Tue·Jun 28, 2022Tuesday·June 28, 2022

1. 01*

   Measurement of muon pairs produced via $\gamma \gamma$ scattering in non-ultraperipheral Pb+Pb collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02$ TeV with the ATLAS detector

   ATLAS Collaboration

   Results of a measurement of dimuon photoproduction in non-ultraperipheral Pb+Pb collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02$ TeV are presented. The measurement uses ATLAS data from the 2015 and 2018 Pb+Pb data-taking periods at the LHC with an integrated luminosity of $1.94{\mathrm{nb}}^{-1}$. The $\gamma \gamma \to {\mu }^{+}{\mu }^{-}$ pairs are identified via selections on pair momentum asymmetry and acoplanarity. Differential cross-sections for dimuon production are measured in different centrality, average muon momentum and pair rapidity intervals as functions of acoplanarity and $k_{\perp }$, the transverse momentum kick of one muon relative to the other. Measurements are also made as a function of the rapidity separation of the muons and the angle of the muon pair relative to the second-order event plane to test whether magnetic fields generated in the quark-gluon plasma affect the measured muons. A prior observation of a centrality-dependent broadening of the acoplanarity distribution is confirmed. Furthermore, the improved precision of the measurement reveals a depletion in the number of pairs having small acoplanarity or $k_{\perp }$ values in more central collisions. The acoplanarity distributions in a given centrality interval are observed to vary with the mean-$p_{\mathrm{T}}$ of the muons in the pair, but the $k_{\perp }$ distributions do not. Comparisons with recent theoretical predictions are made. The predicted trends associated with effects of magnetic fields on the dimuons are not observed.

   nucl-exhep-exPRC(2023)·31 citations
2. 02*

   Manipulation of Nuclear Isomers with Lasers: Mechanisms and Prospects

   Zhiguo Ma🇨🇳 · Changbo Fu🇨🇳 · Wanbing He🇨🇳 · Yugang Ma🇨🇳

   Over one hundred years have passed since the nuclear isomer was first introduced, in analogy with chemical isomers to describe long-lived excited nuclear states. In 1921, Otto Hahn discovered the first nuclear isomer ${}^{234m}$Pa. After that, step by step, it was realized that different types of nuclear isomers exist, including spin isomer, K isomer, seniority isomers, and ``shape and fission'' isomer. The spin isomer occurs when the spin change $\Delta I$ of a transition is very large. The larger $\Delta I$, the lower the electromagnetic transition rates, the longer the half-lives. The K-isomer exists due to the significant change in K, where K is the projection of the total angular momentum on the symmetry axis. The seniority isomers arise due to a very small transition probability in seniority conserving transitions around semi-magic nuclei, where the seniority, which corresponds to the number of unpaired nucleons, is a reasonably pure quantum number. For a so-called shape isomer, the inhibition of the decay transition comes from the associated shape changes. It is caused by that a nucleus is trapped in a deformed shape which is its secondary minimum and is hard to decay back to its ground state.

   nucl-exphysics.plasm-phSci.Bull.(2022)·6 citations
3. 03*

   Investigation of ${}^{11}$B and ${}^{40}$Ca levels at 8-9 MeV by Nuclear Resonance Fluorescence

   D. Gribble (1 and 2) · C. Iliadis (1 and 2) · R.V.F. Janssens (1 and 2) · U. Friman-Gayer (2 and 3)🇸🇪 · Krishichayan (2 and 3)🇺🇸 · S. Finch (2 and 3) ((1) UNC Chapel Hill, (2) Triangle Universities Nuclear Laboratory (TUNL), (3) Duke University)🇺🇸

   We report on the measurement of ${}^{11}$B and ${}^{40}$Ca levels between excitation energies of 8 and 9 MeV using nuclear resonance fluorescence (NRF). The experiment was carried out with nearly-monoenergetic and linearly polarized photon beams provided by the High-Intensity $\gamma$-ray Source (HI$\gamma$S) facility at the Triangle Universities Nuclear Laboratory (TUNL). States in ${}^{11}$B are important for calibrations of NRF measurements, while the properties of ${}^{40}$Ca levels impact potassium nucleosynthesis in globular clusters. For ${}^{40}$Ca, we report on improved excitation energies and an unambiguous $2^{-}$ assignment for the state at 8425 keV. For ${}^{11}$B, we obtained improved values for $\gamma$-ray multipolarity mixing ratios and branching ratios of the 8920 keV level.

   nucl-exPRC(2022)·8 citations
4. 04*

   Nucleon axial form factor at large momentum transfers

   Chen Chen🇨🇳 · Craig D. Roberts🇨🇳

   Using a Poincaré-covariant quark+diquark Faddeev equation and related symmetry-preserving weak interaction current, we deliver parameter-free predictions for the nucleon axialvector form factor, $G_A(Q^2)$, on the domain $0\le x=Q^2/m_N^2\le 10$, where $m_N$ is the nucleon mass. We also provide a detailed analysis of the flavour separation of the proton $G_A$ into contributions from valence $u$ and $d$ quarks; and with form factors available on such a large $Q^2$ domain, predictions for the flavour-separated axial-charge light-front transverse spatial density profiles. Our calculated axial charge ratio $g_A^d/g_A^u=-0.32(2)$ is consistent with available experimental data and markedly larger in magnitude than the value typical of nonrelativistic quark models. The value of this ratio is sensitive to the strength of axialvector diquark correlations in the Poincaré-covariant nucleon wave function. Working with a realistic axialvector diquark content, the $d$ and $u$ quark transverse density profiles are similar. Some of these predictions could potentially be tested with new data on threshold pion electroproduction from the proton at large $Q^2$.

   ↳ hep-phhep-exhep-latnucl-ex+1EPJA(2022)·22 citations
5. 05*

   Shear induced polarization: Collisional contributions

   Shu Lin🇨🇳 · Ziyue Wang🇨🇳

   It has been realized that thermal shear plays a similar role as thermal vorticity in polarizing spin of particles in heavy ion collisions. We point out that shear has a fundamental difference that it leads to particle redistribution in the medium. The redistribution gives rise to an additional contribution to spin polarization through the self-energy, which is parametrically the same order as the one considered so far in the literature. The self-energy contribution is in general gauge dependent. We introduce double gauge links stretching along the Schwinger-Keldysh contour to restore gauge invariance. We also generalize the straight path to adapt to the Schwinger-Keldysh contour. We find another contribution associated with the gauge link, which is also parametrically the same order. We illustrate the two contributions with a massive probe fermion in massless QED plasma with shear. A modest suppression of spin polarization is found from the combined contributions when the probe fermion has momentum much greater than the temperature.

   ↳ hep-phcond-mat.mes-hallnucl-exnucl-thJHEP(2022)·32 citations
6. 06*

   Spatial correlation of a particle-hole pair with a repulsive isovector interaction

   K. Hagino🇯🇵 · H. Sagawa

   We study the spatial correlation of a particle-hole pair in the isovector channel in ${}^{56}$Co and ${}^{40}$K nuclei. To this end, we employ the Hartree-Fock+Tamm-Dancoff approximation with the Skyrme interaction. We find a large concentration of the two-body density at positions where the neutron particle and the proton hole states locate on the opposite side to each other with respect to the core nucleus. This feature originates from a repulsive nature of the isovector residual interaction, which is in stark contrast to the dineutron correlation with an attractive pairing interaction between the valence neutrons discussed e.g., in ${}^{11}$Li and ${}^6$He. A possible experimental implication of the repulsive correlation is also discussed.

   ↳ nucl-thnucl-exPRC(2022)·1 citation
7. 07*

   Nuclear charge radii in Bayesian neural networks revisited

   Xiao-Xu Dong · Rong An🇨🇳 · Jun-Xu Lu🇨🇳 · Li-Sheng Geng🇨🇳

   In this work, a refined Bayesian neural network (BNN) based approach with six inputs including the proton number, mass number, and engineered features associated with the pairing effect, shell effect, isospin effect, and ``abnormal" shape staggering effect of ${}^{181,183,185}$Hg, is proposed to accurately describe nuclear charge radii. The new approach is able to well describe the charge radii of atomic nuclei with $A\ge 40$ and $Z\ge 20$. The standard root-mean-square (rms) deviation is $0.014$ fm for both the training and validation data. In particular, the predicted charge radii of proton-rich and neutron-rich calcium isotopes are found in good agreement with data. We further demonstrate the reliability of the BNN approach by investigating the variations of the rms deviation with extrapolation distances, mass numbers, and isospin asymmetries.

   ↳ nucl-thnucl-exPLB(2023)·54 citations
8. 08*

   Conserving approximations to dilute equilibrium systems. Pair interaction potential

   E.E. Kolomeitsev🇷🇺 · P.D. Lukianov · D.N. Voskresensky🇷🇺

   We study self-consistent approximations such as the $\Phi$-derivable and virial approaches to dilute strongly interacting systems in equilibrium. We consider a system of non-relativistic fermions of one kind interacting via a pair potential Thermodynamical quantities are expressed in terms of various spectral functions. We review the $\Phi$ derivable approximation scheme demonstrating the exact conservation of the Noether and the Botermans-Malfliet fermion number densities, and then for $\Phi$ described by the tadpole and sandwich diagrams we show the coincidence of these two number densities. As examples of test pair potentials, we consider the Yukawa central nucleon-nucleon potentials within Walecka, CD Bonn, and Reid parameterizations, and the corresponding classical Lennard-Jones potentials. Expressions for the second and third virial coefficients are derived and analyzed for $\Phi$ described by the tadpole and sandwich diagrams. Next, we focus on the virial approach to the equation of state. Classical, semiclassical, and purely quantum approaches are studied in detail. Then, different extrapolations of the virial equation of state are considered including the van~der~Waals form and excluded-volume models. We derive the expression for the second virial coefficient using the effective range approximation for the scattering amplitude and compare the result with the purely quantum result using the experimental phase shifts. Attention is focused on the problem of anomalously large value of the nucleon-nucleon scattering length appearing due to the presence of the quasi-bound state in nucleon-nucleon scattering, which can be destroyed in the matter because of the action of the Pauli blocking. We present results for the second virial coefficient subtracting this term. We discuss the validity of such a procedure to describe the equation of state of the nuclear matter in the virial limit.

   ↳ nucl-thastro-ph.HEnucl-exPhys.Part.Nucl.(2024)·1 citation
9. 09*

   The hadronic nucleus-nucleus cross section and the nucleon size

   Govert Nijs🇺🇸 · Wilke van der Schee🇨🇭

   Even though the total hadronic nucleus-nucleus cross section is among the most fundamental observables, it has only recently been measured precisely for lead-lead collisions at the LHC. This measurement implies the nucleon width should be below 0.7 fm, which is in contradiction with all known state-of-the-art Bayesian estimates. We study the implications of the smaller nucleon width on quark-gluon plasma properties such as the bulk viscosity. The smaller nucleon width dramatically improves the description of several triple-differential observables.

   ↳ nucl-thhep-phnucl-exPRL(2022)·53 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.