Measurements of Angular Distributions of Muons From Upsilon Meson Decays in p p-bar Collisions at sqrt(s)=1.96 TeV

TL;DR

This paper reports the first comprehensive measurements of angular distributions and spin alignment of Upsilon mesons in proton-antiproton collisions at 1.96 TeV, revealing nearly isotropic decay patterns.

Contribution

It provides the first full angular distribution measurements as functions of transverse momentum for Upsilon mesons in specific frames, including the first spin alignment measurement of Upsilon(3S).

Findings

Angular distributions are nearly isotropic within the studied kinematic range.

First measurement of Upsilon(3S) spin alignment.

Angular distributions vary with transverse momentum.

Abstract

The angular distributions of muons from Upsilon(1S,2S,3S) to mu+mu- decays are measured using data from proton anti-proton collisions at sqrt(s)=1.96 TeV corresponding to an integrated luminosity of 6.7 /fb and collected with the CDF II detector at the Fermilab Tevatron. This analysis is the first to report the full angular distributions as functions of transverse momentum pT for the Upsilon mesons in both the Collins-Soper and s-channel helicity frames. This is also the first measurement of spin alignment of Upsilon(3S) mesons. Within the kinematic range of Upsilon rapidity |y|<0.6 and pT up to 40 GeV/c, the angular distributions are found to be nearly isotropic.