Measurement of the polar-angle distribution of leptons from W boson decay as a function of the W transverse momentum in proton-antiproton collisions at sqrt{s}=1.8 TeV

TL;DR

This paper measures how the angular distribution of leptons from W boson decays varies with the W's transverse momentum in proton-antiproton collisions, confirming Standard Model predictions about polarization states.

Contribution

It provides the first detailed measurement of the polarization-dependent angular distribution of leptons from W decays as a function of W transverse momentum.

Findings

The ratio of longitudinal to transverse W polarization increases with W transverse momentum.

The measurement aligns with Standard Model predictions.

The analysis uses data from the CDF detector at sqrt{s}=1.8 TeV.

Abstract

We present a measurement of the coefficient alpha_2 of the leptonic polar-angle distribution from W boson decays, as a function of the W transverse momentum. The measurement uses an 80+/-4 pb^{-1} sample of proton-antiproton collisions at sqrt{s}=1.8 TeV collected by the CDF detector and includes data from both the W->e+nu and W->mu+nu decay channels. We fit the W boson transverse mass distribution to a set of templates from a Monte Carlo event generator and detector simulation in several ranges of the W transverse momentum. The measurement agrees with the Standard Model expectation, whereby the ratio of longitudinally to transversely polarized W bosons, in the Collins-Soper W rest frame, increases with the W transverse momentum at a rate of approximately 15% per 10 GeV/c.