Jet substructure observables can reveal details of the parton fragmentation and hadronization processes that create a jet. We measure a new substructure observable, the charge correlator ratio ($r_c$), that characterizes the fraction of string-like fragmentation by distinguishing the charge signs of leading and subleading charged particles within jets. This can further our understanding of non-perturbative QCD and provide tests for phenomenological hadronization models. Moreover, by measuring $r_c$ with jets created in heavy-ion collisions, we probe for potential modifications of the hadronization process due to the presence of the Quark Gluon Plasma.

We present the first fully corrected results of $r_c$ at RHIC, in $\sqrt{s}=200$ GeV $pp$ collisions recorded by the STAR detector, and compare them with Monte Carlo predictions. Additionally, we present progress on the first measurement of $r_c$ in heavy-ion collisions, with $\sqrt{s_{\mathrm{{NN}}}}=200$ GeV Ru+Ru and Zr+Zr collisions.