Nuclear Theory·nucl-th

Friday·August 6, 2021

7 papers—2 primary·5 cross-listed

03
Dynamical diquarks in the $γ^{(*)} p \to N (1535) \frac{1}{2}^{-}$ transition
Khépani Raya🇨🇳 · L. X. Gutiérrez-Guerrero🇲🇽 · Adnan Bashir🇲🇽 · Lei Chang🇨🇳 · Zhu-Fang Cui🇨🇳 · Ya Lu🇨🇳 · Craig D. Roberts🇨🇳 · Jorge Segovia🇨🇳
The $γ^{(*)} + p \to N (1535) \frac{1}{2}^{-}$ transition is studied using a symmetry-preserving regularisation of a vector $\otimes$ vector contact interaction (SCI). The framework employs a Poincaré-covariant Faddeev equation to describe the initial and final state baryons as quark+di\-quark composites, wherein the diquark correlations are fully dynamical, interacting with the photon as allowed by their quantum numbers and continually engaging in breakup and recombination as required by the Faddeev kernel. The presence of such correlations owes largely to the mechanisms responsible for the emergence of hadron mass; and whereas the nucleon Faddeev amplitude is dominated by scalar and axial-vector diquark correlations, the amplitude of its parity partner, the $N (1535) \frac{1}{2}^{-}$ , also contains sizeable pseudoscalar and vector diquark components. It is found that the $γ^{(*)} + p \to N (1535) \frac{1}{2}^{-}$ helicity amplitudes and related Dirac and Pauli form factors are keenly sensitive to the relative strengths of these diquark components in the baryon amplitudes, indicating that such resonance electrocouplings possess great sensitivity to baryon structural details. Whilst SCI analyses have their limitations, they also have the virtue of algebraic simplicity and a proven ability to reveal insights that can be used to inform more sophisticated studies in frameworks with closer ties to quantum chromodynamics.
↳ hep-phhep-latnucl-exnucl-thEPJA(2021)·43 citations
04
Collision energy dependence of the critical end point from baryon number fluctuations in the Linear Sigma Model with quarks
Alejandro Ayala🇲🇽 · Bilgai Almeida Zamora🇲🇽 · J. J. Cobos-Martínez🇲🇽 · S. Hernández-Ortiz🇺🇸 · L. A. Hernández🇿🇦 · Alfredo Raya🇲🇽 · María Elena Tejeda-Yeomans🇲🇽
We show that the Linear Sigma Model with quarks produces an effective description of the QCD phase diagram and of the system's equilibrium distribution properties that deviate from those of the Hadron Resonance Gas Model. The deviation is due to the inclusion of plasma screening properties, encoded in the contribution of the ring diagrams and thus to the introduction of a key feature of plasmas near phase transitions, namely, long-range correlations. After fixing the model parameters using input from LQCD for the crossover transition at vanishing chemical potential, we study the location of the Critical End Point in the effective QCD phase diagram. We use the model to study baryon number fluctuations and show that in heavy-ion collisions, the CEP can be located for collision energies $s_{N N} \sim 2$ GeV, namely, in the lowest NICA or within the HADES energy domain.
↳ hep-phhep-thnucl-thEPJA(2022)·14 citations
05
Two-particle scattering from finite-volume quantization conditions using the plane wave basis
Lu Meng🇩🇪 · E. Epelbaum🇩🇪
We propose an alternative approach to Lüscher's formula for extracting two-body scattering phase shifts from finite volume spectra with no reliance on the partial wave expansion. We use an effective-field-theory-based Hamiltonian method in the plane wave basis and decompose the corresponding matrix elements of operators into irreducible representations of the relevant point groups. The proposed approach allows one to benefit from the knowledge of the long-range interaction and avoids complications from partial wave mixing in a finite volume. We consider spin-singlet channels in the two-nucleon system and pion-pion scattering in the $ρ$ -meson channel in the rest and moving frames to illustrate the method for non-relativistic and relativistic systems, respectively. For the two-nucleon system, the long-range interaction due to the one-pion exchange is found to make the single-channel Lüscher formula unreliable at the physical pion mass. For S-wave dominated states, the single-channel Lüscher method suffers from significant finite-volume artifacts for a $L = 3$ ~fm box, but it works well for boxes with $L > 5$ ~fm. However, for P-wave dominated states, significant partial wave mixing effects prevent the application of the single-channel Lüscher formula regardless of the box size (except for the near-threshold region). Using a toy model to generate synthetic data for finite-volume energies, we show that our effective-field-theory-based approach in the plane wave basis is capable of a reliable extraction of the phase shifts. For pion-pion scattering, we employ a phenomenological model to fit lattice QCD results at the physical pion mass. The extracted P-wave phase shifts are found to be in a good agreement with the experimental results.
↳ hep-lathep-phnucl-thJHEP(2021)·46 citations
06
Triple nuclear collisions - a new method to explore the matter properties under new extreme conditions
O. V. Vitiuk🇺🇦 · V. M. Pugatch🇺🇦 · K.A. Bugaev🇺🇦 · P. P. Panasiuk🇺🇦 · N. S. Yakovenko🇺🇦 · B. E. Grinyuk🇺🇦 · E. S. Zherebtsova🇷🇺 · M. Bleicher🇩🇪 · L.V. Bravina🇳🇴 · A.V. Taranenko🇷🇺 · E.E. Zabrodin🇳🇴
We suggest to explore an entirely new method to experimentally and theoretically study the phase diagram of strongly interacting matter based on the triple nuclear collisions (TNC). We simulated the TNC using the UrQMD 3.4 model at the beam center-of-mass collision energies $s_{N N} = 200$ GeV and $s_{N N} = 2.76$ TeV. It is found that in the most central and simultaneous TNC the initial baryonic charge density is about 3 times higher than the one achieved in the usual binary nuclear collisions at the same energies. As a consequence, the production of protons and $Λ$ -hyperons is increased by a factor of 2 and 1.5, respectively. Using the MIT Bag model equation we study the evolution of the central cell in TNC and demonstrate that for the top RHIC energy of collision the baryonic chemical potential is 2-2.5 times larger than the one achieved in the binary nuclear collision at the same type of reaction. Based on these estimates, we show that TNC offers an entirely new possibility to study the QCD phase diagram at very high baryonic charge densities.
↳ hep-phnucl-thEPJ Web Conf.(2022)·1 citation
07
Strangeness content of the pion in the U(3) Nambu-Jona-Lasinio model
Fabio L Braghin🇧🇷
The Nambu-Jona-Lasinio model is considered with flavor-dependent coupling constants $G_{ij} [(ψ ˉ λ_{i} ψ) (ψ ˉ λ_{j} ψ) + (ψ ˉ i γ_{5} λ_{i} ψ) (ψ ˉ i γ_{5} λ_{j} ψ)]$ for $i, j = 0, 1.. N_{f}^{2} - 1$ , and $N_{f} = 3$ . A self consistent calculation of quark effective masses and coupling constants is performed making the strange quark effective mass to vary considerably. Quantum mechanical mixings between up, down and strange constituent quarks yields a strangeness content of the light u and d quarks constituent and of the pion. Different types of estimates for the strangeness contribution for the pion mass are provided. Mixing type interactions, $G_{i \neq = j}$ , induce the light mesons mixings and estimates for the $π^{0} - η$ and $η - η^{'}$ mixings are provided. The $η - π^{0}$ mixing is argued to be an indication of the strangeness content of the pion.
↳ hep-phnucl-thJ.Phys.G(2022)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE

Dynamical diquarks in the γ(∗)p→N(1535)21​− transition

Collision energy dependence of the critical end point from baryon number fluctuations in the Linear Sigma Model with quarks

Two-particle scattering from finite-volume quantization conditions using the plane wave basis

Triple nuclear collisions - a new method to explore the matter properties under new extreme conditions

Strangeness content of the pion in the U(3) Nambu-Jona-Lasinio model

Affiliations

Dynamical diquarks in the $γ^{(*)} p \to N (1535) \frac{1}{2}^{-}$ transition