Measurement of $J\mathrm{/}\psi$ polarization in $pp$ collisions at $\sqrt{s}=7$ TeV

An angular analysis of the decay $J\mathrm{/}\psi \to {\mu }^{+}{\mu }^{-}$ is performed to measure the polarization of prompt $J\mathrm{/}\psi$ mesons produced in $pp$ collisions at $\sqrt{s}=7\mathrm{T}\mathrm{e}\mathrm{V}$. The dataset corresponds to an integrated luminosity of 0.37 fb${}^{-1}$ collected with the LHCb detector. The measurement is presented as a function of transverse momentum, $p_{\mathrm{T}}$, and rapidity, $y$, of the $J\mathrm{/}\psi$ meson, in the kinematic region $2 < p_$\mathrm{T}$ < 15; $\mathrm{G}\mathrm{e}\mathrm{V}$/c$and$2.0<y<4.5$.