The effect of hadronic scatterings on the measurement of vector meson spin alignments in heavy-ion collisions * *The work of D. Y. Shen and J. H. Chen was Supported in part by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34030000), the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008) and the National Natural Science Foundation

Abstract

Spin alignments of vector mesons and hyperons in relativistic heavy-ion collisions have been proposed as signals of global polarization. The STAR experiment first observed the polarization. Recently, the ALICE collaboration measured the transverse momentum ( ) and the collision centrality dependence of , and spin alignments during Pb-Pb collisions at = 2.76 TeV. A large signal is observed in the low region of mid-central collisions for , while the signal is much smaller for , and these have not been understood yet. Since vector mesons have different lifetimes and their decay products have different scattering cross sections, they suffer from different hadronic effects. In this paper, we study the effect of hadronic interactions on the spin alignment of , , and mesons in relativistic heavy-ion collisions with a multi-phase transport model. We find that hadronic scatterings lead to a deviation of the observed spin alignment matrix element away from the true value for and mesons (with a bigger effect on ) while the effect is negligible for the meson. The effect depends on the kinematic acceptance: the observed value is lower than the true value when the pseudorapidity ( ) coverage is small, while there is little effect when the coverage is large. Hence, this study provides valuable information to understand the vector meson spin alignment signals observed during the experiments.