Observation of Multiplicity Dependent Prompt χc1(3872) and ψ(2S) Production in pp Collisions

Physical Review Letters. 2021. Vol. 126. No. 9. Article 092001.

Aaij R., Beteta C. A., Arzymatov K., Belavin V., Boldyrev A., Borisyak M., Derkach D., Гайнцева Т. А., Hushchyn M., Kazeev N., Maevskiy A., Филиппов А. А., Попов С. А., Ratnikov F., Ryzhikov A., Ustyuzhanin A., LHCb C.

The production of χc1(3872) and ψ(2S) hadrons is studied as a function of charged particle multiplicity in pp collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2  fb−1. For both states, the fraction that is produced promptly at the collision vertex is found to decrease as charged particle multiplicity increases. The ratio of χc1(3872) to ψ(2S) cross sections for promptly produced particles is also found to decrease with multiplicity, while no significant dependence on multiplicity is observed for the equivalent ratio of particles produced away from the collision vertex in b-hadron decays. This behavior is consistent with a calculation that models the χc1(3872) structure as a compact tetraquark. Comparisons with model calculations and implications for the binding energy of the χc1(3872) state are discussed.

Keywords: high energy physics, физика высоких энергий

Publication based on the results of: Machine learning to check and improve the quality of data collected at the Large Hadron Collider and other particle physics experiments (2021)