Search for the Elusive Jet-Induced Diffusion Wake in Z/γ-Jets with 2D Jet Tomography in High-Energy Heavy-Ion Collisions.

Diffusion wake is an unambiguous part of the jet-induced medium response in high-energy heavy-ion collisions that leads to a depletion of soft hadrons in the opposite direction of the jet propagation. New experimental data on Z-hadron correlation in Pb+Pb collisions at the Large Hadron Collider show, however, an enhancement of soft hadrons in the direction of both the Z and the jet. Using a coupled linear Boltzmann transport and hydro model, we demonstrate that medium modification of partons from the initial multiple parton interaction (MPI) gives rise to a soft hadron enhancement that is uniform in azimuthal angle while jet-induced medium response and soft gluon radiation dominate the enhancement in the jet direction.

Gradient Tomography of Jet Quenching in Heavy-Ion Collisions.

Transverse momentum broadening and energy loss of a propagating parton are dictated by the space-time profile of the jet transport coefficient q[over ^] in a dense QCD medium. The spatial gradient of q[over ^] perpendicular to the propagation direction can lead to a drift and asymmetry in parton transverse momentum distribution. Such an asymmetry depends on both the spatial position along the transverse gradient and path length of a propagating parton as shown by numerical solutions of the Boltzmann transport in the simplified form of a drift-diffusion equation.

Bayesian Extraction of Jet Energy Loss Distributions in Heavy-Ion Collisions.

Based on the factorization in perturbative QCD, a jet cross section in heavy-ion collisions can be expressed as a convolution of the jet cross section in p+p collisions and a jet energy loss distribution. Using this simple expression and the Markov Chain Monte Carlo method, we carry out Bayesian analyses of experimental data on jet spectra to extract energy loss distributions for both single inclusive and γ-triggered jets in Pb+Pb collisions with different centralities at two colliding energies at the Large Hadron Collider. The average jet energy loss has a dependence on the initial jet energy that is slightly stronger than a logarithmic form and decreases from central to peripheral collisions.

An equation-of-state-meter of quantum chromodynamics transition from deep learning.

A primordial state of matter consisting of free quarks and gluons that existed in the early universe a few microseconds after the Big Bang is also expected to form in high-energy heavy-ion collisions. Determining the equation of state (EoS) of such a primordial matter is the ultimate goal of high-energy heavy-ion experiments. Here we use supervised learning with a deep convolutional neural network to identify the EoS employed in the relativistic hydrodynamic simulations of heavy ion collisions.

Vortical Fluid and Λ Spin Correlations in High-Energy Heavy-Ion Collisions.

Fermions become polarized in a vortical fluid due to spin-vorticity coupling, and the polarization density is proportional to the local fluid vorticity. The radial expansion converts spatial vortical structures in the transverse plane to spin correlations in the azimuthal angle of final Λ hyperons' transverse momentum in high-energy heavy-ion collisions. Using a (3+1)D viscous hydrodynamic model with fluctuating initial conditions from a multiphase transport (AMPT) model, we reveal two vortical structures that are common in many fluid dynamic systems: a right-handed toroidal structure around each beam direction for transverse vorticity and pairing of longitudinal vortices with opposite signs in the transverse plane.