New Measurements of Upsilon Spin Alignment at the Tevatron

TL;DR

This paper presents a new analysis of Upsilon meson decays at the Tevatron, measuring muon angular distributions to study Upsilon polarization, revealing nearly isotropic distributions up to high transverse momentum, with results compared to theoretical models.

Contribution

It provides new measurements of Upsilon polarization at the Tevatron, highlighting discrepancies with other experiments and comparing results with advanced QCD calculations.

Findings

Angular distributions are nearly isotropic up to 40 GeV/c transverse momentum.

Results are consistent with previous CDF measurements.

Discrepancies exist with D0 experiment results.

Abstract

We describe a new analysis of Upsilon(nS) to mu+mu- decays collected in proton anti-proton collisions with the CDF II detector at the Fermilab Tevatron. This analysis measures the angular distributions of the final state muons in the Upsilon rest frame, providing new information about Upsilon production polarization. We find the angular distributions to be nearly isotropic up to Upsilon transverse momentum of 40 GeV/c, consistent with previous measurements by CDF, but inconsistent with results obtained by the D0 experiment. The results are compared with recent NLO calculations based on color-singlet matrix elements and non-relativistic QCD with color-octet matrix elements.