Nature of the two z-components in prompt ψ(2S) and χc1(3872) production within jets

Characterize the nature of the two distinct components observed in the z = pT(tag)/pT(jet) distributions for prompt ψ(2S) and χc1(3872) meson production within jets in pp collisions at √s = 13 TeV as measured by the LHCb experiment, identifying their physical origins and underlying production mechanisms (e.g., isolated versus nonisolated production).

Background

This paper presents the first measurement of ψ(2S) and χc1(3872) meson production within fully reconstructed jets at LHCb using pp collisions at √s = 13 TeV. The fragmentation function z = pT(tag)/pT(jet) is measured differentially in both jet and tag transverse momentum and separated into prompt and displaced production.

In the results, the prompt ψ(2S) z distributions exhibit two apparent components: an isolated component near z ≈ 1 and a nonisolated component centered around z ≈ 0.7. While displaced production is generally well described by parton-shower predictions, the prompt distributions differ significantly from fixed-order NRQCD predictions, motivating clarification of the physical origins of these two components.

The authors state explicitly that the exact nature of these two components for prompt ψ(2S) and χc1(3872) production is not clear, and they indicate that further theoretical development is required to understand the second component. This forms the basis of the open problem.