Measurement of the polarization of the $upsilon_1S$ and $upsilon_2S$ states in $p arp$ collisions at $sqrts$ = 1.96-TeV

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 $alpha=(sigma_{T}-2sigma_{L})/(sigma_{T}_s162sigma_{L})$, 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.