Higher Order Collins Modulations in Transversely Polarized Quark Fragmentation

TL;DR

This paper investigates higher order modulations in the Collins effect during quark hadronization, revealing that multiple emissions lead to complex angular dependencies that depend on quark spin flip probabilities.

Contribution

It introduces a quark-jet model that predicts higher order Collins modulations up to fourth order, linking these effects to quark spin flip dynamics during hadronization.

Findings

Higher order Collins modulations up to fourth order are observed.

Modulation size and sign depend on quark spin flip probabilities.

Results are model-independent for the quark-jet mechanism.

Abstract

The Collins effect describes the modulation of the hadron production by a transversely polarized quark with the sine of the polar angle, $\varphi$, between the produced hadron's transverse momentum and the quark spin. We employ a quark-jet model to describe multiple hadron emissions by such a quark, taking the Collins effect into account. The resulting hadron distributions exhibit modulation up to fourth order in $\sin(\varphi)$ when only two hadron emissions are allowed, rising with any further increase in the number of emitted hadrons. These new effects are a direct consequence of the quark-jet mechanism for quark hadronization, which do not depend on the details of the model used for elementary hadron emission. The size and the sign of the higher order terms are directly connected with the probabilities of quark spin flip in the elementary emission process, with opposing sign favored and unfavored Collins functions only being generated if quark spin flip is preferential. Experimental studies of these effects should therefore provide a critical test of the quark hadronization mechanism, which in turn will lead to a deeper understanding of the transverse spin structure of hadrons.