The VII-th International Conference on the Initial Stages of High-Energy Nuclear Collisions : Initial Stages 2023

Determination of the neutron skin of Pb-208 from ultrarelativistic reactions at the Large Hadron Collider

Not scheduled

20m

Copenhagen

Poster The initial stages and nuclear structure in heavy-ion collisions

Speaker

Govert Nijs (Massachusetts Institute of Technology)

Description

Determined by the nuclear equation of state, the neutron skin of heavy nuclei enables us to connect properties of strong-interaction matter from the nuclear scale ($10^{-15}$ m) to that of neutron stars ($10^3$ m). Of particular interest is the nucleus $^{208}$Pb, owing to its plain structure and experimental availability. Within the hydrodynamic model of heavy-ion collisions, we employ Bayesian inference methods to extract the matter distribution of $^{208}$Pb, as given by the sum of neutron and proton distributions, from the analysis of over 600 data points in the soft sector of ultrarelativistic $^{208}$Pb+$^{208}$Pb collisions performed at the CERN Large Hadron Collider (LHC). We show that measurements of cross sections and transverse momentum distributions constrain the size of the colliding objects. This leads to a precise determination of the matter radius, $r_{\rm matter}=5.550\pm0.036$ fm, matching the predictions of density functional and ab initio calculations of nuclear structure. The resulting neutron skin of $^{208}$Pb is $\Delta r_{np}=0.218\pm0.057$ fm, yielding a picture of nuclear matter consistent with the deductions of low-energy experiments. We establish thus high-energy nuclear reactions at colliders as a new precision tool to measure neutron distributions in atomic nuclei.