The nature of

The structure of exotic resonances that do not trivially fit the usual quark model expectations has been a matter of intense scientific debate during the last two decades. A possible way of estimating the size of these states is to study their behavior when immersed in QCD matter. Recently, LHCb has measured the relative abundance of the exotic $$X(3872)$$ over the ordinary $$\psi (2S)$$. We use the comover interaction model to study the yield of a compact $$X(3872)$$. To confirm the reliability of the model in high-multiplicity pp collisions, we describe the suppression of excited over ground $$\Upsilon $$ states. With this at hand, we show that the size of the compact $$X(3872)$$ would be slightly larger than that of the $$\psi (2S)$$. If the $$X(3872)$$ is instead assumed to be a meson molecule of large size, we argue that its evolution in QCD matter should be described 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 contrast with data