Recent UPC J/\psi results from ATLAS

by Peter Steinberg (BNL)

Tuesday May 13, 2025, 11:00 AM → 1:00 PM US/Eastern

Small Seminar Room

In this talk, I will discuss the recent measurement of coherent, exclusive $J/\psi \rightarrow \mu^+\mu^-$ production in ultraperipheral Pb+Pb collisions at $\sqrt{s_{NN}} = 5.36$ TeV. The dataset was recorded in 2023 and corresponds to an integrated luminosity of $\mathcal{L} = 76.5\ \mu\mathrm{b}^{-1}$. Exclusive $J/\psi$ candidates were selected with a dedicated track-sensitive trigger based on the ATLAS transition radiation tracker. Although the trigger is sensitive to both leptonic decay modes ($\mu^+\mu^-$ and $e^+e^-$), the measurement is performed only for the dimuon channel. The analysis reconstructs the dimuon invariant mass using inner-detector muon tracks only, since the available muon $p_T$ range precludes standard muon reconstruction and identification algorithms. Differential cross-sections, $d\sigma/dy$, are measured as a function of $J/\psi$ rapidity and compared with theoretical predictions. After interpolation to the lower beam energy ($\sqrt{s_{NN}} = 5.02$ TeV), the results are also contrasted with previous LHC Run 2 measurements at the same energy.