Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · 2411.09782

Exploring the interplay of helicity and global-frame spin density matrix elements

Gavin Wilks·Zhenyu Ye
View original source ↗Read source document ↗Export metadata ↓

Abstract

A significant $\phi$-meson global spin alignment ($\rho_{00}$) signal was measured in Au+Au collisions at $\sqrt{s_{NN}}\le62$ GeV. Conventional physics mechanisms such as $s(\bar{s})$ spin polarization fail to accommodate this $\rho_{00}$ signal, motivating further investigation into its origin. Recent studies from a general framework utilizing the gauge/gravity duality predict that there could be non-zero helicity-frame spin alignment generated by the relative motion of $s\bar{s}$ pairs to the thermal background in heavy-ion collisions, leading to significant global $\rho_{00}$. In this work, we derive the expected relationships between $\phi$-meson helicity and global-frame spin density matrix elements and confirm these analytical results using Monte Carlo simulations. The effects on these relationships from finite elliptic flow and various kinematic selections are also examined. Additionally, we extract $\rho_{00}$ simultaneously with the off-diagonal elements from the 2-dimensional $\theta^{*}$ and $\beta$ angular dimensions, as opposed to the standard 1-dimensional extraction of $\rho_{00}$. These angles describe the direction of a daughter kaon's momentum in the $\phi$-meson's rest frame, where $\theta^{*}$ is the polar angle with respect to the chosen spin-quantization axis, and $\beta$ is the azimuthal angle in the perpendicular plane. This 2-dimensional method allows us to consider possible effects from finite geometric acceptance and detector efficiencies, which could couple to the spin density matrix elements and influence the extraction of these elements within the same frame. The studies presented in this work explore the relationships between helicity and global-frame spin density matrix elements and possible detector effects on the 2-dimensional extraction of spin density matrix elements.

Explore related subjects

nucl-th

Keep this discovery

BibTeXRIS

Gavin Wilks, Zhenyu Ye. 2024-11-14. Exploring the interplay of helicity and global-frame spin density matrix elements. https://arxiv.org/abs/2411.09782

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Fission Modes and Fragment Shell Structures in $^{258}$Md$^*$ from Six-Dimensional Langevin Calculations

The fission of $^{258}$Md$^*$ is calculated in the excitation energy range of $E^*=6$--36 MeV using a six-dimensional Langevin equation. The calculated events are classified into two symmetric and two asymmetric fission modes based on the fragment mass and the quadrupole deformations of the two fragments at scission. The symmetric modes are separated by their total kinetic energies into the short (high TKE) and superlong (low TKE) modes, whereas the asymmetric modes differ in mass asymmetry. With increasing excitation energy, the yield of the short mode decreases, whereas the combined yield of the two asymmetric modes increases, as observed in the in-beam prompt-fission study of $^{258}$Md$^*$. From an analysis of the fragment shapes and associated single-particle levels, the short mode and the dominant asymmetric mode with the smaller mass asymmetry are found to involve a compact fragment characterized by deformed shell gaps at $Z=52$ and $N=84$, while the complementary fragments have different quadrupole deformations in the two modes.

nucl-th↗
arXiv2026

Classification of fission modes in $^{236}$U using a six-dimensional Langevin approach

Thermal neutron-induced fission of $^{235}$U is studied using a six-dimensional Langevin approach based on the Cassini shape parametrization. Scission events are classified into Asymmetric 1 (AS1), Asymmetric 2 (AS2), and Superlong (SL) fission modes by applying the $k$-means algorithm to the fragment mass and the quadrupole deformations of both fragments. For each mode, proton and neutron single-particle levels are calculated for representative fragments to examine their shell structures. The AS1 heavy fragment exhibits proton gaps at $Z=50$ and 52 and neutron gaps at $N=82$ and 84, whereas well-developed gaps appear at $Z=56$ and $N=88$ in the AS2 heavy fragment. The mass splits of AS1 and AS2 are close to those of the conventional Standard I and Standard II modes, respectively. However, the average total kinetic energy is lower for AS1 than for AS2, opposite to the conventional ordering of Standard I and Standard II. This reversal reflects the more elongated shape of the AS1 light fragment. The SL mode is conventionally interpreted in terms of macroscopic liquid-drop effects, whereas the pronounced proton shell gap at $Z=46$ suggests that proton shell effects also contribute to the elongated symmetric configuration. The classification based on fragment mass and the quadrupole deformations of both fragments provides a basis for distinguishing fission modes and examining the corresponding fragment shell structures at scission.

nucl-th↗
arXiv2026

Gogny interaction from beginnings to current challenges

The main goal of the present review article is to gather for the first time various facets of the phenomenological effective Gogny interaction which was originally proposed in the 70's. This involves both nuclear phenomena of interest that led to its creation and evolution as well as highly technical aspects that led the objectives to be achieved. With this in mind, we propose a discussion structured around four points. After a general introduction, the history and philosophy of the Gogny interaction is exposed. In particular, one highlights an intuitive way of guiding the determination of the parameters of the phenomenological interaction with the results obtained from a realistic interaction using Hartree-Fock calculations and second order corrections and a G-matrix. One also shows that physical phenomena such as pairing or fission were essential to improve the parameterization. The evolution of the original analytical form over the years is also discussed. The second point concern the emulator that was used for the generation of parameterizations. Its modifications, consistent with the evolution of the analytical form, are given. Other fitting procedures, more recent, are also evoked. The third key point is dedicated to the role of the nuclear matter in the fitting process and the acceptance of a parameterization. The objective of the last key point is to highlight some results obtained with the Gogny interaction in nuclear structure, fission and reactions that have allowed to interpret experimental data.

nucl-th↗