Fields In Heavy Ion Collisions Research Articles

Erratum: Synchrotron radiation by fast fermions in heavy-ion collisions [Phys. Rev. C82, 034904 (2010)

We study the synchrotron radiation of gluons by fast quarks in strong magnetic field produced by colliding relativistic heavy-ions. We argue that due to high electric conductivity of plasma, time variation of the magnetic field is slow and estimate its relaxation time. We calculate the energy loss due to synchrotron radiation of gluons by fast quarks. We find that the typical energy loss per unit length for a light quark at LHC is a few GeV per fm. This effect alone predicts quenching of jets with $p_\bot$ up to about 20 GeV. We also show that the spin-flip transition effect accompanying the synchrotron radiation leads to a strong polarization of quarks and leptons with respect to the direction of the magnetic field. Observation of the lepton polarization may provide a direct evidence of existence of strong magnetic field in heavy-ion collisions.

Photon decay in a strong magnetic field in heavy-ion collisions

We calculate the photon pair production rate in a strong magnetic field created in off-central heavy-ion collisions. Photon decay leads to depletion of the photon yield by a few percent at RHIC and by as much as 20% at the LHC. It also generates a substantial azimuthal asymmetry (``elliptic flow'') of the final photon distribution. We estimate ${v}_{2}\ensuremath{\approx}2$% at RHIC and ${v}_{2}\ensuremath{\approx}14$% at LHC. Photon decay measurements is an important tool for studying the magnetic fields in early stages of heavy-ion collisions.

CGC and initial state effects in Heavy Ion Collisions

A brief review of the phenomenological studies in the field of heavy ion collisions based on the Color Glass Condensate theory and, in particular, of those relying in the use of the BK equation including running coupling effects is presented.

Synchrotron radiation by fast fermions in heavy-ion collisions

We study the synchrotron radiation of gluons by fast quarks in strong magnetic field produced by colliding relativistic heavy ions. We argue that due to high electric conductivity of plasma, the magnetic field is almost constant during the entire plasma lifetime. We calculate the energy loss due to synchrotron radiation of gluons by fast quarks. We find that the typical energy loss per unit length for a light quark at the Large Hadron Collider is a few GeV per fm. This effect alone predicts quenching of jets with ${p}_{\ensuremath{\perp}}$ up to about 20 GeV. We also show that the spin-flip transition effect accompanying the synchrotron radiation leads to a strong polarization of quarks and leptons with respect to the direction of the magnetic field. Observation of the lepton polarization may provide a direct evidence of existence of strong magnetic field in heavy-ion collisions.

How particles emerge from decaying classical fields in heavy ion collisions: Towards a kinetic description of the Glasma

We develop the formalism discussed previously in hep-ph/0601209 and hep-ph/0605246 to construct a kinetic theory that provides insight into the earliest “Glasma” stage of a high energy heavy ion collision. Particles produced from the decay of classical fields in the Glasma obey a Boltzmann equation whose novel features include an inhomogeneous source term and new contributions to the collision term. We discuss the power counting associated with the different terms in the Boltzmann equation and outline the transition from the field dominated regime to the particle dominated regime in high energy heavy ion collisions.

Thermalization of Color Gauge Fields in Heavy Ion Collisions and Nielsen-Olesen Instability

We analyze the behavior of unstable modes in glasma produced initially in high energy heavy ion collisions, by using a simple model of homogeneous longitudinal color electric and magnetic fields. The unstable modes can be approximately described as Nielsen-Olesen unstable modes under the homogeneous longitudinal gauge fields. We find that the NielsenOlesen unstable modes show properties very similar to those of the exponentially increasing unstable modes in glasma demonstrated recently by Romatschke and Venugopalan. We discuss why such effective weak magnetic fields used in the model are appropriate to analyze the instability of the initial strong inhomogeneous gauge fields. Our analysis indicates that the decay of the gauge fields in glasma is caused by not Weibel instability but Nielsen-Olesen instability.

Quark-antiquark production from classical fields in heavy-ion collisions:1+1dimensions

Classical color fields produced by the small-x wave functions of colliding ultrarelativistic nuclei have been numerically computed. We set up the framework for computing the production of small-mass quark-antiquark pairs in these color fields by numerically integrating the Dirac equation. This computation is essential for understanding the conversion of the initial gluonic state to a chemically equilibrated quark-gluon plasma. To illustrate and overcome technical difficulties associated with the longitudinal dimension, we first consider numerically the case of one time + one longitudinal space dimension.

Expansion Rates at RHIC

A detailed description of the temporal evolution of the thermodynamic fields in heavy ion collisions is presented within a hydrodynamic framework. Particular attention is devoted to the evolution of the collective flow fields and their space-time gradients.

Dissipation and Fluctuation at the Chiral Phase Transition

Utilizing the Langevin scenario for the linear sigma model we investigate the effect of friction and white noise on the evolution and stability of collective pionic fields in heavy ion collisions. We find that the smaller the volume the more stable pionic fluctuations become (the avergae mass increases). On the other hand the variance of the mass square increases even more, so for a system preheated in 10 fm3 volume individual trajectories do become unstable during a rapid one dimensional expansion in contrast to the ensemble averaged solution. This result supports the idea of looking for disoriented chiral condensate (DCC) formation in individual events.

Unified Theory of Electrons and Photons in Heavy Ion Collisions

We present a unified formulation of the interaction of electrons with the electromagnetic field in heavy ion collisions, based on quantized interacting fields. This reduces the effort in treating many-electron systems substantially, as compared with the usual S-matrix theory. Both formalisms are shown to be equivalent. The simplification achieved by our new approach is demonstrated in detail for the example of quasi-molecular radiation

Delta electrons as a probe of strong magnetic fields in heavy ion collisions

We propose that the spin polarization of delta electrons should be used as a measure of the strong magnetic fields ( B∼10 17 G) induced by the nuclear motion in collisions of very heavy ions. The polarization is typically of the order of 10–20 percent in Pb-Pb and U-U collisions. We also discuss the bombarding energy dependence up to E 1ab = 200MeV/ u, where 500 keV level splitting between spin up and down states is obtained.