QCD corrections to polarization of J/\psi and \Upsilon at Fermilab Tevatron and CERN LHC

TL;DR

This paper calculates next-to-leading order QCD corrections to the polarization of J/psi and Upsilon particles at Fermilab and CERN, revealing significant changes in polarization predictions and addressing previous discrepancies with experimental data.

Contribution

It provides the first detailed NLO QCD correction calculations for Upsilon polarization and compares different polarization summation methods, improving theoretical understanding.

Findings

NLO corrections change J/psi polarization from transverse to longitudinal.

Upsilon polarization at NLO is transverse at small p_t, similar to J/psi.

The results help reconcile theory with experimental polarization measurements.

Abstract

In this work, we present more detail of the calculation on the NLO QCD corrections to polarization of direct J/psi production via color singlet at Tevatron and LHC, as well as the results for Upsilon for the first time. Our results show that the J/psi polarization status drastically changes from transverse polarization dominant at LO into longitudinal polarization dominant in the whole range of the transverse momentum $p_t$ of J/psi when the NLO corrections are counted. For Upsilon production, the p_t distribution of the polarization status behaves almost the same as that for J/psi except that the NLO result is transverse polarization at small p_t range. Although the theoretical evaluation predicts a larger longitudinal polarization than the measured value at Tevatron, it may provide a solution towards the previous large discrepancy for J/psi and Upsilon polarization between theoretical predication and experimental measurement, and suggests that the next important step is to calculate the NLO corrections to hadronproduction of color octet state J/psi^(8) and Upsilon^(8). Our calculations are performed in two ways, namely we do and do not analytically sum over the polarizations, and then check them with each other.