Search results for "Exchange"
showing 10 items of 2035 documents
Response of asymmetric nuclear matter to isospin-flip probes
1999
Abstract We investigate the RPA response of asymmetric nuclear matter to external fields which induce charge exchange between nucleons, both at zero and finite temperature. Closed expressions are obtained for the RPA response in each spin channel when the nucleon–nucleon interaction is of the Skyrme type. Exchange terms are fully taken into account. We consider the transferred momentum, asymmetry and temperature as the relevant parameters of our study. Special emphasis is given to the role of neutron excess in relation to the collective states at low momentum.
Double charge exchange reactions as a probe for neutrinoless double beta decay nuclear matrix elements
2020
Abstract The formalism to describe heavy-ion double charge exchange (DCE) processes in the eikonal and small-momentum transfer approximations introduced in Phys. Rev. C 98, 061601(R) (2018) is briefly discussed. It is also shown that, under the previous approximations, the heavy-ion DCE cross-section can be factorized in terms of a reaction and a nuclear part. A double charge exchange effective potential is explicitly derived in the closure approximation and also for the first time the explicit form of the DCE nuclear matrix elements, that are of the form of double Gamow-Teller and double Fermi. The recent hypothesis of a linear correlation between double Gamow-Teller neutrinoless double be…
Tz=−1→0βdecays ofNi54,Fe50,Cr46, andTi42and comparison with mirror(He3,t)measurements
2015
We have studied the β decay of the Tz=−1, f7/2 shell nuclei Ni54, Fe50, Cr46, and Ti42 produced in fragmentation reactions. The proton separation energies in the daughter Tz=0 nuclei are relatively large (≈4–5 MeV) so studies of the γ rays are essential. The experiments were performed at GSI as part of the Stopped-beam campaign with the RISING setup consisting of 15 Euroball Cluster Ge detectors. From the newly obtained high precision β-decay half-lives, excitation energies, and β branching ratios, we were able to extract Fermi and Gamow-Teller transition strengths in these β decays. With these improved results it was possible to compare in detail the Gamow-Teller (GT) transition strengths …
Two-body Mechanisms in Pion Scattering and Pion Photoproduction on the Trinucleon
1995
A breakdown of the Impulse Approximation is studied in pion photoproduction and pion charge exchange on 3He at high momentum transfers. The usual DWIA formalism with Faddeev wave functions which works well for small momentum transfers deviates from experimental measurements by up to two orders of magnitude for Q 2 > 6 fm−2. It is found that the explicit inclusion of two-body mechanisms, where the photon or pion is absorbed on one nucleon and the pion is emitted from another nucleon removes most of the disagreement with the data.
Soft modes and mode splitting in paramagnetic TbP§
1980
In contrast to spin-only systems the paramagnetic phases of systems with crystal field split ground multiplets exhibit magnetic excitations of finite energy. In the presence of a magnetic exchange coupling the excitons will propagate through the lattice. A measurement of the dispersion allows in principle an insight into the exchange interaction, which is of fundamental importance for the understanding of the magnetic phenomena. Unfortunately the evolution of the dispersion at low temperatures is in most cases interrupted by the onset of magnetic order due to an alignment of the magnetic moments of the crystal field ground state. A noticeable dispersion of well-defined excitons is only expe…
Prediction of Swirling Flow in a Corrugated Channel
1991
Laminar and turbulent flow in a corrugated channel is simulated using HARWELL-FLOW3D. The channel represents a typical cell within a proposed design for the heat-transfer element of a rotary regenerator. Velocity vectors in planes perpendicular and parallel to the axis of a corrugation are visualised using Harwell’s graphics package, OUTPROC. Both programs were mn on Harwell’s Cray 2. The velocity vector plots show clear evidence of swirl, which is thought to be the mechanism responsible for the high rates of heat transfer in this type of heat-exchanger geometry. The swirl strength is shown to be a function of the channel geometry.
Directly proving the bosonic nature of photons
2021
A simple yet effective optical set-up, employing two controllable, indistinguishable photons, is proven to allow a direct measurement of the exchange phase due to the bosonic particle statistics.
Antiscreening of the Ampère force in QED and QCD plasmas
2013
The static forces between electric charges and currents are modified at the loop level by the presence of a plasma. While electric charges are screened, currents are not. The effective coupling constant at long distances is enhanced in both cases as compared to the vacuum, and by different amounts, a clear sign that Lorentz symmetry is broken. We investigate these effects quantitatively, first in a QED plasma and secondly using non-perturbative simulations of QCD with two light degenerate flavors of quarks.
Heavy meson-antimeson molecules in effective field theory: The role of one pion exchange and heavy quark spin symmetry
2012
In this contribution we study heavy meson-antimeson molecules from the effective field theory perspective. In particular, we are concerned with the role of the one pion exchange interaction and heavy quark spin symmetry in the description of molecular states. As we will show, one pion exchange is in general a perturbative effect. This means that at lowest order we can describe the molecular states in terms of contact interactions only, a remarkable simplification. The application of heavy quark spin symmetry will be very interesting, as we will be able to predict new heavy meson-antimeson bound states from known ones. For instance, if we assume that the X(3872) is in fact a JPC = 1++ DD/DD …
QCD Confinement and the Meson Spectrum
2003
From QCD and lattice calculations two specific forms of quark confining potential, a strict linear and a screened linear confinement, come out. Both forms of the potential, implemented by the one gluon exchange interaction, are applied to the description of heavy quarkonia: cc and bb. Applications to light hadrons, mesons and baryons, are also commented.