Measurement of the polarization of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states in $p\bar{p}$ collisions at $\sqrt{s}=$1.96 TeV

TL;DR

This study measures the polarization of $5S$ and $2S$ bottomonium states in proton-antiproton collisions, revealing $p_T$-dependent polarization patterns and comparing results with theoretical predictions.

Contribution

First measurement of $5S$ and $2S$ polarization as a function of transverse momentum in $par{p}$ collisions at 1.96 TeV.

Findings

Significant $p_T$-dependent longitudinal polarization observed for $5S$.

Results show polarization varies with transverse momentum.

Comparison indicates some models align with observed polarization patterns.

Abstract

We present a study of the polarization of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states using a $1.3 $ fb$^{-1}$ data sample collected by the D0 experiment in 2002--2006 during Run II of the Fermilab Tevatron Collider. We measure the polarization parameter $\alpha=(\sigma_{T}-2\sigma_{L})/(\sigma_{T}+2\sigma_{L})$, where $\sigma_{T}$ and $\sigma_{L}$ are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum ($p_{T}^{\Upsilon}$) for the $\Upsilon(1S)$ and $\Upsilon(2S)$. Significant $p_{T}^{\Upsilon}$-dependent longitudinal polarization is observed for the $\Upsilon(1S)$. A comparison with theoretical models is presented.