Speaker
Description
Light-ion collisions at the LHC provide access to parton energy loss in compact systems with a controlled initial geometry and a direct pp baseline at the same energy. In 2025, ATLAS recorded $8~\mathrm{nb}^{-1}$ of O+O and $1~\mathrm{nb}^{-1}$ of Ne+Ne collisions at $\sqrt{s_{\mathrm{NN}}}=5.36~\mathrm{TeV}$, matching a previously collected $400~\mathrm{pb}^{-1}$ $pp$ reference sample. Using anti-$k_t$ $R=0.4$ jets, ATLAS measured the dijet transverse momentum balance in O+O collisions via the distribution of $x_J~\equiv~p_{\mathrm{T},2}/p_{\mathrm{T},1}$ for back-to-back dijets with $63 < p_{\mathrm{T},1} \leq 251~\mathrm{GeV}$ as a function of event activity. A centrality-dependent modification of the $x_J$ distributions is observed in O+O relative to $pp$, with the largest modification in the most central O+O events, consistent with Pb+Pb results at comparable event activity. In the same light-ion datasets, ATLAS quantified the geometric dependence of jet quenching by measuring jet azimuthal anisotropies $v_n$ in O+O and Ne+Ne collisions. Together, the dijet-balance and jet-$v_n$ observables provide complementary constraints on the magnitude of energy loss and its path-length dependence in light nuclear collision systems at LHC energies.
| Is this an experimental talk? | Yes |
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| Is this on behalf of a collaboration? | Yes |
| Which collaboration? | ATLAS |
| Are you willing to present as a poster if it is not selected for oral presentation? | Yes |