Measuring quark polarizations at ATLAS and CMS

TL;DR

This paper explores methods for measuring quark polarizations at the LHC using baryon decays, aiming to provide insights into new physics processes and proposing calibration strategies with existing datasets.

Contribution

It introduces practical techniques for quark polarization measurement at ATLAS and CMS, including calibration methods and future measurement proposals.

Findings

Run 2 dataset allows ~10% precision in polarization measurements

Polarization transfer from quarks to baryons can be characterized

Calibration strategies using Standard Model samples are feasible

Abstract

Being able to measure the polarization of quarks produced in various processes at the LHC would be of fundamental significance. Measuring the polarizations of quarks produced in new physics processes, once discovered, can provide crucial information about the new physics Lagrangian. In a series of recent papers, we have investigated how quark polarization measurements can be done in practice. The polarizations of heavy quarks (b and c) are expected to be largely preserved in the lightest baryons they hadronize into, the Lambda_b and Lambda_c, respectively. Furthermore, it is known experimentally that s-quark polarization is preserved as well, in Lambda baryons. We study how ATLAS and CMS can measure polarizations of b, c and s quarks using certain decays of these baryons. We propose to use the Standard Model ttbar and Wc samples to calibrate these measurements. We estimate that the Run 2 dataset will suffice for measuring the quark polarizations in these Standard Model samples with precisions of order 10%. We also propose various additional measurements for the near and far future that would help characterize the polarization transfer from the quarks to the baryons.