$\Upsilon(nS)$ polarizations in $pp$ collisions at $\sqrt{s}=$ 7 and 8 TeV by the LHCb collaboration

Abstract

A polarization measurement carried out for the $\Upsilon(1S)$, $\Upsilon(2S)$ and $\Upsilon(3S)$ mesons produced in pp collisions at $\sqrt{s}=$ 7 and 8 TeV is presented. Data samples used for the polarization measurement were collected by the LHCb experiment during the 2011 and 2012 data taking runs with integrated luminosities of 1 and 2 fb$^{-1}$, respectively. The measurement has been performed in three polarization frames, using an angular distribution analysis of the $\Upsilon\to\mu^{+}\mu^{-}$ decays in the kinematic region of the $\Upsilon$ transverse momentum $p_{T}^{\Upsilon}<30$ GeV/c and rapidity $2.2<y^{\Upsilon}<4.5$. No large polarization is observed.