The European Physical Journal A最新文献

The ¹⁶O+¹⁶O fusion reaction is important for understanding explosive oxygen burning during late evolutionary stages of massive stars as well as for understanding low-energy heavy-ion fusion-reaction mechanism. This paper represents the first step to determine the excitation function for the major exit channels, (alpha +^{28})Si and (p+^{31})P, toward stellar energies indirectly by the Trojan Horse Method via the ¹⁶O(²⁰Ne,(alpha {}^{28})Si)⁴He and ¹⁶O(²⁰Ne,(p{}^{31})P)⁴He three-body reactions. Indeed, here we report on a validity test of the approach showing, for the first time, the possibility to use ²⁰Ne as Trojan Horse nucleus. Results on the reaction channel identification and reaction mechanism determination, with particular emphasis on the momentum distribution of the (alpha -^{16})O inter-cluster motion in the projectile ²⁰Ne nucleus are thoroughly discussed. Fair agreements of the present results with theoretical predictions indicate a possibility to identify the quasi-free process, which is the first step for the application of the Trojan Horse method to independently measure the ¹⁶O+¹⁶O fusion cross section in the next future.

Heavy-ion storage rings present a novel approach to studying nuclear reactions for astrophysics that have so far resisted traditional methods. In this paper, we report the first nuclear reactions studied in a ring at sub-MeV centre-of-mass energies. This is a major advance in nuclear reaction measurements at rings that lays the foundations for future investigations to address key problems in nuclear astrophysics affecting a wide range of stellar environments. We investigated the (^{15})N(p,p)(^{15})N and (^{15})N(p,(alpha ))(^{12})C reactions in inverse kinematics from E = 1.125 MeV/u down to E = 426 keV/u, using the CARME array in the low-energy CRYRING@ESR heavy-ion storage ring, located at the GSI Helmholtz Center for Heavy Ion Research. Our (p,p) scattering results are in excellent agreement with theoretical R matrix predictions. We also report on a (p,(alpha )) measurement at E = 426 keV/u, corresponding to E(_textrm{cm}) = 403 keV, by far the lowest energy at which a nuclear reaction has ever been measured in a heavy-ion storage ring.

The effective mass of heavy quark in QGP is related to the heavy quark potential at a large distance. In this study we test different heavy quark potentials, namely, the screened potential such as the free energy and the internal energy of the heavy quark pair in QGP, and the unscreened potential, which was recently proposed by the HotQCD Collaboration, through the thermal production of charm quarks in heavy-ion collisions at the LHC. We find that the free energy potential overestimates charm production in heavy-ion collisions at the LHC, while the unscreened potential produces results closest to the experimental data from the ALICE Collaboration among the three potentials.

Within the Color Glass Condensate (CGC) effective field theory, we investigate the long-range rapidity correlations in proton-lead (p-Pb) collisions at (sqrt{s_{textrm{NN}}}=5.02) TeV. A distinctive correlation rebound is observed, where the correlation bounces after reaching a minimum at large rapidity gaps ((|Delta eta |>2)). The rebound means a strong correlation appears at large rapidity gap. Studying the rebound structures can thus illuminate the formation of the ridge. We find that the rebound is most obvious when the transverse momenta of two measured particles are around 2 (mathrm {GeV/c}), and it moves to larger rapidity gaps at higher collision energies. Beyond that, the rapidity correlations in p-Pb collisions show asymmetry when the transverse momenta of two particles differ. The asymmetry, a unique signature of the asymmetric collisions, vanishes when the transverse momenta of two particles coincide. These findings provide direct insight into gluon saturation and quantum evolution.

We study the spin-averaged elastic scattering cross sections of the (Upsilon (1{textbf{S}}))–(Upsilon (1textbf{S})) system using a QCD-motivated potential framework and the Resonating Group Method (RGM). The interaction incorporates a geometric form factor based on the minimal-area variable (s_{min }), supported by lattice studies of multi-quark Wilson-loop geometries. Compared with the conventional Gaussian form, the (s_{min })–based overlap yields slightly larger cross sections near threshold, reflecting its harder short-distance structure and its closer compatibility with the compact (Upsilon (1textbf{S})) wavefunction. A sensitivity analysis over the physically motivated range (k_f = 0.40)–0.70 shows that while the magnitude varies smoothly with the stiffness parameter, the rapid suppression with increasing kinetic energy remains stable across all values. The results confirm that short-range dynamics dominate bottomonium–bottomonium interactions, consistent with expectations from generalized Gauss-law potentials and leading-twist QCD analyses. The modest near-threshold enhancement may offer useful input for interpreting (Upsilon ) suppression patterns in heavy-ion collisions, where quarkonium interactions with the medium play an important role.

In this work we study the meson properties in the framework of an effective quark model. We start from the Bethe-Salpeter equation choosing the interaction kernel in nonlocal form with the Gaussian meson vertex function, characterized by a meson size parameter (Lambda _H). We demonstrate the model’s predictive power by applying it to both light and heavy systems. Key results include a calculation of the (pi ^0rightarrow gamma gamma ) decay width and the pion transition form factor (F_{pi gamma }(Q^2)), which reproduces experimental data from low to high (Q^2). We further predict the electromagnetic properties of heavy quarkonia, obtaining the two-photon decay widths of (eta _c) and (eta _b) and the radiative decay widths of (J/psi ) and (Upsilon ), all of which show consistency with available data and other theoretical approaches. The model provides a computationally efficient and unified framework for describing mesons from the light to heavy quark sectors.

Neutron irradiation experiments are performed at the China Academy of Engineering Physics (CAEP) to determine the (n,d*) reaction cross-section of the even Z-even N ⁷⁸Kr at five neutron energies (13.59 ± 0.12, 13.86 ± 0.15, 14.13 ± 0.16, 14.70 ± 0.13, and 14.94 ± 0.02 MeV) using a high-pressure spherical gas sample. In order to determine the ⁷⁸Kr(n,d*)⁷⁷Br reaction cross section, the influence of ⁷⁸Kr(n,2n)⁷⁷Kr via EC(100%) decay is subtracted. The neutron energies and their uncertainties are calculated using the Q-value equation of the ³H(d,n)⁴He reaction, which takes into account the solid angle of the sample. Reaction ⁹³Nb(n,2n)^92mNb is used to monitor the neutron flux. The self-absorption and cascade of rays, as well as the geometry and solid angle of the sample, are corrected. The cross-section of the ⁷⁸Kr(n,d*)⁷⁷Br reaction is measured and reported for the first time. The measured results are compared to the results of available empirical and systematic formulas, theoretical results obtained using TALYS-2.0 with an adjustable density of six energy levels, and evaluation database results. The reaction ⁷⁸Kr(n,d*)⁷⁷Br cross-section determined for the first time in this experiment is of great significance for verifying the nuclear reaction models, improving the databases, and systematics.

(^{50})Cr and (^{53})Cr are very relevant in criticality safety benchmarks related to nuclear reactors. The discrepancies of up to 30% between the neutron capture cross section evaluations have an important effect on the (k_{eff}) and (k_{infty }) in criticality benchmarks particularly sensitive to chromium. In this work, the (^{50,53})Cr(n,(gamma )) cross sections are to be determined between 1 and 100 keV with an 8–10% accuracy following the requirements of the NEA High Priority Request List (HPRL) to solve the current discrepancies. We have measured these reactions by the time-of-flight technique at the EAR1 experimental area of the n_TOF facility, using an array of four C(_6)D(_6) detectors with very low neutron sensitivity. The highly-enriched samples used are significantly thinner than in previous measurements, thus minimizing the multiple-scattering effects. We have produced, and analysed with the R-matrix analysis code SAMMY, capture yields featuring 33 resonances of (^{50})Cr and 51 of (^{53})Cr with an accuracy between 5% and 9%, hence fulfilling the requirements made by the NEA. The differential and integral cross sections have been compared to previous data and evaluations. The new measured (^{50,53})Cr(n,(gamma )) cross sections provide a valuable input for upcoming evaluations, which are deemed necessary given that the results presented herein do not support the increase in both cross sections proposed in the recent INDEN evaluation.

The present study focuses on the measurement and analysis of the cross sections of 35 fission like residues (with mass numbers 74 (le ) A (le ) 111) and 10 fusion-like residues in the ¹⁴N+¹⁷⁵Lu reactions at energies (approx ) 75.8 MeV, 79.7 MeV and 84.0 MeV, respectively. The measurements have been carried out using the recoil catcher technique followed by off-beam activation (gamma )-ray spectroscopy. Analysis of fusion reaction data reveals the presence of complete and incomplete fusion mechanisms in the ¹⁴N+¹⁷⁵Lu reactions at these energies. In addition to the fusion contribution, a substantial amount of fission following the complete and incomplete fusion is also observed. The experimentally deduced post-fission observables mass ((sigma _{A})) and charge ((sigma _{Z})) dispersion parameters from the isotopic and isobaric distributions of fission fragments are found to be in good agreement with their values reported in the literature and calculated theoretically as well. Such consistency refers to the production of these fission fragments from the equilibrated compound nucleus ((^{189}Pt^{*})) in ¹⁴N+¹⁷⁵Lu reactions. This finding is also verified by the observations of the symmetric mass distributions of fission fragments which are found to have a single-humped Gaussian shape and their mass variances ((sigma ^{2}_{M})) follow the exponential trend with excitation energy, a characteristic of compound nucleus fission. The consistency in the isotopic, isobaric and mass distributions of the fission fragments in the ¹⁴N+¹⁷⁵Lu system enhances an additional understanding of compound nucleus fission in heavy-ion reactions.