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

Abstract

We present a study of the polarization of the ${\rm Y}(1S)$ and ${\rm Y}(2S)$ 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 ($p_T^{{\rm Y}}$) for the ${\rm Y}(1S)$ and ${\rm Y}(2S)$. Significant $p_T^{{\rm Y}}$-dependent longitudinal polarization is observed for the ${\rm Y}(1S)$. A comparison with theoretical models is presented.

7 pages, 4 figures, 2 tables, submitted to Phys. Rev. Letters

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