First observation of ultra-long-range azimuthal correlations in low multiplicity pp and p–Pb collisions at the LHC
- Acharya, Shreyasi et al
- arXiv:2504.02359CERN-EP-2025-080
 | The ultra-long-range (\(|\Delta \eta| > 5.0\)) per-trigger yield, measured as a function of \(\Delta \eta\) and \(\Delta \varphi\) in p--Pb collisions at \(\sqrt{s_{\text{NN}}} = 5.02\)~TeV for \(7 < N_{\text{ch}} < 40\), shows a double-ridge structure after non-flow removal using the template-fit method. |
 | The \(N_{\text{ch}}\) dependence of the second-order two-particle correlation coefficient \( V_{2\Delta} (\text{2PC}) \), estimated using the template-fit method, in pp (\(|\Delta \eta| > 5.0\)) collisions at \(\sqrt{s} = 13\) TeV and p--Pb (\(|\Delta \eta| > 5.0\) and \(|\Delta \eta| > 6.5\)) collisions at \(\sqrt{s_{\text{NN}}} = 5.02\) TeV. |
 | Left: The \( N_{\rm ch} \) dependence of the second-order two-particle correlation coefficient \( V_{2\Delta} (\rm{2PC}) \), estimated using the template-fit method, in pp (\( |\Delta \eta| > 5.0 \)) collisions at \( \sqrt{s} = 13 \)~TeV, and compared with predictions from the 3D-Glauber + MUSIC + UrQMD model~\cite{Zhao:2022ugy}, as well as with PYTHIA8 variations with string-shoving~\cite{Bierlich:2017vhg, Bierlich:2014xba} and ropes~\cite{Bierlich:2022ned} implementations. Right: The $N_{\rm ch}$ dependence of the \( V_{2\Delta} (\rm{2PC}) \), estimated using template-fit method, in p--Pb ($|\Delta \eta| > 5.0$ and $|\Delta \eta| > 6.5$) collisions at $\snn=5.02$~TeV and its comparison with the 3D-Glauber + MUSIC + UrQMD predictions. |
 | Left: The \( N_{\rm ch} \) dependence of the second-order two-particle correlation coefficient \( V_{2\Delta} (\rm{2PC}) \), estimated using the template-fit method, in pp (\( |\Delta \eta| > 5.0 \)) collisions at \( \sqrt{s} = 13 \)~TeV, and compared with predictions from the 3D-Glauber + MUSIC + UrQMD model~\cite{Zhao:2022ugy}, as well as with PYTHIA8 variations with string-shoving~\cite{Bierlich:2017vhg, Bierlich:2014xba} and ropes~\cite{Bierlich:2022ned} implementations. Right: The $N_{\rm ch}$ dependence of the \( V_{2\Delta} (\rm{2PC}) \), estimated using template-fit method, in p--Pb ($|\Delta \eta| > 5.0$ and $|\Delta \eta| > 6.5$) collisions at $\snn=5.02$~TeV and its comparison with the 3D-Glauber + MUSIC + UrQMD predictions. |