Measurement of transverse $\Lambda$ and $\bar{\Lambda}$ hyperon polarization in $p$Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV

TL;DR

This study measures the transverse polarization of Lambda hyperons in proton-lead collisions at 5.02 TeV, finding no significant polarization or dependence on transverse momentum or Feynman-x, and compares results with previous experiments.

Contribution

First measurement of Lambda hyperon transverse polarization in pPb collisions at 5.02 TeV, showing no polarization and providing data for understanding hyperon spin phenomena in nuclear collisions.

Findings

Transverse polarization compatible with zero for both Lambda and anti-Lambda hyperons.

No significant dependence of polarization on transverse momentum or Feynman-x.

Results consistent with previous measurements at different energies and collision types.

Abstract

The transverse polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons is measured in $p$Pb collisions collected by the LHCb experiment at a nucleon-nucleon center-of-mass energy of $5.02$ TeV. The polarization is averaged over hyperon transverse momentum in the ranges $0.15 < p_{T} < 6.00 $ GeV/$c$, and Feynman-$x$ in the ranges $0.005 < x_{F} < 0.040$ (forward region) and $-0.10 < x_{F} < -0.01$ (backward region) defined relative to the proton beam direction. The transverse polarization is found to be compatible with zero for both $\Lambda$ and $\bar{\Lambda}$ hyperons. The results are also measured as a function of $p_{T}$ and $x_{F}$ with no significant dependence on these variables observed. The results are compared with previous experimental measurements at different center-of-mass energies and collision environments.