Dmitri E. Kharzeev

The Effects of topological charge change in heavy ion collisions: 'Event by event P and CP violation'

Abstract Quantum chromodynamics (QCD) contains field configurations which can be characterized by a topological invariant, the winding number Q w . Configurations with non-zero Q w break the charge-parity ( CP ) symmetry of QCD. We consider a novel mechanism by which these configurations can separate charge in the presence of a background magnetic field—the “chiral magnetic effect”. We argue that sufficiently large magnetic fields are created in heavy ion collisions so that the chiral magnetic effect causes preferential emission of charged particles along the direction of angular momentum. Since separation of charge is CP -odd, any observation of the chiral magnetic effect could provide a clear demonstration of the topological nature of the QCD vacuum. We give an estimate of the effect and conclude that it might be observed experimentally.

Chiral magnetic effect

Topological charge changing transitions can induce chirality in the quark-gluon plasma by the axial anomaly. We study the equilibrium response of the quark-gluon plasma in such a situation to an external magnetic field. To mimic the effect of the topological charge changing transitions we will introduce a chiral chemical potential. We will show that an electromagnetic current is generated along the magnetic field. This is the chiral magnetic effect. We compute the magnitude of this current as a function of magnetic field, chirality, temperature, and baryon chemical potential.

Heavy quarkonium physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

Parity violation in hot QCD: Why it can happen, and how to look for it

The arguments for the possibility of violation of P and CP symmetries of strong interactions at finite temperature are presented. A new way of observing these effects in heavy ion collisions is proposed—it is shown that parity violation should manifest itself in the asymmetry between positive and negative pions with respect to the reaction plane. Basing on topological considerations, we derive a lower bound on the magnitude of the expected asymmetry, which may appear within the reach of the current and/or future heavy ion experiments.

Charge separation induced by P-odd bubbles in QCD matter

Abstract We examine the recent suggestion that P - and CP -odd effects in QCD matter can induce electric charge asymmetry with respect to reaction plane in relativistic heavy ion collisions. General arguments are given which confirm that the angular momentum of QCD matter in the presence of nonzero topological charge should induce an electric field aligned along the axis of the angular momentum. A simple formula relating the magnitude of charge asymmetry to the angular momentum and topological charge is derived. The expected asymmetry is amenable to experimental observation at RHIC and LHC; we discuss the recent preliminary STAR result in light of our findings. Possible implications of charge separation phenomenon in cosmology and astrophysics are discussed as well.

Cronin effect and high p(T) suppression in pA collisions

We review the predictions of the theory of a color glass condensate for a gluon production cross section in

Parton saturation and Npart scaling of semi-hard processes in QCD

p(d)A

Universal properties of bulk viscosity near the QCD phase transition

collisions. We demonstrate that, at moderate energies, when the gluon production cross section can be calculated in the framework of the McLerran-Venugopalan model, it has only a partonic level Cronin effect in it. At higher energies or rapidities corresponding to smaller values of the Bjorken x, quantum evolution becomes important. The effect of quantum evolution at higher energies or rapidities is to introduce the suppression of high-

Chiral magnetic and vortical effects in high-energy nuclear collisions—A status report

{p}_{T}

Chiral magnetic conductivity

gluons slightly decreasing the Cronin enhancement. At still higher energies or rapidities quantum evolution leads to the suppression of produced gluons at all values of