Measurements of jet quenching using semi-inclusive hadron+jet distributions in pp and central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=5.02$ TeV

The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high $p_{\mathrm{T}}$) charged hadron, in pp and central Pb$-$Pb collisions at center-of-mass energy per nucleon$-$nucleon collision $\sqrt{s_{\mathrm{N}\mathrm{N}}}=5.02$ TeV. The large uncorrelated background in central Pb$-$Pb collisions is corrected using a data-driven statistical approach, which enables precise measurement of recoil jet distributions over a broad range in $p_{\mathrm{T},\mathrm{c}\mathrm{h}\mathrm{j}\mathrm{e}\mathrm{t}}$ and jet resolution parameter $R$. Recoil jet yields are reported for $R=0.2$, 0.4, and 0.5 in the range $7<p_{\mathrm{T},\mathrm{c}\mathrm{h}\mathrm{j}\mathrm{e}\mathrm{t}}<140$ GeV$\mathrm{/}c$ and $\pi \mathrm{/}2<\mathrm{\Delta }\phi <\pi$, where $\mathrm{\Delta }\phi$ is the azimuthal angular separation between hadron trigger and recoil jet. The low $p_{\mathrm{T},\mathrm{c}\mathrm{h}\mathrm{j}\mathrm{e}\mathrm{t}}$ reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark-gluonnplasma generated in high-energy nuclear collisions. Comparison of $p_{\mathrm{T},\mathrm{c}\mathrm{h}\mathrm{j}\mathrm{e}\mathrm{t}}$ distributions from pp and central Pb$-$Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.