963 research outputs found
Eigenmodes of Decay and Discrete Fragmentation Processes
Linear rate equations are used to describe the cascading decay of an initial
heavy cluster into fragments. This representation is based upon a triangular
matrix of transition rates. We expand the state vector of mass multiplicities,
which describes the process, into the biorthonormal basis of eigenmodes
provided by the triangular matrix. When the transition rates have a scaling
property in terms of mass ratios at binary fragmentation vertices, we obtain
solvable models with explicit mathematical properties for the eigenmodes. A
suitable continuous limit provides an interpolation between the solvable
models. It gives a general relationship between the decay products and the
elementary transition rates.Comment: 6 pages, plain TEX, 2 figures available from the author
Higher twist jet broadening and classical propagation
The transverse broadening of jets produced in deep-inelastic scattering (DIS)
off a large nucleus is studied in the collinear limit. A class of medium
enhanced higher twist corrections are re-summed to calculate the transverse
momentum distribution of the produced collinear jet. In contrast to previous
approaches, resummation of the leading length enhanced higher twist corrections
is shown to lead to a two dimensional diffusion equation for the transverse
momentum of the propagating jet. Results for the average transverse momentum
obtained from this approach are then compared to the broadening expected from a
classical Langevin analysis for the propagation of the jet under the action of
the fluctuating color Lorentz force inside the nucleons. The set of
approximations that lead to identical results from the two approaches are
outlined. The relationship between the momentum diffusion constant and the
transport coefficient is explicitly derived.Comment: 17 pages, 6 figures, revtex4, references added, typos corrected,
discussion update
Hard collinear gluon radiation and multiple scattering in a medium
The energy loss of hard jets produced in the Deep-Inelastic scattering (DIS)
off a large nucleus is considered in the collinear limit. In particular, the
single gluon emission cross section due to multiple scattering in the medium is
calculated. Calculations are carried out in the higher-twist scheme, which is
extended to include contributions from multiple transverse scatterings on both
the produced quark and the radiated gluon. The leading length enhanced parts of
these power suppressed contributions are resummed. Various interferences
between such diagrams lead to the Landau-Pomeranchuk-Migdal (LPM) effect. We
resum the corrections from an arbitrary number of scatterings and isolate the
leading contributions which are suppressed by one extra power of the hard scale
. All powers of the emitted gluon forward momentum fraction are
retained. We compare our results with the previous calculation of single
scattering per emission in the higher-twist scheme as well as with multiple
scattering resummations in other schemes. It is found that the leading
() contribution to the double differential gluon production cross
section, in this approach, is equivalent to that obtained from the single
scattering calculation once the transverse momentum of the final quark is
integrated out. We comment on the generalization of this formalism to
Monte-Carlo routines.Comment: 30 pages, 7 figures, revtex4, typos correcte
Photon bremsstrahlung and diffusive broadening of a hard jet
The photon bremsstrahlung rate from a quark jet produced in deep-inelastic
scattering (DIS) off a large nucleus is studied in the collinear limit. The
leading medium-enhanced higher twist corrections which describe the multiple
scattering of the jet in the nucleus are re-summed to all orders of twist. The
propagation of the jet in the absence of further radiative energy loss is shown
to be governed by a transverse momentum diffusion equation. We compute the
final photon spectrum in the limit of soft photons, taking into account the
leading and next-to-leading terms in the photon momentum fraction y. In this
limit, the photon spectrum in a physical gauge is shown to arise from two
interfering sources: one where the initial hard scattering produces an
off-shell quark which immediately radiates the photon and then undergoes
subsequent soft re-scattering; alternatively the quark is produced on-shell and
propagates through the medium until it is driven off-shell by re-scattering and
radiates the photon. Our result has a simple formal structure as a product of
the photon splitting function, the quark transverse momentum distribution
coming from a diffusion equation and a dimensionless factor which encodes the
effect of the interferences encountered by the propagating quark over the
length of the medium. The destructive nature of such interferences in the small
y limit are responsible for the origin of the Landau-Pomeranchuck-Migdal (LPM)
effect. Along the way we also discuss possible implications for quark jets in
hot nuclear matter.Comment: 24 pages, 3 figures, Revtex
Resolving the J/\psi RHIC puzzles at LHC
Experiments with gold-gold collisions at RHIC have revealed (i) stronger
suppression of charmonium production at forward rapidity than at midrapidity
and (ii) the similarity between the suppression degrees at RHIC and SPS
energies. To describe these findings we employ the model that includes nuclear
shadowing effects, calculated within the Glauber-Gribov theory,
rapidity-dependent absorptive mechanism, caused by energy-momentum
conservation, and dissociation and recombination of the charmonium due to
interaction with co-moving matter. The free parameters of the model are tuned
and fixed by comparison with experimental data at lower energies. A good
agreement with the RHIC results concerning the rapidity and centrality
distributions is obtained for both heavy Au+Au and light Cu+Cu colliding
system. For pA and A+A collisions at LHC the model predicts stronger
suppression of the charmonium and bottomonium yields in stark contrast to
thermal model predictions.Comment: SQM2008 proceedings, 6 page
Large distance behaviour of light cone operator product in perturbative and nonperturbative QCD regimes
We evaluate the coordinate space dependence of the matrix elements of the
commutator of the electromagnetic and gluon currents in the vicinity of the
light-cone but at large distances within the parton model, DGLAP, the
resummation approaches to the small x behaviour of DIS processes, and for the
Unitarity Bound. We find that an increase of the commutator with relative
distance as is the generic property of QCD
at small but fixed space-time interval in perturbative and
nonperturbative QCD regimes. We explain that the factor follows within the
dipole model (QCD factorization theorem) from the properties of Lorents
transformation. The increase of disappeares at central impact parameters
if cross section of DIS may achieve the Unitarity Limit. We argue that such
long range forces are hardly consistent with thermodynamic equilibrium while a
Unitarity Limit may signal equilibration. Possible implications of this new
long range interaction are briefly discussed.Comment: 23 page
Inclusive production in a QCD and N=4 SYM motivated model for soft interactions
The results presented in this paper differ from our previous unsuccessful
attempt to predict the rapidity distribution at . The original
version of our model (GLMM) only summed a particular class of Pomeron diagrams
(enhanced diagrams). We believe that this was the reason for our failure to
describe the inclusive LHC data. We have developed a new approach
(GLM) that also includes the summation of the semi-enhanced diagrams.This
contribution is essential for a successful description of the inclusive
distributions, which is presented here.Comment: 4 pages, 3 figure
Space-Time Evolution of Ultrarelativistic Quantum Dipoles in Quantum Electrodynamics
We discuss space-time evolution of ultrarelativistic quantum dipole in QED.
We show that the space-time evolution can be described, in a certain
approximation, by means of a regularized wave function, whose parameters are
determined by the process of the dipole creation by a local current. We derive
using these wave functions the dipole expansion law, that is found to coincide
parametrically in the leading order with the one suggested by Farrar,
Frankfurt,Liu and Strikman.Comment: 15 page
Double parton distributions in the leading logarithm approximation of perturbative QCD
Recent CDF measurements of the inclusive cross section for a double parton
scattering attach a great importance to any theoretical calculations of
two-particle distribution functions. Using a parton interpretation of the
leading logarithm diagrams of perturbative QCD theory, generalized
Lipatov-Altarelli-Parisi-Dokshitzer equations for the two-parton distributions
are re-obtained. The solutions of these equations are not at all the product of
two single-parton distributions what is usually applied to the current analysis
as ansatz.Comment: 8 pages, LaTe
Scaling laws for the elastic scattering amplitude
The partial differential equation for the imaginary part of the elastic
scattering amplitude is derived. It is solved in the black disk limit. The
asymptotical scaling behavior of the amplitude coinciding with the geometrical
scaling is proved. Its extension to preasymptotical region and modifications of
scaling laws for the differential cross section are considered.Comment: 6 p. arXiv admin note: substantial text overlap with arXiv:1206.547
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