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Nuclear Physics Seminar -Riccardo Longo (UIUC) "Probing proton size fluctuations and nuclear effects via dijet measurements in heavy ion collisions at the LHC"

Event Type
Physics Department
464 Loomis
Dec 4, 2023   1:00 pm  
Riccardo Longo
Brandy Koebbe
Originating Calendar
Physics - Nuclear Physics Seminar

The measurement of dijets at the LHC is a powerful microscope that allows for investigating the nucleon and nuclear structure as a function of the kinematics of the initial state. 

In this talk, I will present the recent ATLAS measurement of the centrality dependence of the dijet per-event yield at center-of-mass energy 8.16 TeV in p+Pb collisions (arXiv:2309.00033). 

In p+Pb collisions, the event centrality reflects the impact parameter and, in this analysis, was characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter.

The central-to-peripheral ratio of the per-event dijet yields, RCP was studied as a function of variables that reflect the kinematics of the initial hard parton scattering process. 

The RCP shows a scaling with the Bjorken-x of the parton originating from the proton, xp, while no such trend is observed as a function of xPb.

By profiting from the full acceptance of the ATLAS high-performance calorimeter, this analysis covers a broad parton momentum fraction range, from the valence region down to x~ 10-3 and xPb ~ 4 · 10-4.

These results represent a unique input to understanding the role of small proton spatial configurations in p+Pb collisions and, together with ATLAS dijets in ultra-peripheral Pb+Pb collisions, provide a direct link between heavy ion physics at the LHC and the future Electron-Ion Collider. 

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