1,972 research outputs found
Nuclear multifragmentation induced by electromagnetic fields of ultrarelativistic heavy ions
We study the disintegration of nuclei by strong electromagnetic fields
induced by ultrarelativistic heavy ions. The proposed multi-step model includes
1) the absorption of a virtual photon by a nucleus, 2) intranuclear cascades of
produced hadrons and 3) statistical decay of the excited residual nucleus. The
combined model describes well existing data on projectile fragmentation at
energy 200 GeV per nucleon. Electromagnetic multifragmentation of nuclei is
predicted to be an important reaction mechanism at RHIC and LHC energies.Comment: 18 LaTeX pages including 4 figures, uses epsf.sty. Submitted to
Phys.Rev.
Simultaneous Heavy Ion Dissociation at Ultrarelativistic Energies
We study the simultaneous dissociation of heavy ultrarelativistic nuclei
followed by the forward-backward neutron emission in peripheral collisions at
colliders. The main contribution to this particular heavy-ion dissociation
process, which can be used as a beam luminosity monitor, is expected to be due
to the electromagnetic interaction. The Weizsacker-Williams method is extended
to the case of simultaneous excitation of collision partners which is simulated
by the RELDIS code. A contribution to the dissociation cross section due to
grazing nuclear interactions is estimated within the abrasion model and found
to be relatively small.Comment: Talk given at Bologna 2000 Conference - Structure of the Nucleus at
the Dawn of the Century, May 29 - June 3, 2000, 4 pages, 2 figure
Proton and carbon-ion minibeam therapy: from modeling to treatment
Arrays of minibeams of protons and C in tissue-like media were modeled
with Geant4 toolkit. A set of beam energies was used in simulations to provide
a Spead-out Bragg peak (SOBP) extended by 6 cm in depth for protons as well as
for C. In both cases, beams of 0.3 mm or 0.5 mm FWHM were arranged at
the entrance to a water phantom either on a rectangular or an hexagonal grid to
compare two kinds of projectiles and different minibeam patterns. Differential
and cumulative dose-volume histograms (DVH) were calculated and compared for
protons and C as dose uniformity metrics. A uniform dose distribution
was easily achieved with protons due to an enhanced lateral scattering of these
projectiles in comparison to C. The cumulative DVHs calculated for 0.3
mm or 0.5 mm minibeams almost coincide in the target volume, but diverge for
different grid patterns. In contrast, cumulative entry DVHs were found similar
for both grid patterns, but different for 0.3 mm and 0.5 mm minibeams.Comment: 8 pages, 5 figures, talk given at the XXV International Baldin
Seminar on High Energy Physics Problems "Relativistic Nuclear Physics and
Quantum Chromodynamics", September 18-23, 2023, Dubna, Russi
Gene pool similarities and differences between Ukrainians and Russians of slobozhanshchina based on Y-chromosome data
Results from studying Y chromosomal polymorphisms of Russian and Ukrainian populations are presented for Slobozhanshina, which is a contemporary border region, inhabited in the 17th–18th centuries at the “Wild Field” boundary due to migrations of both the Russians from the north and Ukrainians from the west. In general, the Ukrainian and Russian populations of Slobozhanshchina are very close genetically; their set and frequency range of Y chromosome haplogroups are typical for Eastern Europe. However, a detailed analysis of highly informative Y chromosome markers showed that both nations retain the ethnic specificity of their gene pools after 3.5 centuries of coexistence in the same historical territory: the Ukrainian popula tions are similar to the rest of Ukraine, and Russian populations gravitate towards the south of European Rus sia. The persistent genetic differences may be due to the spatial characteristics of marriage migration and the predominant ethnic environmentyesBelgorod State National Research Universit
Evaluation of the total photoabsorption cross sections for actinides from photofission data and model calculations
We have calculated the fission probabilities for 237-Np, 233,235,238-U,
232-Th, and nat-Pb following the absorption of photons with energies from 68
MeV to 3.77 GeV using the RELDIS Monte-Carlo code. This code implements the
cascade-evaporation-fission model of intermediate-energy photonuclear
reactions. It includes multiparticle production in photoreactions on
intranuclear nucleons, pre-equilibrium emission, and the statistical decay of
excited residual nuclei via competition of evaporation, fission, and
multifragmentation processes. The calculations show that in the GeV energy
region the fission process is not solely responsible for the entire total
photoabsorption cross section, even for the actinides: ~55-70% for 232-Th,
\~70-80% for 238-U, and ~80-95% for 233-U, 235-U, and 237-Np. This is because
certain residual nuclei that are created by deep photospallation at GeV photon
energies have relatively low fission probabilities. Using the recent
experimental data on photofission cross sections for 237-Np and 233,235,238-U
from the Saskatchewan and Jefferson Laboratories and our calculated fission
probabilities, we infer the total photoabsorption cross sections for these four
nuclei. The resulting cross sections per nucleon agree in shape and in
magnitude with each other. However, disagreement in magnitude with
total-photoabsorption cross-section data from previous measurements for nuclei
from C to Pb calls into question the concept of a ``Universal Curve'' for the
photoabsorption cross section per nucleon for all nuclei.Comment: 39 pages including 11 figure
Mutual heavy ion dissociation in peripheral collisions at ultrarelativistic energies
We study mutual dissociation of heavy nuclei in peripheral collisions at
ultrarelativistic energies. Earlier this process was proposed for beam
luminosity monitoring via simultaneous registration of forward and backward
neutrons in zero degree calorimeters at Relativistic Heavy Ion Collider.
Electromagnetic dissociation of heavy ions is considered in the framework of
the Weizsacker-Williams method and simulated by the RELDIS code. Photoneutron
cross sections measured in different experiments and calculated by the GNASH
code are used as input for the calculations of dissociation cross sections. The
difference in results obtained with different inputs provides a realistic
estimation for the systematic uncertainty of the luminosity monitoring method.
Contribution to simultaneous neutron emission due to grazing nuclear
interactions is calculated within the abrasion model. Good description of CERN
SPS experimental data on Au and Pb dissociation gives confidence in predictive
power of the model for AuAu and PbPb collisions at RHIC and LHC.Comment: 46 pages with 7 tables and 13 figures, numerical integration accuracy
improved, next-to-leading-order corrections include
Coherent Vector Meson Photoproduction with Nuclear Breakup in Relativistic Heavy Ion Collisions
Relativistic heavy ions are copious sources of virtual photons. The large
photon flux gives rise to a substantial photonuclear interaction probability at
impact parameters where no hadronic interactions can occur. Multiple
photonuclear interactions in a single collision are possible. In this letter,
we use mutual Coulomb excitation of both nuclei as a tag for moderate impact
parameter collisions. We calculate the cross section for coherent vector meson
production accompanied by mutual excitation, and show that the median impact
parameter is much smaller than for untagged production. The vector meson
rapidity and transverse momentum distribution are very different from untagged
exclusive vector meson production.Comment: 14 pages, including 4 figure
Particle emission following Coulomb excitation in ultrarelativistic heavy-ion collisions
We study nuclear reactions induced by virtual photons associated with
Lorentz-boosted Coulomb fields of ultrarelativistic heavy ions. Evaporation,
fission and multifragmentation mechanisms are included in a new RELDIS code,
which describes the deexcitation of residual nuclei formed after single and
double photon absorption in peripheral heavy-ion collisions. Partial cross
sections for different dissociation channels, including the multiple neutron
emission ones, are calculated and compared with data when available. Rapidity
and transverse momentum distributions of nucleons, nuclear fragments and pions,
produced electromagnetically, are also calculated. These results provide
important information for designing large-rapidity detectors and zero-degree
calorimeters at RHIC and LHC. The electromagnetic dissociation of nuclei
imposes some constrains on the investigation of exotic particle production in
gamma-gamma fusion reactions.Comment: 26 LaTeX pages including 8 figures, uses epsf.st
Inclusive meson production in peripheral collisions of ultrarelativistic heavy ions
There exist several proposals to use Weizs\"{a}cker-Williams photons
generated by ultrarelativistic heavy ions to produce exotic particles in
fusion reactions. To estimate the background conditions for such
reactions we analyze various mechanisms of meson production in very peripheral
collisions of ultrarelativistic heavy ions at RHIC and LHC energies. Besides
fusion they include also electromagnetic interactions
and strong nucleon-nucleon interactions in grazing collisions. All these
processes are characterised by low multiplicities of produced particles.
and events are simulated by corresponding Monte Carlo codes,
RELDIS and FRITIOF. In each of these processes a certain fraction of pions is
produced close to the mid-rapidity region that gives a background for the
events. The possibility of selecting mesons produced in
fusion events via different cut procedures is
demonstrated.Comment: 27 pages with 4 eps-figures included, uses axodraw.sty Tab.2 and 3
correcte
The Physics of Ultraperipheral Collisions at the LHC
We discuss the physics of large impact parameter interactions at the LHC:
ultraperipheral collisions (UPCs). The dominant processes in UPCs are
photon-nucleon (nucleus) interactions. The current LHC detector configurations
can explore small hard phenomena with nuclei and nucleons at photon-nucleon
center-of-mass energies above 1 TeV, extending the range of HERA by a
factor of ten. In particular, it will be possible to probe diffractive and
inclusive parton densities in nuclei using several processes. The interaction
of small dipoles with protons and nuclei can be investigated in elastic and
quasi-elastic and production as well as in high
production accompanied by a rapidity gap. Several of these phenomena
provide clean signatures of the onset of the new high gluon density QCD regime.
The LHC is in the kinematic range where nonlinear effects are several times
larger than at HERA. Two-photon processes in UPCs are also studied. In
addition, while UPCs play a role in limiting the maximum beam luminosity, they
can also be used a luminosity monitor by measuring mutual electromagnetic
dissociation of the beam nuclei. We also review similar studies at HERA and
RHIC as well as describe the potential use of the LHC detectors for UPC
measurements.Comment: 229 Pages, 121 figure
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