Speaker
Description
High-transverse-momentum charged hadrons probe jet--QGP interactions, yet sizable suppression persists in highly peripheral heavy-ion collisions, where final-state energy loss should be weak. We factorize the nuclear modification factor as $R_{\mathrm{AA}}=R_{\mathrm{AA}}^{\mathrm{bias}}R_{\mathrm{AA}}^{\mathrm{med}}$, separating initial-state geometric bias from medium modification. A HIJING-based initial condition incorporates the nucleon--nucleon impact-parameter dependence of both the inelastic collision probability and hard-scattering multiplicity. Jet evolution is simulated with an improved, scale-segmented linear Boltzmann transport model coupled to Pythia and a (3+1)-dimensional hydrodynamic QGP background; revised fake- and negative-parton treatments stabilize hadronization in dilute systems. For Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV, the geometric factor remains near unity in central events but deviates by more than 5% beyond 50% centrality. Although HIJING broadens the hard-vertex distribution in peripheral collisions, this has little influence on $R_{\mathrm{AA}}$ because parton energy loss is weak. Instead, dilute nucleon overlap reduces the hard-scattering yield per binary collision, producing a sizable suppression in 50--70% and a significant suppression in 70--90% collisions. Combining geometric bias with jet--QGP interactions yields a satisfactory description of CMS charged-hadron $R_{\mathrm{AA}}$ from central to peripheral events, showing that highly peripheral suppression is predominantly geometric and should not be interpreted as evidence for strong jet quenching alone.
