1,904 research outputs found
Slow Proton Production in Semi-Inclusive Deep Inelastic Scattering off Deuteron and Complex Nuclei: Hadronization and Final State Interaction Effects
The effects of the final state interaction in slow proton production in semi
inclusive deep inelastic scattering processes off nuclei, A(e,e'p)X, are
investigated in details within the spectator and target fragmentation
mechanisms; in the former mechanism, the hard interaction on a nucleon of a
correlated pair leads, by recoil, to the emission of the partner nucleon,
whereas in the latter mechanism proton is produced when the diquark, which is
formed right after the visrtual photon-quark interaction, captures a quark from
the vacuum. Unlike previous papers on the subject, particular attention is paid
on the effects of the final state interaction of the hadronizing quark with the
nuclear medium within an approach based upon an effective time-dependent cross
section which combines the soft and hard parts of hadronization dynamics in
terms of the string model and perturbative QCD, respectively. It is shown that
the final state interaction of the hadronizing quark with the medium plays a
relevant role both in deuteron and complex nuclei; nonetheless, kinematical
regions where final state interaction effects are minimized can experimentally
be selected, which would allow one to investigate the structure functions of
nucleons embedded in the nuclear medium; likewise, regions where the
interaction of the struck hadronizing quark with the nuclear medium is
maximized can be found, which would make it possible to study non perturbative
hadronization mechanisms.Comment: 35 pages, 12 figures, accepted for pubblication in Phys. Rev.
Invariants and Coherent States for Nonstationary Fermionic Forced Oscillator
The most general form of Hamiltonian that preserves fermionic coherent states
stable in time is found in the form of nonstationary fermion oscillator.
Invariant creation and annihilation operators and related Fock states and
coherent states are built up for the more general system of nonstationary
forced fermion oscillator.Comment: 13 pages, Latex, no figure
Correlation femtoscopy of small systems
The basic principles of the correlation femtoscopy, including its
correspondence to the Hanbury Brown and Twiss intensity interferometry, are
re-examined. The main subject of the paper is an analysis of the correlation
femtoscopy when the source size is as small as the order of the uncertainty
limit. It is about 1 fm for the current high energy experiments. Then the
standard femtoscopy model of random sources is inapplicable. The uncertainty
principle leads to the partial indistinguishability and coherence of closely
located emitters that affect the observed femtoscopy scales. In thermal systems
the role of corresponding coherent length is taken by the thermal de Broglie
wavelength that also defines the size of a single emitter. The formalism of
partially coherent phases in the amplitudes of closely located individual
emitters is used for the quantitative analysis. The general approach is
illustrated analytically for the case of the Gaussian approximation for
emitting sources. A reduction of the interferometry radii and a suppression of
the Bose-Einstein correlation functions for small sources due to the
uncertainty principle are found. There is a positive correlation between the
source size and the intercept of the correlation function. The peculiarities of
the non-femtoscopic correlations caused by minijets and fluctuations of the
initial states of the systems formed in and collisions are also
analyzed. The factorization property for the contributions of femtoscopic and
non-femtoscopic correlations into complete correlation function is observed in
numerical calculations in a wide range of the model parameters.Comment: 34 pages, 5 figures. In the version 4 some stylistic improvements
were made, some misprints were corrected. The results and conclusions are not
change
Quantum optical effective-medium theory for loss-compensated metamaterials
A central aim in metamaterial research is to engineer sub-wavelength unit
cells that give rise to desired effective-medium properties and parameters,
such as a negative refractive index. Ideally one can disregard the details of
the unit cell and employ the effective description instead. A popular strategy
to compensate for the inevitable losses in metallic components of metamaterials
is to add optical gain material. Here we study the quantum optics of such
loss-compensated metamaterials at frequencies for which effective parameters
can be unambiguously determined. We demonstrate that the usual effective
parameters are insufficient to describe the propagation of quantum states of
light. Furthermore, we propose a quantum-optical effective-medium theory
instead and show that it correctly predicts the properties of the light
emerging from loss-compensated metamaterials.Comment: 6 pages, 3 figures. Accepted for Physical Review Letter
Correlations in atomic systems: Diagnosing coherent superpositions
While investigating quantum correlations in atomic systems, we note that
single measurements contain information about these correlations. Using a
simple model of measurement -- analogous to the one used in quantum optics --
we show how to extract higher order correlation functions from individual
"phtotographs" of the atomic sample. As a possible application we apply the
method to detect a subtle phase coherence in mesoscopic superpostitions.Comment: 4 pages, 2 figures, provisionally accepted to Physical Review Letter
Covariant boost and structure functions of baryons in Gross-Neveu models
Baryons in the large N limit of two-dimensional Gross-Neveu models are
reconsidered. The time-dependent Dirac-Hartree-Fock approach is used to boost a
baryon to any inertial frame and shown to yield the covariant energy-momentum
relation. Momentum distributions are computed exactly in arbitrary frames and
used to interpolate between the rest frame and the infinite momentum frame,
where they are related to structure functions. Effects from the Dirac sea
depend sensitively on the occupation fraction of the valence level and the bare
fermion mass and do not vanish at infinite momentum. In the case of the kink
baryon, they even lead to divergent quark and antiquark structure functions at
x=0.Comment: 13 pages, 12 figures; v2: minor correction
Coherent states \`a la Klauder-Perelomov for the P\"oschl-Teller potentials
In this paper we present a scheme for constructing the coherent states of
Klauder-Perelomov's type for a particle which is trapped in P\"oschl-Teller
potentials
A Test of the Eikonal Approximation in High-Energy (e,e'p) Scattering
The Glauber method is extensively used to describe the motion of a hadronic
projectile in interaction with the surrounding nuclear medium. One of the main
approximations consists in the linearization of the wave equation for the
interacting particle. We have studied the consequences of such an assumption in
the case of the reaction
at high proton momenta by comparing the results with the predictions obtained
when all the ingredients of the calculation are unchanged but the second-order
differential equation for the scattered wave, which is solved exactly for each
partial wave up to a maximum of 120 spherical harmonics. We find that the
Glauber cross section is always larger by a factor , even at
vanishing missing momenta. We give a quantum-mechanical explanation of this
discrepancy. Nevertheless, a good correlation is found between the two
predictions as functions of the missing momentum, especially in parallel
kinematics.Comment: LaTeX, 8 pages, 4 figures uuencoded, accepted for publication on
Phys. Lett.
Nuclear transparencies for nucleons, knocked-out under various semi-inclusive conditions
Using hadron dynamics we calculate nuclear transparencies for protons,
knocked-out in high-, semi-inclusive reactions. Predicted transparencies
are, roughly half a standard deviation above the NE18 data. The latter contain
the effects of binned proton missing momenta and mass, and of finite detector
acceptances. In order to test sensitivity we compare computed transparencies
without restrictions and the same with maximal cuts for missing momenta and the
electron energy loss. We find hardly any variation, enabling a meaningful
comparison with data and predictions based on hadron dynamics. Should
discrepancies persist in high-statistics data, the above may with greater
confidence be attributed to exotic components in the description of the
outgoing proton.Comment: 13 pages + 3 figsin appended PS file, report # WIS-94/43/Oct-P
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