A Linear Boltzmann Transport model within perturbative QCD is developed for the study of parton propagation inside the quark-gluon plasma. Both leading partons and thermal recoil partons are tracked so that one can also study jet-induced medium excitations. In this study, we implement the complete set of elastic parton scattering processes and investigate elastic parton energy loss, transverse momentum broadening and their nontrivial energy and length dependence. We further investigate medium modifications of the jet shape and fragmentation functions of reconstructed jets. Contributions from thermal recoil partons are found to have significant influences on jet shape, fragmentation functions and angular distribution of reconstructed jets.

γ-jet production is considered one of the best probes of the hot quark-gluon plasma in high-energy heavy-ion collisions since the direct γ can be used to gauge the initial energy and momentum of the associated jet. This is investigated within the Linear Boltzmann Transport (LBT) model for jet propagation and jet-induced medium excitation. With both parton energy loss and medium response from jet-medium interaction included, LBT can describe experimental data well on γ-jet correlation in Pb+Pb collisions at the Large Hadron Collider. Multiple jets associated with direct γ production are found to contribute significantly to γ-jet correlation at small p jet T < p γ T and large azimuthal angle relative to the opposite direction of γ. Jet medium interaction not only suppresses the leading jet at large p jet T but also sub-leading jets at large azimuthal angle. This effectively leads to the narrowing of γ-jet correlation in azimuthal angle instead of broadening due to jet-medium interaction. The γ-jet profile on the other hand will be broadened due to jet-medium interaction and jet-induced medium response. Energy flow measurements relative to the direct photon is illustrated to reflect well the broadening and jet-induced medium response.

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The suppression factor for single inclusive jets in Pb+Pb collisions at the Large Hadron Collider (LHC) has a weak dependence on the transverse momentum pT and remains almost the same at two colliding energies, √ s = 2.76 and 5.02 TeV, though the central rapidity density of bulk hadrons increases by about 20%. This phenomenon is investigated within the Linear Boltzmann Transport (LBT) model, which includes elastic and inelastic processes based on perturbative QCD for both jet shower and recoil medium partons as they propagate through a quark-gluon plasma (QGP). With the dynamic evolution of the QGP given by the 3+1D CLVisc hydrodynamic model with event-byevent fully fluctuating initial conditions, single inclusive jet suppression in Pb+Pb collisions from LBT agrees well with experimental data. The weak √ s and pT -dependence of the jet suppression factor at LHC are found to result directly from the √ s-dependence of the initial jet pT spectra and slow pT -dependence of the jet energy loss. Contributions from jet-induced medium response, influence of radial expansion, both of which depend on jet-cone size, and jet flavor composition all conjoin to give a slow pT -dependence of jet energy loss and the single jet suppression factor RAA, their dependence on √ s and jet-cone size. Single inclusive jet suppression at √ s = 200 GeV is also predicted that actually decreases slightly with pT in the pT < 50 GeV/c range because of the steeper initial jet spectra though the pT -dependence of the jet energy loss is weaker than that at LHC.

Transverse momentum broadening and energy loss of a propagating parton are dictated by the spacetime profile of the jet transport coefficientq in a dense QCD medium. The spatial gradient ofq 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. In high-energy heavy-ion collisions, this asymmetry with respect to a plane defined by the beam and trigger particle (photon, hadron, or jet) with a given orientation relative to the event plane is shown to be closely related to the transverse position of the initial jet production in full event-by-event simulations within the linear Boltzmann transport model. Such a gradient tomography can be used to localize the initial jet production position for more detailed study of jet quenching and properties of the quark-gluon plasma along a given propagation path in heavy-ion collisions.

Based on the factorization in perturbative QCD, a jet cross sections 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 P b + P b 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. The extracted jet energy loss distributions with a scaling behavior in x = ∆pT / ∆pT have a large width. These are consistent with the linear Boltzmann transport model simulations, in which the observed jet quenching is caused on the average by only a few out-of-cone scatterings.

Abstract.We report the first measurement of the total charge-loss cross section Gtot=aem+anuo and partial cross sections (for AZ = 1, 2, ... After presenting our data, we focus on the problem of disentangling two modes of high-energy nucleus-nucleus interactions -a nuclear mode which takes place when a relativistic projectile and a target pass each other within the range of the strong force and an electromagnetic mode which occurs at larger impact parameters such that only the virtual photons from either the target or the projectile can interact with the other. Particle telescopes [2][3][4][5][6][7], plastic track detectors [8][9][10][11][12], and nuclear emulsions [13,14] have been used to separate nuclear and electromagnetic contributions to charge-changing interactions of projectiles, and gamma-ray spectroscopy [15][16][17][18] and particle telescopes [2,3,7,19] have been used to study nuclear and electromagnetic processes in which neutrons are emitted from a target. In all these experiments it is assumed that, if the impact parameter is less than a critical value, roughly the sum of radii of projectile and target, the interaction is purely nuclear; if not, it is purely electromagnetic. In this view the cross section is the sum of the two contributions:

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