Polarization in Quarkonium Production

TL;DR

This paper investigates the spin alignment of Upsilon states produced in proton-antiproton collisions, providing the first comprehensive three-dimensional angular distribution analysis, revealing nearly isotropic decays regardless of transverse momentum.

Contribution

It presents the first complete three-dimensional angular distribution measurements of Upsilon decays in hadronic collisions, using a novel data-driven background method and frame-invariant analysis.

Findings

Decays are nearly isotropic across all frames.

Angular distributions show no significant polarization even at high transverse momentum.

Analysis confirms consistency across different reference frames.

Abstract

Production mechanisms for quarkonium states in hadronic collisions remain difficult to understand. The decay angular distributions of J/$\psi$ or $\Upsilon(nS)$ states into $\mu^+ \mu^-$ final states are sensitive to the matrix elements in the production process and provide a unique tool to evaluate different models. This talk will focus on new results for the spin alignment of $\Upsilon(nS)$ states produced in $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV using the CDF II detector at the Fermilab Tevatron. The data sample corresponds to an integrated luminosity of 6.7 fb$^{-1}$. The angular distributions are analyzed as functions of the transverse momentum of the dimuon final state in both the Collins-Soper and the s-channel helicity frames using a unique data-driven background determination method. Consistency of the analysis is checked by comparing frame-invariant quantities derived from parametrizations of the angular distributions measured in each choice of reference frame. This analysis is the first to quantify the complete three-dimensional angular distribution of $\Upsilon(1S), \Upsilon(2S)$ and $\Upsilon(3S)$ decays. The decays are nearly isotropic in all frames, even when produced with large transverse momentum.