Measurements of \(\psi (2S)\) and \(\chi _{c1}(3872)\) production within fully reconstructed jets

Abstract

This paper presents the first measurement of \(\psi {(2S)}\) and \(\chi _{c1}(3872)\) meson production within fully reconstructed jets. Each quarkonium state (tag) is reconstructed via its decay to the \({{J \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }} \)(\(\rightarrow \) \(\mu ^+\mu ^-\))\(\pi ^+\pi ^-\) final state in the forward region using proton-proton collision data collected by the LHCb experiment at the center-of-mass-energy of \(13\text {TeV} \) in 2016, corresponding to an integrated luminosity of \(1.64\,\text {\,fb} ^{-1} \). The fragmentation function, presented as the ratio of the quarkonium-tag transverse momentum to the full jet transverse momentum (\(p_{\textrm{T}} (\text {tag})/p_{\textrm{T}} (\text {jet})\)), is measured differentially in \(p_{\textrm{T}} (\text {jet})\) and \(p_{\textrm{T}} (\text {tag})\) 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.