EPJ A Highlight - Lattice Improvement in Lattice Effective Field Theory

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The dimer-boson inverse scattering length $1/a_{3}$ versus lattice spacing at LO, NLO, and N2LO. The vertical lines give the upper limits of the fit range

Lattice calculations using the framework of effective field theory have been applied to a wide range of few-body and many-body systems. One of the challenges of these calculations is to remove systematic errors arising from the nonzero lattice spacing. While the lattice improvement program pioneered by Symanzik provides a formalism for doing this and has already been utilized in lattice effective field theory calculations, the effectiveness of the improvement program has not been systematically benchmarked.

In this work lattice improvement is used to remove lattice errors for a one-dimensional system of bosons with zero-range interactions. To this aim the improved lattice action up to next-to-next-to-leading order is constructed and it is verified that the remaining errors scale as the fourth power of the lattice spacing for observables involving as many as five particles. These results provide a guide for increasing the accuracy of future calculations in lattice effective field theory with improved lattice actions.

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EPJ A Highlight - The P2-Experiment - A future high-precision measurement of the weak mixing angle at low momentum transfer

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The experimental setup of the P2-experiment to measure the weak mixing angle at the new electron accelerator MESA in Mainz.

The P2-experiment at the new electron accelerator MESA in Mainz aims at a high-precision determination of the weak mixing angle at the permille level at low Q2. This accuracy is comparable to existing measurements at the Z-pole but allows for sensitive tests of the Standard Model up to a mass scale of 50 TeV. The weak mixing angle will be extracted from a measurement of the parity violating asymmetry in elastic electron-proton scattering. The asymmetry measured at P2 is smaller than any asymmetry measured so far in electron scattering, with an unprecedented accuracy. This review just published in EPJ A describes the underlying physics and the innovative experimental techniques, such as the Cherenkov detector, beam control, polarimetry, and the construction of a novel liquid hydrogen high-power target. The physics program of the MESA facility comprises indirect, high-precision search for physics beyond the Standard Model, measurement of the neutron distribution in nuclei, transverse single-spin asymmetries, and a possible future extension to the measurement of hadronic parity violation.

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EPJ A Highlight - The power of resolution in charge-exchange reactions

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Spectra of the 76Ge(3He,t)76As reaction unveiling an enormous number of resolved states at low excitation energies. Five color-coded spectra are stacked on top of each other showing the angular dependences. The isobaric analog state (IAS), GT resonance (GTR) and spin-dipole resonance (SDR) are indicated.

This review highlights the extraordinary power of the hadronic charge-exchange reactions at intermediate energies and at highest spectral resolution, as exemplified by the (n,p)-type (d,2He) and the (p,n)-type (3He,t) reactions. The review shows how areas of nuclear physics, astrophysics and particle physics alike benefit from such enhanced resolution. A major part of this review focuses on weak interaction processes in nuclei, especially on those, where neutrinos play a pivotal role like in solar neutrino induced reactions or in ßß decay. Unexpected and even surprising new features of nuclear structure are being unveiled as a result of high resolution. (See figure).

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EPJ A has a new Editor in Chief for Theoretical Physics II

David Blaschke

From October 2018 David Blaschke succeeds Tamás S. Biró as Editor in Chief of EPJ A for the section Theoretical Physics II: Hadron Physics and Quark Matter.

David Blaschke is Professor for Theoretical Physics of the University of Wroclaw and leading scientist at the Joint Institute for Nuclear Research in Dubna. His research interest is in developing quantum field theoretical models of strongly interacting matter to describe the transition from hadronic matter to the quark gluon plasma in the QCD phase diagram. He studies applications of these models to the physics of compact stars, their mergers and to relativistic heavy-ion collisions.

EPJ A Highlight - Solid deuterium surface degradation at ultracold neutron sources

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Highest intensities of ultracold neutrons (UCN) are in worldwide demand for fundamental physics experiments. Tests of the Standard Model of particle physics and searches for physics beyond it are performed with UCN.

Two of the leading UCN sources, at PSI and at LANL, are based on solid deuterium (sD2) at temperatures around 5 K. Here, together with NCSU they joined forces to understand UCN intensity decreases observed during pulsed neutron production. The study shows that the decrease can be completely explained by the build-up of frost on the sD2 surface during operation. Pulsed proton beams hitting the spallation targets generate heat pulses causing cycles of D2 sublimation and subsequent resublimation on the sD2 surface. Even very small frost flakes can act as total reflectors for UCN and cause an intensity decrease.

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EPJ A Highlight - The Soreq Applied Research Accelerator Facility (SARAF)

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Layout of SARAF, including the accelerator and the research areas.

The Soreq Applied Research Accelerator Facility (SARAF) is under construction in the Soreq Nuclear Research Center at Yavne, Israel. Phase I of SARAF (SARAF-I) is already in operation, generating scientific results in several fields of interest, especially the astrophysical s-process. When completed at the beginning of the next decade, SARAF-II will be a user facility for basic and applied nuclear physics, based on a 40 MeV, 5 mA CW proton/deuteron superconducting linear accelerator. This review presents first a technical overview of SARAF-I and II, including a description of the accelerator and its irradiation targets, and provides a survey of existing research programs at SARAF-I. It then describes in some detail the research potential at the completed facility. SARAF-II’s cutting-edge specifications, with its unique liquid lithium target technology, will enable world-competitive research plans in several disciplines: precision studies of beyond-Standard-Model effects by trapping light exotic radioisotopes (including meaningful studies already at SARAF-I); extended nuclear astrophysics research with higher-energy neutrons, including generation and studies of exotic neutron-rich isotopes relevant to the astrophysical r-process; nuclear structure of exotic isotopes; high-energy neutron cross sections for basic nuclear physics and material science research, including neutron-induced radiation damage; neutron-based imaging with an imaging plane flux similar to that of a 5 MW research reactor; accelerator-based neutron therapy; and, last but not least, novel radiopharmaceuticals development and production.

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EPJ A Highlight - Unresolved puzzles in exotic nuclei

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Closed points are matter radii extracted from experiments for isotopes of Helium (diamonds), Lithium (squares), and Beryllium (triangles).

A new review highlights the historical developments in our understanding of the nuclear structure of unstable and unbound forms of helium, lithium and beryllium

Research into the origin of elements is still of great interest. Many unstable atomic nuclei live long enough to be able to serve as targets for further nuclear reactions - especially in hot environments like the interior of stars. And some of the research with exotic nuclei is, for instance, related to nuclear astrophysics. In this review published in EPJ A, Terry Fortune from the University of Pennsylvania, in Philadelphia, USA, discusses the structure of unstable and unbound forms of Helium, Lithium, and Beryllium nuclei that have unusually large neutron to proton ratios - dubbed ‘exotic’ light nuclei. The author offers an account of historical milestones in measurements and the interpretation of results pertaining to these nuclei.

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EPJ A - New Structure of the Editorial Board and Editor-in-Chief Appointments

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Editorial Board Meeting Heidelberg 2017

EPJ is pleased to announce significant changes concerning the editorial structure of EPJ A. Following the continuous growth and broadening of the journal’s scope over the past few years, the theory section has now been divided into Theory I (Nuclear Physics) and Theory II (Hadron Physics and Quark Matter). Theory I is headed by Prof. Thomas Duguet, who has been newly appointed for this position, while Theory II continues to be headed by Prof. Tamás Biró. Further, and with immediate effect, Prof. Maria Jose Garcia Borge has been appointed Editor-in-Chief for the Experimental Physics section of the journal.

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EPJ A Highlight - From experiment to evaluation, the case of n+238U

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Evaluated nuclear data represent the bridge between experimental and theoretical achievements and final user applications. The complex evolution from experimental data towards final data libraries forms the cornerstone of any evaluation process. Since more than 90% of the fuel in most nuclear power reactors consists of 238U, the respective neutron induced cross sections are of primary importance towards accurate neutron transport calculations. Despite this significance, the relevant experimental data for the 238U(n,γ) capture reaction have only recently provided for a consistent description of the resonance region. In this work, the 238U(n,γ) average cross sections were evaluated in the energy region 5-150 keV, based on recommendations by the IAEA Neutron Standards projects and experimental data not included in previous evaluations.

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EPJ A Highlight - Nuclear and Quark Matter at High Temperature

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Left: sample spectral densities, Right: the resulting scaled energy densities.

In high-temperature field theory applied to nuclear physics, in particular to relativistic heavy-ion collisions, it is a longstanding question how hadrons precisely transform into a quark-gluon matter and back. The change in the effective number of degrees of freedom is rather gradual than sudden, despite the identification of a single deconfinement temperature. In order to gain an insight into this issue while considering the structure of the QGP we review the spectral function approach and its main consequences for the medium properties, including the shear viscosity. The figure plots a sample spectral density on the left and the effective number of degrees of freedom (energy density relative to the free Boltzmann gas) to the right. Two thin spectral lines result in a doubled Stefan-Boltzmann limit (SB), while any finite width reduces the result down to a single SB. When spectral lines become wide, their individual contributions to energy density and pressure drops. Continuum parts have negligible contribution. This causes the melting of hadrons like butter melts in the Sun, with no latent heat in this process.

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Editor-in-Chief
R. E. Continetti
ISSN: 2195-7045 (Electronic Edition)

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