The European Physical Journal A最新文献

The two-body strong decays of the (f_0(1370)/f_0(1500)), (f_0(1710)), (a_0(1710)), (f_2(1270)), (f_2'(1525)), and (K_2^*(1430)) resonances are investigated, assuming them as dynamically generated states of two vector mesons via S-wave interactions. Based on the strong couplings of these scalar and tensor mesons to the vector-vector channels, their partial decay widths to all the possible two-body pseudoscalar meson-pseudoscalar meson final states are calculated considering the triangular diagrams involving the exchange of pseudoscalar mesons. It is found that some of the obtained ratios of branching fractions are compatible with the available experimental measurements. However, to further validate the model calculations and precisely determine the nature of these scalar and tensor mesons, more accurate experimental measurements are indispensable. We anticipate that in the future, the BESIII, BelleII, and LHCb collaborations will carry out these crucial measurements, which will significantly contribute to the understanding of the properties of these scalar and tensor mesons.

We study (B_c) production in high-energy nuclear collisions in a transport approach with dissociation and regeneration at finite temperatures. Due to the rare production in p+p collisions and the strong combination of uncorrelated c and ({bar{b}}) quarks in the quark-gluon plasma, the (B_c) yield is significantly enhanced in the nuclear collisions at the Large Hadron Collider. Moreover, the centrality and momentum-dependent yield of (B_c) sensitively reflect the thermalization degree of bottom quarks. And the newly observed experimental data favors a far from the thermal bottom quark distribution in the quark-gluon plasma.

In high energy heavy ion collisions, the initial configurations of the colliding nuclei play an important role in determining the reaction type and the products of the reaction. The initial arrangement of nucleons within the overlap region of two colliding nuclei is generally asymmetric and such asymmetries reflect themselves in the measurement final state momentum anisotropy. Also initial distribution of the nucleons are subjected to large quantum fluctuation causing large energy deposition in a small region. The final state observables related momentum anisotropies although sensitive to such localized fluctuations but their true effect gets diluted because these observables are calculated by averaging over a set of events. Also, such fluctuations in the initial states are random and uncontrolled. Thus, identifying their effect from event-averaged final state observable is difficult. However, it would be interesting to know the origin of such fluctuations and how these fluctuation are eventually translated to the final state. In this work, we at first introduce such localized fluctuations in the initial configurations, also called hot spots, by implementing spatial rearrangements of nucleon position in the colliding nuclei in the central Pb + Pb collisions at (hbox {E}_{lab}) = 20 AGeV ((sqrt{s}) = 6.27 GeV) using the UrQMD event generator. Then the final state distributions of one or two dimensional variables e.g., ((eta ), (phi ), (p_T)) and ((eta -p_T), (phi -p_T), (eta -phi )) of the produced pions are analysed using the principal component analysis (PCA) technique. The eigenvalues of the principal components have been studied for various initial configurations, event fractions containing hot spots in the initial condition and for event centralities with an aim to find it’s sensitivity to the initial hot spot configurations.

Prompt fission (gamma )-ray spectra (PFGS) extending to very low photon energies have been measured in the (^{232})Th(n,f) reaction over a range of incident neutron energies below the second chance fission threshold, for which no data are available. Fission events were detected with an ionization chamber containing (^{232})Th foils, and the coincident prompt fission (gamma )-rays were detected using two CeBr(_{3}) scintillation detectors. The measured spectra were unfolded using the corresponding response matrices of the detectors, simulated using Geant4, to obtain the PFGS in the (gamma )-ray energy region of 0.1–1.2 MeV. Surprisingly, significant reduction in photon intensity is observed for the (^{232})Th(n,f) reaction below the photon energy of 0.4 MeV when compared with the available data of (^{238})U(n,f) and (^{239})Pu(n,f) reactions at similar excitation energies. Moreover, the average (gamma )-ray multiplicity, (bar{M_gamma }), is found to be (sim 40%) lower and the average photon energy, (epsilon _{gamma }), is found to be (sim 50%) higher for (^{232})Th(n,f) reaction as compared to (^{238})U(n,f) and (^{239})Pu(n,f) reactions in the (gamma )-ray energy region of (0.1-1.2) MeV. It is found that the GEF model fails to predict the observed features of the PFGS in the (^{232})Th(n,f) reaction. The present experimental results may provide important insight in improving the current models addressing fast neutron induced fission of actinides.

Short-range correlations (SRCs) are a universal feature of nuclear structure. A wide range of measurements, primarily using electron scattering, have revealed SRC properties, such as their abundance in different nuclei, as well as the strong preference for proton-neutron pairing over proton-proton or neutron-neutron pairing. Despite the inherent complexity of many-body systems, a number of the salient features of electron scattering measurements are described by a simple, factorized theory called Generalized Contact Formalism. A key element of this theory, the factorization of the interaction with a hard probe, has yet to be tested. An experiment conducted at Jefferson Lab in 2021 collected data from scattering a tagged photon beam, with an energy up to 10 GeV, from several nuclear targets, measuring final state particles in the large-acceptance GlueX spectrometer. In this paper, we propose a test of probe factorization by measuring cross section ratios sensitive to proton-proton pair prevalence and relative SRC abundances in ⁴He and ¹²C. We present GCF predictions of the observables and make projections of the expected precision the experiment can achieve.

In many astrophysical scenarios, such as core-collapse supernovae and neutron star mergers, as in well as heavy-ion collision experiments, transitions between thermally populated nuclear excited states have been shown to play an important role. Because of its simplicity and ability to extrapolate, the finite-temperature quasiparticle random phase approximation (FT-QRPA) is an efficient method for studying the properties of hot nuclei. The statistical ensembles in the FT-QRPA make the theory much richer than its zero-temperature counterpart, but also obscure the meaning of various physical quantities. In this work, we clarify several aspects of the FT-QRPA, including notation seen in the literature, and demonstrate how to extract physical quantities from the theory. To illustrate the correct treatment of finite-temperature transitions, we place special emphasis on the charge-exchange transitions described by the proton-neutron FT-QRPA (FT-PNQRPA). With the FT-PNQRPA built on the nuclear energy-density functional theory, we obtain solutions in a relativistic matrix approach and also in the non-relativistic finite amplitude method. We show that the proper treatment of de-excitations from thermally populated excited states causes the Ikeda sum rule to be fulfilled. In addition, we demonstrate the impact of these transitions on stellar electron capture (EC) rates in ( ^{58,78})Ni. While their inclusion does not affect the EC rates in ( ^{58})Ni, the rates in ( ^{78})Ni are dominated by de-excitations for temperatures (T > 0.5) MeV. In systems with a large negative Q-value, the inclusion of de-excitations within the FT-QRPA is necessary for a complete description of reaction rates at finite temperature.

Providing reliable data on the properties of atomic nuclei and infinite nuclear matter to astrophysical applications remains extremely challenging, especially when treating both properties coherently within the same framework. Methods based on energy density functionals (EDFs) enable manageable calculations of nuclear structure throughout the entire nuclear chart and of the properties of infinite nuclear matter across a wide range of densities and asymmetries. To address these challenges, we present BSkG4, the latest Brussels-Skyrme-on-a-Grid model. It is based on an EDF of the extended Skyrme type with terms that are both momentum and density-dependent, and refines the treatment of (^1S_0) nucleon pairing gaps in asymmetric nuclear matter as inspired by more advanced many-body calculations. The newest model maintains the accuracy of earlier BSkGs for known atomic masses, radii and fission barriers with rms deviations of 0.633 MeV w.r.t. 2457 atomic masses, 0.0246 fm w.r.t. 810 charge radii, and 0.36 MeV w.r.t 45 primary fission barriers of actinides. It also improves some specific pairing-related properties, such as the (^1S_0) pairing gaps in asymmetric nuclear matter, neutron separation energies, (Q_beta ) values, and moments of inertia of finite nuclei. This improvement is particularly relevant for describing the r-process nucleosynthesis as well as various astrophysical phenomena related to the rotational evolution of neutron stars, their oscillations, and their cooling.

We have recently developed a nuclear model, which is a natural extension of the pn-QRPA model, specially designed to describe double charge exchange (DCE) processes generated by two-body DCE transition operators. It is based on the Quasiparticle Tamm–Dancoff approximation (QTDA) for pn and 2p2n excitations in intermediate and final nuclei, respectively, and will be called DCEQTDA. As such, this model, having the same number of free parameters as the pn-QRPA, also brings into play the excitations of four quasiparticles to build up the final nuclear states, which are then used to evaluate the nuclear matrix elements (NMEs) for all (0^+) and (2^+) final states, including resonances, and not just for the ground state as in pn-QRPA. In addition, it allows us to evaluate: (a) the values of (Q_{{beta }{beta }}), (b) the excitation energies in final nuclei, and (c) the DCE sum rules, which are fulfilled in the DCEQTDA. So far, this model has been used mainly to calculate double beta decays with the emission of two neutrinos ((2nu beta beta )-decay). Here, we extend it to the study of these processes when no neutrinos are emitted ((0nu beta beta )-decay), evaluating them in a series of nuclei, but paying special to: (i) (^{76})Se, which have been measured recently in the GERDA and MAJORANA experiments, and (ii) (^{124})Te, for which the first direct observation of the double electron capture (2nu ) has been performed with the XENON1T dark matter detector. We obtain good agreement with the data for both the ground state and the excited states. The validity of the DCEQTDA model is checked by comparing the calculation with the experimental data for the (2nu {beta }{beta }) NMEs, and for the (Q_{{beta }{beta }}), in a series of nuclei.

The Q value of the double-beta ((beta ^-beta ^-)) decay of (^{104})Ru ((Q_{beta ^-beta ^-})-value) was determined using the JYFLTRAP double Penning trap mass spectrometer employing the Phase-Imaging Ion Cyclotron Resonance (PI-ICR) method. The obtained value of 1297.705(36) keV is in agreement with the current literature value of 1299.4(27) keV but is over 70 times more precise. As a consistency check on a 100 eV level, we also measured the precisely known (^{102})Pd double-electron capture Q value, (Q_textrm{ECEC}=1203.531(92)) keV, which agrees with the literature value of 1203.47(4) keV. The measured Q value of (^{104})Ru (beta ^-beta ^-) decay was used in calculations of the phase-space factors of the double-beta decay. Also, the nuclear matrix elements were calculated using the microscopic interacting boson model (IBM-2) as a nuclear model and compared with other available results. With these theoretical calculations based on the measured Q value, the estimates for the two-neutrino and neutrinoless double-beta decay half-lives of (^{104})Ru were calculated to be (t_{1/2}^{2nu beta beta }>5.449times 10^{21}) years and (t_{1/2}^{0nu beta beta }>5.775times 10^{26}) years, respectively. The calculated (2nu beta ^-beta ^-) half-life is longer than the current experimental lower limit but short enough to be potentially within reach with future high precision experiments.