Physics Main Calendar

Light-ion collisions provide a new length scale on which to probe the quark-gluon plasma (QGP), since the transverse extent of the overlapping region is much larger than p+Pb but much smaller than Pb+Pb.  The presence of parton energy loss in this system is of particular interest, given that this phenomenon was observed in Pb+Pb but not in p+Pb.  ATLAS collected an integrated luminosity of 8 1/nb in O+O collisions in July of 2025.  In this talk, I will present a recent ATLAS preliminary measurement of the dijet momentum balance (xJ) at center-of-mass energy 5.36 TeV in O+O collisions. The pair-normalized xJ yields indicate that dijets in central O+O events are slightly more imbalanced than in pp.  This result provides unique input into understanding the path length dependence of energy loss in high-pT probes transversing the QGP.