2021 Impact factor 1.611
Atomic, Molecular, Optical and Plasma Physics

EPJ A Topical Issue: An Experimental Program with Positron Beams at Jefferson Lab

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The perspective of high energy and high duty cycle polarized positron beams in complement to the existing CEBAF (Continuous Electron Beam Accelerator Facility) electron beams is attracting a lot of interest. Following the proof-of-principle PEPPo (Polarized Electrons for Polarized Positrons) experiment demonstrating a new scheme for producing highly polarized positrons, the Jefferson Lab (JLab) Positron Working Group (PWG) engaged in the thorough development of the experimental program that would be achieved at JLab with such beams. It encompasses the determination of the physics quantities that characterize nucleons and nuclei structure: electromagnetic form factors, generalized polarizabilities, parton distributions, and generalized parton distributions. It also concerns some of the hottest questions of the field as the charge radius of the proton and the occurrence of physics beyond the standard model through the search of low mass dark matter particles, the measurement of weak neutral-current couplings, and the investigation of charged lepton flavour violation.

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EPJA appoints Patrizia Rossi as Managing Editor for Reviews and Letters to the Editor (experiment)

Patrizia Rossi

The publishers of The European Physical Journal A: Hadrons and Nuclei are pleased to announce the appointment of Dr Patrizia Rossi as Managing Editor for Reviews and Letters to the Editor (experiment) as of 1 January 2022.

Patrizia Rossi is the Deputy Associate Director for Nuclear Physics at Jefferson Lab (JLab), Research Professor at George Washington University, and Research Director at the Frascati National Laboratories of INFN-Italy (on leave). Her scientific research focuses on hadron and nuclear physics using electromagnetic probes. This research aims to study the structure of the nucleon and the nature of the strong interaction in terms of fundamental constituents of QCD. Her most recent investigations are related to the study of the transverse momentum parton distribution functions for which she is co-spokesperson for several experiments.

EPJ A Highlight - Celebrating the impacts of Jacques Raynal’s work in the development of nuclear reaction formalism, codes and analysis

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This topical article edition of EPJ A is dedicated to the memory of French nuclear physicist Jacques Raynal, who passed away on April 10th, 2020.

It illustrates, through a series of peer-reviewed articles, the various facets of what Raynal and his colleagues accomplished, as well as the profound influence of his results in several domains of nuclear reactions, both for theory formalism and for the analysis and understanding of experimental observables. The articles also demonstrate how his work paved the way for the future development of concepts and numerical codes for nuclear reaction calculations.

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EPJ A Highlight - Celebrating the life and work of Mahir Hussein through cutting-edge research

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A new collection of papers focusing on the dynamics of nuclei pays fitting tribute to Iraqi/Brazilian physicist Mahir Saleh Hussein.

On 16th May 2019 Iraqi/ Brazilian physicist Mahir Saleh Hussein passed away leaving behind a distinguished career of achievements in a broad range of physics disciplines. There is, perhaps, no better way of paying tribute to this influential figure in physics than presenting a collection of cutting-edge, peer-reviewed papers. A special edition of EPJ A, edited by Valdir Guimarães, Universidade de São Paulo Instituto de Física, Brazil, Carlos Bertulani, Department of Physics of the Texas A&M University-Commerce, USA, and Nicolas Alamanos, Deputy Director of the Institute of Research into the Fundamental Laws of the Universe (IRFU), France, brings together a collection of papers focusing on nuclei clustering and dynamics as a fitting tribute to Hussein.

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EPJ A Highlight - THOR: Driving collaboration in heavy-ion collision research

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Analysing collisions between heavy ions. Image by Pcharito - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/ index.php?curid=31433194

As an expansive platform for collaboration between different research groups, the THOR COST Action has enabled hundreds of physicists studying the aftermath of high-energy collisions between heavy ions to improve their predictions.

In the universe’s earliest moments, particles existed in an unimaginably hot plasma, whose behaviour was governed by deeply complex webs of interaction between individual particles. Today, researchers can recreate these exotic conditions through high-energy collisions between heavy ions, whose products can tell us much about how hot, strongly-interacting matter behaves. Yet without extensive, highly coordinated collaborations between researchers across many different backgrounds, studies like this simply wouldn’t be possible. This Topical Issue of EPJ A draws together a large collection of papers inspired by the theory of hot matter and relativistic heavy-ion collisions (THOR) European Cooperation in Science and Technology (COST) Action. Running between November 2016 and April 2021, THOR has provided a way for over 300 researchers involved in heavy-ion collision analysis to freely exchange their ideas, leading to exciting new advances in the wider field of particle physics.

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EPJ A Highlight - Paving the way for effective field theories

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Cover picture: image courtesy of Germain Caminade (http://germaincaminade.com/)

A detailed analysis of theories which approximate the underlying properties of physical systems could lead to new advances in studies of low-energy nuclear processes

Over the past century, a wide variety of models have emerged to explain the complex behaviours which unfold within atomic nuclei at low energies. However, these theories bring up deep philosophical questions regarding their scientific value. Indeed, traditional epistemological tools have been rather elaborated to account for a unified and stabilised theory rather than to apprehend a plurality of models. Ideally, a theory is meant to be reductionist, unifying and fundamentalist. In view of the intrinsic limited precision of their prediction and of the difficulty in assessing a priori their range of applicability, as well as of their specific and disconnected character, traditional nuclear models are necessarily deficient when analysed by means of standard epistemological interpretative frameworks.

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EPJ A Highlight - Automated symmetry adaption in nuclear many-body theory

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Symmetry reduction process of a prototypical many-body expression leading to an equivalent symmetry-reduced form. Recoupling coefficients arising from the AMC program are shown in red.

The extreme cost of solving the A-nucleon Schrödinger equation can be minimized by leveraging rotational symmetry and, thus, enable the computation of observables in heavy nuclei and/or with high precision.

The associated reduction process, which amounts to re-expressing the working equations in terms of rotationally-invariant objects, requires lengthy symbolic manipulations of elaborate algebraic identities.

For the first time, this involved process is automated by a powerful graph-theory-based tool, the AMC code, which condenses months of error-prone derivations into a simple computational task performed within seconds.

The AMC program tightens the gap for a full automation of the many-body workflow, thereby lowering the time required to build and test novel quantum many-body formalisms.

EPJ A Highlight - Emergence of nuclear rotation from elementary interactions between the nucleons

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Rotational bands in an ab initio calculations for the nuclear excitation spectrum of 11Be.

Nuclei are quantum many-body systems which exhibit emergent degrees of freedom, from shell structure and clustering to collective rotations and vibrations. Such emergent phenomena are traditionally the domain of phenomenological models, yet their description can now be placed on a more fundamental footing in terms of microscopic theory. The nature and emergence of rotational bands are presently investigated in light nuclei through ab initio nuclear many-body calculations. Beyond simply analyzing spectroscopic signatures, the structural insight are investigated in terms of angular momentum coupling schemes and group theoretical correlations as underpinnings for the rotational structure.

EPJ A Highlight - Advancing AGATA – Future Science with The Advanced Gamma Tracking Array

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Artist's view of the 4p AGATA spectrometer showing the mechanical holding frame (yellow) and cryostat dewars (blue) of the Ge detectors.

AGATA – the Advanced Gamma Tracking Array is a multi-national European project for the ultimate high-resolution gamma-ray spectrometer for nuclear physics capable of measuring γ rays from a few tens of keV to beyond 10 MeV, with unprecedented efficiency, excellent position resolution for individual γ-ray interactions and correspondingly unparalleled angular resolution, and very high count-rate capability. AGATA will be a flag ship spectrometer and have an enormous impact on nuclear structure studies at the extremes of isospin, mass, angular momentum, excitation energy and temperature. It will enable us to uncover and understand hitherto hidden secrets of the atomic nucleus.

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EPJ A Highlight - Towards the solution of the “hyperon puzzle”

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Neutron star’s mass-radius relation with and without hyperons. Masses of the pulsars PSR J0348+0432 and PSR J0740+6620 are shown with their observation uncertainties.

The possible presence of strange matter in the core of neutron stars has given rise to the so-called hyperon puzzle: hyperonic degrees of freedom are energetically allowed in the extreme density conditions believed to exist in the core of Neutron Stars, but hyperons reduce the internal pressure of the star, which then cannot compensate the gravitational field to sustain the most massive compact stars observed.

This work reports on the effect of three-body interactions when including a Lambda hyperon on the properties of hyper-nuclei and Neutron Stars. State-of-the-art three-body chiral effective interactions are introduced in a microscopic Brueckner-Hartree-Fock calculation.

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Editors-in-Chief
A. Beige, J. Burgdörfer and S. Ptasinska
"I take this opportunity to thank the EPJD editorial office for the rapid and efficient processing of our paper.

Mauro Temporal

ISSN (Print Edition): 1434-6060
ISSN (Electronic Edition): 1434-6079

© EDP Sciences, Società Italiana di Fisica and Springer-Verlag