The European Physical Journal A 

About: The European Physical Journal A is an academic journal published by Springer Science+Business Media. The journal publishes majorly in the area(s): Computer science & Neutron. It has an ISSN identifier of 1434-6001. Over the lifetime, 382 publications have been published receiving 576 citations. The journal is also known as: EPJ A & The European physical journal.

Multi-reference many-body perturbation theory for nuclei

Abstract: The neon isotopic chain displays a rich phenomenology, ranging from clustering in the ground-state of the self-conjugate doubly open-shell stable $^{20}$Ne isotope to the physics of the island of inversion around the neutron-rich $^{30}$Ne isotope. This second (i.e. Paper II) of the present series proposes an extensive ab initio study of neon isotopes based on two complementary many-body methods, i.e. the quasi-exact in-medium no-core shell model (IM-NCSM) and the projected generator coordinate method (PGCM) that is ideally suited to capturing strong static correlations associated with shape deformation and fluctuations. Calculations employ a state-of-the-art generation of chiral effective field theory Hamiltonians and evaluate the associated systematic uncertainties. In spite of missing so-called dynamical correlations, which can be added via the multi-reference perturbation theory proposed in the first paper (i.e. Paper I) of the present series, the PGCM is shown to be a suitable method to tackle the low-lying spectroscopy of complex nuclei. Still, describing the physics of the island of inversion constitutes a challenge that seems to require the inclusion of dynamical correlations. This is addressed in the third paper (i.e. Paper III) of the present series.

Status and initial physics performance studies of the MPD experiment at NICA

Abstract: The Nuclotron-base Ion Collider fAcility (NICA) is under construction at the Joint Institute for Nuclear Research (JINR), with commissioning of the facility expected in late 2022. The Multi-Purpose Detector (MPD) has been designed to operate at NICA and its components are currently in production. The detector is expected to be ready for data taking with the first beams from NICA. This document provides an overview of the landscape of the investigation of the QCD phase diagram in the region of maximum baryonic density, where NICA and MPD will be able to provide significant and unique input. It also provides a detailed description of the MPD set-up, including its various subsystems as well as its support and computing infrastructures. Selected performance studies for particular physics measurements at MPD are presented and discussed in the context of existing data and theoretical expectations.

Analysis of the doubly-charmed tetraquark molecular states with the QCD sum rules

Abstract: In the present work, we investigate the scalar, axialvector and tensor doubly-charmed tetraquark molecular states without strange, with strange and with doubly-strange via the QCD sum rules, and try to make assignment of the $$T^+_{cc}$$ from the LHCb collaboration in the scenario of molecular states. The predictions favor assigning the $$T^+_{cc}$$ to be the lighter $$DD^{*}$$ molecular state with the spin-parity $$J^P=1^+$$ and isospin $$I=0$$ , while the heavier $$DD^{*}$$ molecular state with the spin-parity $$J^P=1^+$$ and isospin $$I=1$$ still escapes experimental detections, the observation of the heavier $$DD^{*}$$ molecular state would shed light on the nature of the $$T_{cc}^+$$ . All the predicted doubly-charmed tetraquark molecular states can be confronted to the experimental data in the future.

Multi-reference many-body perturbation theory for nuclei

Abstract: 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 ( $$e_{\mathrm {max}}=4$$ ) model space demonstrate that exact binding energies of closed- ( $${}^{16}\mathrm {O}$$ ) and open-shell ( $${}^{18}\mathrm {O}$$ , $${}^{20}\mathrm {Ne}$$ ) 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.