Abstract
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.
Highlights
The last two decades witnessed a remarkable progress in heavy meson spectroscopy
We use the comover interaction model to study the yield of a compact X (3872)
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
Summary
To include final state interactions for compact states, we follow the comover interaction model (CIM) [19,20,34,35,36]. The density of quarkonium ρQ, at a given transverse position s and rapidity y, for a collision of impact parameter b, evolves following τ dρQ dτ (b, s, y) = −. Where vσ Q is velocity times the cross section of quarkonium dissociation, averaged over the momentum distributions of the comoving particles, whose transverse density is ρc at initial time τi. The previous equation can already be used for an estimate of the qualitative behavior of the yields as a function of multiplicity This can be done by neglecting the dependence on the variables and consider average values only. The normalization is fixed to reproduce the minimum-bias pp multiplicity—i.e. the pp multiplicity averaged over all impact parameters Proceeding this way, the quarkonium yields are obtained weighting Eq (2) with the pp overlap function. The error on vσ Q depends on the uncertainty of Teff, and on whether considering pionic or gluonic comovers σQgeo vσ Q ψ (2 S) X (3872) tetraquark X (3872) molecule
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
