The European Physical Journal A最新文献

We extend the theoretical approach which includes the dynamical and statistical stages for the description of the nucleosynthesis in central collisions of relativistic ions. Previously, this approach was successfully applied to describe experimental data on both normal nuclei and single strange hypernuclei production in the GSI and RHIC-BES energy range. We predict the multiplicities of double strange hypernuclei up to (^4_{varLambda varLambda })H and further intermediate mass nuclei up to (^8)Be for Au+Au central collisions at (sqrt{s_{NN}}) = 3 GeV, recently explored by the STAR experiments. These nuclei can be identified by the measurement of the correlated particles coming after their decay. Such observations are a crucial test for the nucleosynthesis mechanism.

This study focuses on the evolution of magnetized quark–gluon plasma (QGP) within the framework of magneto-hydrodynamics (MHD). We investigate the temporal and spatial dynamics of QGP with additional second-order viscous corrections, considering the effects of a magnetic field generated during the early stages of relativistic heavy-ion collisions. In our analysis, we assume boost invariance along the beamline, represented by the (z)-coordinate, and fluid expansion along the (x)-direction. The magnetic field is assumed to be oriented perpendicular to the reaction plane, aligning with the (y)-direction. Additionally, we consider the fluid to have infinite electrical conductivity, simplifying the treatment of electromagnetic effects. To characterize the system, we solve the coupled Maxwell’s equations and the conservation equations of relativistic hydrodynamics. This approach allows us to elucidate the time and space dependence of key physical quantities, including the energy density, fluid velocity, and magnetic field within the transverse plane of the viscous, magnetized plasma. By deriving these quantities, we also compute the hadron spectra and perform a comparative analysis with experimental data to validate our theoretical predictions.

Explicit expressions for the leading chiral hyperon-nucleon-nucleon three-body forces have been derived by Petschauer et al (Phys Rev C93:014001, 2016). An important prerequisite for including these three-body forces in few- and many-body calculations is the accuracy and efficiency of their partial-wave decomposition. A careful benchmark of the (Lambda )NN potential matrix elements, computed using two robust and efficient partial-wave decomposition methods, is presented. In addition, results of a first quantitative assessment for the contributions of ({Lambda })NN forces to the separation energies in (A=3-5) hypernuclei are reported.

The technique of dynamic nuclear polarization (DNP) to enhance the intrinsically low sensitivity of an NMR experiment has been around since the early 1950s. While the technique is not new, recent advances in microwave technology, mainly driven by new developments in telecommunication technology, magnet technology, and quasi-optics allow researchers to perform DNP experiments in a ground-breaking new way. In this review article, we will give an overview of the current state of modern instrumentation for DNP spectroscopy and its sister technique Electron Paramagnetic Resonance (EPR) spectroscopy.

In the Felsenkeller shallow-underground site, protected from cosmic muons by a 45 m thick rock overburden, a research laboratory including a 5 MV Pelletron ion accelerator and a number of radioactivity-measurement setups is located. The laboratory and its installations are described in detail. The background radiation has been studied, finding suppression factors of 40 for cosmic-ray muons, 200 for ambient neutrons, and 100 for the background in germanium (gamma )-ray detectors. Using an additional active muon veto, typically the background is just twice as high as in very deep underground laboratories. The properties of the accelerator including its external and internal ion sources and beam line are given. For the radioactivity counting setup, detection limits in the 10(^{-4}) Bq range have been obtained. Practical aspects for the usage of the laboratory by outside scientific users are discussed.

Photoactivation of a natural bismuth target was performed in bremsstrahlung beams with maximum energies of 40 MeV, 50 MeV and 60 MeV. Several products of (γ,xn) reactions were identified in the gamma spectra and saturation activities and flux averaged sections were calculated for them. The obtained values were compared with the results based on TALYS estimates of the cross sections of the observed reactions. TALYS estimates were calculated for all combinations of photon strength function and level density (a total of 54 of them) with the intention of evaluating which of them shows the best agreement with the experimental results. The minimum and maximum estimates of the saturation activity obtained from the 54 photon SF and LD model combinations differ in most cases by an order of magnitude. The experimental values fall within this range. At 60 MeV, the experimental values of the saturation activity are lower than most TALYS estimates. A similar result is observed at 50 MeV, but to a somewhat lesser extent, while at 40 MeV, approximately the same number of saturation activities obtained from the TALYS cross-sections give both higher and lower estimates compared to the experiment. The flux averaged cross sections calculated using the TENDL estimates are two to three times larger than the experimental ones. By comparing experimental and theoretical values of flux-averaged cross sections for the formation of ²⁰⁶Bi, it was observed that good agreement was shown by those combinations of SF and LD models that are phenomenological in their formulation. No such trend was observed for other bismuth isotopes. There is a significant need to measure the cross sections of nuclear reactions with a higher multiplicity of emitted particles to provide experimental material for further development of models for calculating reaction cross sections.

Recently (The PANDA collaboration, arXiv:2201.03852v2) the PANDA collaboration studied the feasibility of determining the spin and parity of the (Xi (1690)^{-}) and (Xi (1820)^{-}) resonances in the (Lambda K^-) system produced in (bar{p}p) collisions via the reaction channel (overline{p} p rightarrow bar{Xi }^{+} Lambda K^{-}). The present paper aims to study these reactions using a model-independent irreducible tensor formalism developed earlier. This study leads us to identify the partial-wave amplitude and the observable, which would be zero if (Xi (1690)^{-}) or (Xi (1820)^{-}) had spin-1/2, provided these resonances are produced at threshold (s-wave production).

Bogoliubov many-body perturbation theory (BMBPT) relying on the breaking of U(1) global gauge symmetry has been recently formulated and applied to extend the applicability of standard perturbation theory to ab initio calculations of atomic nuclei away from shell closures. So far, practical applications have been limited to second-order calculations due to the lack of a generic algorithm to constrain the average particle number of the symmetry-broken state. This limitation is presently lifted and a general BMBPT formalism is presented that allows to constrain the particle-number expectation value at arbitrary order P. The constraint can be incorporated in closed form by solving a polynomial equation of degree (P-1). The numerical procedure is illustrated through BMBPT(3) calculations of calcium isotopes using a nuclear Hamiltonian derived within chiral effective field theory.

We utilized the AMPT model to simulate the shear viscous transport dynamics of parton matter in Au + Au collisions at a constant specific shear viscosity and varying phase transition temperatures at (sqrt{s_{NN}}=200,textrm{GeV}). The resulting charged hadron spectra and anisotropic flow profiles correspond closely with experimental data. The transverse momentum spectra and longitudinal decorrelations are essentially unaffected by the phase transition temperature. An increase in the phase transition temperature leads to a rise in particle yields at midrapidity, accompanied by a decrease in both elliptic and triangular flows over a range of transverse momenta and pseudorapidities.

The pseudoscalar and vector four-quark states (bb{overline{c}}{overline{c}}) are studied in the context of the QCD sum rule method. We model (T_{text { PS}} ) and (T_{text {V}}) as structures built of diquarks ( b^{T}Cgamma _{5}b), ({overline{c}}C{overline{c}}^{T}) and (b^{T}Cgamma _{5}b), ({overline{c}}Cgamma _{mu }gamma _{5}{overline{c}}^{T}), respectively, with C being the charge conjugation matrix. The spectroscopic parameters of the tetraquarks (T_{text {PS}}) and (T_{text {V}}), i.e., their masses and current couplings are calculated using QCD two-point sum rule method. We evaluate the full widths of (T_{text {PS}}) and (T_{text {V}}) by taking into account their kinematically allowed decay channels. In the case of the pseudoscalar particle they are processes (T_{text {PS}} rightarrow B_{c}^{-}B_{c}^{*-}), (B_{c}^{-}B_{c}^{-}(1^{3}P_{0})) and (B_{c}^{*-}B_{c}^{-}(1^{1}P_{1})). The vector state (T_{text {V}}) can dissociate to meson pairs (2 B_{c}^{-}), (2 B_{c}^{*-}) and ( B_{c}^{-}B_{c}^{-}(1^{1}P_{1})). Partial widths of these decays are determined by the strong couplings at relevant tetraquark-meson-meson vertices, which evaluated in the context of the three-point sum rule approach. Predictions obtained for the mass and full width of the pseudoscalar (m =(13.092pm 0.095)~text {GeV}), (Gamma _{text {PS} }=(63.7pm 13.0)~text {MeV}) and vector ({widetilde{m}} =(13.15pm 0.10)~ text {GeV}), (Gamma _{text {V}}=(53.5pm 10.3)~text {MeV}) tetraquarks can be useful for analyses of different four-quark resonances.