Joint Bayesian Inference for Extraction of Charmonium Long Distance Matrix Elements Using PYTHIA

Abstract

We present a joint Bayesian extraction of the nonrelativistic QCD long-distance matrix elements (LDMEs) for $J/ψ$, $ψ(2S)$, and $χ_c$ production, using short-distance coefficients and feed-down structure implemented in PYTHIA 8.317. Rather than fitting each charmonium state separately, we construct channel-resolved responses that link parent production to daughter feed-down and infer all LDMEs simultaneously from 286 prompt charmonium measurements in $pp$ collisions at $\sqrt{s}=5.02$-13 TeV at the LHC. The extracted LDMEs provide a good description of the data, with an overall $χ^2/\mathrm{ndf}=1.18$. We also provide a positivity-constrained set that can be used directly as PYTHIA input. Using the extracted LDMEs, we predict prompt $J/ψ$ and $ψ(2S)$ cross sections at high transverse momentum in $pp$ collisions at $\sqrt{s}=200$ GeV, which can be tested with RHIC data.