Nuclear Theory·nucl-th

Tuesday·May 4, 2021

12 papers—5 primary·7 cross-listed

06
[Submitted on 1 May 2021] (cross-list from hep-ph)
Analysis of the differential cross section and photon beam asymmetry data for $γ p \to η^{'} p$
Yu Zhang🇨🇳 · Ai-Chao Wang🇨🇳 · Neng-Chang Wei🇨🇳 · Fei Huang🇨🇳
The photoproduction reaction of $γ p \to η^{'} p$ is investigated based on an effective Lagrangian approach in the tree-level approximation, with the purpose being to understand the reaction mechanisms and to extract the resonance contents and the associated resonance parameters in this reaction. Apart from the $t$ -channel $ρ$ and $ω$ exchanges, $s$ - and $u$ -channel nucleon exchanges, and generalized contact term, the exchanges of a minimum number of nucleon resonances in the $s$ channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that a satisfactory description of the available data on both differential cross sections and photon beam asymmetries can be obtained by including in the $s$ channel the exchanges of the $N (1875) 3/ 2^{-}$ and $N (2040) 3/ 2^{+}$ resonances. The reaction mechanisms of $γ p \to η^{'} p$ are discussed and a prediction for the target nucleon asymmetries is presented.
Comments:
10 pages, 5 figures. Version published in PRD. arXiv admin note: text overlap with arXiv:2002.04213
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2105.00186 [pdf]
PRD(2021)·7 citations
07
[Submitted on 1 May 2021] (cross-list from hep-ph)
Coulomb effects in the decays $Υ (4 S) \to B B ˉ$
A.I. Milstein🇷🇺 · S.G. Salnikov🇷🇺
A simple exactly solvable model is proposed for describing the decays $Υ (4 S) \to B^{0} B ˉ^{0}$ and $Υ (4 S) \to B^{+} B^{-}$ . Our predictions agree with available experimental data. Using this model, we analyze the Coulomb effects in the spectra of these decays. It is shown that the frequently used assumption of factorization of Coulomb effects is not fulfilled. The Coulomb interaction leads to the difference in the positions and heights of the peaks corresponding to the charged and neutral modes. As a result, the ratio of probability of $Υ (4 S) \to B^{+} B^{-}$ decay and $Υ (4 S) \to B^{0} B ˉ^{0}$ decay is a nontrivial function of energy.
Comments:
5 pages, 4 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2105.00190 [pdf]
PRD(2021)·13 citations
08
[Submitted on 2 May 2021] (cross-list from hep-ph)
Constraints on the kinetic mixing parameter $ϵ^{2}$ for the light dark photons from dilepton production in heavy-ion collisions in the few-GeV energy range
Ida Schmidt (Frankfurt Uni.)🇩🇪 · Elena Bratkovskaya (GSI, Darmstadt, Frankfurt Uni.)🇩🇪 · Malgorzata Gumberidze (GSI, Darmstadt)🇩🇪 · Romain Holzmann (GSI, Darmstadt)🇩🇪
The vector $U$ -bosons, or so called 'dark photons', are one of the possible candidates for the dark matter mediators. They are supposed to interact with the standard matter via a 'vector portal' due to the $U (1) - U (1)^{'}$ symmetry group mixing which might make them visible in particle and heavy-ion experiments. While there is no confirmed observation of dark photons, the detailed analysis of different experimental data allows to estimate the upper limit for the kinetic mixing parameter $ϵ^{2}$ depending on the mass $M_{U}$ of $U$ -bosons which is also unknown. In this study we present theoretical constraints on the upper limit of $ϵ^{2} (M_{U})$ in the mass range $M_{U} \leq 0.6$ GeV from the comparison of the calculated dilepton spectra with the experimental data from the HADES Collaboration at SIS18 energies where the dark photons are not observed. Our analysis is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces well the measured dilepton spectra in $p + p$ , $p + A$ and $A + A$ collisions. Additionally to the different dilepton channels originating from interactions and decays of ordinary matter particles (mesons and baryons), we incorporate the decay of hypothetical $U$ -bosons to dileptons, $U \to e^{+} e^{-}$ , where the $U$ -bosons themselves are produced by the Dalitz decay of pions $π^{0} \to γ U$ , $η$ -mesons $η \to γ U$ and Delta resonances $Δ \to N U$ . Our analysis can help to estimate the requested accuracy for future experimental searches of 'light' dark photons by dilepton experiments.
Comments:
11 pages, 5 figures, extended version, to be published in Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2105.00569 [pdf]
PRD(2021)·10 citations
09
[Submitted on 2 May 2021] (cross-list from hep-ph)
The proton charge radius
Haiyan Gao🇺🇸 · Marc Vanderhaeghen🇩🇪
Nucleons (protons and neutrons) are the building blocks of atomic nuclei, and are responsible for more than 99\% of the visible matter in the universe. Despite decades of efforts in studying its internal structure, there are still a number of puzzles surrounding the proton such as its spin, and charge radius. Accurate knowledge about the proton charge radius is not only essential for understanding how quantum chromodynamics (QCD) works in the non-perturbative region, but also important for bound state quantum electrodynamics (QED) calculations of atomic energy levels. It also has an impact on the Rydberg constant, one of the most precisely measured fundamental constants in nature. This article reviews the latest situation concerning the proton charge radius in light of the new experimental results from both atomic hydrogen spectroscopy and electron scattering measurements, with particular focus on the latter. We also present the related theoretical developments and backgrounds concerning the determination of the proton charge radius using different experimental techniques. We discuss upcoming experiments, and briefly mention the deuteron charge radius puzzle at the end.
Comments:
49 pages, 28 figures, review prepared for Rev. Mod. Phys
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2105.00571 [pdf]
RMP(2022)·162 citations
10
[Submitted on 3 May 2021] (cross-list from hep-ph)
Quark model analysis of the Weinberg operator contribution to the nucleon EDM
Nodoka Yamanaka🇺🇸 · Emiko Hiyama🇯🇵
The Weinberg operator (chromo-electric dipole moment of gluon) is a CP violating quantity generated in many candidates of new physics beyond the standard model, and it contributes to observables such as the electric dipole moments (EDM) of the neutron or atoms which are currently measured in experiments. In this proceedings contribution, we report on our result of the evaluation of the Weinberg operator contribution to the nucleon EDM in the nonrelativistic quark model using the Gaussian expansion method.
Comments:
6 pages, 3 figures, proceedings of the 8th Asia-Pacific conference on Few-Body problems in Physics (APFB2020), Kanazawa, Japan, March 2021
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2105.00583 [pdf]
Few Body Syst.(2021)·0 citations
11
[Submitted on 23 Apr 2021] (cross-list from astro-ph.HE)
The I-Love-Q Relations for Superfluid Neutron Stars
Cheung-Hei Yeung🇨🇳 · Lap-Ming Lin🇨🇳 · Nils Andersson🇬🇧 · Greg Comer🇺🇸
The I-Love-Q relations are approximate equation-of-state independent relations that connect the moment of inertia, the spin-induced quadrupole moment, and the tidal deformability of neutron stars. In this paper, we study the I-Love-Q relations for superfluid neutron stars for a general relativistic two-fluid model: one fluid being the neutron superfluid and the other a conglomerate of all charged components. We study to what extent the two-fluid dynamics might affect the robustness of the I-Love-Q relations by using a simple two-component polytropic model and a relativistic mean field model with entrainment for the equation-of-state. Our results depend crucially on the spin ratio $Ω_{n} / Ω_{p}$ between the angular velocities of the neutron superfluid and the normal component. We find that the I-Love-Q relations can still be satisfied to high accuracy for superfluid neutron stars as long as the two fluids are nearly co-rotating $Ω_{n} / Ω_{p} \approx 1$ . However, the deviations from the I-Love-Q relations increase as the spin ratio deviates from unity. In particular, the deviation of the Q-Love relation can be as large as $O (10%)$ if $Ω_{n} / Ω_{p}$ differ from unity by a few tens of percent. As $Ω_{n} / Ω_{p} \approx 1$ is expected for realistic neutron stars, our results suggest that the two-fluid dynamics should not affect the accuracy of any gravitational waveform models for neutron star binaries that employ the relation to connect the spin-induced quadrupole moment and the tidal deformability.
Comments:
Invited contribution to Universe's Special Issue "Superfluidity and Superconductivity in Neutron Stars" (Guest Editor: Nicolas Chamel)
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
2105.00798 [pdf]
Universe(2021)·22 citations
12
[Submitted on 3 May 2021] (cross-list from hep-ph)
Vector and Axial-Vector Mesons in Nuclear Matter
Ralf-Arno Tripolt🇩🇪 · Christopher Jung🇩🇪 · Lorenz von Smekal🇩🇪 · Jochen Wambach🇩🇪
As a first step towards a realistic phenomenological description of vector and axial-vector mesons in nuclear matter, we calculate the spectral functions of the $ρ$ and the $a_{1}$ meson in a chiral baryon-meson model as a low-energy effective realization of QCD, taking into account the effects of fluctuations from scalar mesons, nucleons, and vector mesons within the Functional Renormalization Group (FRG) approach. The phase diagram of the effective hadronic theory exhibits a nuclear liquid-gas phase transition as well as a chiral phase transition at a higher baryon-chemical potential. The in-medium $ρ$ and $a_{1}$ spectral functions are calculated by using the previously introduced analytically-continued FRG (aFRG) method. Our results show strong modifications of the spectral functions in particular near the critical endpoints of both phase transitions which may well be of relevance for electromagnetic rates in heavy-ion collisions or neutrino emissivities in neutron-star merger events.
Comments:
16 pages, 10 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2105.00861 [pdf]
PRD(2021)·42 citations

Affiliations

first authorsco-authorsvia INSPIRE

Analysis of the differential cross section and photon beam asymmetry data for γp→η′p

Coulomb effects in the decays Υ(4S)→BBˉ

Constraints on the kinetic mixing parameter ϵ2 for the light dark photons from dilepton production in heavy-ion collisions in the few-GeV energy range

The proton charge radius

Quark model analysis of the Weinberg operator contribution to the nucleon EDM

The I-Love-Q Relations for Superfluid Neutron Stars

Vector and Axial-Vector Mesons in Nuclear Matter

Affiliations

Analysis of the differential cross section and photon beam asymmetry data for $γ p \to η^{'} p$

Coulomb effects in the decays $Υ (4 S) \to B B ˉ$

Constraints on the kinetic mixing parameter $ϵ^{2}$ for the light dark photons from dilepton production in heavy-ion collisions in the few-GeV energy range