Nuclear Theory·nucl-th

Wednesday·November 3, 2021

8 papers—4 primary·4 cross-listed

01
[Submitted on 1 Nov 2021]
Medium modification of jet shape observables in Pb-Pb collisions at $s_{N N}$ = 2.76 TeV using EPOS and JEWEL event generators
Sumit Kumar Saha🇮🇳 · Debojit Sarkar🇺🇸 · Subhasis Chattopadhyay🇮🇳 · Ashik Ikbal Sheikh🇮🇳 · Sidharth Kumar Prasad🇮🇳
The substructure of charged jets gets modified due to the presence of the medium in heavy-ion collisions which is an indication of redistribution of energy inside the jet cone. It helps to understand the energy loss mechanisms of jets in the medium. A model dependent study of the modification of differential jet shape $(ρ (r))$ and the angularity (g) due to medium, has been performed in the most central Pb-Pb collisions at 2.76 TeV in the jet range of 20-40 GeV/c.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2111.01200 [pdf]
NPA(2021)·0 citations
02
[Submitted on 2 Nov 2021]
Multi-reference many-body perturbation theory for nuclei III -- Ab initio calculations at second order in PGCM-PT
Mikael Frosini🇫🇷 · Thomas Duguet🇫🇷 · Jean-Paul Ebran🇫🇷 · Benjamin Bally🇪🇸 · Heiko Hergert🇺🇸 · Tomás R. Rodríguez🇪🇸 · Robert Roth🇩🇪 · Jiangming Yao🇹🇼 · Vittorio Somà🇫🇷
In spite of missing dynamical correlations, the projected generator coordinate method (PGCM) was recently shown to be a suitable method to tackle the low-lying spectroscopy of complex nuclei. Still, describing absolute binding energies and reaching high accuracy eventually requires the inclusion of dynamical correlations on top of the PGCM. In this context, the present work discusses the first realistic results of a novel multi-reference perturbation theory (PGCM-PT) that can do so within a symmetry-conserving scheme for both ground and low-lying excited states. First, proof-of-principle calculations in a small ( $e_{max} = 4$ ) model space demonstrate that exact binding energies of closed- (\nucl{O}{16}) and open-shell (\nucl{O}{18}, \nucl{Ne}{20}) nuclei are reproduced within $0.5 - 1.5%$ at second order, i.e. through PGCM-PT(2). Moreover, profiting from the pre-processing of the Hamiltonian via multi-reference in-medium similarity renormalization group transformations, PGCM-PT(2) can reach converged values within smaller model spaces than with an unevolved Hamiltonian. Doing so, dynamical correlations captured by PGCM-PT(2) are shown to bring essential corrections to low-lying excitation energies that become too dilated at leading order, i.e., at the strict PGCM level. The present work is laying the foundations for a better understanding of the optimal way to grasp static and dynamical correlations in a consistent fashion, with the aim of accurately describing ground and excited states of complex nuclei via ab initio many-body methods.
Subjects:
Nuclear Theory (nucl-th); Computational Physics (physics.comp-ph)
arXiv:
2111.01461 [pdf]
EPJA(2022)·91 citations
03
[Submitted on 2 Nov 2021]
Microscopic version of the Bohr-Mottelson model and its application
H. G. Ganev
The shell-model coupling scheme of the proton-neutron symplectic model (PNSM), defined by the following dynamical symmetry chain $S p (12, R) \supset S U (1, 1) \otimes S O (6) \supset U (1) \otimes S U_{p n} (3) \otimes S O (2) \supset S O (3)$ , is considered. It is shown that it corresponds to a microscopic version of the Bohr-Mottelson collective model which captures the original relationships between its exactly solvable submodel limits. This variant of the PNSM provides an interesting and relevant shell-model symplectic-based framework for exploring the nuclear collective dynamics. Some simple applications of the present theory to different nuclei with various collective properties are given.
Comments:
11 pages, 2 figures, to appear in the Proceedings of the international workshop on Shapes and Dynamics of Atomic Nuclei: Contemporary Aspects (SDANCA21), Sofia, Bulgaria, 16-18 September 2021, ed. N. Minkov
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2111.01659 [pdf]
Bulg.J.Phys.(2021)·2 citations
04
[Submitted on 2 Nov 2021]
Modification of $Z^{0}$ leptonic invariant mass in ultrarelativistic heavy ion collisions as a measure of the electromagnetic field
Yifeng Sun🇮🇹 · Vincenzo Greco🇮🇹 · Xin-Nian Wang🇺🇸
An extraordinary strong magnetic field, $e B_{0} \approx 1 0^{18}$ Gauss, is expected to be generated in non-central ultrarelativistic heavy ion collisions and it is envisaged to induce several effects on hot QCD matter including the possibility of local parity and local parity and charge conjugation symmetry violations. A direct signature of such e.m. fields and a first quantitative measurement of its strength and lifetime are still missing. We point out that both the mean value of leptonic invariant mass of $Z^{0}$ boson, reconstructed by its decaying lepton pairs, and the relative width are modified in relativistic heavy ion collisions due to the presence of strong initial e.m. fields. We propose a measurement of the leptonic invariant mass of $Z^{0}$ as a novel probe of the strength of the $B_{y}$ . Both shifts could be up to about few hundred MeV and are found to depend on the integral of $B_{y}$ over the time duration quadratically (approximate). Hence it provides a novel and clear probe of electromagnetic fields, which can be tested experimentally.
Comments:
6 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2111.01716 [pdf]
PLB(2022)·9 citations
05
[Submitted on 1 Nov 2021] (cross-list from hep-lat)
$b ˉ c ˉ q_{1} q_{2}$ four-quark states from Lattice QCD
M. Padmanath🇮🇳 · Nilmani Mathur🇩🇪
We present the results of a lattice calculation of four-quark states with the quark contents $b ˉ c ˉ q_{1} q_{2}$ where $q_{1}, q_{2} \in u, d, s$ . For the spin 1 states, when the light quark ( $q_{1}, q_{2}$ ) masses are lighter, we find at least one energy level below the possible elastic threshold energy levels. These calculations are performed on three dynamical $N_{f} = 2 + 1 + 1$ highly improved staggered quark ensembles at lattice spacings of about 0.12, 0.09, and 0.06 fm. We use the overlap action for light to charm quarks while a non-relativistic action with non-perturbatively improved coefficients is employed for the bottom quark.
Comments:
9 pages, 6 figures. Proceedings of the 38th International Symposium on Lattice Field Theory (LATTICE2021)
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2111.01147 [pdf]
PoS(2022)·17 citations
06
[Submitted on 1 Nov 2021] (cross-list from hep-ph)
Positivity and renormalization of parton densities
John Collins🇺🇸 · Ted C. Rogers🇺🇸 · Nobuo Sato🇺🇸
There have been recent debates about whether $MS$ parton densities exactly obey positivity bounds (including the Soffer bound), and whether the bounds should be applied as a constraint on global fits to parton densities and on nonperturbative calculations. A recent paper (JHEP $11$ (2020) 129) appears to provide a proof of positivity in contradiction with earlier work by other authors. We examine their derivation and find that its primary failure is in the apparently uncontroversial statement that bare pdfs are always positive. We show that under the conditions used in the derivation, that statement fails. We provide some elementary calculations in a model QFT that show how this situation can generically arise in reality. In addition, we observe that the methods used in the derivation are in common with much, but not all, other work where factorization is derived. Our examination pinpoints considerable difficulties with these methods that render them either wrong or highly problematic. The issue of positivity highlights that these methods can lead to wrong results of phenomenological importance. From our analysis we identify the restricted situations in which positivity can be violated.
Comments:
24 pages, 3 figures, version published in physical review D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2111.01170 [pdf]
PRD(2022)·59 citations
07
[Submitted on 2 Nov 2021] (cross-list from hep-ph)
The $η$ - and $η^{'}$ -nucleus interactions and the search for $η$ , $η^{'}$ - mesic states
Steven D. Bass🇦🇹 · Volker Metag🇩🇪 · Pawel Moskal🇵🇱
The isoscalar $η$ and $η^{'}$ mesons are special in QCD, being linked both to chiral symmetry and to non-perturbative glue associated with the axial anomaly. The properties of these mesons in medium are sensitive to how these dynamics work in the nuclear environment. In contrast to pionic and kaonic atoms which are mainly bound by the Coulomb interaction with some corrections due to the strong force (Coulomb assisted binding), the $η$ and $η^{'}$ as neutral mesons can only be bound by the strong interaction. Is this interaction strong enough? This topic has inspired a vigorous program of experiments, conducted in close contact with theory, One has to determine the complex $η$ , $η^{'}$ -nucleus potential. Does the real part $V$ provide a sufficiently deep potential? Is the imaginary part $W$ small enough to allow for narrow states that can more easily be detected experimentally, i.e. $∣ W ∣ ≪ ∣ V ∣$ ? The $η^{'}$ effective mass is observed to be suppressed by $\approx - 40$ MeV at nuclear matter density. Bound state searches are ongoing. This article gives an overview of the status of knowledge in this field together with an outlook to future experiments.
Comments:
26 pages, 12 figures. arXiv admin note: text overlap with arXiv:1810.12290
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2111.01388 [pdf]
In: Tanihata, I., Toki, H., Kajino, T. (e…·11 citations
08
[Submitted on 2 Nov 2021] (cross-list from hep-ph)
Hadronic structure on the light-front II: QCD strings, Wilson lines and potentials
Edward Shuryak🇺🇸 · Ismail Zahed🇺🇸
This is the second paper on hadronic wave functions in the light front formulation. We first consider only confinement effects, using the classical Nambu-Gotto string with massive end points in the light cone gauge. We derive the light-front Hamiltonian and show how to solve it, using an expansion in suitable basis functions. We next discuss the correlators of Wilson lines on the light front, leading to an effective Hamiltonian that includes spin effects. At the end, we consider a separate problem of instanton-induced interactions, at the origin of the pion as a massless Goldstone mode on the light front.
Comments:
31 pages, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2111.01775 [pdf]
PRD(2023)·23 citations

Affiliations

first authorsco-authorsvia INSPIRE