Jet radius dependence of dijet momentum balance in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

This note describes a measurement of the jet radius dependence of the momentum balance between leading back-to-back dijets in 1.7~\inb\ of Pb+Pb collisions collected in 2018 and 260~\ipb\ of pp collisions collected in 2017 by the ATLAS detector at the LHC. Both data sets were collected at $\sqrtsnn =$5.02 TeV. The jets used in this analysis are reconstructed with the \antikt\ algorithm with jet radius parameters, $R$, of 0.2, 0.3, 0.5 and 0.6 and the momentum balance distributions are constructed for leading jets with transverse momentum (\pt) from 100 GeV (200 GeV) to 562 GeV for R = 0.2 and R = 0.3 (R = 0.5 and R=0.6) jets. The results are compared to previous measurements of the same quantity made with R = 0.4 jets. The absolutely normalized momentum balance distributions are constructed to compare measurements in Pb+Pb collisions directly to those in pp collisions. For all jet radii considered here, there is a stronger suppression of balanced jets in central Pb+Pb collisions compared to that for imbalanced ones. For balanced jets there is no significant jet radius dependence on this suppression. For imbalanced jets, particularly at the lower selections on leading jet \pt, the level of suppression decreases with increasing jet radius. Additionally, pair nuclear modification factors are measured. As was previously observed for R = 0.4 jets, the subleading jets are found to be more suppressed than leading jets, indepedent of jet radius. These new measurements should provide new constraints on jet quenching scenarios in the quark-gluon plasma.