Nuclear Mass Number Research Articles

Universality of Nucleon–Nucleon Correlations in Nuclei and Cumulative Pion Production

The structure of nuclear matter at short internucleon distances is one of the poorly studied aspects of nuclear physics. At distances of the order of the nucleon radius, nuclear matter is represented by the pairs of correlated nucleons with relative momenta exceeding the Fermi momenta that emerge for a short time. Such structures, whose local density is comparable to the density of neutron stars, arise from fluctuations in the average nuclear density. One of the important characteristics of nucleon–nucleon correlations is their universality implying the independence of their properties from the nuclear mass number. Therefore, the peculiarities of these objects of nuclear structure reflect the properties of nuclear matter rather than specific nuclei. Information about the short-distance physics is extracted from the analysis of processes with high energy–momentum transfers. Until now, the property of universality has been observed in electron–nucleus collisions only for the breakup of nucleon pairs. In this paper we analyze the data on the cumulative production of pions by protons on a set of nuclear targets and for the first time have established the existence of universality of two-nucleon correlations in the production of π+ and π– mesons. We have obtained evidence for the involvement of three-nucleon correlations in the production of pions beyond the kinematics of their production in interactions with two-nucleon objects.

Diagram of High-Energy Nuclear Collisions

Many new particles, mostly hadrons, are produced in high-energy collisions between atomic nuclei. The most popular models describing the hadron-production process are based on the creation, evolution and decay of resonances, strings or quark–gluon plasma. The validity of these models is under vivid discussion, and it seems that a common framework for this discussion is missing. Here, for the first time, we explicitly introduce the diagram of high-energy nuclear collisions, where domains of the dominance of different hadron-production processes in the space of laboratory-controlled parameters, the collision energy and nuclear-mass number of colliding nuclei are indicated. We argue that the recent experimental results suggest the location of boundaries between the domains, allowing for the first time to sketch an example diagram. Finally, we discuss the immediate implications for experimental measurements and model development following the proposed sketch of the diagram.

Scaling properties of exclusive vector meson production cross section from gluon saturation

It is already known from phenomenological studies that in exclusive deep-inelastic scattering off nuclei there appears to be a scaling behavior of vector meson production cross section in both nuclear mass number, $A$, and photon virtuality, $Q^{2}$, which is strongly modified due to gluon saturation effects. In this work we continue those studies in a realistic setup based upon using the Monte Carlo event generator Sar{\em t}re. We make quantitative predictions for the kinematics of the Electron-Ion Collider, focusing on this $A$ and $Q^{2}$ scaling picture, along with establishing a small region of squared momentum transfer, $t$, where there are signs of this scaling that may potentially be observed at the EIC. Our results are represented as pseudo-data of vector meson production diffractive cross section and/or their ratios, which are obtained by parsing data collected by the event generator through smearing functions, emulating the proposed detector resolutions for the future EIC.

Evolution of the γ -ray strength function in neodymium isotopes

The experimental gamma-ray strength functions (gamma-SFs) of 142,144-151Nd have been studied for gamma-ray energies up to the neutron separation energy. The results represent a unique set of gamma-SFs for an isotopic chain with increasing nuclear deformation. The data reveal how the low-energy enhancement, the scissors mode and the pygmy dipole resonance evolve with nuclear deformation and mass number. The data indicate that the mechanisms behind the low-energy enhancement and the scissors mode are decoupled from each other.

Beam-normal single-spin asymmetry in elastic scattering of electrons from a spin-0 nucleus

We study the beam-normal single-spin asymmetry (BNSSA) in high-energy elastic electron scattering from several spin-0 nuclei. Existing theoretical approaches work in the plane-wave formalism and predict the BNSSA to scale as $\ensuremath{\sim}A/Z$ with the atomic number $Z$ and nuclear mass number $A$. While this prediction holds for light and intermediate nuclei, a striking disagreement in both the sign and the magnitude of BNSSA was observed by the PREX collaboration for $^{208}\mathrm{Pb}$, coined the ``PREX puzzle.'' To shed light on this disagreement, we go beyond the plane-wave approach which neglects Coulomb distortions known to be significant for heavy nuclei. We explicitly investigate the dependence of BNSSA on $A$ and $Z$ by (i) including inelastic intermediate states' contributions into the Coulomb problem in the form of an optical potential, (ii) by accounting for the experimental information on the $A$-dependence of the Compton slope parameter, and (iii) giving a thorough account of the uncertainties of the calculation. Despite of these improvements, the PREX puzzle remains unexplained. We discuss further strategies to resolve this riddle.

Nuclear polarization effects in atoms and ions

Nuclear structure effects lead to small corrections to electron energy-level shifts and isotope shifts in neutral atoms but have enhanced effects on heavy hydrogenlike ions. The authors analyze how nuclear structure effects scale with nuclear charge, mass number, and other parameters in various atoms and ions, with an emphasis on heavy hydrogenlike ions.

Drell-Yan nuclear modification due to nuclear effects of nPDFs and initial-state parton energy loss * *Supported partially by National Natural Science Foundation of China (11405043), Natural Science Foundation of Hebei Province (A2018209269) and Science and Technology Foundation of Hebei Education Department (ZD2020104)

By globally analyzing nuclear Drell-Yan data including all incident energies, the nuclear effects of nuclear parton distribution functions (nPDFs) and initial-state parton energy loss are investigated. Based on the Landau-Pomeranchuk-Migdal (LPM) regime, the calculations are carried out by means of analytic parametrizations of quenching weights derived from the Baier-Dokshitzer-Mueller-Peign -Schiff (BDMPS) formalism and using the new EPPS16 nPDFs. It is found that the results are in good agreement with the data and the role of the energy loss effect in the suppression of Drell-Yan ratios is prominent, especially for low-mass Drell-Yan measurements. The nuclear effects of nPDFs become more obvious with increasing nuclear mass number A, the same as the energy loss effect. By a global fit, the transport coefficient extracted is GeV2/fm. In addition, to avoid diminishing the QCD NLO correction to the data form of Drell-Yan ratios, separate calculations of the Compton differential cross section ratios at 120 GeV are performed, which provides a feasible way to better distinguish the gluon energy loss in Compton scattering. It is found that the role of the initial-state gluon energy loss in the suppression of Compton scattering ratios is not very important and disappears with the increase of .

Proton-proton interactions and onset of deconfinement

The NA61/SHINE experiment at the CERN SPS is performing a uniqe study of the phase diagram of strongly interacting matter by varying collision energy and nuclear mass number of colliding nuclei. In central Pb+Pb collisions the NA49 experiment found structures in the energy dependence of several observables in the CERN SPS energy range that had been predicted for the transition to a deconfined phase. New measurements of NA61/SHINE find intriguing similarities in p+p interactions for which no deconfinement transition is expected at SPS energies. Possible implications will be discussed.

Core-collapse Supernova Explosions Driven by the Hadron-quark Phase Transition as a Rare r-process Site

Abstract Supernova explosions of massive stars are one of the primary sites for the production of the elements in the universe. Up to now, stars with zero-age main-sequence masses in the range of 35–50 M ⊙ had mostly represented the failed supernova explosion branch. In contrast, it has been demonstrated recently that the appearance of exotic phases of hot and dense matter, associated with a sufficiently strong phase transition from nuclear matter to the quark-gluon plasma at high baryon density, can trigger supernova explosions of such massive supergiant stars. Here, we present the first results obtained from an extensive nucleosynthesis analysis for material being ejected from the surface of the newly born proto-neutron stars of such supernova explosions. These ejecta contain an early neutron-rich component and a late-time high-entropy neutrino-driven wind. The nucleosynthesis robustly overcomes the production of nuclei associated with the second r-process peak, at nuclear mass number A ≃ 130, and proceeds beyond the formation of the third peak (A ≃ 195) to the actinides. These yields may account for metal-poor star observations concerning r-process elements such as strontium and europium in the Galaxy at low metallicity, while the actinide yields suggests that this source may be a candidate contributing to the abundances of radioactive 244Pu measured in deep-sea sediments on Earth.

Latest predictions from the EbyE NLO EKRT model

We present the latest results from the NLO pQCD + saturation + viscous hydrodynamics (EbyE NLO EKRT) model. The parameters in the EKRT saturation model are fixed by the charged hadron multiplicity in the 0-5 % 2.76 TeV Pb+Pb collisions. The s, A and centrality dependence of the initial particle production follows then from the QCD dynamics of the model. This allows us to predict the s and A dependence of the particle production. We show that our results are in an excellent agreement with the low-pT data from 2.76 TeV and 5.02 TeV Pb+Pb collisions at the LHC as well as with the data from the 200 GeV Au+Au collisions at RHIC. In particular, we study the centrality dependences of hadronic multiplicities, flow coefficients, and various flow correlations. Furthermore, the nuclear mass number dependence of the initial particle production and hydrodynamic evolution can be tested in the 5.44 TeV Xe+Xe collisions at the LHC. To this end, we show our predictions for charged particle multiplicities, and in particular, show how the deformations of the Xe nuclei reflect into the flow coefficients.

Systematics of strong nuclear amplification of gluon saturation from exclusive vector meson production in high energy electron–nucleus collisions

We show that gluon saturation gives rise to a strong modification of the scaling in both the nuclear mass number A and the virtuality Q2 of the vector meson production cross-section in exclusive deep-inelastic scattering off nuclei. We present qualitative analytic expressions for how the scaling exponents are modified as well as quantitative predictions that can be tested at an Electron–Ion Collider.

Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process

We explore heavy element nucleosynthesis in neutrino-driven winds from rapidly-rotating, strongly magnetized proto-neutron stars for which the magnetic dipole is aligned with the rotation axis, and the field is assumed to be a static force-free configuration. We process the proto-magnetar wind trajectories calculated by Vlasov et al 2014 through the r-process nuclear reaction network SkyNet using contemporary models for the evolution of the wind electron fraction during the proto-neutron star cooling phase. Although we do not find a successful second or third peak r-process for any rotation period P, we show that proto-magnetars with P around 1-5 ms produce heavy element abundance distributions that extend to higher nuclear mass number than from otherwise equivalent spherical winds (with the mass fractions of some elements enhanced by factors of 100-1000). The heaviest elements are synthesized by outflows emerging along flux tubes which graze the closed zone and pass near the equatorial plane outside the light cylinder. Due to dependence of the nucleosynthesis pattern on the magnetic field strength and rotation rate of the proto-neutron star, natural variations in these quantities between core collapse events could contribute to the observed diversity of the abundances of weak r-process nuclei in metal-poor stars. Further diversity, including possibly even a successful third-peak r-process, could be achieved for misaligned rotators with non-zero magnetic inclination with respect to the rotation axis. If proto-magnetars are central engines for GRBs, their relativistic jets should contain a high mass fraction of heavy nuclei of characteristic average mass number A of order 100, providing a possible source for ultra-high energy cosmic rays comprised of heavy nuclei with an energy spectrum that extends beyond the nominal GZK cut-off for protons or iron nuclei.

Diffractive ρ production at small x in future electron–ion colliders

The future electron–ion (eA) collider is expected to probe the high energy regime of the quantum chromodynamics (QCD), with the exclusive vector meson production cross section being one of the most promising observables. In this paper we complement previous studies of exclusive processes presenting a comprehensive analysis of diffractive ρ production at small x. We compute the coherent and incoherent cross sections taking into account non-linear QCD dynamical effects and considering different models for the dipole–proton scattering amplitude and vector meson wave function. The dependence of these cross sections on the energy, photon virtuality, nuclear mass number and squared momentum transfer is analysed in detail. Moreover, we compare the non-linear predictions with those obtained in the linear regime. Finally, we also estimate the exclusive photon, and ϕ production and compare with the results obtained for ρ production. Our results demonstrate that the analysis of diffractive ρ production in future electron–ion colliders will be important in understanding the non-linear QCD dynamics.

RELATIVE CONTRIBUTIONS OF THE WEAK, MAIN, AND FISSION-RECYCLING r-PROCESS

ABSTRACT There has been a persistent conundrum in attempts to model the nucleosynthesis of heavy elements by rapid neutron capture (the r-process). Although the locations of the abundance peaks near nuclear mass numbers 130 and 195 identify an environment of rapid neutron capture near closed nuclear shells, the abundances of elements just above and below those peaks are often underproduced by more than an order of magnitude in model calculations. At the same time, there is a debate in the literature as to what degree the r-process elements are produced in supernovae or the mergers of binary neutron stars. In this paper we propose a novel solution to both problems. We demonstrate that the underproduction of nuclides above and below the r-process peaks in main or weak r-process models (like magnetohydrodynamic jets or neutrino-driven winds in core-collapse supernovae) can be supplemented via fission fragment distributions from the recycling of material in a neutron-rich environment such as that encountered in neutron star mergers (NSMs). In this paradigm, the abundance peaks themselves are well reproduced by a moderately neutron-rich, main r-process environment such as that encountered in the magnetohydrodynamical jets in supernovae supplemented with a high-entropy, weakly neutron-rich environment such as that encountered in the neutrino-driven-wind model to produce the lighter r-process isotopes. Moreover, we show that the relative contributions to the r-process abundances in both the solar system and metal-poor stars from the weak, main, and fission-recycling environments required by this proposal are consistent with estimates of the relative Galactic event rates of core-collapse supernovae for the weak and main r-process and NSMs for the fission-recycling r-process.

The SOFIA experiment: Measurement of236U fission fragment yields in inverse kinematics

The SOFIA (Studies On FIssion with Aladin) experiment aims at measuring fission-fragments isotopic yields with high accuracy using inverse kinematics at relativistic energies. This experimental technique allows to fully identify the fission fragments in nuclear charge and mass number, thus providing very accurate isotopic yields for low energy fission of a large variety of fissioning systems. This report focuses on the latest results obtained with this set-up concerning electromagnetic-induced fission of 236U.

Quasiparticle structure of superheavy nuclei along theα-decay chain of115288

Background: Recent experiments on $\ensuremath{\alpha}$-decay of odd-odd superheavy nuclei give important information on the structure of the low-lying states of these nuclei. For this reason, it is interesting to calculate the excitation spectra of superheavy nuclei in the framework of different approaches and compare the results with the experimental data.Purpose: To calculate the excitation energies of the two-quasiparticle states of nuclei belonging to the $\ensuremath{\alpha}$-decay chain of $^{288}115$ nucleus.Method: Two different single-particle potentials, modified two-center and Skyrme-based potentials, are used to calculate the energies of two-quasiparticle states.Results: The spectra of the low-lying states are calculated. An evolution of the splitting of the pseudospin doublets and an evolution of the energies of the unique parity single-particle states with the nuclear mass number are investigated. The $\ensuremath{\alpha}$-decay spectra of nuclei belonging to the $\ensuremath{\alpha}$-decay chain of $^{288}115$ are obtained and compared with the experimental data. A possibility of the $E1$ transitions in $^{276}\mathrm{Mt}$ following $\ensuremath{\alpha}$ decay of $^{288}115$ is considered.Conclusion: The $E1$ transitions in $^{276}\mathrm{Mt}$ might be related to the transitions $n9/2[604]\ensuremath{\rightarrow}n11/2[725],\phantom{\rule{0.16em}{0ex}}n11/2[725]\ensuremath{\rightarrow}n9/2[615]$, and $p9/2[505]\ensuremath{\rightarrow}p11/2[615]$. Besides the $E1$ transitions, the strong $M1$ and $M2$ transitions are expected in $^{276}\mathrm{Mt}$.

Study of quark mass dependence of binding energy for light nuclei in2+1flavor lattice QCD

We investigate the formation of light nuclei with the nuclear mass number less than or equal to four in $2+1$ flavor QCD using a nonperturbative improved Wilson quark and Iwasaki gauge actions. The quark mass is decreased from our previous work to the one corresponding to the pion mass of 0.30 GeV. In each multinucleon channel, the energy shift of the ground state relative to the assembly of free nucleons is calculated on two volumes, whose spatial extents are 4.3 and 5.8 fm. From the volume dependence of the energy shift, we distinguish a bound state of multinucleons from an attractive scattering state. We find that all the ground states measured in this calculation are bound states. As in the previous studies at larger ${m}_{\ensuremath{\pi}}$, our result indicates that at ${m}_{\ensuremath{\pi}}=0.30\text{ }\text{ }\mathrm{GeV}$ the effective interaction between nucleons in the light nuclei is relatively stronger than the one in nature, since the results for the binding energies are larger than the experimental values and a bound state appears in the dineutron channel, which is not observed in experiment. Possible sources of systematic error in this calculation are discussed.

Deeply virtual Compton scattering at smallxin future electron-ion colliders

The study of exclusive processes in the future electron-ion ($eA$) colliders will be an important tool to investigate the QCD dynamics at high energies as they are in general driven by the gluon content of the target which is strongly subject to parton saturation effects. In this paper we compute the coherent and incoherent cross sections for the deeply virtual Compton scattering (DVCS) process relying on the color dipole approach and considering different models for the dipole - proton scattering amplitude. The dependencies of the cross sections with the energy, photon virtuality, nuclear mass number and squared momentum transfer are analysed in detail. We demonstrate that the ratio between the incoherent and coherent cross sections decreases at smaller values of $Q^2$ and increases at smaller values of $A$. We show that the coherent cross section dominates at small $t$ and exhibits the typical diffractive pattern, with the number of dips in the range $|t| \le 0.3$ GeV$^2$ increasing with the mass atomic number. Our results indicate that the position of the dips are independent of the model used to treat the dipole - proton interaction as well as of the center-of-mass energy.

NUCLEOSYNTHESIS CONSTRAINTS ON THE NEUTRON STAR-BLACK HOLE MERGER RATE

We derive constraints on the time-averaged event rate of neutron star-black hole (NS-BH) mergers by using estimates of the population-integrated production of heavy rapid neutron-capture (r-process) elements with nuclear mass numbers A > 140 by such events in comparison to the Galactic repository of these chemical species. Our estimates are based on relativistic hydrodynamical simulations convolved with theoretical predictions of the binary population. This allows us to determine a strict upper limit of the average NS-BH merger rate of ~6*10^-5 per year. We quantify the uncertainties of this estimate to be within factors of a few mostly because of the unknown BH spin distribution of such systems, the uncertain equation of state of NS matter, and possible errors in the Galactic content of r-process material. Our approach implies a correlation between the merger rates of NS-BH binaries and of double NS systems. Predictions of the detection rate of gravitational-wave signals from such compact-object binaries by Advanced LIGO and Advanced Virgo on the optimistic side are incompatible with the constraints set by our analysis.

New Fission Fragment Distributions andr-Process Origin of the Rare-Earth Elements

Neutron star (NS) merger ejecta offer a viable site for the production of heavy r-process elements with nuclear mass numbers A≳140. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular, the fission fragment yields determine the creation of 110≲A≲170 nuclei. Here, we apply a new scission-point model, called SPY, to derive the fission fragment distribution (FFD) of all relevant neutron-rich, fissioning nuclei. The model predicts a doubly asymmetric FFD in the abundant A≃278 mass region that is responsible for the final recycling of the fissioning material. Using ejecta conditions based on relativistic NS merger calculations, we show that this specific FFD leads to a production of the A≃165 rare-earth peak that is nicely compatible with the abundance patterns in the Sun and metal-poor stars. This new finding further strengthens the case of NS mergers as possible dominant origin of r nuclei with A≳140.