical resonator of effective mass $m_{\mathrm{eff}}$ in a cat state $\left|\alpha\right> + \left|-\alpha\right>$. Measure the cat decoherence rate $\Gamma_{\mathrm{cat}}$ versus $\mid\alpha\mid^2$ and $m_{\mathrm{eff}}$, and compare with the bath model $\Gamma_{\mathrm{cat}} = 2 \mid\alpha\mid^2 \Gamma_{\mathrm{m}} (2 n_{\mathrm{th}} + 1)$, with $\Gamma_{\mathrm{m}}$ the mechanical energy damping rate and $n_{\mathrm{th}}$ the thermal phonon number, plus two-level-system defect noise. Answer: whether all decoherence is accounted for, and any excess as a function of mass.

Systematic Wigner-function tomography of cats across masses and separations with independently measured bath parameters.