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

TL;DR

This study measures how $ ext{ψ}(2S)$ and $ ext{χ}_{c1}(3872)$ mesons are produced within jets in proton-proton collisions, revealing discrepancies with theoretical models for prompt quarkonium production.

Contribution

First measurement of quarkonium production within fully reconstructed jets, differentiating prompt and displaced sources using LHCb data at 13 TeV.

Findings

Displaced quarkonium fragmentation functions agree with parton-shower predictions.

Prompt quarkonium distributions significantly differ from NRQCD predictions.

Provides new insights into quarkonium production mechanisms within 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 $J/\psi$($\rightarrow\mu^+\mu^-$)$\pi^+\pi^-$ 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 ($p_{\mathrm{T}}(\text{tag})/p_{\mathrm{T}}(\text{jet})$), is measured differentially in $p_{\mathrm{T}}(\text{jet})$ and $p_{\mathrm{T}}(\text{tag})$ 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.