159 research outputs found
Forward particle production in proton-nucleus collisions at next-to-leading order
We consider the next-to-leading order (NLO) calculation of single inclusive
particle production at forward rapidities in proton-nucleus collisions and in
the framework of the Color Glass Condensate (CGC). We focus on the quark
channel and the corrections associated with the impact factor. In the first
step of the evolution the kinematics of the emitted gluon is kept exactly (and
not in the eikonal approximation), but such a treatment which includes NLO
corrections is not explicitly separated from the high energy evolution. Thus,
in this newly established "factorization scheme", there is no "rapidity
subtraction". The latter suffers from fine tuning issues and eventually leads
to an unphysical (negative) cross section. On the contrary, our reorganization
of the perturbation theory leads by definition to a well-defined cross section
and the numerical evaluation of the NLO correction is shown to have the correct
size.Comment: 7 pages, 5 figures, based on talk given at QCD@Work, 25-28 June 2018,
Matera, Ital
Multi-gluon correlations in the Color Glass Condensate
The Color Glass Condensate is a universal state of matter which can manifest
itself in hadronic processes involving small-x partons, like DIS and pp, pA and
AA collisions at high energy. Observables are given in terms of multi-gluon
correlators, whose ensemble evolves according to a RG equation, the JIMWLK
equation. We focus on recent progress towards its solution which lead to
quasi-exact, analytic expressions for the multi-gluon correlators at high
energy.Comment: 4 pages, 3 figures, based on talk given at Hard Probes 2012, 27 May -
1 Jun 2012, Cagliari, Ital
JIMWLK evolution for multi-particle production with rapidity correlations
We study multi-particle production with rapidity correlations in
proton-nucleus collisions at high energy in the Color Glass Condensate
framework. The high-energy evolution responsible for such correlations is
governed by a generalization of the JIMWLK equation describing the simultaneous
evolution of the strong nuclear color fields in the direct amplitude and the
complex conjugate amplitude. This functional equation can be used to derive
ordinary evolution equations for the cross-sections for particle production,
but the ensuing equations appear to be too complicated to be useful in
practice, including in the limit of a large number of colors Nc. We propose an
alternative formulation based on a Langevin process, which is valid for generic
Nc and is better suited for numerical implementations. For illustration, we
present the stochastic equations which govern two gluon production with
arbitrary rapidity separation.Comment: 8 pages, 6 figures, based on talk given at IS 2013, 8 - 14 Sep 2013,
Illa da Toxa, Spai
JIMWLK evolution: from color charges to rapidity correlations
We study multi-particle production with rapidity correlations in high-energy
p+A collisions. In the context of the Color Glass Condensate, the evolution for
such correlations is governed by a generalization of the JIMWLK equation which
evolves the strong nuclear fields both in the amplitude and in the complex
conjugate one. We give the equivalent Langevin formulation, whose main
ingredient is the color charge density linked to a projectile parton (a Wilson
line).Comment: 4 pages, 2 figures, based on talk given at Hard Probes 2013, 4 - 8
Nov 2013, Cape Town, South Afric
Running coupling effects in the evolution of jet quenching
We study the consequences of including the running of the QCD coupling in the
equation describing the evolution of the jet quenching parameter in
the double logarithmic approximation. To start with, we revisit the case of a
fixed coupling, for which we obtain exact solutions valid for generic values of
the transverse momentum (above the medium saturation scale) and corresponding
to various initial conditions. In the case of a running coupling, we construct
approximate solutions in the form of truncated series obtained via successive
iterations, whose convergence is well under control. We thus deduce the
dominant asymptotic behavior of the renormalized in the limit of a
large evolution time , with the size of the medium
and the typical wavelength of a medium constituent. We show that the
asymptotic expansion is universal with respect to the choice of the initial
condition at and, moreover, it is remarkably similar to the corresponding
expansion for the saturation momentum of a shockwave (a large nucleus). As
expected, the running of the coupling significantly slows down the increase of
with in the asymptotic regime at . For the
phenomenologically interesting value , we find an enhancement factor
close to 3, independently of the initial condition and for both fixed and
running coupling.Comment: 25 pages, 5 figure
JIMWLK evolution for multi-particle production in Langevin form
Within the effective theory for the Color Glass Condensate, we study
multi-particle production with rapidity correlations in proton-nucleus
collisions at high energy. The high-energy evolution responsible for such
correlations is governed by a generalization of the JIMWLK equation which
describes the simultaneous evolution of the (strong) nuclear color fields in
the direct amplitude and the complex conjugate amplitude. This functional
equation can be used to derive ordinary evolution equations for the
cross-sections for particle production (a generalization of the Balitsky
hierarchy). However, the ensuing equations appear to be too complicated to be
useful in practice, including in the limit where the number of colors is large.
To circumvent this problem, we propose an alternative formulation of the
high-energy evolution as a Langevin process, which is better suited for
numerical implementations. This process is directly oriented towards the
calculation of the cross-sections, so its detailed structure depends upon the
nature of the final state. We present the stochastic equations appropriate for
two gluon production, and also for three gluon production, with generic
rapidity differences.Comment: 28 pages, 5 figure
General specifications for the development of a PC-based simulator of the NASA RECON system
The general specifications for the design and implementation of an IBM PC/XT-based simulator of the NASA RECON system, including record designs, file structure designs, command language analysis, program design issues, error recovery considerations, and usage monitoring facilities are discussed. Once implemented, such a simulator will be utilized to evaluate the effectiveness of simulated information system access in addition to actual system usage as part of the total educational programs being developed within the NASA contract
KARL: A Knowledge-Assisted Retrieval Language
Data classification and storage are tasks typically performed by application specialists. In contrast, information users are primarily non-computer specialists who use information in their decision-making and other activities. Interaction efficiency between such users and the computer is often reduced by machine requirements and resulting user reluctance to use the system. This thesis examines the problems associated with information retrieval for non-computer specialist users, and proposes a method for communicating in restricted English that uses knowledge of the entities involved, relationships between entities, and basic English language syntax and semantics to translate the user requests into formal queries. The proposed method includes an intelligent dictionary, syntax and semantic verifiers, and a formal query generator. In addition, the proposed system has a learning capability that can improve portability and performance. With the increasing demand for efficient human-machine communication, the significance of this thesis becomes apparent. As human resources become more valuable, software systems that will assist in improving the human-machine interface will be needed and research addressing new solutions will be of utmost importance. This thesis presents an initial design and implementation as a foundation for further research and development into the emerging field of natural language database query systems
Testing the Gaussian Approximation to the JIMWLK Equation
In processes involving small-x partons, like in deep inelastic scattering and
in hadronic collisions at high energy, the final state can be expressed in
terms of correlators of Wilson lines. We study such high-point correlators
evolving according to the JIMWLK equation and we confirm the results of
previous numerical and analytic work, by using an independent method, that the
solution to the JIMWLK equation can be very well approximated by an appropriate
Gaussian wavefunction. We explore both fixed and running coupling evolution,
where in the latter the scale is set according to various prescriptions. As a
byproduct, we also numerically confirm to high accuracy the validity of the law
governing the behavior of the S-matrix close to the unitarity limit, the
Levin-Tuchin formula. We furthermore outline how to calculate correlators with
open color indices.Comment: 25 pages, 11 figures. v2: minor corrections, one equation added,
updated to match published versio
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