1,529 research outputs found
Selected Topics in High Energy Semi-Exclusive Electro-Nuclear Reactions
We review the present status of the theory of high energy reactions with
semi-exclusive nucleon electro-production from nuclear targets. We demonstrate
how the increase of transferred energies in these reactions opens a complete
new window in studying the microscopic nuclear structure at small distances.
The simplifications in theoretical descriptions associated with the increase of
the energies are discussed. The theoretical framework for calculation of high
energy nuclear reactions based on the effective Feynman diagram rules is
described in details. The result of this approach is the generalized eikonal
approximation (GEA), which is reduced to Glauber approximation when nucleon
recoil is neglected. The method of GEA is demonstrated in the calculation of
high energy electro-disintegration of the deuteron and A=3 targets.
Subsequently we generalize the obtained formulae for A>3 nuclei. The relation
of GEA to the Glauber theory is analyzed. Then based on the GEA framework we
discuss some of the phenomena which can be studied in exclusive reactions,
these are: nuclear transparency and short-range correlations in nuclei. We
illustrate how light-cone dynamics of high-energy scattering emerge naturally
in high energy electro-nuclear reactions.Comment: LaTex file with 51 pages and 23 eps figure
Probing Short Range Nucleon Correlations in High Energy Hard Quasielastic pd Reactions
We show that the strong dependence of the amplitude for hard scattering
on the collision energy can be used to magnify the effects of short range
nucleon correlations in quasielastic scattering. Under specific
kinematical conditions the effect of initial and final state interactions can
be accounted for by rescaling the cross section calculated within the plane
wave impulse approximation. The feasibility to investigate the role of
relativistic effects in the deuteron wave function is demonstrated by comparing
the predictions of different formalisms. Binding effects due to short range
correlations in deuteron are discussed as well.Comment: 18 pages (LaTex) + 10 postscript figs (available on request
Feynman Graphs and Generalized Eikonal Approach to High Energy Knock-Out Processes
The cross section of hard semi-exclusive reactions for fixed
missing energy and momentum is calculated within the eikonal approximation.
Relativistic dynamics and kinematics of high energy processes are unambiguously
accounted for by using the analysis of appropriate Feynman diagrams. A
significant dependence of the final state interactions on the missing energy is
found, which is important for interpretation of forthcoming color transparency
experiments. A new, more stringent kinematic restriction on the region where
the contribution of short-range nucleon correlations is enhanced in
semi-exclusive knock-out processes is derived. It is also demonstrated that the
use of light-cone variables leads to a considerable simplification of the
description of high-energy knock-out reactions.Comment: 24 pages, LaTex, two Latex and two ps figures, uses FEYNMAN.tex and
psfig.sty. Revisied version to appear in Phys. Rev.
Nuclear Shadowing in the Structure Function
Nuclear modification of the structure function is investigated.
Although it could be estimated in the medium and large regions from the
nuclear structure function , it is essentially unknown at small . The
nuclear structure function at small is investigated in two
different theoretical models: a parton-recombination model with rescaling
and an aligned-jet model. We find that these models predict completely
different behavior at small : {\it antishadowing} in the first parton model
and {\it shadowing} in the aligned-jet model. Therefore, studies of the ratio
at small could be useful in discriminating among different
models, which produce similar shadowing behavior in the structure function
. We also estimate currently acceptable nuclear modification of at
small by using experimental data and baryon-number
conservation.Comment: 10 pages, Latex, Figs.1 and 2 are not included, Complete postscript
file including the figures is available at
ftp://ftp.cc.saga-u.ac.jp/pub/paper/riko/quantum1/saga-he-78.ps.gz or at
http://www.cc.saga-u.ac.jp/saga-u/riko/physics/quantum1/structure.htm
Color Screening and the Suppression of the Charmonium State Yield in Nuclear Reactions
We discuss the new data for the production of the meson in pA
collisions at 450 GeV at CERN-SPS (of the NA50-collaboration) [1]. We extract
from the CERN data mb under the assumption that the
is produced as a result of the space-time evolution of a point-like
pair which expands with time to the full size of the charmonium
state. In the analysis we assume the existence of a relationship between the
distribution of color in a hadron and the cross section of its interaction with
a nucleon. However, our result is rather sensitive to the pattern of the
expansion of the wave packet and significantly larger values of are not ruled out by the data. We show that recent CERN data confirm the
suggestion of [2] that color fluctuations of the strengths in
charmonium-nucleon interaction are the major source of suppression of the
yield as observed at CERN in both pA and AA collisions.Comment: 10 pages, 5 figures (one with color
J/\Psi production, polarization and Color Fluctuations
The hard contributions to the heavy quarkonium-nucleon cross sections are
calculated based on the QCD factorization theorem and the nonrelativistic
quarkonium model. We evaluate the nonperturbative part of these cross sections
which dominates at GeV at the Cern Super Proton
Synchrotron (SPS) and becomes a correction at TeV at
the CERN Large Hadron Collider (LHC). \J production at the CERN SPS is well
described by hard QCD, when the larger absorption cross sections of the
states predicted by QCD are taken into account. We predict an -dependent
polarization of the states. The expansion of small wave packets is
discussed.Comment: 13 pages REVTEX, 1 table, 2 PostScript, corrected some typo
Evidence for Color Fluctuations in Hadrons from Coherent Nuclear Diffraction}
A QCD-based treatment of projectile size fluctuations is used to compute
inelastic diffractive cross sections for coherent
hadron-nuclear processes. We find that fluctuations near the average size give
the major contribution to the cross section with contribution
from small size configurations.
The computed values of are consistent with the limited
available data. The importance of coherent diffraction studies for a wide range
of projectiles for high energy Fermilab fixed target experiments is emphasized.
The implications of these significant color fluctuations for relativistic heavy
ion collisions are discussed.Comment: Report number DOE/ER 40427-13-N93 11 pages, 3 figures available from
author Mille
Coulomb induced diffraction of energetic hadrons into jets
The electromagnetic (e.m.) current conservation and renormalizability of QCD
are used to calculate the amplitude of energetic hadron(photon) diffraction
into several jets with large relative transverse momenta off the
nucleon(nucleus) Coulomb field. Numerical estimates of the ratio of e.m. and
strong amplitudes show that within the kinematic range where the leading twist
approximation for the strong amplitude is applicable, the e.m. contribution can
be neglected. In pA scattering at LHC and in the fragmentation of a photon into
two jets in ultraperipheral AA collisions in the black limit (which maybe
realistic at LHC) e.m. contribution may win.Comment: 10 page
Taking the self out of self-rule
Many philosophers believe that agents are self-ruled only when ruled by their (authentic) selves. Though this view is rarely argued for explicitly, one tempting line of thought suggests that self-rule is just obviously equivalent to rule by the self. However, the plausibility of this thought evaporates upon close examination of the logic of âself-ruleâ and similar reflexives. Moreover, attempts to rescue the account by recasting it in negative terms are unpromising. In light of these problems, this paper instead proposes that agents are self-ruled only when not ruled by others. One reason for favouring this negative social view is its ability to yield plausible conclusions concerning various manipulation cases that are notoriously problematic for nonsocial accounts of self-rule. A second reason is that the account conforms with ordinary usage. It is concluded that self-rule may be best thought of as an essentially social concept
End-point singularities of Feynman graphs on the light cone
We show that some Lorentz components of the Feynman integrals calculated in
terms of the light-cone variables may contain end-point singularities which
originate from the contribution of the big-circle integral in the complex k_
plane. These singularities appear in various types of diagrams (two-point
functions, three-point functions, etc) and provide the covariance of the
Feynman integrals on the light-cone. We propose a procedure for calculating
Feynman integrals which guarantees that the end-point singularities do not
appear in the light-cone representations of the invariant amplitudes.Comment: final version to appear in PLB; few references adde
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