The possibility of radiation of high-energy gamma quanta with energies of the order of 100 GeV by ultrarelativistic electrons on nuclei in strong X-ray fields with intensities up to $\sim 10^{27}\ \text{Wcm}^{-2}$ has been theoretically studied. It is shown that this effect can be realized under special experimental conditions in the process of resonant spontaneous bremsstrahlung radiation of ultrarelativistic electrons on nuclei in an external electromagnetic field. These special experimental conditions determine the characteristic energy of the electrons. This characteristic energy should be significantly less than the energy of the initial electrons. Under these conditions, spontaneous gamma quanta are emitted in a narrow cone with energies close to the energy of the initial electrons. Moreover, the resonant differential cross-sections of such processes can exceed the corresponding differential cross-section without an external field by twenty orders of magnitude. The results obtained can explain the occurrence of high-energy gamma quanta near pulsars and magnetars.
The generation of narrow beams of high-energy positrons (electrons) in the process of resonant photogeneration of ultrarelativistic electron-positron pairs by high-energy gamma quanta in the field of the nucleus and a strong electromagnetic wave is theoretically predicted. It is shown that if the energy of the initial gamma quanta significantly exceeds the characteristic energy of the process, then ultrarelativistic positrons (for channel A) or electrons (for channel B) are emitted with energies very close to the energy of gamma quanta. Moreover, the resonant differential cross-section of such…
We propose a unified space-time picture of baryon stopping and quark-gluon plasma creation in ultrarelativistic heavy-ion collisions. It is assumed that the highly Lorentz contracted nuclei are decelerated by the coherent color field which is formed between them after they pass through each other. This process continues until the field is neutralized by the Schwinger mechanism. Conservation of energy and momentum allow us to calculate the energy losses of the nuclear slabs and the initial energy density of the quark-gluon plasma.
We consider a Euclidean extension of the wedge form of Hamiltonian dynamics, which explicitly accounts for the strong localization of the first interaction in nuclear collisions. A new principle of the analytic continuation via the tetrad vector is introduced. We discover the existence of self-dual solutions with short life-times (ephemerons) and conjecture that these vacuum fluctuations can lower the Euclidean action of the system of the colliding nuclei, thus enforcing a breakdown of the nuclei coherence. We suggest that the ephemerons can be identified with the gluons-partons, which are res…
We show that the boost variable, the conjugate to the coordinate rapidity, which is associated with the center-of-mass motion, encodes the information about the finite size of colliding nuclei in a Lorentz-invariant way. The quasi-elastic forward color-changing scattering between the quantum boost states rapidly grows with the total energy of the collision and leads to an active breakdown of the color coherence at the earliest moments of the collision. The possible physical implications of this result are discussed.
Explicit formulas which describe muon pair production in reaction $γν\to μ^+ μ^- ν$ through neutrino magnetic moment are obtained and used to derive in the leading approximation cross section of muon pair production in $νN$-scattering due to neutrino magnetic moment. This cross section appears to be proportional to $\log^4 E_ν$. Comparison with experimental data on tridents production provides an upper bound $μ_{ν_μ} < 4*10^{-8} μ_B$, which is approximately two orders of magnitude weaker than that from $ν_μe$ elastic scattering data.
Dispersion theory of nucleon (nucleus) Compton scattering spin polarizabilities and quasi-optical $γ$-ray polarization plane rotation and birefringence effect in a matter with polarized protons (nuclei)
We argue that the classical evolution of small x modes in the collision of two ultrarelativistic nuclei is described on a transverse lattice by the Kogut--Susskind Hamiltonian in 2+1-dimensions coupled to an adjoint scalar field. The initial conditions for the evolution are provided by the non--Abelian Weizsäcker--Williams fields which constitute the classical parton distributions in each of the nuclei. We outline how lattice techniques developed for real time simulations of field theories in thermal equilibrium can be used to study non--perturbatively, thermalization and classical gluon radia…
The classical Yang-Mills equations are solved perturbatively in covariant gauge for a collision of two ultrarelativistic nuclei. The nuclei are taken as ensembles of classical color charges on eikonal trajectories. The classical gluon field is computed in coordinate space up to cubic order in the coupling constant g. We construct the Feynman diagrams corresponding to this field and show the equivalence of the classical and diagrammatic approaches. An argument is given which demonstrates that at higher orders in g the classical description of the process breaks down. As an application, we calcu…
Basing on model concepts we research the monojet-to-dijet ratio as a function of the jet energy detection threshold in ultrarelativistic collisions of nuclei. We provide an comparative analysis of the contribution to monojet yield from gluon radiation before initial hard parton-parton scattering and from non-symmetric dijet energy losses in quark-gluon plasma, which expected to be created in ultrarelativistic heavy ion collisions.
Using the quasiclassical Green's function in the Coulomb field, we analyze the probabilities of single and multiple $e^+e^-$-pair production at fixed impact parameter $b$ between colliding ultrarelativistic heavy nuclei. We perform calculations in the Born approximation with respect to the parameter $Z_Bα$, and exactly in $Z_Aα$, $Z_{A}$ and $Z_{B}$ are the charge numbers of the corresponding nuclei. We also obtain the approximate formulas for the probabilities valid for $Z_Aα, Z_Bα\lesssim 1$.
The mean transverse momentum in high energy nuclear collisions is studied. The formation of a Color Glass Condensate results in an increase of the square of the mean transverse momentum with the charged multiplicity per unit rapidity and unit transverse area. This prediction is in agreement with the presently available data, in particular with the heavy-ion data, lending support to the notion that the transverse momentum spectra in ultrarelativistic collisions of heavy nuclei might be controlled by intrinsic transverse momentum broadening and not by hadronic rescattering, i.e. transverse flow.
Some recent experimental results obtained in collisions of heavy nuclei ($\sqrt{s}=200$ GeV) at BNL Relativistic Heavy-Ion Collider (RHIC) are discussed. The probes of dense matter created in heavy-ion collision by quarkonia, $D$ and $B$ mesons containing heavy charm and beauty quarks are considered. The centrality, rapidity and transverse momentum dependences of the nuclear modification factor and elliptic flow coefficient are presented and their possible theoretical interpretation is provided.
It is assumed that strong chromofields are generated at early stages of ultrarelativistic heavy-ion collisions which give rise to a collective deceleration of net baryons from colliding nuclei. We have solved classical equations of motion for baryonic slabs under the action of a time-dependent longitudinal chromoelectric field. It is demonstrated that the slab final rapidities are rather sensitive to the strength and decay time of the chromofield as well as to the back reaction of the produced partonic plasma. The net-baryon rapidity loss of about 2 units, found for most central Au-Au collisio…
The Coulomb corrections to the cross section of $e^+e^-$ pair production in ultrarelativistic nuclear collisions are calculated in the next-to-leading approximation with respect to the parameter $L=\ln γ_Aγ_B$ ($γ_{A,B}$ are the Lorentz factors of colliding nuclei). We found considerable reduction of the Coulomb corrections even for large $γ_Aγ_B$ due to the suppression of the production of $e^+e^-$ pair with the total energy of the order of a few electron masses in the rest frame of one of the nuclei. Our result explains why the deviation from the Born result were not observed in the experime…
The process of resonant spontaneous bremsstrahlung radiation during the scattering of ultrarelativistic electrons with energies of the order $\sim 100\ \text{GeV}$ by the nuclei in strong laser fields with intensities up to $I\sim {{10}^{24}}\ \text{Wc}{\text{m}^{\text{-2}}}$ is theoretically studied. Under resonant conditions, an intermediate electron in the wave field enters the mass shell. As a result, the initial second-order process by the fine structure constant is effectively reduced to two first-order processes: laser-stimulated Compton effect and laser-assisted Mott process. The reson…
We present a new approach for calculating electromagnetic excitation of nuclei as well as probabilities of emission and distributions of neutrons from decays of excited nuclear systems for ultrarelativistic, ultraperipheral heavy ion collisions. Excitation functions for $γ$ + Pb $\to$ Pb$^*$ are parametrized using physics-motivated components: excitation of giant resonances, quasi-deuteron absorption mechanism, excitation of nucleon resonances as well as high-energy dissociation of protons and neutrons. Neutron emission (up to 10 neutrons) from low-energy excitations of $^{208}$Pb is modelled …
At the colliders RHIC and LHC, nuclei at the ultrarelativistic energies of $100$ GeV/A and $2.7$ TeV/A will be smashed together with the hope of creating an elusive and short-lived state of matter called the quark gluon plasma. The initial conditions which determine the dynamical evolution of the quark gluon matter formed in the central region after the collision depend crucially on the small $x$ component of the nuclear wavefunction before the collision. In this comment, we discuss recent work which argues that, for large nuclei, weak coupling techniques in QCD can be used to calculate the di…
We extend previous work on high energy nuclear collisions in the Color Glass Condensate model to study collisions of finite ultrarelativistic nuclei. The changes implemented include a) imposition of color neutrality at the nucleon level and b) realistic nuclear matter distributions of finite nuclei. The saturation scale characterizing the fields of color charge is explicitly position dependent, $Λ_s=Λ_s(x_T)$. We compute gluon distributions both before and after the collisions. The gluon distribution in the nuclear wavefunction before the collision is significantly suppressed below the saturat…
We construct an analytical expression for the distribution of gluons in the state immediately following a heavy ion collision in the quasi-classical limit of QCD given by McLerran-Venugopalan model. The resulting gluon number distribution function includes the effects of all multiple rescatterings of gluons with the nucleons of both colliding nuclei. The typical transverse momentum k of the produced gluons is shown to be of the order of the saturation scale of the nuclei Qs, as predicted by Mueller. We analyze the properties of the obtained distribution and demonstrate that due to multiple res…
Hydrodynamical analysis of experimental data of ultrarelativistic heavy ion collisions seems to indicate that the hot QCD matter created in the collisions thermalizes very quickly. Theoretically, we have no idea why this should be true. In this proceeding, I will describe how the thermalization takes place in the most theoretically clean limit -- that of large nuclei at asymptotically high energy per nucleon, where the system is described by weak-coupling QCD. In this limit, plasma instabilities dominate the dynamics from immediately after the collision until well after the plasma becomes near…
We suggest that the ultrarelativistic collisions of heavy ions provide the simplest situation for the study of strong interactions which can be understood from first principles and without any model assumptions about the microscopic structure of the colliding nuclei. We argue that the boost-invariant geometry of the collision, and the existence of hard partons in the final states, both supported by the data, make a sufficient basis for the quantum theory of the phenomenon. We conclude that the quantum nature of the entire process is defined by its global geometry, which is enforced by a macros…
We study coherent Coulomb excitation of ultrarelativistic nuclei passing through the aligned crystal target. We develop multiple scattering theory description of this process which consistently incorporates both the specific resonant properties of particle-crystal interactions and the shadowing effect typical of the diffractive scattering. We emphasise that the effect of quantum mechanical diffraction makes the physics of ultrarelativistic nuclear excitations entirely different from the physics of non-relativistic atomic excitations experimentally studied so far. It is found that at small tran…
The production of $J/Ψ$ mesons in central collisions of heavy nuclei is investigated as a function of collision energy. Two contributions are considered simultaneously: early (hard) production coupled with subsequent suppression in a Quark-Gluon Plasma, as well as thermal recombination of primordially produced $c$ and $\bar c$ quarks at the hadronization transition. Whereas the former still constitutes the major fraction of the observed $J/Ψ$ abundance at SpS energies, the latter dominates the yield at RHIC. The resulting excitation function for the number of $J/Ψ$'s over open charm pairs exhi…
Monopole-antimonopole pairs connected by strings and monopole-string networks with $N>2$ strings attached to each monopole can be formed at phase transitions in the early universe. In such hybrid defects, monopoles accelerate under the string tension and can reach ultrarelativistic Lorentz factors, $γ\gg 1$. We study the radiation of gauge quanta by accelerating monopoles. For monopoles with a chromomagnetic charge, we also discuss the high-energy hadron production through emission of virtual gluons and their subsequent fragmentation into hadrons. The relevant parameter for gauge boson radiati…
We employ the Weizsaecker-Williams method of virtual quanta to study disintegration of nuclei in magnetic field. We explore a variety of field configurations and conclude that for the energy range of interest for applications to cosmic rays (10^{18}-10^{21} eV) such disintegrations are not a significant source of energy or flux loss for any realistic acceleration mechanism.
We review a consistent description of the fusion and saturation of partons in the Lorentz-contracted ultrarelativistic nuclei in terms of a nuclear attenuation of color dipole states of the photon and collective Weizsäcker-Williams (WW) gluon structure function of a nucleus. Diffractive DIS provides a basis for the definition of the WW nuclear glue. The point that all observables for DIS off nuclei are uniquely calculable in terms of the nuclear WW glue amounts to a new form of factorization in the saturation regime.
We review the physics of nuclear matter at high energy density and the experimental search for the Quark-Gluon Plasma at the Relativistic Heavy Ion Collider (RHIC). The data obtained in the first three years of the RHIC physics program provide several lines of evidence that a novel state of matter has been created in the most violent, head-on collisions of $Au$ nuclei at $\sqrt{s}=200$ GeV. Jet quenching and global measurements show that the initial energy density of the strongly interacting medium generated in the collision is about two orders of magnitude larger than that of cold nuclear mat…
The creation of loosely bound objects in heavy ion collisions, e.g. light clusters, near the phase transition temperature $\left(T_{\rm ch} \approx 155 \, \rm{MeV} \right)$ has been a puzzling observation that seems to be at odds with Big Bang nucleosynthesis suggesting that deuterons and other clusters are formed only below a temperature $T\approx 0.1-1 \, \text{MeV}$. We solve this puzzle by showing that the light cluster abundancies in heavy ion reactions stay approximately constant from chemical freeze-out to kinetic freeze-out. To this aim we develop an extensive network of coupled reacti…
Collisions between heavy atomic nuclei at ultra-relativistic energies are carried out at particle colliders to produce the quark-gluon plasma, a state of matter where quarks and gluons are not confined into hadrons, and colour degrees of freedom are liberated. This state is thought to be produced as a transient phenomenon before it fragments into thousands of particles that reach the particle detectors. Despite two decades of investigations, one of the big open questions is to obtain an experimental determination of the temperature reached in a heavy-ion collision, and a simultaneous determina…
We consider the production of ultrarelativistic positronium (Ps) in $γA \to Ps + A$ and $e A \to Ps + e A$ processes where $A$ is an atom or a nucleus with charge $Ze$. For the photoproduction of para- and ortho-Ps and the electroproduction of para-Ps we obtain the most complete description compared with previous works. It includes high order $Z α$ corrections and polarization effects. The accuracy of the obtained cross sections is determined by omitted terms of the order of the inverse Ps Lorentz factor squared. The studied high order multi-photon electroproduction of ortho-Ps dominates for t…
The initial energy density produced in an ultrarelativistic heavy ion collision can, in the color glass condensate framework, be factorized into a product of the integrated gluon distributions of the nuclei. Although this energy density is well defined without any infrared cutoff besides the saturation scale, it is apparently logarithmically ultraviolet divergent. We argue that this divergence is not physically meaningful and does not affect the behavior of the system at any finite proper time.
Using a Thomas-Fermi model, we calculate the structure of the electrosphere of the quark antimatter nuggets postulated to comprise much of the dark matter. This provides a single self-consistent density profile from ultrarelativistic densities to the nonrelativistic Boltzmann regime that use to present microscopically justified calculations of several properties of the nuggets, including their net charge, and the ratio of MeV to 511 keV emissions from electron annihilation. We find that the calculated parameters agree with previous phenomenological estimates based on the observational supposit…
We discuss potential attainability by the Hanbury Brown and Twiss (HBT) interferometry of photons to probe the spacetime geometry of the primordial plasma created by ultrarelativistic heavy-ion collisions. A possible effect to distort the HBT image is due to an interaction between emitted photon and an extremely strong magnetic field induced by the colliding heavy nuclei in the peripheral collisions. We examine the effects of variation of the refraction index in the strong magnetic field that is called the vacuum birefringence.
Radiation reaction is the influence of the electromagnetic field emitted by a charged particle on the dynamics of the particle itself. Here we report experimental radiation emission spectra from ultrarelativistic positrons in silicon in a regime where both quantum and radiation-reaction effects dominate the dynamics of the positrons. We found that each positron emits multiple photons with energy comparable to its own energy, revealing the importance of quantum photon recoil. Moreover, the shape of the emission spectra indicates that photon emissions occur in a nonlinear regime where positrons …
