The European Physical Journal A最新文献

We investigate identified particle production in Oxygen–Oxygen (O–O) collisions at (sqrt{s_textrm{NN}}=~)7 TeV using the A Multi-Phase Transport (AMPT) model with string melting (SM). The study employs transverse spherocity as an event-shape observable to classify events into jetty (hard-QCD dominated) and isotropic (soft-QCD dominated) categories. This classification enables a detailed examination of transverse momentum spectra ((p_textrm{T} )), mean transverse momentum ((langle p_textrm{T} rangle )), and integrated yields (dN/dy) for the identified particles: pions, kaons, and protons for different centrality classes. Our findings reveal distinct particle production behaviors between isotropic and jetty events. Isotropic events dominate low-(p_textrm{T}) regions, while jetty events contribute significantly at high-(p_textrm{T}), with a crossing point in the spectra that shifts with particle mass and collision centrality. Additionally, nuclear density profiles—Woods–Saxon, harmonic oscillator, and (alpha )-clustered—exhibit measurable effects on (langle p_textrm{T} rangle ) and yields, particularly in central collisions, with (alpha )-clustered profiles showing enhanced radial flow. The trends of (langle p_textrm{T} rangle ) and yield variations suggest that collective effects are more prominent in central events and for heavier particles. The results emphasize the utility of spherocity in probing QGP-like behavior and highlight the sensitivity of observables to the initial-state geometry. This work provides valuable theoretical input for upcoming experimental investigations at the LHC.

We present a theoretical framework that extends the usual particle-particle RPA to include the coupling to low-energy collective excitations of the core. Taking into account also the coupling of the continuum, we compute the full excitation spectrum of (J^{pi }=0^+) pair modes starting from closed shell nuclei, including the well-known low-lying and bound Pairing Vibration on par with the predicted high-lying pairing vibration, often called Giant Pairing Vibration. Applications to ¹⁴C, ¹⁸O, and ¹³²Sn are presented.

We investigate how intense electromagnetic fields from heavy nuclei modify the Bethe–Heitler process in electron–nucleus scattering at the EIC and EicC. By introducing an effective electromagnetic coupling constant that accounts for Coulomb correction and Sudakov resummation, we demonstrate that the surrounding photon field of the nucleus can significantly alter cross sections. These medium-induced modifications suggest that in nuclear reaction processes, high-density bosonic fields can modify hard processes, which must be taken into account to improve the accuracy of theoretical predictions.

Working with a Poincaré-covariant quark + diquark, q(qq), Faddeev equation approach to nucleon structure, a refined symmetry preserving current for electron + nucleon elastic scattering is developed. The parameters in the interaction current are chosen to ensure that the q(qq) picture reproduces selected results from contemporary 3-body analyses of nucleon elastic electromagnetic form factors. Although the subset of fitted results is small, the q(qq) picture reproduces almost all the 3-body predictions and often results in better agreement with available data. Notably, the q(qq) framework predicts a zero in (G_E^p/G_M^p), the absence of such a zero in (G_E^n/G_M^n), and a zero in the proton’s d-quark Dirac form factor. Derived q(qq) results for proton flavour-separated light-front-transverse number and anomalous magnetisation densities are also discussed. With the q(qq) framework thus newly benchmarked, one may proceed to comparisons with a broader array of 3-body results. This may enable new steps to be made toward answering an important question, viz. is the quark + fully-interacting diquark picture of baryon structure only a useful phenomenology or does it come close to expressing robust features of baryon structure?

The theoretical description of nuclear structure in rare earth nuclei represents a significant challenge for many shell models. This difficulty stems from the size of the configuration space involved. Methods based on symmetries provide significant advantages. Furthermore, the pseudo-SU(3) shell model has proven to be very useful in the description of these systems. In particular, we propose to study the energy spectra of the rotational bands with normal deformation at low and medium spin ((Jle 35/2)), the quadrupole moments, and the deformation parameter (gamma ) associated with the states, as well as the B(E2) transition strengths in the (^{167,169,171})Lu nuclei. The Hamiltonian includes (Q cdot Q), Nilsson, and pairing terms, parameterized in a systematic way, in addition to three rotor-like terms that enable fine tuning of the spectra. Our calculations predict collective rotational bands with prolate normal deformation in most cases. The exception is the (1/2^+) band in (^{171})Lu with a triaxial shape. The quadrupole moments vary along the bands, increasing in absolute value with spin. The (gamma ) deformation parameter remains nearly constant along the bands, and the B(E2) values suggest bands with collective character and normal deformation. The agreement and limitations of the model are discussed.

We present the valence quark distributions of the kaons in an isospin asymmetric dense strange medium consisting of nucleons and hyperons. The comparative analysis of in-medium parton distribution functions, electromagnetic form factors, and charge densities with respect to the free space distributions is studied in the light-cone quark model. The medium effects are incorporated in these distribution functions by using the effective quark masses, computed from the chiral SU(3) quark mean field model for finite values of baryon density, isospin asymmetry, and strangeness fraction parameters. We observe a suppression of the kaon electromagnetic form factors and a redistribution of charge density in high-density strange matter.

We study the (D^0 rightarrow rho ^0 phi ), (omega phi ) decays which proceed in a direct mode via internal emission with equal rates. Yet, the experimental branching ratio for the (rho ^0 phi ) mode is twice as big as that for the (omega phi ) mode. We find a natural explanation based on the extra indirect mechanism where (K^{*+} K^{*-}) is produced via external emission and that channel undergoes final state interaction with other vector–vector channels to lead to the (rho ^0 phi ), (omega phi ) final states, with transition amplitudes dominated by the (a_0(1710)) resonance, recently discovered, and (f_0(1710)) respectively. The large coupling of the (a_0(1710)) to the (rho ^0 phi ) channel is mostly responsible for this large ratio of the production rates.