Abstract
The dependence of the production of the $X(3872)$ meson on the hadron multiplicity in $pp$ collisions has been used as evidence against $X$ being a charm-meson molecule. The argument is based in part on the incorrect assumption that the cross section for the breakup of $X$ by scattering with comovers can be approximated by a geometric cross section inversely proportional to the binding energy of $X$. The breakup cross section should instead be approximated by the probability-weighted sum of the cross sections for the scattering of comoving pions from the charm-meson constituents of $X$, which is insensitive to the binding energy. A simple modification of the comover interaction model gives excellent fits to the data from the LHCb collaboration on the multiplicity dependence of the production of $X$ and $\psi(2S)$ using parameters compatible with $X$ being a loosely bound charm-meson molecule.
Highlights
[ known as χc1ð3872Þ] in 2003 [1], dozens of other exotic heavy hadrons not predicted by the quark model have been discovered [2,3,4,5]
The X was discovered in the decay mode J=ψπþπ−, and it has since been observed in six other decay modes
Esposito et al have used the comover interaction (CI) model to calculate the dependence of the prompt X-to-ψ0 ratio on the charged-particle multiplicity Nch [12]
Summary
Since the unexpected discovery of the Xð3872Þ meson [ known as χc1ð3872Þ] in 2003 [1], dozens of other exotic heavy hadrons not predicted by the quark model have been discovered [2,3,4,5]. Esposito et al have used the comover interaction (CI) model to calculate the dependence of the prompt X-to-ψ0 ratio on the charged-particle multiplicity Nch [12] Their result for X as a compact tetraquark is consistent with the LHCb data, while their result for X as a molecule with a geometric cross section decreases much too rapidly with. We show below that a simple modification of the CI model provides excellent fits to the LHCb data on the multiplicity dependence of X and ψ0 production with parameters compatible with X being a loosely bound charm-meson molecule
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