Speaker
Description
We present a novel measurement of in-jet azimuthal asymmetry at $\sqrt{s}=91.2\,\mathrm{GeV}$ in $e^+e^-$ collisions, providing a precision vacuum reference and a controlled bridge to possible QGP-like collectivity in heavy-ion collisions. Using archived ALEPH data and validated simulations, we extract fully unfolded, per-jet constituent Fourier harmonics $V_n$ $(n=1\text{-}3)$ with respect to the jet axis. We compare the Winner-Take-All axis, defined by WTA recombination and aligned with the hardest branch, with the E-scheme axis, defined by the vector sum of the four-momenta of in-jet constituents, to quantify the sensitivity of the measured harmonics to soft jet constituents and recoil effects. The results are compared to multiple modern event generators to test the modeling of vacuum jet substructure.
To study possible flow-driven effects on these observables, we use a dedicated Monte Carlo framework that injects a tunable flow-like modulation at the constituent level and measures the corresponding response in $V_n$. We further discuss related in-jet azimuthal structures observed in PbPb collisions and examine how the $e^+e^-$ vacuum baseline can help separate vacuum fragmentation, medium response, and possible flow-driven contributions. Future prospects and possible extensions of this study will also be discussed.
