The $v_2(M_{\mu\mu})$ distribution in 5-60\% centrality and 2 $< \pt <$ 15 GeV/$c$. The data is fitted with

\begin{equation}
  v_{2}(M_{\mu\mu}) = \alpha(M_{\mu\mu})v_{2}^{\Upsilon{\rm (1S)}} + [1-\alpha(M_{\mu\mu})]v_{2}^{B}(M_{\mu\mu}),
\end{equation}
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where $v_{2}^{\Upsilon{\rm (1S)}}$ is the flow coefficient of the signal, $v_{2}^B$ is the $M_{\mu\mu}$-dependent flow coefficient of the background and $\alpha(M_{\mu\mu})$ is the signal fraction, obtained from the fit of the $M_{\mu\mu}$ distribution.
The background $v_2^B$ is modeled as a second-order polynomial function of $M_{\mu\mu}$.

The plot, as well as all other plots in this group, is based on 2015+2018 Pb-Pb data.