Speaker
Description
This talk presents recent ATLAS measurements investigating correlations between the 'ridge' - azimuthal correlations between particles in the underlying event that extend over all rapidities - and hard scattering processes in $pp$ and $p$+Pb collisions. To study this soft-hard correlation, measurements of two-particle correlations in with two different particle-pair selections are studied. In the first case, charged particles associated with jets are excluded from the correlation analysis. In the second, correlations are measured between particles within jets and charged particles from the underlying event. In $pp$ collisions, excluding jet-associated particles does not affect the ridge, and no significant azimuthal correlations are found between jet-associated particles and the underlying event, ruling out hard-process contributions to the $pp$ ridge. New measurements extending this analysis to $p$+Pb collisions are also presented. Prior $p$+Pb flow measurements have indicated a small but significant high-$p_{\mathrm{T}}$ $v_2$ up to a $p_{\mathrm{T}}$ of 50 GeV. This is in contrast to suppression measurements which indicate no clear suppression of high-$p_{\mathrm{T}}$ hadrons. These jet-tagged measurements can thus provide insight into the origin of the high-$p_{\mathrm{T}}$ $v_2$ observed in $p$+Pb collisions.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | ATLAS Collaboration |
