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Title: Nonuniversality Aspects of Nonlinear k{sub perpendicular} Factorization for Hard Dijets

Abstract

The origin of breaking of conventional linear k{sub perpendicular} factorization for hard processes in a nuclear environment is by now well established. The realization of the nonlinear nuclear k{sub perpendicular} factorization which emerges instead was found to change from one jet observable to another. Here we demonstrate how the pattern of nonlinear k{sub perpendicular} factorization, and especially the role of diffractive interactions, in the production of dijets off nuclei depends on the color properties of the underlying pQCD subprocess.

Authors:
 [1];  [2];  [1];  [3];  [4]
  1. Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich (Germany)
  2. (Russian Federation)
  3. L.D. Landau Institute for Theoretical Physics, Moscow 117940 (Russian Federation)
  4. (Germany)
Publication Date:
OSTI Identifier:
20699603
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 95; Journal Issue: 22; Other Information: DOI: 10.1103/PhysRevLett.95.221803; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COLOR MODEL; FACTORIZATION; INTERACTIONS; NONLINEAR PROBLEMS; QUANTUM CHROMODYNAMICS

Citation Formats

Nikolaev, N.N., L.D. Landau Institute for Theoretical Physics, Moscow 117940, Schaefer, W., Zakharov, B.G., and Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich. Nonuniversality Aspects of Nonlinear k{sub perpendicular} Factorization for Hard Dijets. United States: N. p., 2005. Web. doi:10.1103/PhysRevLett.95.221803.
Nikolaev, N.N., L.D. Landau Institute for Theoretical Physics, Moscow 117940, Schaefer, W., Zakharov, B.G., & Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich. Nonuniversality Aspects of Nonlinear k{sub perpendicular} Factorization for Hard Dijets. United States. doi:10.1103/PhysRevLett.95.221803.
Nikolaev, N.N., L.D. Landau Institute for Theoretical Physics, Moscow 117940, Schaefer, W., Zakharov, B.G., and Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich. Fri . "Nonuniversality Aspects of Nonlinear k{sub perpendicular} Factorization for Hard Dijets". United States. doi:10.1103/PhysRevLett.95.221803.
@article{osti_20699603,
title = {Nonuniversality Aspects of Nonlinear k{sub perpendicular} Factorization for Hard Dijets},
author = {Nikolaev, N.N. and L.D. Landau Institute for Theoretical Physics, Moscow 117940 and Schaefer, W. and Zakharov, B.G. and Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich},
abstractNote = {The origin of breaking of conventional linear k{sub perpendicular} factorization for hard processes in a nuclear environment is by now well established. The realization of the nonlinear nuclear k{sub perpendicular} factorization which emerges instead was found to change from one jet observable to another. Here we demonstrate how the pattern of nonlinear k{sub perpendicular} factorization, and especially the role of diffractive interactions, in the production of dijets off nuclei depends on the color properties of the underlying pQCD subprocess.},
doi = {10.1103/PhysRevLett.95.221803},
journal = {Physical Review Letters},
number = 22,
volume = 95,
place = {United States},
year = {Fri Nov 25 00:00:00 EST 2005},
month = {Fri Nov 25 00:00:00 EST 2005}
}
  • Based on an approach to non-Abelian propagation of color dipoles in a nuclear medium, we formulate a nonlinear k{sub perpendicular} factorization for the breakup of photons and pions into forward hard dijets in terms of the collective Weizsaecker-Williams glue of nuclei. We find quite distinct practical consequences of nonlinear nuclear k{sub perpendicular} factorization for interactions of pointlike photons and nonpointlike pions. In the former case, the large transverse momentum p{sub perpendicular} of jets comes from the intrinsic momentum of quarks and antiquarks in the photon, and nuclear effects manifest themselves as an azimuthal decorrelation with an acoplanarity momentum of themore » order of the nuclear saturation momentum Q{sub A}. In the breakup of pions off free nucleons to the leading order in pQCD, the spectator parton has a small transverse momentum and the hard dijet cross section is suppressed. In the breakup of pions off heavy nuclei, the forward hard jets are predicted to be entirely decorrelated. We comment on the sensitivity of the pionic dijet cross section to the pion distribution amplitude. The predicted distinction between the breakup of photons and pions can be tested by the sphericity and thrust analysis of the forward hadronic system in the COMPASS experiment at CERN.« less
  • The origin of the breaking of conventional linear k{sub perpendicular} factorization for hard processes in a nuclear environment is by now well established. The realization of the nonlinear nuclear k{sub perpendicular} factorization which emerges instead was found to change from one jet observable to another. A basic ingredient of the master formula for the dijet spectrum is the S matrix for color-singlet multiparton states, and here we report on an important technical progress, the evaluation of the four-gluon color-dipole cross section operator. It describes the coupled seven-channel non-Abelian intranuclear evolution of the four-gluon color-singlet states. An exact diagonalization of thismore » seven-channel problem is possible for large number of colors N{sub c} and allows a formulation of nonlinear k{sub perpendicular} factorization for production of gluon-gluon dijets. The momentum spectra for dijets in all possible color representations are reported in the form of explicit quadratures in terms of the collective nuclear unintegrated glue. Our results fully corroborate the concept of universality classes.« less
  • At the partonic level, a typical final state in small-x deep inelastic scattering off nuclei and hard proton-nucleus collisions can be characterized by the multiplicity of color-excited nucleons. Within the Reggeon field theory, each color-excited nucleon is associated with the unitarity cut of the Pomeron exchanged between the projectile and nucleus. In this communication we derive the unitarity rules for the multiplicity of excited nucleons, alias cut pomerons, alias topological cross sections, for typical hard dijet production processes. We demonstrate how the coupled-channel non-Abelian intranuclear evolution of color dipoles, inherent to pQCD, gives rise to the Reggeon field theory diagramsmore » for final states in terms of the uncut, and two kinds of cut, Pomerons. Upon the proper identification of the uncut and cut-Pomeron exchanges, the topological cross sections for dijet production follow in a straightforward way from the earlier derived nonlinear k{sub perpendicular} factorization quadratures for the inclusive dijet cross sections. The concept of a coherent (collective) nuclear glue proves extremely useful for the formulation of the Reggeon field theory vertices of multi-Pomeron--cut and uncut--couplings to particles and between themselves. A departure of our unitarity cutting rules from the ones suggested by the pre-QCD Abramovsky-Kancheli-Gribov rules, stems from the coupled-channel features of non-Abelian intranuclear pQCD. We propose a multiplicity resummation as a tool for the isolation of topological cross sections for single-jet production.« less
  • We review the origin, and salient features, of the breaking of the conventional linear k perpendicular-factorization for hard processes in a nuclear environment. A realization of the nonlinear k perpendicular-factorization which emerges instead is shown to depend on color properties of the underlying pQCD subprocesses. We discuss the emerging universality classes and extend nonlinear k perpendicular-factorization to AGK unitarity rules for the excitation of the target nucleus.
  • The breaking of conventional linear k{sub perpendicular} factorization for hard processes in a nuclear environment is by now well established. Here we report a detailed derivation of the nonlinear k{sub perpendicular}-factorization relations for the production of quark-gluon dijets. This process is the dominant source of dijets in the proton hemisphere of proton-nucleus collisions at energies of the relativistic heavy ion collider (RHIC). The major technical problem is a consistent description of the non-Abelian intranuclear evolution of multiparton systems of color dipoles. Following the technique developed in our early work [N. N. Nikolaev, W. Schaefer, B. G. Zakharov, and V. R.more » Zoller, J. Exp. Theor. Phys. 97, 441 (2003)], we reduce the description of the intranuclear evolution of the qggq state to the 3x3 system of coupled equations in the space of color-singlet 4-parton states |33>, |66>, and vertical bar 1515> (and their large-N{sub c} generalizations). At large number of colors N{sub c}, the eigenstate (vertical bar 66>- vertical bar 1515>)/{radical}(2) decouples from the initial state vertical bar 33>. The resulting nuclear distortions of the dijet spectrum exhibit much similarity to those found earlier for forward dijets in deep inelastic scattering. Still there are certain distinctions regarding the contribution from color-triplet qg final states and from coherent diffraction excitation of dijets. To the large-N{sub c} approximation, we identify four universality classes of nonlinear k{sub perpendicular} factorization for hard dijet production.« less