Light Quark Fragmentation in Polarized Z0 Decays at SLD

TL;DR

This paper presents the first measurements of baryon number ordering along the quark-antiquark axis and the parity-violating coupling of the Z0 to strange quarks, using polarized electron-positron collisions at SLD.

Contribution

It introduces novel methods for analyzing rapidity distributions and provides the most precise measurement of A_s to date, confirming Standard Model predictions.

Findings

First direct observation of baryon number ordering along the q-qbar axis.

Most precise measurement of the parity-violating coupling A_s.

Results consistent with Standard Model expectations.

Abstract

We report results on two physics topics from the SLD experiment at the SLAC Linear Collider, using our full sample of 550,000 events of the type e+e- --> Z0 --> q-q(bar). The electron beam was polarized, enabling the quark and antiquark hemispheres to be tagged in each event. One physics topic is the first study of rapidities signed such that positive rapidity is along the quark rather than antiquark direction. Distributions of ordered differences in signed rapidity between pairs of particles are analyzed, providing the first direct observation of baryon number ordering along the q-q(bar) axis. The other topic is the first direct measurement of A_s, the parity-violating coupling of the Z0 to strange quarks, by measuring the left-right forward-backward production asymmetry in polar angle of the tagged s-quark. We obtain A_s = 0.895 +- 0.066(stat.) +- 0.062(syst.), which is consistent with the Standard Model and is currently the most precise measurement of this quantity.