Differential measurements of jet substructure and partonic energy loss in Au <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>+</mml:mo></mml:math> Au collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi>N</mml:mi><mml:mi>N</mml:mi></mml:mrow></mml:msub></mml:msqrt><mml:mo>=</mml:mo><mml:mn>200</mml:mn></mml:mrow></mml:math> GeV

The STAR collaboration presents jet substructure measurements related to both the momentum fraction and opening angle within jets in \pp \AuAu collisions at \sqrtsn $= 200$ GeV. observables include SoftDrop groomed (\zg), radius (\rg), subjet (\zsj) (\tsj). latter observable is introduced for first time. Fully corrected are presented compared leading order Monte Carlo models. \tsj~distributions reflect utilized as a proxy resolution scale of medium collisions. We compare data from those which embedded minimum-bias events effects detector smearing heavy-ion collision underlying event. shown be more robust background than \zg~and \rg. observe no significant modifications two highest-energy, back-to-back jets, resulting distribution angles splittings that vacuum-like. also report differential di-jet imbalance ($A_{\rm{J}}$) varying \tsj. find qualitative differences energy loss signatures angular scales range $0.1 < $ \tsj 0.3$, possible interpretation this population high pairs, due soft medium-induced gluon radiation single color-charge it traverses medium.