New results from the NPL ATLAS Heavy Ion Group first shown at Hard Probes 2023

3/31/2023 2:13:20 PM

This week, two Illinois Nuclear Physics Graduate Students (Aric Tate and Xiaoning Wang) and one Post-Doctoral Research Associate (Dr. Riccardo Longo),  working on data analysis for the ATLAS Heavy Ion program with Prof. Anne Sickles, presented their results at the 11th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions in Aschaffenburg, Germany. 

Xiaoning Wang presented her new measurement [ATLAS-CONF-2023-007] using ATLAS Pb+Pb data for the first time at Hard Probes 2023 (slides available here). This result investigates properties of the quark-gluon plasma, a special state of matter in which elementary particles dissolve into a dense, hot soup of quarks and gluons, produced at extreme temperatures and densities of the Large Hadron Collider at CERN. By measuring the angular modulation of particle productions, Xiaoning’s work provides new insights into the geometry and fluctuations in the QGP. With improved statistics, this work has pushed the measurement to an unprecedented kinematic range and attracted the attention of theorists at the conference. 

Aric Tate and Riccardo Longo presented a poster and a talk about their new results on the production of dijets in p+Pb collisions at 8.16 TeV [ATLAS-CONF-2023-011]. The study of dijet production provides a direct probe of the hard scattering between the two partons (one extracted from the proton, the other from a Pb nuclei). The yield of dijets was studied in terms of three kinematic variables and in different centrality classes, fully constraining the hard parton-parton process kinematics and allowing for the construction of a central-to-peripheral yield ratio. The results show a suppression of the dijet production in central events compared to peripheral, strongly correlated with the fraction of momentum carried by the parton extracted from the proton. The data can be interpreted as a manifestation of so-called color fluctuations, causing protons containing high momentum partons to have smaller than average size and interaction strength with the nucleus.