The European Physical Journal A最新文献

While the (^{14})N(p,(gamma ))(^{15})O reaction plays a key role in the hydrogen-burning processes in various stellar conditions, its reaction rate is not known with sufficient precision. Therefore, the first scientific project at the recently launched Bellotti Ion Beam Facility of the Laboratori Nazionali del Gran Sasso was the measurement of the (^{14})N(p,(gamma ))(^{15})O reaction cross section in the proton energy range between 250 and 1500 keV. In this paper, the experimental techniques are summarized with special emphasis on the description of solid state nitrogen target production and characterization. The first results of the reaction yield measured at 55(^circ ) detection angle are also presented.

The half-lifes of the nuclear isomeric states in ⁵⁷Fe at 14.4 keV and 136.5 keV above the ground state are measured with unprecedented precision using hybrid pixel detectors based on Timepix3 technology. These detectors enable dead-time-free single-photon detection and provide simultaneous measurements of photon energy and arrival time, allowing for nanosecond-scale determination of time differences between characteristic X-rays and (gamma )-rays emitted during the electron-capture decay of ⁵⁷Co. Employing the delayed coincidence technique, the half-life of the 14.4-keV state is determined as (t^{14.4 text { keV}}_{1/2} = 97.82(5)) ns, achieving a fourfold improvement in precision over previous measurements. The half-life of the 136.5-keV state is measured as (t^{136 text { keV}}_{1/2}= 8.730(17)) ns, reducing the uncertainty by a factor of two. These results are discussed in the context of previous works.

Many studies on the fission fragment mass distribution in the sub-lead and pre-actinide region have proposed the presence of asymmetric components in this mass region, primarily due to proton shells corresponding to Z ≈ 36, 38. Present studies have been carried out to investigate the mass distributions in the ³⁵Cl + ¹⁷⁶Yb → ²¹¹Fr and ³⁵Cl + ¹⁶⁵Ho → ²⁰⁰Po reactions in the mass region around ~ 200, a transition between the sub-lead and actinide region. Mass distribution studies have been carried out near the entrance channel Coulomb barrier using the recoil catcher technique, followed by off-line γ-ray spectrometry of the fission products. The broad Gaussian nature of the mass distribution in the ³⁵Cl + ¹⁷⁶Yb reaction indicates a dominant symmetric fission contribution. The mass distributions for the ³⁵Cl + ¹⁷⁶Yb and ³⁵Cl + ¹⁶⁵Ho reactions were found to be in gross agreement with GEF (Schmidt et al. in Nucl Data Sheets 131:107, 2016; Schmidt and Jurado in Rep Prog Phys 81:106301, 2018). The GEF model predicts a dominant symmetric fission contribution along with the contribution from the asymmetric fission mode corresponding to Z ≈ 38. The most probable charge, Z_P was varied within a range of ± 1.5 units with respect to that obtained using the unchanged charge density hypothesis to obtain the best agreement with GEF. However, a few experimental mass yields in the mass regions corresponding to Z ≈ 50–52 and Z ≈ 54–56 were observed to be still higher (more than ~ 50%) compared to the GEF predictions. A similar enhancement observed in the corresponding fission product yields indicates possible contributions from the conventional asymmetric fission modes, in addition to the shell corresponding to Z ≈ 38.

The forward–backward (FB) asymmetry of b quarks in (e^+e^-) collisions at the Z pole measured at LEP, (A_{_{textsc {fb}}}^{0,b}= 0.0992pm 0.0016), remains today one of the electroweak precision observables with the largest disagreement (2.4(sigma )) with respect to the Standard Model prediction, ((A_{_{textsc {fb}}}^{0,b})_{_textrm{th}} = 0.1030 pm 0.0002). Beyond the dominant statistical uncertainties, QCD effects, such as b-quark showering and hadronization, are the leading sources of (A_{_{textsc {fb}}}^{0,b}) systematic uncertainty, and have not been revised in the last twenty years. We reassess the QCD uncertainties of the eight original (A_{_{textsc {fb}}}^{0,b}) LEP measurements, using modern parton shower pythia 8 and vincia simulations with nine different implementations of soft and collinear radiation as well as of parton fragmentation. Our analysis, combined with NNLO massive b-quark corrections independently computed, indicates total propagated QCD uncertainties of (sim )0.7% and (sim )0.3% for the lepton- and jet-charge analyses, respectively, that are about a factor of two smaller than those of the original LEP results. Accounting for such updated QCD effects leads to a new (A_{_{textsc {fb}}}^{0,b}= 0.0995pm 0.0016) average, with a data-theory tension slightly reduced from 2.4(sigma ) to 2.2(sigma ). Confirmation or resolution of this long-term discrepancy requires a new high-luminosity (e^+e^-) collider collecting orders-of-magnitude more data at the Z pole to significantly reduce the dominant (A_{_{textsc {fb}}}^{0,b}) statistical uncertainties, and to improve our understanding of b-quark showering and hadronization.

The electric E1 and magnetic M1 dipole responses of the (N=Z) nucleus ²⁸Si were investigated in a nuclear resonance fluorescence experiment at the ELBE accelerator of the Helmholtz Zentrum Dresden-Rossendorf. The investigated energy range extends to 13.0 MeV, which corresponds to the kinetic energy of the electrons that were used to produce the unpolarised bremsstrahlung in the entrance channel of the ²⁸Si((gamma ,gamma ^{prime })) reaction. The bremsstrahlung photons excited three (J^{pi }=1^-), seven (J^{pi }=1^+), and several (J^{pi }=2^+) states. De-excitation (gamma ) rays were detected using the four high-purity germanium detectors of the (gamma )ELBE setup. The excellent background conditions allowed to identify nine previously unobserved (gamma )-ray transitions. In the investigated energy region of up to 13.0 MeV a total (sum _i B(M1, 0^+ rightarrow 1^+_i)= 5.0(3)~mu _N^2) strength is firmly observed with a possible addition of (B(M1, 0^+ rightarrow 1^+_i) le 0.14~mu _N^2) from levels for which the data allows to establish only an upper limit. Furthermore, below 13 MeV this (N=Z) nucleus exhibits a marginal isoscalar E1 strength of (sum _i B(E1, 0^+ rightarrow 1^-)= 2.6(3) times 10^{-3}) (hbox {e}^2 hbox {fm}^2), which exhausts only 0.026(2) % of the energy-weighted sum rule.

We study the inverse problem of analyzing femtoscopic correlation functions with an efficient tool to extract the maximum information possible about the interaction between the involved coupled-channel hadrons, and derive the existence of possible bound states. The method is flexible enough to accommodate non-molecular components and the effect of missing channels relevant for the interaction. We apply the method to realistic correlation functions for the (D^{*+}D^0) and (D^{*0}D^+) pairs derived consistently from the properties of the (T_{cc}(3875)^+). We can extract the existence of a bound state, its (D^{*+}D^0)-(D^{*0}D^+) molecular nature, the probabilities of each channel, as well as scattering lengths and effective ranges, together with the size of the source function, all of these quantities with relatively good precision. We analyze (pseudo) data generated with source sizes of (1,text {fm}) and (5,text {fm}), and observe that the uncertainties are larger for the second case.

A rich spectrum of giant resonances of different multipolarities and spin and isospin structure was expected on theoretical grounds. In the nineteen seventies, the isoscalar giant quadrupole resonance (ISGQR) was discovered in electron scattering followed by the isoscalar giant monopole resonance (ISGMR) in inelastic α scattering. In the last 5 decades, the compression modes the ISGMR and isoscalar giant dipole resonance (ISGDR) were extensively studied because of their importance for the determination of the nuclear-matter incompressibility and consequently their implications for the equation of state (EOS) of nuclear matter. Though the nuclear matter incompressibility (K_∞) has been reasonably well determined (~ 240 ± 20 MeV) through comparison of experimental results on several spherical nuclei with microscopic calculations, the asymmetry term was determined with larger uncertainty. This has been addressed in measurements on a series of stable Sn and Cd isotopes, which resulted in a value of K_τ =  − 550 ± 100 MeV for the asymmetry term in the nuclear incompressibility. The nuclear matter incompressibility and the asymmetry term are key parameters of the equation of state (EOS) of nuclear matter.

The isomeric ratios and cross sections were measured up to 50 MeV for production of ^198m,gAu, ^197m,gHg, ^195m,gHg and other Hg, Au and Pt radionuclides in irradiation of natural platinum by alpha-particles using the stacked-foil activation technique and offline gamma-ray spectrometry. The simultaneous decay curve analysis was applied to the emission rates of more than 40 gamma lines to directly derive the independent cross sections of all products without determining the cumulative cross sections. The measured cross sections and isomeric ratios were compared with those compiled in the EXFOR library and simulated by TALYS-2.0. We found that the ^natPt((alpha ),x)^198g+mAu, ^197g+mHg and ^195g+mHg cross sections are fairly reproduced by the simulation, while the simulation result requires adjustment of the spin cutoff parameter for better reproduction of the isomeric ratios.

The impact of Angela Bracco’s work on the electric dipole response of nuclei is discussed using three examples of current nuclear structure problems: disentangling different contributions to the decay width of the giant dipole resonance, the equivalence of photoabsorption and emission and the nature of the pygmy dipole resonance.

This work investigates hot quark matter under the thermodynamic conditions characteristic of a binary neutron star (BNS) merger remnants. We used the density-dependent quark mass model (DDQM) to access the microscopic nuclear equation of state (EoS) in a series of snapshots. The strange quark matter (SQM) is studied at finite temperature and entropy, in the presence of electrons and muons and their corresponding neutrinos to simulate the BNS merger conditions. For the first time, we introduced temperature into the DDQM model using a lattice QCD-motivated approach to construct both isentropic and isothermal EoSs. We observe that as the entropy of the SQM increases, the merger remnant becomes more massive and increases in size, whereas the neutrino abundance also increases. In the fixed-temperature case, on the other hand, we observe that the entropy spreads from the surface towards the center of the remnant. We determine the particle distribution in the core of the remnants, the structure of the remnant, the temperature profile, sound velocity, and the polytropic index, and discuss their effects. The strange-quark star (SQS) remnants satisfy the (2,mathrm{M_odot }) mass constraint associated with neutron stars (NS).