405 research outputs found
Strangeness production in antiproton-nucleus annihilation
The results of the microscopic transport calculations of -nucleus
interactions within a GiBUU model are presented. The dominating mechanism of
hyperon production is the strangeness exchange processes
and . The calculated rapidity spectra of hyperons are
significantly shifted to forward rapidities with respect to the spectra of
hyperons. We argue that this shift should be a sensitive test for the
possible exotic mechanisms of -nucleus annihilation. The production of
the double -hypernuclei by interaction with a secondary target
is calculated.Comment: Proceedings of the 12th Int. Workshop on Meson Production, Properties
and Interaction (MESON-2012), Cracow, 31.05-05.06.201
Strongly damped nuclear collisions: zero or first sound ?
The relaxation of the collective quadrupole motion in the initial stage of a
central heavy ion collision at beam energies AMeV is studied
within a microscopic kinetic transport model. The damping rate is shown to be a
non-monotonic function of E_{lab} for a given pair of colliding nuclei. This
fact is interpreted as a manifestation of the zero-to-first sound transition in
a finite nuclear system.Comment: 15 pages, 4 figure
Multifragmentation of charge asymmetric nuclear systems
The multifragmentation of excited spherical nuclear sources with various N/Z
ratios and fixed mass number is studied within dynamical and statistical
models. The dynamical model treats the multifragmentation process as a final
stage of the growth of density fluctuations in unstable expanding nuclear
matter. The statistical model makes a choice of the final multifragment
configuration according to its statistical weight at a global thermal
equilibrium. Similarities and differences in the predictions of the two models
on the isotopic composition of the produced fragments are presented and the
most sensitive observable characteristics are discussed.Comment: 15 pages, 8 figure
Transfer of synthetic human chromosome into human induced pluripotent stem cells for biomedical applications
Alphoid(tetO)-type human artificial chromosome (HAC) has been recently synthetized as a novel class of gene delivery vectors for induced pluripotent stem cell (iPSC)-based tissue replacement therapeutic approach. This HAC vector was designed to deliver copies of genes into patients with genetic diseases caused by the loss of a particular gene function. The alphoid(tetO)-HAC vector has been successfully transferred into murine embryonic stem cells (ESCs) and maintained stably as an independent chromosome during the proliferation and differentiation of these cells. Human ESCs and iPSCs have significant differences in culturing conditions and pluripotency state in comparison with the murine naïve-type ESCs and iPSCs. To date, transferring alphoid(tetO)-HAC vector into human iPSCs (hiPSCs) remains a challenging task. In this study, we performed the microcell-mediated chromosome transfer (MMCT) of alphoid(tetO)-HAC expressing the green fluorescent protein into newly generated hiPSCs. We used a recently modified MMCT method that employs an envelope protein of amphotropic murine leukemia virus as a targeting cell fusion agent. Our data provide evidence that a totally artificial vector, alphoid(tetO)-HAC, can be transferred and maintained in human iPSCs as an independent autonomous chromosome without affecting pluripotent properties of the cells. These data also open new perspectives for implementing alphoid(tetO)-HAC as a gene therapy tool in future biomedical applications
Formation of double- hypernuclei at PANDA
We study the formation of single- and double- hypernuclei in
antiproton-induced reactions relevant for the forthcoming PANDA experiment at
FAIR. We use the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model
with relativistic mean-fields for the description of non-equilibrium dynamics
and the statistical multifragmentation model (SMM) for fragment formation. This
combined approach describes the dynamical properties of strangeness and
fragments in low energy -induced reactions fairly well. We then focus
on the formation of double- hypernuclei in high energy
-nucleus collisions on a primary target including the complementary
-induced reactions to a secondary one, as proposed by the PANDA
collaboration. Our results show that a copious production of double-
hyperfragments is possible at PANDA. In particular, we provide first
theoretical estimations on the double- production cross section, which
strongly rises with decreasing energy of the secondary -beam.Comment: 20 pages, 11 figures, Nuclear Physics A, in pres
Shear Viscosity of a Hot Pion Gas
The shear viscosity of an interacting pion gas is studied using the Kubo
formalism as a microscopic description of thermal systems close to global
equilibrium. We implement the skeleton expansion in order to approximate the
retarded correlator of the viscous part of the energy-momentum tensor. After
exploring this in theory we show how the skeleton expansion can be
consistently applied to pions in chiral perturbation theory. The shear
viscosity is determined by the spectral width, or equivalently, the mean
free path of pions in the heat bath. We derive a new analytical result for the
mean free path which is well-conditioned for numerical evaluation and discuss
the temperature and pion-mass dependence of the mean free path and the shear
viscosity. The ratio of the interacting pion gas exceeds the lower
bound from AdS/CFT correspondence.Comment: 12 pages, 7 figures. Revision includes additional Appendix B. Matches
published versio
Thermal analysis of production of resonances in relativistic heavy-ion collisions
Production of resonances is considered in the framework of the
single-freeze-out model of ultra-relativistic heavy ion collisions. The
formalism involves the virial expansion, where the probability to form a
resonance in a two-body channel is proportional to the derivative of the
phase-shift with respect to the invariant mass. The thermal model incorporates
longitudinal and transverse flow, as well as kinematic cuts of the STAR
experiment at RHIC. We find that the shape of the pi+ pi- spectral line
qualitatively reproduces the preliminary experimental data when the position of
the rho peak is lowered. This confirms the need to include the medium effects
in the description of the RHIC data. We also analyze the transverse-momentum
spectra of rho, K*(892), and f_0(980), and find that the slopes agree with the
observed values. Predictions are made for eta, eta', omega, phi, Lambda(1520),
and Sigma(1385).Comment: minor modifications, a reference adde
Rapidity distribution as a probe for elliptical flow at intermediate energies
Interplay between the spectator and participant matter in heavy-ion
collisions is investigated within isospin dependent quantum molecular dynamics
(IQMD) model in term of rapidity distribution of light charged particles. The
effect of different types and size rapidity distributions is studied in
elliptical flow. The elliptical flow patterns show important role of the nearby
spectator matter on the participant zone. This role is further explained on the
basis of passing time of the spectator and expansion time of the participant
zone. The transition from the in-plane to out-of-plane is observed only when
the mid-rapidity region is included in the rapidity bin, otherwise no
transition occurs. The transition energy is found to be highly sensitive
towards the size of the rapidity bin, while weakly on the type of the rapidity
distribution. The theoretical results are also compared with the experimental
findings and are found in good agreement.Comment: 8 figure
Hadronic observables from SIS to SPS energies - anything strange with strangeness ?
We calculate and (+) rapidity
distributions and compare to experimental data from SIS to SPS energies within
the UrQMD and HSD transport approaches that are both based on string, quark,
diquark () and hadronic degrees of freedom. The
two transport models do not include any explicit phase transition to a
quark-gluon plasma (QGP). It is found that both approaches agree rather well
with each other and with the experimental rapidity distributions for protons,
's, and . Inspite of this apparent agreement both
transport models fail to reproduce the maximum in the excitation function for
the ratio found experimentally between 11 and 40 AGeV. A
comparison to the various experimental data shows that this 'failure' is
dominantly due to an insufficient description of pion rapidity distributions
rather than missing 'strangeness'. The modest differences in the transport
model results -- on the other hand -- can be attributed to different
implementations of string formation and fragmentation, that are not
sufficiently controlled by experimental data for the 'elementary' reactions in
vacuum.Comment: 46 pages, including 15 eps figures, to be published in Phys. Rev.
Dilepton production in heavy ion collisions at intermediate energies
We present a unified description of the vector meson and dilepton production
in elementary and in heavy ion reactions. The production of vector mesons
() is described via the excitation of nuclear resonances ().
The theoretical framework is an extended vector meson dominance model (eVMD).
The treatment of the resonance decays with arbitrary spin is
covariant and kinematically complete. The eVMD includes thereby excited vector
meson states in the transition form factors. This ensures correct asymptotics
and provides a unified description of photonic and mesonic decays. The
resonance model is successfully applied to the production in
reactions. The same model is applied to the dilepton production in elementary
reactions (). Corresponding data are well reproduced. However, when
the model is applied to heavy ion reactions in the BEVALAC/SIS energy range the
experimental dilepton spectra measured by the DLS Collaboration are
significantly underestimated at small invariant masses. As a possible solution
of this problem the destruction of quantum interference in a dense medium is
discussed. A decoherent emission through vector mesons decays enhances the
corresponding dilepton yield in heavy ion reactions. In the vicinity of the
-peak the reproduction of the data requires further a substantial
collisional broadening of the and in particular of the meson.Comment: 32 pages revtex, 19 figures, to appear in PR
- …