Spin alignment measurements using vector mesons with ALICE detector at the LHC

Abstract

We present new measurements related to spin alignment of ${\mathrm{K}}^{\ast 0}$ vector mesons at mid-rapidity for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 and 5.02 TeV. The spin alignment measurements are carried out with respect to production plane and second order event plane. At low $p_{\mathrm{T}}$ the spin density matrix element ${\rho }_{00}$ for ${\mathrm{K}}^{\ast 0}$ is found to have values slightly below 1/3, while it is consistent with 1/3, i.e. no spin alignment, at high $p_{\mathrm{T}}$. Similar values of ${\rho }_{00}$ are observed w.r.t. both production plane and event plane. Within statistical and systematic uncertainties, ${\rho }_{00}$ values are also found to be independent of $\sqrt{s_{\mathrm{NN}}}$. ${\rho }_{00}$ also shows centrality dependence with maximum deviation from 1/3 for mid-central collisions w.r.t. both the kinematic planes. The measurements for ${\mathrm{K}}^{\ast 0}$ in pp collisions at $\sqrt{s}$ = 13 TeV and for ${\mathrm{K}}_{\mathrm{S}}^0$ (a spin 0 hadron) in 20-40% central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV are consistent with no spin alignment.

arXiv comment4 pages, 4 figures, Proceedings of the XXVIIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2018), 13-19 May 2018

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• Practical considerations for the effect of finite coverage on the azimuthal dependence of global spin alignment