Observation of structures in the $J/\ddot{I}ˆ+\ddot{I}ˆ(2S)$ mass spectrum with the ATLAS detector

Abstract

A search for resonant structures in the $J/\ddot{I}ˆ+\ddot{I}ˆ$(2S) mass spectrum is performed using proton--proton collision data at $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 140 fb${}^{-1}$, recorded by the ATLAS experiment at the LHC. The decay channels of $J/\ddot{I}ˆ+\ddot{I}ˆ\text{(2S)}\to 4\hat{I}¼$ and $J/\ddot{I}ˆ+\ddot{I}ˆ\text{(2S)}\to 4\hat{I}¼+2\ddot{I}€$ are analyzed. An excess near 6.9 GeV is observed in both channels with a combined significance of 8.9$\ddot{I}ƒ$. No significant signal is observed near 7.2 GeV, and an upper limit on its yield relative to $X$(6900) is provided. A simultaneous fit with the di-$J/\ddot{I}ˆ$ channel is carried out under assumptions regarding the resonance interferences, yielding a ratio of the partial decay widths between the $J/\ddot{I}ˆ+\ddot{I}ˆ\text{(2S)}$ and di-$J/\ddot{I}ˆ$ channels of $1.08\pm 0.20_{-0.17}^{+0.40}$ for the resonance near 6.9 GeV.

41 pages in total, author list starting page 24, 5 figures, 8 tables, published on Phys. Rev. D. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2023-01/