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The structure of exotic resonances that do not trivially fit the usual quarkmodel expectations has been a matter of intense scientific debate during thelast two decades. A possible way of estimating the size of these states is tostudy their behavior when immersed in QCD matter. Recently, LHCb has measuredthe relative abundance of the exotic $X(3872)$ over the ordinary $\psi(2S)$. Weuse the comover interaction model to study the yield of a compact $X(3872)$. Toconfirm the reliability of the model in high-multiplicity $pp$ collisions, wedescribe the suppression of excited over ground $\Upsilon$ states. With this athand, we show that the size of the compact $X(3872)$ would be slightly largerthan that of the $\psi(2S)$. If the $X(3872)$ is instead assumed to be a mesonmolecule of large size, we argue that its evolution in QCD matter should bedescribed via a coalescence model, as suggested by data on deuteron production.We show that the predictions of this model for the $X(3872)$ are in contrastwith data.

The nature of $X(3872)$ from high-multiplicity $pp$ collisions