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22–26 Sep 2025
Asia/Shanghai timezone

Hyperon local polarization in pPb collisions at CMS

Not scheduled
3h 30m
Oral Spin in heavy ion collisions Parallel

Speaker

Chenyan Li

Description

The observation of hyperon polarization along beam direction ($P_z$) in nucleus-nucleus collisions has opened a new way to study the complex vortical structures of the QGP. With the high-statistics data collected by the CMS experiment, we present the first $P_z$ results for $\Lambda$ and $\bar{\Lambda}$ particles in pPb collision at $\sqrt{s_{NN}}= 8.16$ TeV over a wide transverse momentum ($p_{T}$) and charged particle multiplicity ($N_\mathrm{trk}^\mathrm{offline}$) range. The $P_z$ values decrease as a function of $N_\mathrm{trk}^\mathrm{offline}$, but increase with $p_{T}$. A hydrodynamic model that describes the observed $P_z$ values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the pPb results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies.

Primary authors

Chenyan Li Jinlong Zhang (Shandong University) Zhenyu Chen (Shandong University)

Presentation materials

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