Measuring polarization of light quarks at ATLAS and CMS

TL;DR

This paper explores the potential of using Lambda baryon polarization measurements in ATLAS and CMS to characterize new physics involving strange quarks, highlighting advantages over previous LEP measurements and discussing extensions to up and down quarks.

Contribution

It introduces the use of LHC ttbar events for polarization measurements, offering a more detailed and less model-dependent approach compared to LEP data.

Findings

ATLAS and CMS can achieve competitive sensitivity with 100/fb data.

ttbar samples provide multiple handles to disentangle quark flavor contributions.

Potential to measure polarizations of up and down quarks.

Abstract

Polarization of strange quarks is preserved to a high degree when they hadronize into Lambda baryons, as observed in Z decays at LEP. This opens up the possibility for ATLAS and CMS to use strange-quark polarization measurements as a characterization tool for new physics scenarios that produce such quarks. Measurements in ttbar samples would be useful for obtaining additional information about the polarization transfer from the strange quark to the Lambda baryon. Already with 100/fb in Run 2, ttbar samples in ATLAS and CMS become competitive in sensitivity with the Z samples of the LEP experiments. Moreover, while the LEP measurements were done inclusively over all quark flavors, which makes their interpretation dependent on various modeling assumptions, ttbar events at the LHC offer multiple handles for disentangling the different contributions experimentally. We also discuss the possibility of measuring polarizations of up and down quarks.