Low-energy Nuclear Physics Research Articles

Decoupling in the similarity renormalization group for nucleon-nucleon forces

Decoupling via the similarity renormalization group (SRG) of low-energy nuclear physics from high-energy details of the nucleon-nucleon interaction is examined for two-body observables and few-body binding energies. The universal nature of this decoupling is illustrated and errors from suppressing high-momentum modes above the decoupling scale are shown to be perturbatively small.

Chiral perturbation theory: An effective field theory

The concept of an effective field theory (EFT), i.e. a theory which is valid only in a limited range of parameter space, is one which has become highly developed recently. After presenting familiar examples from the realms of classical and quantum mechanics together with condensed matter physics, we show that QCD has an intriguing parallel with superconductivity in that, by using quark–antiquark (mesonic) degrees of freedom and exploiting the symmetries of the theory, a useful and powerful theory–chiral perturbation theory–results, which offers a complete and rigorous description of low energy particle and nuclear physics.

Extension of the Monte-Carlo code MOCADI to fusion-evaporation reactions

The Monte-Carlo code MOCADI has been extended, besides to fission and fragmentation reactions, also to fusion-evaporation reactions. The updated version includes the cross sections and the reaction kinematics for the production of evaporation residues calculated according to the statistical model code PACE2, while the atomic interaction with matter can be treated either with the code ATIMA or with the code TRIM. The present version of MOCADI can now be employed world-wide for design studies of new low-energy nuclear physics facilities and for the optimization of experiments involving fusion-evaporation reactions, e.g. mass measurements, laser spectroscopy, super-heavy synthesis.

Building a universal nuclear energy density functional

This talk describes a new project in SciDAC II in the area of low-energy nuclear physics. The motivation and goals of the SciDAC are presented as well as an outline of the theoretical and computational methodology that will be employed. An important motivation is to have more accurate and reliable predictions of nuclear properties including their binding energies and low-energy reaction rates. The theoretical basis is provided by density functional theory, which the only available theory that can be systematically applied to all nuclei. However, other methodologies based on wave function methods are needed to refine the functionals and to make applications to dynamic processes.

Modern topics in theoretical nuclear physics

Over the past five years there have been profound advances in nuclear physics based on effective field theory and the renormalization group. In this review, we summarize these advances and discuss how they impact our understanding of nuclear systems and experiments that seek to unravel their unknowns. We discuss future opportunities and focus on modern topics in low-energy nuclear physics, with special attention on the strong connections to many-body atomic and condensed-matter physics, as well as to astrophysics. This makes it an exciting era for nuclear physics.PACS Nos.: 21.60.–n, 21.30.Fe

Hadron production from resonance decay in relativistic collisions

A statistical model for decay and formation of heavy hadronic resonances is formulated. The resonance properties become increasingly uncertain with increasing resonance mass. Drawing on analogy with the situation in low-energy nuclear physics, we employ the Weisskopf approach to the resonance processes. In the large-mass limit, the density of resonance states in mass is governed by a universal Hagedorn-like temperature TH. As resonances decay, progressively more and more numerous lighter states get populated. For TH≃170 MeV, the model describes data for the hadron yield ratios at the RHIC and SPS energies under the extreme assumption of a single heavy resonance giving rise to measured yields.

The NuSTAR facilty at FAIR

The NuSTAR facility at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt with its high intensity secondary beams of short-lived ions at relativistic energies will be unique worldwide. The combination of relativistic in-flight fragmentation and fission products with storage rings and the simultaneous availability of stored antiprotons and electrons will allow unique experiments to be performed that will address the fundamental and long-standing questions of low energy nuclear physics. A brief review of the experimental capabilities that have been proposed for experiments at the Super-FRagment-Separator at FAIR and a selection of the physics questions that will be addressed is given. Only a short glimpse at the physics questions being addressed and the observables providing answers to these questions can be given here.

A New approach for cross section measurements at low energies using a monolithic silicon telescope

We propose a new experimental technique for the study of low-energy nuclear reactions using a monolithic silicon telescope, which has a thin silicon layer with a thickness of 1 μ m. A feasibility study of this technique for the investigation of the 8 Li( α ,n) 11 B reaction at low energies has been performed using the GEANT4 simulation code and a calibrated alpha source. Our results indicate the possibility of a novel technique for low-energy nuclear physics experiments relevant to astrophysics.

Counter terms for low momentum nucleon–nucleon interactions

There is much current interest in treating low energy nuclear physics using the renormalization group (RG) and effective field theory (EFT). Inspired by this RG-EFT approach, we study a low-momentum nucleon–nucleon (NN) interaction, V low- k , obtained by integrating out the fast modes down to the scale Λ∼2 fm −1. Since NN experiments can only determine the effective interaction in this low momentum region, our chief purpose is to find such an interaction for complex nuclei whose typical momenta lie below this scale. In this paper we find that V low- k can be highly satisfactorily accounted for by the counter terms corresponding to a short range effective interaction. The coefficients C n of the power series expansion ∑ C n q n for the counter terms have been accurately determined, and results derived from several meson-exchange NN interaction models are compared. The counter terms are found to be important only for the S, P and D partial waves. Scaling behavior of the counter terms is studied. Finally we discuss the use of these methods for computing shell model matrix elements.

Instanton contribution to the pion electromagnetic form factor atQ2>1GeV2

We study the effects of instantons on the charged pion electromagnetic form factor at intermediate momenta. In the single instanton approximation (SIA), we predict the pion form factor in the kinematic region ${Q}^{2}=2--10{\mathrm{GeV}}^{2}.$ By developing the calculation in a mixed time-momentum representation, it is possible to maximally reduce the model dependence and to calculate the form factor directly. We find the intriguing result that the SIA calculation coincides with the vector dominance monopole form, up to a surprisingly high momentum transfer ${Q}^{2}\ensuremath{\sim}10{\mathrm{GeV}}^{2}.$ This suggests that vector dominance for the pion holds beyond low energy nuclear physics.

Radioactive beam experiments with large gamma-ray detector arrays

High-resolution γ-ray spectroscopy is one of the most powerful and versatile experimental techniques in low-energy nuclear physics research. With the continuing development of hyper-pure germanium (HPGe) detector technology, including multi-crystal detectors, contact segmentation, and digital signal processing techniques, large γ-ray detector arrays will continue to play a major role in the experimental programs at existing and future radioactive ion beam facilities. This paper provides an overview of recent progress in, and future plans for, the development of large γ-ray spectrometers at such facilities, including the recent commissioning of the 8π spectrometer at ISAC-I and the proposed TRIUMF-ISAC gamma-ray escape suppressed spectrometer array for the ISAC-II facility.

The operational performance of the Yale ESTU

The ESTU began operation in 1988 and achieved the design voltage of 20 MV in 1990. Since that time, improvements to the gas handling system, negative ion injector, accelerator terminal and control system have greatly increased its capability and reliability. Today, the ESTU can efficiently produce an extensive assortment of stable ions at wide-ranging energies in support of low-energy nuclear physics.

Three-Compton telescope: theory, simulations, and performance

The advent of highly segmented gamma-ray detectors with good energy resolution has made a new class of gamma-ray detectors possible. These instruments record the positions and energies of each individual gamma-ray interaction with high precision. Analysis of the individual interactions can provide energy and directional information, even for events with only partial energy deposition. Advantages over traditional gamma-ray detectors include enhanced efficiency, background rejection, gamma-ray imaging, and sensitivity to polarization. Consider those gamma-rays that interact three or more times in the detector. The energy of the gamma-ray that initiated one of these events is uniquely determined by measuring the energies of the first two interactions and the scatter angle of the second interaction. The precision of this measurement is limited by the energy and position resolution of the detector, but also from Doppler broadening that results from gamma-ray scattering off-bound electrons in the detector. It is also essential to correctly sequence the first three interactions. The importance of Doppler broadening is greater in higher Z-materials, thus silicon becomes a good choice for the detector material. We discuss performance and simulations of the multiple Compton telescope. Possible applications include an advanced Compton telescope (ACT) for astrophysics, a medical multiple-gamma detector high-energy imaging survey instrument, and a gamma-ray tracking detector for future low-energy nuclear physics experiments.

The u– d quark mass difference and nuclear charge symmetry breaking

The group theoretical analysis of the Coleman-Glashow tadpole picture of "meson-mixing" is quantitatively reproduced by the u-d constituent quark mass difference in quantum loop calculations of the self-energies of mesons. This demonstration that the Coleman-Glashow scales can be directly calculated from the constituent $u - d$ quark mass difference finishes the link between charge symmetry breaking in low energy nuclear physics and the $u - d$ quark mass difference in particle physics.

Equivalence of model space techniques and the renormalization group for a separable model problem

Lee–Suzuki similarity transformations and Krenciglowa–Kuo folded diagrams are two common methods used to derive energy independent model space effective interactions for nuclear many-body systems. We demonstrate that these two methods are equivalent to a Renormalization Group (RG) analysis of a well-studied problem in quantum mechanics. The effective low-momentum potentials V eff obtained from model space methods are shown to obey the same scaling equation for V eff that RG arguments predict. This indicates that model space methods might be of interest to those studying low-energy nuclear physics using Effective Field Theories (EFT). We find the new result that all of the different energy independent model space techniques yield a unique low-momentum V eff when applied to the toy model under consideration.

X-ray spectrometry using polycapillary X-ray optics and position sensitive detector

Polycapillary X-ray optics (capillary X-ray lens) are now popular in X-ray fluorescence (XRF) analysis. Such an X-ray lens can collect X-rays emitted from an X-ray source in a large solid angle and form a very intense X-ray microbeam which is very convenient for microbeam X-ray fluorescence (MXRF) analysis giving low minimum detection limits (MDLs) in energy dispersive X-ray fluorescence (EDXRF). A new method called position sensitive X-ray spectrometry (PSXS) which combines an X-ray lens used to form an intense XRF source and a position sensitive detector (PSD) used for wavelength dispersive spectrometry (WDS) measurement was developed recently in the X-ray Optics Laboratory of Institute of Low Energy Nuclear Physics (ILENP) at Beijing Normal University. Such a method can give high energy and spacial resolution and high detection efficiency simultaneously. A short view of development of both the EDXRF using a capillary X-ray lens and the new PSXS is given in this paper.

Implications for the πNN coupling constant from pp and np spin transfer measurements

A complete set of spin-transfer coefficients for forward-angle pp elastic scattering at 198 MeV has been measured at the Indiana University Cyclotron Facility, with uncertainties far smaller than previous measurements. These particular observables, and this kinematic regime, were specifically chosen to maximize the sensitivity of these measurements to the neutral pion-nucleon coupling constant, a fundamental quantity in low and intermediate energy nuclear physics whose value remains highly controversial. To achieve the desired experimental uncertainty, several components of the apparatus required calibration at a higher level of precision than had been previously achieved, and new procedures in data acquisition and analysis were developed in order to minimize many of the possible sources of systematic error. Our primary conclusion from this work is that our results provide strong support for modern potential models of the NN interaction in which a relatively weak pion coupling is employed (g02 ≈ 13.6). Moreover, our data deviate significantly from the predictions of older potentials in which g02 is ~14.4. Calculations carried out in a one-boson exchange framework, using the Bonn B potential, suggest that most of these differences can be accounted for by simply reducing the πNN coupling from 14.4 to 13.6 for the long-range (higher partial wave) pion contributions in these models.

Exotic nuclei: Recent highlights and perspectives

The present article aims at giving an aperçu on the important effort nowadays invested into radioactive beam experiments. Selected and very recent examples are used in order to demonstrate the remarkable progress obtained just before the turn of this century. Together with the advent of new radioactive beam facilities, planned or already under construction, these recent experiments point to the new opportunities and open the perspectives for low-energy nuclear physics of the next millenaire. A short discussion of the different aspects of making (beams of) nuclei far from stability is included in order to present the variety of the possible technical approaches and their complementarity.

Lasers as a bridge between atomic and nuclear physics

This paper reviews the application of visible and ultraviolet laser radiation to several topics in low-energy nuclear physics. We consider laser-induced nuclear anti-Stokes transitions, laser-assisted and laser-induced internal conversion, and the electron bridge and inverse electron bridge mechanisms as tools for deexcitation and excitation of low-lying nuclear isomeric states. A study of the anomalously low-lying nuclear isomeric states (in the case of the 229Th nucleus) is presented in detail.

Isospin symmetry breakings as from QCD sum rules

We investigate isospin symmetry breakings, especially those connected with pion-nucleon couplings and the neutron-proton mass difference, by making use of the method of QCD sum rules in the presence of an external pion field. Manifestations of such isospin symmetry breakings are examined briefly in relation to low-energy nucleon-nucleon 1 S 0 scatterings. We discuss the prospect of understanding the various isospin symmetry breaking phenomena observed in low-energy nuclear physics by extending chiral perturbation theory ( χPT) to include isospin symmetry breakings (ISB). We emphasize that QCD sum rules help to establish χPT/ISB out of QCD by eliminating an excessive number of ISB condensate parameters, making χPT/ISB a worthy extension of χPT.