17,506 research outputs found
Transverse-Mass Effective Temperature in Heavy-Ion Collisions from AGS to SPS
Transverse-mass spectra in Au+Au and Pb+Pb collisions in incident energy
range from 2A to 160A GeV are analyzed within the model of 3-fluid dynamics. It
is shown that dynamical description of freeze-out, accepted in this model,
naturally explains the incident energy behavior of inverse-slope parameters of
these spectra observed in experiment. Simultaneous reproduction of the
inverse-slopes of all considered particles (protons, pions and kaons) suggests
that these particles belong to the same hydrodynamic flow at the instant of
their freeze-out.Comment: 4 pages, 3 figure
Relativistic Heavy-Ion Collisions within 3-Fluid Hydrodynamics: Hadronic Scenario
A 3-fluid hydrodynamic model for simulating relativistic heavy-ion collisions
is introduced. Alongside with two baryon-rich fluids, the new model considers
time-delayed evolution of a third, baryon-free (i.e. with zero net baryonic
charge) fluid of newly produced particles. Its evolution is delayed due to a
formation time, during which the baryon-free fluid neither thermalizes nor
interacts with the baryon-rich fluids. After the formation it starts to
interact with the baryon-rich fluids and quickly gets thermalized. Within this
model with pure hadronic equation of state, a systematic analysis of various
observables at incident energies between few and about 160A GeV has been done
as well as comparison with results of transport models. We have succeeded to
reasonably reproduce a great body of experimental data in the incident energy
range of E_{lab} = (1-160)A GeV. The list includes proton and pion rapidity
distributions, proton transverse-mass spectra, rapidity distributions of Lambda
and antiLambda hyperons, elliptic flow of protons and pions (with the exception
of proton v2 at 40A GeV), multiplicities of pions, positive kaons, phi-mesons,
hyperons and antihyperons, including multi-strange particles. This agreement is
achieved on the expense of substantial enhancement of the interflow friction as
compared to that estimated proceeding from hadronic free cross sections.
However, we have also found out certain problems. The calculated yield of K^-
is approximately by a factor of 1.5 higher than that in the experiment. We have
also failed to describe directed transverse flow of protons and pion at E_{lab}
> 40A GeV. This failure apparently indicates that the used EoS is too hard and
thereby leaves room for a phase transition.Comment: 30 pages, 20 figures, 2 tables. Version accepted for publication in
Phys. Rev.
Frustrated spin ladder with alternating spin-1 and spin-1/2 rungs
We study the impact of the diagonal frustrating couplings on the quantum
phase diagram of a two-leg ladder composed of alternating spin-1 and spin-1/2
rungs. As the coupling strength is increased the system successively exhibits
two gapped paramagnetic phases (a rung-singlet and a Haldane-like
non-degenerate states) and two ferrimagnetic phases with different
ferromagnetic moments per rung. The first two states are similar to the phases
studied in the frustrated spin-1/2 ladder, whereas the magnetic phases appear
as a result of the mixed-spin structure of the model. A detailed
characterization of these phases is presented using density-matrix
renormalization-group calculations, exact diagonalizations of periodic
clusters, and an effective Hamiltonian approach inspired by the analysis of
numerical data. The present theoretical study was motivated by the recent
synthesis of the quasi-one-dimensional ferrimagnetic material
FeFe (trans-1,4-cyclohexanedicarboxylate) exhibiting a similar
ladder structure.Comment: 10 pages, 8 figure
On the polarization properties of the charmed baryon Lambda^+_c in the Lambda^+_c -> p + K^- + pi^+ + pi^0 decay
The polarization properties of the charmed Lambda^+_c baryon are investigated
in weak non-leptonic four-body Lambda^+_c -> p + K^- + pi^+ + pi^0 decay. The
probability of this decay and the angular distribution of the probability are
calculated in the effective quark model with chiral U(3)XU(3) symmetry
incorporating Heavy Quark Effective theory (HQET) and the extended
Nambu-Jona-Lasinio model with a linear realization of chiral U(3)XU(3)
symmetry. The theoretical value of the probability of the decay Lambda^+_c -> p
+ K^- + pi^+ + pi^0 relative to the probability of the decay Lambda^+_c -> p +
K^- + pi^+ does not contain free parameters and fits well experimental data.
The application of the obtained results to the analysis of the polarization of
the Lambda^+_c produced in the processes of photo and hadroproduction is
discussed.Comment: 10 pages, no figures, Late
On kaonic deuterium. Quantum field theoretic and relativistic covariant approach
We study kaonic deuterium, the bound K^-d state A_(K d). Within a quantum
field theoretic and relativistic covariant approach we derive the energy level
displacement of the ground state of kaonic deuterium in terms of the amplitude
of K^-d scattering for arbitrary relative momenta. Near threshold our formula
reduces to the well-known DGBT formula. The S-wave amplitude of K^-d scattering
near threshold is defined by the resonances Lambda(1405), Sigma(1750) and a
smooth elastic background, and the inelastic channels K^- d -> NY and K^- d ->
NY pion, with Y = Sigma^(+/-), Sigma^0 and Lambda^0, where the final-state
interactions play an important role. The Ericson-Weise formula for the S-wave
scattering length of K^-d scattering is derived. The total width of the energy
level of the ground state of kaonic deuterium is estimated using the
theoretical predictions of the partial widths of the two-body decays A_(Kd) ->
NY and experimental data on the rates of the NY-pair production in the
reactions K^-d -> NY. We obtain Gamma_{1s} = (630 +/-100) eV. For the shift of
the energy level of the ground state of kaonic deuterium we predict
epsilon_(1s) = (353 +/-60)eV.Comment: 73 pages,10 figures, Latex, We have slightly corrected the
contribution of the double scattering. The change of the S-wave scattering
length of K^-d scattering does not go beyond the theoretical uncertainty,
which is about 18
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