arXiv subjects
Publications and source records attributed to T. Lappi.
We calculate proton and nuclear diffractive structure functions in the IPsat (Kowalski-Teaney) dipole model. This parametrization has previously been shown to provide good agreement with inclusive F_2 measurements and exclusive vector meson measurements at HERA. We discuss how the impact parameter dependence crucially affects our analysis, in particular for small beta.
The Color Glass Condensate is an effective theory description for the small momentum fraction x degrees of freedom in a high energy hadron or nucleus, which can be understood in terms of strong classical gluon fields. We discuss the resulting picture of the initial conditions in a relativistic heavy ion collision. We describe recent work to show that the leading logarithms of the collision energy can be factorized into the renormalization group evolution of the small x wavefunction. We then describe how this framework can be used to understand the long range rapidity correlations observed by the RHIC experiments.
We obtain a novel result in QCD for long range rapidity correlations between gluons produced in the collision of saturated high energy hadrons or nuclei. This result, obtained in a high energy factorization framework, provides strong justification for the Glasma flux tube picture of coherent strong color fields. Our formalism can be applied to "near side ridge" events at RHIC and in future studies of long range rapidity correlations at the LHC.
This is a short review of some RHIC results that have been most important for the small x physics community. We discuss saturation effects in deuteron-gold collisions, particle production in gold-gold collisions and some effects of the large "glasma" field configurations in the early stages of the collision.
The Color Glass Condensate (CGC), describing the physics of the nonlinear gluonic interactions of QCD at high energy, provides a consistent first-principles framework to understand the initial conditions of heavy ion collisions. This talk reviews some aspects of the initial conditions at RHIC and discusses implications for LHC heavy ion phenomenology. The CGC provides a way compute bulk particle production and understand recent experimental observations of long range rapidity correlations in terms of the classical glasma field in the early stages of the collision.
We review recent work on understanding the next to leading order corrections to the classical fields that dominate the initial stages of a heavy ion collision. We have recently shown that the leading ln(1/x) divergences of these corrections to gluon multiplicities can be factorized into the JIMWLK evolution of the color charge density distributions.
We compute diffractive structure functions for both protons and nuclei in the framework of Color Glass Condensate models with impact parameter dependence. These models have previously been shown to provide good agreement with inclusive F_2 measurements and exclusive vector meson measurements at HERA. For nuclei, they provide good (parameter free) agreement with the inclusive F_2 data. We demonstrate good agreement of our computations with HERA measurements on inclusive diffraction. We extend our analysis to nuclei and predict the pattern of enhancement and suppression of the diffractive structures functions that can be measured at an Electron Ion Collider. We discuss how the impact parameter dependence crucially affects our analysis, in particular for large invariant masses at fixed Q^2.
We extend previous results (arXiv:0804.2630 [hep-ph]) on factorization in high-energy nucleus-nucleus collisions by computing the inclusive multigluon spectrum to next-to-leading order. The factorization formula is strictly valid for multigluon emission in a slice of rapidity of width ΔY< 1/α_s. Our results show that often neglected disconnected graphs dominate the inclusive multigluon spectrum and are essential to prove factorization for this quantity. These results provide a dynamical framework for the Glasma flux tube picture of the striking "ridge"-like correlation seen in heavy ion collisions.
A future high-energy electron-ion collider would explore the non-linear weakly-coupled regime of QCD, and test the Color Glass Condensate (CGC) approach to high-energy scattering. Hard diffraction in deep inelastic scattering off nuclei will provide many fundamental measurements. In this work, the nuclear diffractive structure function F_{2,A}^D is predicted in the CGC framework, and the features of nuclear enhancement and suppression are discussed.
We present results from numerical Classical Yang Mills calculations of the initial stage Glasma field configurations in a relativistic heavy ion collision. We compute the initial gluon multiplicity from RHIC to LHC energies. The initial conditions for the classical field computation are taken from a dipole model parametrization tested on HERA data, meaning that all the parameters, including the normalization and the value of the saturation scale, are fixed from DIS data.
In the color glass condensate framework the saturation scale measured in deep inelastic scattering of high energy hadrons and nuclei can be determined from the correlator of Wilson lines in the hadron wavefunction. These same Wilson lines give the initial condition of the classical field computation of the initial gluon multiplicity and energy density in a heavy ion collision. In this paper the Wilson line correlator in both adjoint and fundamental representations is computed using exactly the same numerical procedure that has been used to calculate gluon production in a heavy ion collision. In particular the discretization of the longitudinal coordinate has a large numerical effect on the relation between the color charge density parameter g^2 mu and the saturation scale Qs. Our result for this relation is Qs = 0.6 g^2 mu, which results in the classical Yang-Mills value for the "gluon liberation coefficient" c = 1.1.
We show that the enhancement of the saturation scale in large nuclei relative to the proton is significantly influenced by the effects of quantum evolution and the impact parameter dependence of dipole cross sections in high energy QCD. We demonstrate that there is a strong A dependence in diffractive deeply inelastic scattering and discuss its sensitivity to the measurement of the recoil nucleus.
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.
Recent estimates that Color Glass Condensate initial conditions may generate a larger initial eccentricity for noncentral relativistic heavy ion collisions (relative to the initial eccentricity assumed in earlier hydrodynamic calculations) have raised the possibility of a higher bound on the viscosity of the Quark Gluon Plasma. We show that this large initial eccentricity results in part from a definition of the saturation scale as proportional to the number of nucleons participating in the collision. A saturation scale proportional to the nuclear thickness function (and therefore independent of the probe) leads to a smaller eccentricity, albeit still larger than the value used in hydrodynamic models. Our results suggest that the early elliptic flow in heavy ion collisions (unlike multiplicity distributions) is sensitive to the universality of the saturation scale in high energy QCD.
The the initial stage of a relativistic heavy ion collision can be described by a classical color field configuration known as the Glasma. The production of quark pairs from this background field is then computed nonperturbatively by numerically solving the Dirac equation in the classical background. The result seems to point towards an early chemical equilibration of the plasma.
We discuss high energy hadronic collisions within the theory of the Color Glass Condensate. We point out that the initial electric and magnetic fields produced in such collisions are longitudinal. This leads to a novel string like description of the collisions, and a large Chern-Simons charge density made immediately after the collision. The presence of the longitudinal magnetic field suggests that essential to the description of these collisions is the decay of Chern-Simons charge.
We compute by numerical integration of the Dirac equation the number of quark-antiquark pairs initially produced in the classical color fields of colliding ultrarelativistic nuclei. While the number of qqbar pairs is parametrically suppressed in the coupling constant, we find that in this classical field model their production rate is comparable to the thermal ratio of gluons/pairs = 9 N_f/32. After isotropization one thus would have quark-gluon plasma in chemical equilibrium.
We compute by numerical integration of the Dirac equation the number of quark-antiquark pairs produced in the classical color fields of colliding ultrarelativistic nuclei. Results for the dependence of the number of quarks on the strength of the background field, the quark mass and time are presented. We also perform several tests of our numerical method. While the number of qqbar pairs is parametrically suppressed in the coupling constant, we find that in this classical field model it could even be compatible with the thermal ratio to the number of gluons.