Neural network biased corrections: Cautionary study in background corrections for quenched jets

Abstract

Jets clustered from heavy ion collision measurements combine a dense background of particles with those actually resulting from a hard partonic scattering. The background contribution to jet transverse momentum ($p_{T}$) may be corrected by subtracting the collision average background; however, the background inhomogeneity limits the resolution of this correction. Many recent studies have embedded jets into heavy ion backgrounds and demonstrated a markedly improved background correction is achievable by using neural networks (NNs) trained with aspects of jet substructure which are used to map measured jet $p_\mathrm{T}$ to the embedded truth jet $p_\mathrm{T}$. However, jet quenching in heavy ion collisions modifies jet substructure, and correspondingly biases the NNs' background corrections. This study investigates those biases by using simulations of jet quenching in central Au+Au collisions at $\sqrt{s_\mathrm{NN}}=200\;\mathrm{GeV}/c$ with hydrodynamically modeled quark-gluon plasma (QGP) evolution. To demonstrate the magnitude of the effect of such biases in measurement, a leading jet nuclear modification factor ($R_\mathrm{AA}$) is calculated and reported using the NN background correction on jets quenched utilizing a brick of QGP.