Gluons at small x in high-energy nuclei overlap in the longitudinal direction, so the nucleus acts as a single source of gluons, like higher Fock components in a single nucleon, which contribute to inelastic collisions with a high multiplicity of pro
duced hadrons. This similarity helps to make a link between nuclear effects in pA and high-multiplicity pp collisions. Such a relation is well confirmed by data for the J/Psi production rate in high-multiplicity pp events measured recently in the ALICE experiment. Broadening of J/Psi transverse momentum is predicted for high-multiplicity pp collisions.
We explore the thermodynamics of the gluon plasma in SU(3) Yang-Mills theory emerging from the non-trivial spatial dynamics of valence gluons. The lattice data suggest that these gluons interact with each other linearly at large spatial separations.
At high temperatures, valence gluons should reproduce the pressure of the non-interacting Stefan-Boltzmann plasma along with the leading perturbative correction. These properties of valence gluons can be modeled in terms of the integral over their trajectories. We calculate such a world-line integral analytically and obtain the pressure and the interaction measure $(varepsilon-3p)/T^4$ of the gluon plasma. Additionally, we account for the contributions of stochastic background fields to these thermodynamic quantities. The results turn out to be in a good agreement with the corresponding lattice data. In particular, the lattice-simulated peak of the interaction measure near the deconfinement critical temperature is reproduced.
We present a quantum-mechanical description of quark-hadron fragmentation in a nuclear environment. It employs the path-integral formulation of quantum mechanics, which takes care of all phases and interferences, and which contains all relevant time
scales, like production, coherence, formation, etc. The cross section includes the probability of pre-hadron (colorless dipole) production both inside and outside the medium. Moreover, it also includes inside-outside production, which is a typical quantum-mechanical interference effect (like twin-slit electron propagation). We observe a substantial suppression caused by the medium, even if the pre-hadron is produced outside the medium and no energy loss is involved. This important source of suppression is missed in the usual energy-loss scenario interpreting the effect of jet quenching observed in heavy ion collisions. This may be one of the reasons of a too large gluon density, reported by such analyzes.
We argue that the radiative energy loss of a parton traversing the quark-gluon plasma is determined by Landau damping of soft modes in the plasma. Using this idea, we calculate the jet quenching parameter of a gluon. The calculation is done in SU(3)
quenched QCD within the stochastic vacuum model. At the LHC-relevant temperatures, the result depends on the gluon condensate, the vacuum correlation length, and the gluon Debye mass. Numerically, when the temperature varies from T=T_c to T=900 MeV, the jet quenching parameter rises from hat q=0 to approximately 1.8 GeV^2/fm. We compare our results with the predictions of perturbative QCD and other calculations.
We give a status report of our work on light cone Hamiltonian lattice QCD. We have derived an effective Hamiltonian $H_{eff}$ which is only quadratic in the momenta and therefore can be simulated by standard methods. For this Hamiltonian we determine
variationally an approximate ground state wave functional in the light cone limit.
