J/psi production in NRQCD: A global analysis of yield and polarization

TL;DR

This paper performs a comprehensive next-to-leading order analysis of J/psi production and polarization using NRQCD, fitting experimental data to determine key parameters and testing predictions against collider results.

Contribution

It provides a global fit of NRQCD long-distance matrix elements to diverse experimental data and assesses polarization predictions, highlighting conflicts and future prospects.

Findings

NRQCD fits describe most data well

Hadroproduction polarization predictions conflict with Tevatron data

Future LHC measurements could confirm or challenge LDME universality

Abstract

We present a rigorous next-to-leading order analysis of J/psi yield and polarization within the factorization theorem of nonrelativistic QCD (NRQCD). To the orders considered, this framework depends on three free parameters, the color-octet long-distance matrix elements. We extract their values in a global fit to inclusive J/psi production data from various hadroproduction, photoproduction, two-photon scattering and electron-positron annihilation experiments. We show that this fit is constrained and stable and describes all data sufficiently well. We then make predictions for J/psi polarization in photo- and hadroproduction and compare them to the currently available data. As for photoproduction, HERA data is not precise enough to draw definite conclusions. But as for hadroproduction, CDF data measured at Tevatron run II is in strong conflict with NRQCD predictions. With early ALICE data being however compatible with NRQCD, the future, more precise polarization measurements at the LHC will thus have the potential to clearly confirm or dismiss LDME universality.