Measurements of ψ ( 2 S ) and χ c 1 ( 3872 ) production within fully reconstructed jets

Abstract

This paper presents the first measurement of ψ ( 2 S ) and χ c 1 ( 3872 ) meson production within fully reconstructed jets. Each quarkonium state (tag) is reconstructed via its decay to the J / ψ ( → μ + μ - ) π + π - final state in the forward region using proton-proton collision data collected by the LHCb experiment at the center-of-mass-energy of 13 TeV in 2016, corresponding to an integrated luminosity of 1.64 \,fb - 1 . The fragmentation function, presented as the ratio of the quarkonium-tag transverse momentum to the full jet transverse momentum ( p T ( tag ) / p T ( jet ) ), is measured differentially in p T ( jet ) and p T ( tag ) bins. The distributions are separated into promptly produced quarkonia from proton-proton collisions and quarkonia produced from displaced b-hadron decays. While the displaced quarkonia fragmentation functions are in general well described by parton-shower predictions, the prompt quarkonium distributions differ significantly from fixed-order non-relativistic QCD (NRQCD) predictions followed by a QCD parton shower.