Interactions In Light Nuclei Research Articles

Investigation of the low-energy kaons hadronic interactions in light nuclei by AMADEUS

Investigation of the low-energy kaons hadronic interactions in light nuclei by AMADEUS

Chiral Three-Nucleon Interactions in Light Nuclei, Neutron-α Scattering, and Neutron Matter.

We present quantum Monte Carlo calculations of light nuclei, neutron-α scattering, and neutron matter using local two- and three-nucleon (3N) interactions derived from chiral effective field theory up to next-to-next-to-leading order (N(2)LO). The two undetermined 3N low-energy couplings are fit to the (4)He binding energy and, for the first time, to the spin-orbit splitting in the neutron-α P-wave phase shifts. Furthermore, we investigate different choices of local 3N-operator structures and find that chiral interactions at N(2)LO are able to simultaneously reproduce the properties of A=3,4,5 systems and of neutron matter, in contrast to commonly used phenomenological 3N interactions.

Investigation of the low-energy kaons hadronic interactions in light nuclei by AMADEUS

The AMADEUS experiment aims to provide unique quality data of K− hadronic interactions with light nuclear targets, in order to solve fundamental open questions in the non-perturbative strangeness QCD sector, like the controversial nature of the Λ(1405) state, the yield of hyperon formation below threshold, the yield and shape of multi-nucleon K− absorption, processes which are intimately connected to the possible existence of exotic antikaon multi-nucleon clusters. AMADEUS takes advantage of the DAΦNE collider, which provides a unique source of monochromatic low-momentum kaons and exploits the KLOE detector as an active target, in order to obtain excellent acceptance and resolution data for K− nuclear capture on H, 4 He, 9 Be and 12 C, both at-rest and in-flight.

Investigation of the low energy kaons hadronic interactions in light nuclei by AMADEUS

The AMADEUS experiment aims to provide unique quality data for K − interaction with nucleons and light nuclei, both at-rest and in-flight (for K − momenta of about 100 MeV). The goal is to solve longstanding open issues in the non-perturbative QCD in the strangeness sector, like the nature of the Λ(1405) state, the resonant versus non-resonant yield in nuclear K − capture and the properties of kaonic nuclear clusters which are strongly related to the multi-nucleon absorption processes. We can take advantage of the DA ΦNE collider representing a unique source of monochromatic low-momentum kaons, whose nuclear interaction with the materials of the KLOE detector (used as an active target) furnish us excellent acceptance and resolution data for K − capture on H, 4He, 9Be and 12C, both at-rest and in-flight. AMADEUS step 0 consisted in the analysis of the 2004-2005 KLOE data. A second step consisted in the implementation in the central region of the KLOE detector of a pure graphite target, providing a high statistic sample of K − 12 C nuclear captures at rest. For the future, new setups for various dedicated targets are under preparation.

Investigation of the low energy kaons hadronic interactions in light nuclei by AMADEUS

The AMADEUS experiment has the aim to perform studies of the low energy hadronic interactions of negatively charged kaons with nucleons and nuclei, which are fundamental to solve longstanding open questions in the non-perturbative QCD in the strangeness sector. The DAΦNE collider provides a unique source of monochromatic low-momentum kaons, whose nuclear interaction with the materials of the KLOE detector (used as an active target) provide us excellent acceptance and resolution data for K− capture on H, 4He, 9Be and 12C, both at-rest and in-flight. AMADEUS step 0 consisted in the analysis of the 2004-2005 KLOE data. A second step consisted in the implementation in the central region of the KLOE detector of a pure graphite target, providing a high statistic sample of K− 12C nuclear captures at rest. For the future, new setups for various dedicated targets are under preparation.

Studies of the ${\boldsymbol{\bar{K}}}\boldsymbol{N}$ interaction at DAΦNE

AMADEUS is an experiment planned to be performed at the DAΦNE e+e− collider of the Frascati National Laboratories (Italy) of INFN, to investigate the antikaon-nuclei interaction at low energies. AMADEUS will perform, for the first time, full-acceptance studies of antikaon interaction in light nuclei, including a complete experimental program for the case of the kaonic nuclear clusters. The study of the absorption of antikaon by the nucleus will provide information concerning the \(\bar{K}N\) interaction and the modification of the kaon mass in the nuclear medium. The experiment is being preceded by the study of the hadronic interactions of K− in the 4He of the drift chamber from the KLOE experiment data.

Multiplicity fluctuations of particles produced in interactions of light nuclei with carbon nuclei at a momentum of 4.2 A GeV/c and their theoretical interpretation

New experimental data on fluctuations in the multiplicities of negatively charged particles in interactions of light nuclei (p, d, 4He, 12C) with carbon nuclei at a momentum of 4.2 A GeV/c in 4π geometry are reported. The data indicate a behavior similar to that earlier observed by the NA49 Collaboration. The cascade evaporation model, FRITIOF model, and UrQMD 1.3 model are used to analyze the data. The dependence of the fluctuations on nuclear collision centrality is theoretically described without any exotic assumptions. According to the FRITIOF model, the dependence of the multiplicity fluctuations on the collision centrality is to a large extent governed by fluctuations in the number of “wounded” nucleons that are associated with the experimental observation conditions. The NA49 Collaboration data are also described.

Probing chiral interactions in light nuclei

Chiral two- and three-nucleon interactions are studied in few-nucleon systems. We investigate the cut-off dependence and convergence with respect to the chiral expansion. It is pointed out that the spectra of light nuclei are sensitive to the three-nucleon force structure. As an example, we present calculations of the 1+ and 3+ states of 6Li using the no-core shell model approach. The results show contributions of the next-to-next-to leading order terms to the spectra, which are not correlated to the three-nucleon binding energy prediction.

Probing chiral interactions in light nuclei

Chiral two- and three-nucleon interactions are studied in few-nucleon systems. We investigate the cut-off dependence and convergence with respect to the chiral expansion. It is pointed out that the spectra of light nuclei are sensitive to the three-nucleon force structure. As an example, we present calculations of the 1 + and 3 + states of 6Li using the no-core shell model approach. The results show contributions of the next-to-next-to leading order terms to the spectra, which are not correlated to the three-nucleon binding energy prediction.

Parity nonconservation in 6Li

In order to extract information about parity nonconservation (PNC)weak interactions inlight nuclei we propose a theoretical investigation of theprobability for the parity forbidden α-decay6Li*I πT = 0+1; E* = 3.56 MeV→α + d. Such a process is calculated in this paperwithin the one-level-one-channel Fonda-Newton approach tonuclear resonance reaction, using an effective PNC interactionHamiltonian. The interior wavefunctions are given by the shellmodel with effective residual interactions given by the OXBASHcode. The exterior wavefunctions are calculated from adouble-folding model interaction potential acting between theα-particle and the deuteron, and obtained with the M3Ynucleon-nucleon interaction. With this theoretical framework we obtainthe parity-nonconservation width decay to be in the followingrange ΓPNC = (0.08-4.7)×10-9 eV.

Electromagnetic and weak interactions in light nuclei studied with the new dynamic model

Antisymmetrized Multicluster Dynamic Model with Pauli projection (AMDMP) recently developed by our group for quantitative description of light nuclei is reviewed and compared to more traditional models like RGM etc. Main emphasis is given to the AMDMP predictions for spectral characteristics and for e.-m. and weak interaction properties of light nuclei. Many advantages of the model developed before as compared with the more traditional models are vividly demonstrated. Among them: (i) a high accuracy and reliability of predictions and absence of any fitting or free parameters, (ii) clear meaning of exchange effects and a physically correct separation of antisymmetrization effect contributions to e.-m. and weak transitions from those to the dynamics of cluster interaction. As particular interesting applications of the model developed we discuss spectra, Coulomb displacements and static characteristics for nuclei with A=6 ( 6He 6Li 6Be) and A=9 ( 9Be and 9B) and elastic and inelastic e.-m. form factors of 6Li and 9Be. A generalization of (A)MDMP version for a quantitative treatment of the complicated near-threshold few body continuum is described. Very high accuracy of the continuum predictions are demonstrated by 4He + d scattering phase shifts and a β-delayed deuteron emission of 6He as examples.

Induced terms of weak nucleon currents in light nuclei

Vector and axial vector currents of the weak interactions in light nuclei are reviewed. Induced terms of the nucleon currents are discussed. Our recent analysis of the new experimental data on the beta-ray angular distribution in the aligned 12B and 12N given by the Osaka group finds a new limit for the induced tensor current and a slightly larger value of the axial charge y. This brings the strength of the induced pseudoscalar current very close to the PCAC value in the muon capture on 12C.

Proposed new experimental case to investigate the weak parity nonconserving couplings in 20F.

A new experiment to investigate the isospin sensitivity of the parity nonconserving (PNC) interaction in light nuclei is proposed. The observable is the PNC asymmetry for the emitted gamma rays from the ${1}^{\mathrm{\ensuremath{-}}}$1 state in $^{20}\mathrm{F}$ (${\mathit{E}}_{\mathit{x}}$=0.983 MeV) partially polarized in the reaction $^{22}\mathrm{Ne}$(d\ensuremath{\rightarrow},${\mathrm{\ensuremath{\alpha}}}_{3}$${)}^{20}$F, which is predicted in the range (2.4--5.8 )\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$. The structure parts of the components of the PNC matrix elements have been carefully calculated for the analysis of the experimental result in terms of the weak coupling constants. A new class of diagrams contributing to the PNC matrix elements has been included for the first time.

Monte Carlo analysis of the four-body final state in the neutron-induced 12C breakup

The expectation spectra obtained by the Monte Carlo simulation of those reaction mechanisms which are known to occur in the interactions of light nuclei have been compared with the experimental distributions of various physical variables obtained from a complete measurement, in 4π geometry, of the 12C(n, n3α) reaction. By the use of this method, contributions of various reaction channels, including the three-body nα 8Be and the four-body nααα simultaneous breakup, have been extracted. The present study has also shown that the Monte Carlo simulation of the sequential reaction mechanism alone may be successfully used in modelling the four-body n3α final state. This is true for any variable or correlation of variables and for any specific experimental condition, provided the known 12C excitation spectra with given branching ratios to the transition via 8Be g.s. are used as input data for the Monte Carlo simulation.

Present status of electromagnetic interactions in light nuclei

Recent electron scattering experiments on the few-nucleon systems are presented. The interpretation of the data in terms of nucleon and meson degrees of freedom is discussed.

Dependence of average characteristics of pi - mesons on number of interacting protons in nucleus-nucleus collisions at 4.2 GeV/c per nucleon.

A 2-m propane bubble chamber was used to study pion production in interactions of light nuclei d,\ensuremath{\alpha}, C with carbon at 4.2 GeV/c per nucleon. The average numbers of participant protons and correlated numbers of participant nucleons were estimated by using the net charge of secondaries. The dependence of the average values of multiplicity, momentum, and angular characteristics of ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ mesons on the number of interacting protons is also studied. The predictions of the Dubna version of the cascade model were found to be in qualitative agreement with results of this analysis.

Interplay between two- and three-body interaction in light nuclei and nuclear matter

A recent study of different models of three-nucleon interaction (TNI) in 3He, 3H, 4He and nuclear matter is extended to study the influence of different choices of the accompanying two-body interaction. A new two-body potential, Argonne υ 14, is coupled with both the Tucson and isobar intermediate-state models of two-pion-exchange TNI, with a phenomenological intermediate-range repulsive TNI added to the latter. Variational calculations are carried out for these systems, and compared to the earlier work. We find that a stronger tensor component in the two-body potential, as typified by a larger deuteron D-state percentage, gives more attraction for the TNI, counteracting the saturation effect obtained when only two-body forces are considered.

Nuclear shape measurement and the validity of the collective model: results for N not=Z nuclei

Previous work which examined the collective-model transition rates in the light of projected wavefunction calculations has been extended to nuclei with N not=Z. Some interesting quantitative effects have been found which have implications for folding-model calculations and ultimately for experiments. A relationship with shell-model calculations is suggested and comments on the inadequacies of certain Skyrme-type interactions for light nuclei are noted. It would appear that 26Mg is a much less 'rotational' nucleus than 24Mg but 22Ne might be a better rotational nucleus than 20Ne. The author suggests that how 'rotational' a nucleus is may depend on the probe it is examined with.

The calculation of logft values and spectroscopic factors for nuclei in the mass range 10?15

Wave functions obtained in previous shell-model calculations [1, 2] for states of nuclei with massesA=10–15 are used to calculate logft values and spectroscopic factors. These wave functions, which were based on a modified surface delta two-body interaction, comprise the following active shell-model spaces: the 1p3/2 and 1p1/2 orbitals for mass 10–14 nuclei and restricted combinations of the 1p1/2, 2s1/2, 1d5/2 and 1d3/2 orbitals for mass 15 nuclei, leading to four different calculations in the latter case. The calculated results support evidence that the modified surface delta interaction is a valid approximation to the effective interaction in light nuclei.

Hyperfine interactions of light nuclei recoil-implanted into iron

The perturbed integral angular distribution technique has been used to study hyperfine interactions of light nuclei recoil-implanted into iron. Heavy- ion-induced fusion-evaporation reactions populated the excited states of $sup 37$Ar, $sup 39$,$sup 40$,$sup 41$K, and $sup 41$Ca, whose deexciting $gamma$ rays were observed in a Ge(Li) detector. In all cases the measured shifts of the angular distributions were found much smaller than the ones calculated using the known values of g factors, lifetimes, and strengths of the internal hyperfine fields. This can be explained under the assumption that only a fraction of the nuclei feel the full internal magnetic field, while the rest of them do not feel any magnetic interaction at all. Different fractions obtained for $sup 40$K and $sup 41$K suggest a migration process on a ns time scale of the implanted ions in the lattice. (AIP)