Interaction In Nuclear Matter Research Articles

Centrality-dependent modification of hadron and jet production in electron-nucleus collisions

Centrality-dependent measurements of hadron and jet cross section attenuation in deep inelastic scattering on nuclei can shed new light on the physics of final-state interactions in nuclear matter, including the path-length dependence of the in-medium parton shower formation and evolution. Recent simulation studies have demonstrated the feasibility of experimental centrality determination in eA reactions at the electron-ion collider via neutron detection in the zero-degree calorimeter. Motivated by these results, we present the first theoretical calculation of the production rate modification for hadrons and jets in central and peripheral ePb collisions. We find that the variation in the suppression of inclusive jet cross section as a function of centrality is less than a factor of two. In more differential measurements, such as the distribution of hadrons versus the hadronization fraction zh, the difference can be enhanced up to an order of magnitude.

Slope parameter of the symmetry energy and the structure of three-particle interactions in nuclear matter

In the first part of this paper, we present a study of the symmetry energy ${a}_{s}$ and its slope parameter $L$ for nuclear matter in the framework of the Fermi-liquid theory of Landau and Migdal. We derive an exact relation between ${a}_{s}$ and $L$, which involves the nucleon effective masses and three-particle Landau-Migdal parameters. We present simple estimates which suggest that there are two main mechanisms to explain the empirical values of $L$: The proton-neutron effective-mass difference in isospin asymmetric matter and the $\ensuremath{\ell}=0$ moment of the isovector in-medium three-particle scattering amplitude. In the second part of this paper, we discuss the general structure of three-particle interactions in nuclear matter in the framework of the Fermi-liquid theory. The connections to the Bethe-Brueckner-Goldstone theory and other approaches are also discussed. We show explicitly how the first few terms in the Faddeev series, together with medium-induced three-particle interactions, emerge naturally in the Fermi-liquid theory.

Study of Ξ−-atom based on the ΞN interaction from QCD on lattice

We report our preliminary theoretical study on Ξ−-atom based on a ΞN interaction extracted from QCD on lattice. First, we study ΞN interaction in nuclear matter. Then, we make a Ξ-nucleus potential in a simple folding procedure. We study Ξ−-60Ni system as an example, and find that energy levels of the atom are shifted downward due to the ΞN interaction.

An effective theory of quarkonia in QCD matter

For heavy quarkonia of moderate energy, we generalize the relevant successful theory, non-relativistic Quantum Chromodynamics (NRQCD), to include interactions in nuclear matter. The new resulting theory, NRQCD with Glauber gluons, provides for the first time a universal microscopic description of the interaction of heavy quarkonia with a strongly interacting medium, consistently applicable to a range of phases, such as cold nuclear matter, dense hadron gas, and quark-gluon plasma. The effective field theory we present in this work is derived from first principles and is an important step forward in understanding the common trends in proton-nucleus and nucleus-nucleus data on quarkonium suppression.

Neutron star matter with strange interactions within constraints by GW170817 in a relativistic quark model

The effect of strange interactions in neutron star matter and the role of the strange meson-hyperon couplings are studied in a relativistic quark model where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to $\ensuremath{\sigma}, \ensuremath{\omega}, \ensuremath{\rho}, {\ensuremath{\sigma}}^{*}$, and $\ensuremath{\phi}$ mesons through mean-field approximations. The meson-baryon couplings are fixed through the SU(6) spin-flavor symmetry and the SU(3) flavor symmetry to determine the hadronic equation of state (EoS). We find that the SU(3) coupling set gives the potential depth between ${\mathrm{\ensuremath{\Lambda}}}^{\ensuremath{'}}\mathrm{s}$ around $\ensuremath{-}5$ MeV and favors a stiffer EoS. Using the stiffest EoS from the SU(3) we determine the tidal Love number ${k}_{2}$, the tidal deformability $\ensuremath{\lambda}$, and the dimensionless tidal deformability ${\mathrm{\ensuremath{\Lambda}}}_{D}$. We obtain a value of ${\mathrm{\ensuremath{\Lambda}}}_{D}=483$ corresponding to a $1.4{M}_{\ensuremath{\bigodot}}$ star while the weighted tidal deformability $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathrm{\ensuremath{\Lambda}}}=624$ for a symmetric binary system of chirp mass $\mathcal{M}=1.188{M}_{\ensuremath{\bigodot}}$. The radius for the canonical neutron star is found to be 13.1 km.

Neutron star matter with Δ isobars in a relativistic quark model

The effect of strange interactions in neutron star matter and the role of the strange meson-hyperon couplings are studied in a relativistic quark model where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to $\sigma$, $\omega$, $\rho$, $\sigma^*$ and $\phi$ mesons through mean-field approximations. The meson-baryon couplings are fixed through the SU(6) spin-flavor symmetry and the SU(3) flavor symmetry to determine the hadronic equation of state (EoS). We find that the SU(3) coupling set gives the potential depth between $\Lambda$s around $-5$ MeV and favours a stiffer EoS.The radius for the canonical neutron star lies within a range of $12.7$ to $13.1$ km.

Optimized chiral N2LO interactions in nuclear matter

We employ modern two- and three-nucleon interactions derived in chiral perturbation theory (ChPT) at next to-next-to leading order (N2LO), to calculate the energy per particle of symmetric nuclear matter and pure neutron matter in the framework of the microscopic Brueckner-Hartree-Fock approach. In particular, we present results concerning two optimized versions at N2LO of chiral potentials ( $ \mathrm{N2LO}_{opt}$ ), fitted to properties of light nuclei. We also employ the recently developed $\mathrm{N2LO}_{sat}$ interaction which has been calculated at the same order of ChPT but fitted in a very different way compared with the $\mathrm{N2LO}_{opt}$ interactions. We find that using these potentials, in general, it is not possible to reproduce all the saturation properties of nuclear matter. In particular the behaviour of the symmetry energy ( $E_{sym}$ predicted by the interactions considered is quite soft. This is shown comparing our results with the empirical constraints on $E_{sym}$ obtained from the data analysis of the excitation energies of isobaric analog states in nuclei and from experimental data of the neutron skin thickness of heavy nuclei. We finally confront our results with similar calculations performed by other research groups using nuclear chiral interactions at various order of ChPT and employing different many-body methods.

Charmonium interaction in nuclear matter at FAIR

We have studied the dissociation of J/ψ mesons in low energy proton-nucleus (p + A) collisions in the energy range of the future SIS100 accelerator at Facility for Anti-proton and Ion Research (FAIR). According to the results of our calculations, various scenarios of J/ψ absorption in nuclear matter show very distinct suppression patterns in the kinematic regime to be probed at FAIR. This suggests that the SIS100 energies are particularly suited to shed light on the issue of interaction of J/ψ resonance in nuclear medium.

Single-particle potential of the Λ hyperon in nuclear matter with chiral effective field theory NLO interactions including effects of YNN three-baryon interactions

Adopting hyperon-nucleon and hyperon-nucleon-nucleon interactions parametrized in chiral effective field theory, single-particle potentials of the $\Lambda$ and $\Sigma$ hyperons are evaluated in symmetric nuclear matter and in pure neutron matter within the framework of lowest order Bruckner theory. The chiral NLO interaction bears strong $\Lambda$N-$\Sigma$N coupling. Although the $\Lambda$ potential is repulsive if the coupling is switched off, the $\Lambda$N-$\Sigma$N correlation brings about the attraction consistent with empirical data. The $\Sigma$ potential is repulsive, which is also consistent with empirical information. The interesting result is that the $\Lambda$ potential becomes shallower beyond normal density. This provides the possibility to solve the hyperon puzzle without introducing ad hoc assumptions. The effects of the $\Lambda$NN-$\Lambda$NN and $\Lambda$NN-$\Sigma$NN three-baryon forces are considered. These three-baryon forces are first reduced to normal-ordered effective two-baryon interactions in nuclear matter and then incorporated in the $G$-matrix equation. The repulsion from the $\Lambda$NN-$\Lambda$NN interaction is of the order of 5 MeV at the normal density, and becomes larger with increasing the density. The effects of the $\Lambda$NN-$\Sigma$NN coupling compensate the repulsion at normal density. The net effect of the three-baryon interactions to the $\Lambda$ single-particle potential is repulsive at higher densities.

Effects of pairing correlations on the neutron skin thickness and the symmetry energy

We investigated effects of pairing correlations on the neutron skin thickness and the symmetry energy of finite nuclei. In this calculation we used Hartree-Fock-Bogoliubov (HFB) method with Skyrme forces and effective pairing interactions. The results have been compared with available experimental data, Hartree-Fock (HF) results as well as the predictions by droplet model (DM). Finally, our discussion was extended to study of the pairing interaction in nuclear matter. Roles of isospin T = 0 pairing in the nuclear matter were also discussed.

Investigating the low-energy K− interactions in nuclear matter with AMADEUS

The AMADEUS collaboration studies low-energy K− interactions with light nuclei in order to clarify some aspects related to the behaviour of hadrons containing strangeness in nuclear medium. One of the main topics is the quest about the possible formation of Kaonic Nuclear Clusters (KNC), which depends on the strength of the anti-kaons interaction with nucleons. In kaonic absorption experiments, the search for KNC is strictly connected with the measurement of the yields of the so-called multi-nucleon absorption processes. In this paper, the study of Σ0p correlated production from K− absorption in 12C, using the KLOE 2004-2005 data set, is reported. The yield of the two nucleon absorption (2NA), when the produced Σ0 and p particles are free from any final state interaction process, was measured for the first time. The contribution of a ppK− bound state was also tested. The best fit is obtained for a ppK− state with a binding energy of 45 MeV and a width of 30 MeV, but the statistical significance is at the level of 1σ only.

Formation of hypernuclei in evaporation and fission processes

There are excellent opportunities to produce excited heavy hyper residues in relativistic hadron and peripheral heavy-ion collisions. We investigate the disintegration of such residues into hyper nuclei via evaporation of baryons and light clusters and their fission. Previously these processes were well known for normal nuclei as the decay channels at low excitation energies. We have generalized these models for the case of hyper-matter. In this way we make extension of nuclear reaction studies at low temperature into the strange sector. We demonstrate how the new decay channels can be integrated in the whole disintegration process. Their importance for mass and isotope distributions of produced hyper-fragments is emphasized. New and exotic isotopes obtained within these processes may provide a unique opportunity for investigating hyperon interaction in nuclear matter.

Hyperon stars in a modified quark meson coupling model

We determine the equation of state (EOS) of nuclear matter with the inclusion of hyperons in a self-consistent manner by using a Modified Quark Meson Coupling Model (MQMC) where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to $\sigma$, $\omega$, and $\rho$ mesons through mean-field approximations. The effect of a nonlinear $\omega$-$\rho$ term on the equation of state is studied. The hyperon couplings are fixed from the optical potential values and the mass-radius curve is determined satisfying the maximum mass constraint of $2$~M$_{\odot}$ for neutron stars, as determined in recent measurements of the pulsar PSR J0348+0432. We also observe that there is no significant advantage of introducing the nonlinear $\omega$-$\rho$ term in the context of obtaining the star mass constraint in the present set of parametrizations.

Solving the problem of anomalous J/ $\psi$ suppression by the MPD experiment on the NICA collider

The meassurements of charmonium states production via their decay on lepton pairs by the MPD experiment on the NICA collider at the energies $ \sqrt{s_{NN}}$ = 4-11 GeV per nucleon could provide important data for solving the problem of anomalous J/ $ \psi$ suppression first observed in central Pb-Pb collisions by the NA50 Collaboration at 158 GeV/nucleon. The anomalous J/ $ \psi$ suppression could be due to the formation of the QGP in the central heavy-ion collisions. However, this effect could be also interpreted as the result of the comover interactions in nuclear matter. The recent experiments at the SPS, at the RHIC, and the LHC reviewed in this article indicate a more complicated picture of the J/ $ \psi$ production including the recombination, medium effects, parton shadowing, and the coherent energy loss mechanism. A more simple production mechanism could be expected at low colliding energies. However, no data were obtained at energies below $ \sqrt{s_{NN}}=17$ GeV for heavy-ion collisions. After the short review of the whole set of the data of charmonium states observation the estimation of the production rate for the MPD/NICA is made.

Reducible chiral four-body interactions in nuclear matter

The method of unitary transformations generates five classes of leading-order reducible chiral four-nucleon interactions which involve pion-exchanges and a spin-spin contact-term. Their first-order contributions to the energy per particle of isospin-symmetric nuclear matter and pure neutron matter are evaluated in detail. For most of the closed four-loop diagrams the occurring integrals over four Fermi-spheres can be reduced to easily manageable one- or two-parameter integrals. One observes substantial cancelations among the different contributions arising from 2-ring and 1-ring diagrams. Altogether, the net attraction generated by the chiral four-nucleon interaction does not exceed values of $-1.3$\,MeV for densities $\rho<2\rho_0$.

Nuclear symmetry energy in a modified quark-meson coupling model

We study nuclear symmetry energy and the thermodynamic instabilities of asymmetric nuclear matter in a self-consistent manner by using a modified quark-meson coupling model where the confining interaction for quarks inside a nucleon is represented by a phenomenologically averaged potential in an equally mixed scalar-vector harmonic form. The nucleon-nucleon interaction in nuclear matter is then realized by introducing additional quark couplings to $\ensuremath{\sigma},\phantom{\rule{0.16em}{0ex}}\ensuremath{\omega}$, and $\ensuremath{\rho}$ mesons through mean-field approximations. We find an analytic expression for the symmetry energy ${\mathcal{E}}_{\mathrm{sym}}$ as a function of its slope $L$. Our result establishes a linear correlation between $L$ and ${\mathcal{E}}_{\mathrm{sym}}$. We also analyze the constraint on neutron star radii in $(pn)$ matter with $\ensuremath{\beta}$ equilibrium.

Soil properties and elements other than hydrogen that can affect the field calibration of a neutron water meter

A neutron water meter (NWM) operates on the principle that emitted high-energy neutrons are thermalised by elastic collisions with atomic nuclei present in soil, such as that of the hydrogen atom. Thermalised neutrons, however, are affected by other nuclear-matter interactions such as their capture by soil elements and properties, thereby decreasing the counts and leading to an underestimation of soil water content (SWC). The objective of this study was to determine which soil and concretion properties and elements (apart from hydrogen) would have a neutron capture effect during the field calibration of a NWM, and whether statistical relationships could be established. Soil and concretion samples from the field calibration of a NWM were analysed for a number of properties and elements. Linear regression analyses revealed that, apart from volumetric SWC, soil and concretion (chloride, potassium, iron and electrical conductivity of soil-paste extract [ECe]) properties were correlated with NWM count ratio. A multiple regression equation containing SWC, soil potassium and ECe, as well as concretion iron, explains 87% of the variation in NWM count ratio. It is recommended that measurements be made on a wider range of soils to establish a more rigorous calibration equation that contains SWC, as well as other soil and concretion parameters.

Nuclear equation of state in a relativistic independent quark model with chiral symmetry and dependence on quark masses

We have calculated the properties of nuclear matter in a self-consistent manner with a quark-meson coupling mechanism incorporating the structure of nucleons in vacuum through a relativistic potential model; where the dominant confining interaction for the free independent quarks inside a nucleon is represented by a phenomenologically average potential in equally mixed scalar-vector harmonic form. Corrections due to spurious center of mass motion as well as those due to other residual interactions, such as the one gluon exchange at short distances and quark-pion coupling arising out of chiral symmetry restoration, have been considered in a perturbative manner to obtain the nucleon mass in vacuum. The nucleon-nucleon interaction in nuclear matter is then realized by introducing additional quark couplings to $\ensuremath{\sigma}$ and $\ensuremath{\omega}$ mesons through mean field approximations. The relevant parameters of the interaction are obtained self-consistently while realizing the saturation properties such as the binding energy, pressure, and compressibility of the nuclear matter. We also discuss some implications of chiral symmetry in nuclear matter along with the nucleon and nuclear $\ensuremath{\sigma}$ term and the sensitivity of nuclear matter binding energy with variations in the light quark mass.

Interplay between the symmetry energy and the strangeness content of neutron stars

The effect of the density dependence of the nucleonic equation of state and the hyperon meson couplings on the star properties, including strangeness content, mass and radius, are studied within a relativistic mean field formalism. It is shown that there is still lacking information on the nucleonic equation of state at supra-saturation densities and on the hyperon interactions in nuclear matter that will allow a clear answer to the question whether the mass of the pulsar J1614-2230 could rule out exotic degrees of freedom from the interior of compact stars. We show that some star properties are affected in a similar way by the density dependence of the symmetry energy and the hyperon content of the star. To disentangle these two effects it is essential to have a good knowledge of the equation of state at supra-saturation densities. A linear correlation between the radius and the strangeness content of a star with a fixed mass is obtained.

Chiral four-body interactions in nuclear matter

An exploratory study of chiral four-nucleon interactions in nuclear and neutron matter is performed. The leading-order terms arising from pion-exchange in combination with the chiral $4\pi$-vertex and the chiral NN$3\pi$-vertex are found to be very small. Their attractive contribution to the energy per particle stays below $0.6\,$MeV in magnitude for densities up to $\rho =0.4\,$fm$^{-3}$. We consider also the four-nucleon interaction induced by pion-exchange and twofold $\Delta$-isobar excitation of nucleons. For most of the closed four-loop diagrams the occurring integrals over four Fermi spheres can either be solved analytically or reduced to easily manageable one- or two-parameter integrals. After summing the individually large contributions from 3-ring, 2-ring and 1-ring diagrams of alternating signs, one obtains at nuclear matter saturation density $\rho_0=0.16\,$fm$^{-3}$ a moderate contribution of $2.35\,$MeV to the energy per particle. The curve $\bar E(\rho)$ rises rapidly with density, approximately with the third power of $\rho$. In pure neutron matter the analogous chiral four-body interactions lead, at the same density $\rho_n$, to a repulsive contribution that is about half as strong. The present calculation indicates that long-range multi-nucleon forces, in particular those provided by the strongly coupled $\pi N \Delta$-system with its small mass-gap of $293\,$MeV, can still play an appreciable role for the equation of state of nuclear and neutron matter.