Search for quasi-particle scattering in the quark-gluon plasma with jet splittings in pp and Pb-Pb collisions at s ₍₍ = 5. 02 TeV

The ALICE Collaboration reports measurements of the large relative transverse momentum (kₓ) component of jet substructure in pp and in central and semicentral Pb-Pb collisions at center-of-mass energy per nucleon pair s₍₍=5. 02 TeV. Enhancement in the yield of such large-kₓ emissions in central Pb-Pb collisions is predicted to arise from partonic scattering with quasi-particles of the quark-gluon plasma. The analysis utilizes charged-particle jets reconstructed by the anti-kₓ algorithm with resolution parameter R=0. 2 in the transverse-momentum interval 60 < pₓ, ₂₇ ₉₄ₓ < 80 GeV/c. The soft drop and dynamical grooming algorithms are used to identify high transverse momentum splittings in the jet shower. Comparison of measurements in Pb-Pb and pp collisions shows medium-induced narrowing, corresponding to yield suppression of high-kₓ splittings, in contrast to the expectation of yield enhancement due to quasi-particle scattering. The measurements are compared to theoretical model calculations incorporating jet quenching, both with and without quasi-particle scattering effects. These measurements provide new insight into the underlying mechanisms and theoretical modeling of jet quenching.