Measurement of dijet transverse momentum balance in O+O and $pp$ collisions at 5.36 TeV with the ATLAS detector

ATLAS Collaboration

Report

PUBDB-2025-05445

Measurement of dijet transverse momentum balance in O+O and $pp$ collisions at 5.36 TeV with the ATLAS detector

ATLAS Collaboration (Collaboration author)DESY*

2025

24 pp. (2025) [10.3204/PUBDB-2025-05445]

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Please use a persistent id in citations: doi:10.3204/PUBDB-2025-05445

Report No.: ATLAS-CONF-2025-010

Abstract: In July 2025, the LHC delivered oxygen-oxygen (O+O) collisions at 5.36 TeV, and the ATLAS experiment collected 8 nb$^{-1}$ of data. This dataset offers a unique opportunity to search for the onset of energy loss effects in a small collision system comparable in transverse size to peripheral Pb+Pb collisions. Compared to those, O+O collisions are characterized by a well-defined geometry that allows a more systematic study of the evolution of the parton shower at different length scales in the medium. This note presents a measurement of the dijet transverse momentum balance in O+O collisions for leading jets with transverse momentum between 63 and 251 GeV as a function of collision centrality. Measurements in $pp$ collisions at the same collision energy are presented as a baseline. Over the range of leading jet transverse momentum reported here, a modification of the momentum balance distributions is observed in O+O collisions, relative to $pp$, with the largest modifications being in central O+O collisions. % This modification is similar to that observed in Pb+Pb collisions at a comparable level of event activity.

Keyword(s): HEAVY IONS ; DIJET MOMENTUM IMBALANCE ; QGP ; OXYGEN

Note: Preliminary results. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2025-010. The authors list may be incomplete!

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