385 research outputs found
Hadron formation in high energy photonuclear reactions
We present a new method to account for coherence length effects in a
semi-classical transport model. This allows us to describe photo- and
electroproduction at large nuclei (A>12) and high energies using a realistic
coupled channel description of the final state interactions that goes beyond
simple Glauber theory. We show that the purely absorptive treatment of the
final state interactions can lead to wrong estimates of color transparency and
formation time effects in particle production. As an example, we discuss
exclusive rho^0 photoproduction on Pb at a photon energy of 7 GeV as well as
K^+ production in the photon energy range 1-7 GeV.Comment: 14 pages, 6 figures, version published in Phys. Rev.
Hadron attenuation in deep inelastic lepton-nucleus scattering
We present a detailed theoretical investigation of hadron attenuation in deep
inelastic scattering (DIS) off complex nuclei in the kinematic regime of the
HERMES experiment. The analysis is carried out in the framework of a
probabilistic coupled-channel transport model based on the
Boltzmann-Uehling-Uhlenbeck (BUU) equation, which allows for a treatment of the
final-state interactions (FSI) beyond simple absorption mechanisms.
Furthermore, our event-by-event simulations account for the kinematic cuts of
the experiments as well as the geometrical acceptance of the detectors. We
calculate the multiplicity ratios of charged hadrons for various nuclear
targets relative to deuterium as a function of the photon energy nu, the hadron
energy fraction z_h=E_h/nu and the transverse momentum p_T. We also confront
our model results on double-hadron attenuation with recent experimental data.
Separately, we compare the attenuation of identified hadrons (pi^\pm, \pi^0,
K^\pm, p and pbar) on Ne and Kr targets with the data from the HERMES
Collaboration and make predictions for a Xe target. At the end we turn towards
hadron attenuation on Cu nuclei at EMC energies. Our studies demonstrate that
(pre-)hadronic final-state interactions play a dominant role in the kinematic
regime of the HERMES experiment while our present approach overestimates the
attenuation at EMC energies.Comment: 61 pages, 19 figures, version accepted for publication in Phys. Rev.
The MultiSite Spectroscopic Telescope campaign: 2m spectroscopy of the V361 Hya variable PG1605+072
We present results and analysis for the 2m spectroscopic part of the
MultiSite Spectroscopic Telescope (MSST) campaign undertaken in May/June 2002.
The goal of the project was to observe the pulsating subdwarf B star PG1605+072
simultaneously in velocity and photometry and to resolve as many of the >50
known modes as possible, which will allow a detailed asteroseismological
analysis. We have obtained over 150 hours of spectroscopy, leading to an
unprecedented noise level of only 207m/s. We report here the detection of 20
frequencies in velocity, with two more likely just below our detection
threshold. In particular, we detect 6 linear combinations, making PG1605+072
only the second star known to show such frequencies in velocity. We investigate
the phases of these combinations and their parent modes and find relationships
between them that cannot be easily understood based on current theory. These
observations, when combined with our simultaneous photometry, should allow
asteroseismology of this most complicated of sdB pulsators.Comment: 9 pages, 5 figures, accepted for publication in A&A; Figure 1 at
lower resolution than accepted versio
Nuclear Attenuation of high energy two-hadron system in the string model
Nuclear attenuation of the two-hadron system is considered in the string
model. The two-scale model and its improved version with two different choices
of constituent formation time and sets of parameters obtained earlier for the
single hadron attenuation, are used to describe available experimental data for
the -dependence of subleading hadron, whereas satisfactory agreement with
the experimental data has been observed. A model prediction for
-dependence of the nuclear attenuation of the two-hadron system is also
presented.Comment: 8 page
Quark energy loss in semi-inclusive deep inelastic scattering of leptons on nuclei
Semi-inclusive deep inelastic scattering on nuclear targets is an ideal tool
to study the energy loss effect of an outgoing quark in a nuclear medium. By
means of the short hadron formation time, the experimental data with quark
hadronization occurring outside the nucleus are picked out. A leading-order
analysis is performed for the hadron multiplicity ratios as a function of the
energy fraction on helium, neon, and copper nuclei relative to deuteron for the
various identified hadrons. It is shown that the nuclear effects on parton
distribution functions can be neglected. It is found that the theoretical
results considering the nuclear modification of fragmentation functions due to
quark energy loss are in good agreement with the experimental data. Whether the
quark energy loss is linear or quadratic with the path length is not
determined. The obtained energy loss per unit length is 0.38 \pm 0.03 GeV/fm
for an outgoing quark by the global fit
Electronic Collective Modes and Superconductivity in Layered Conductors
A distinctive feature of layered conductors is the presence of low-energy
electronic collective modes of the conduction electrons. This affects the
dynamic screening properties of the Coulomb interaction in a layered material.
We study the consequences of the existence of these collective modes for
superconductivity. General equations for the superconducting order parameter
are derived within the strong-coupling phonon-plasmon scheme that account for
the screened Coulomb interaction. Specifically, we calculate the
superconducting critical temperature Tc taking into account the full
temperature, frequency and wave-vector dependence of the dielectric function.
We show that low-energy plasmons may contribute constructively to
superconductivity. Three classes of layered superconductors are discussed
within our model: metal-intercalated halide nitrides, layered organic materials
and high-Tc oxides. In particular, we demonstrate that the plasmon contribution
(electronic mechanism) is dominant in the first class of layered materials. The
theory shows that the description of so-called ``quasi-two-dimensional
superconductors'' cannot be reduced to a purely 2D model, as commonly assumed.
While the transport properties are strongly anisotropic, it remains essential
to take into account the screened interlayer Coulomb interaction to describe
the superconducting state of layered materials.Comment: Final version (minor changes) 14 pages, 6 figure
Performance of multi-aperture grid extraction systems for an ITER-relevant RF-driven negative hydrogen ion source
The ITER neutral beam system requires a negative hydrogen ion beam of 48 A with an energy of 0.87 MeV, and a negative deuterium beam of 40 A with an energy of 1 MeV. The beam is extracted from a large ion source of dimension 1.9 × 0.9 m2 by an acceleration system consisting of seven grids with 1280 apertures each. Currently, apertures with a diameter of 14 mm in the first grid are foreseen.
In 2007, the IPP RF source was chosen as the ITER reference source due to its reduced maintenance compared with arc-driven sources and the successful development at the BATMAN test facility of being equipped with the small IPP prototype RF source (
of the area of the ITER NBI source). These results, however, were obtained with an extraction system with 8 mm diameter apertures.
This paper reports on the comparison of the source performance at BATMAN of an ITER-relevant extraction system equipped with chamfered apertures with a 14 mm diameter and 8 mm diameter aperture extraction system. The most important result is that there is almost no difference in the achieved current density—being consistent with ion trajectory calculations—and the amount of co-extracted electrons. Furthermore, some aspects of the beam optics of both extraction systems are discussed.</jats:p
Space-time evolution of hadronization
Beside its intrinsic interest for the insights it can give into color
confinement, knowledge of the space-time evolution of hadronization is very
important for correctly interpreting jet-quenching data in heavy ion collisions
and extracting the properties of the produced medium. On the experimental side,
the cleanest environment to study the space-time evolution of hadronization is
semi-inclusive Deeply Inelastic Scattering on nuclear targets. On the
theoretical side, 2 frameworks are presently competing to explain the observed
attenuation of hadron production: quark energy loss (with hadron formation
outside the nucleus) and nuclear absorption (with hadronization starting inside
the nucleus). I discuss recent observables and ideas which will help to
distinguish these 2 mechanisms and to measure the time scales of the
hadronization process.Comment: 6 pages, 4 figures. Based on talks given at "Hot Quarks 2006",
Villasimius, Italy, May 15-20, 2006, and at the "XLIV internataional winter
meeting on nuclear physics", Bormio, Italy, Jan 29 - Feb 5, 2006. To appear
in Eur.Phys.J.
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