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1.
We investigate the nuclear size dependence of the distribution of massive lepton pairs produced by hadronic beams. Our principle conclusion is that <p 2 T > of the lepton pair should have a substantial and readily observable component from nuclear rescattering even though the nuclear enhancement exponent α(p T ) lies within present experimental limits. We indicate the relevance of these effects to the study of quark propagation through nuclear matter.  相似文献   

2.
We report on variational calculations of the energy E(ρ, β) of asymmetric nuclear matter having ? = ?n + ?p = 0.05 to 0.35 fm?3, and β = (?n ? ?p/g9 = 0 to 1. The nuclear h used in this work consists of a realistic two-nucleon interaction, called v14, that fits the available nucleon-nucleon scattering data up to 425 MeV, and a phenomenological three nucleon interaction adjusted to reproduce the empirical properties of symmetric nuclear matter. The variational many-body theory of symmetric nuclear matter is extended to treat matter with neutron excess. Numerical and analytic studies of the β-dependence of various contributions to the nuclear matter energy show that at ? < 0.35 fm?3 the β4 terms are very small, and that the interaction energy EI(ρ, β) defined as E(ρ, β) ? TF(ρ, β), where TF is the Fermi-gas energy, is well approximated by EI0(?) + β2EI2(ρ). The calculated symmetry energy at equilibrium density is 30 MeV and it increases from 15 to 38 MeV as ? increases from 0.05 to 0.35 fm?3.  相似文献   

3.
The β-endpoint energies of 6 neutron-rich nuclei with mass numbersA=146 andA=147 have been measured with a plastic scintillator telescope at the on-line mass separator OSTIS. With theQ β-values derived from these experiments and with those obtained in earlier studies, nuclear structure effects in this part of the nuclear chart are investigated. In addition, nuclear masses derived from the experimentalQ β-values are compared with the predictions of theoretical mass calculations.  相似文献   

4.
《Nuclear Physics A》1987,462(4):701-726
When quantumchromodynamics (QCD) is generalized from SU(3) to an SU(Nc) gauge theory, where Nc is the number of colours, it depends on only two parameters: Nc and the bare quark mass mq. A more general understanding of nuclear physics can be achieved by considering what it would be like in worlds with the number of colours different from 3, and bare quark masses different from the “empirical” ones. Such an investigation can be carried out within a framework of meson-exchange interactions. The empirical binding energy of nuclear matter results from a very near cancellation between attractive and repulsive terms which are two orders of magnitude larger and may be expected to depend sensitively on the parameters of QCD. It is indeed found that our world is wedged into a small corner of the two-dimensional manifold of mq versus Nc. If the number of colours were decreased by one, or the bare quark masses raised by more than 20%, nuclear matter would become unbound. By tracing the origin of this state of affairs, one obtains a clearer picture of the relative importance of various effects on the behaviour of the bulk nuclear matter. In particular, correlations like those embodied in the Coester band of saturation points appear to have a broader degree of validity than is implied by fits to the actual physical world only.  相似文献   

5.
The static shear viscosity η0 of symmetric nuclear matter is estimated. It is found, that for reasonable nuclear temperatures the mean free path connected with ηo is considerably larger than the nuclear radii. We therefore conclude, that the concept of viscosity cannot be applied to nuclear fission and heavy ion collisions without taking into account the nuclear surface.  相似文献   

6.
We report experimental results of nuclear magnetic resonance (NMR) at the La site and nuclear quadrupole resonance (NQR) at the As site in the normal state of the superconducting compound LaOs4As12. Measurements have been performed on powder sample obtained from high quality single crystals. The temperature dependences of the nuclear spin-lattice relaxation rates, 1/T1, of 75As and 139La nuclei were measured. No scaling between them was found indicating a local character of relaxation processes. The relaxation of 75As nuclei can consistently be understood in terms of antiferromagnetic spin fluctuations, as deduced from the T-dependence of (1/T1T)=C/(Tθ)1/2.  相似文献   

7.
The endpoint energies ofβ-transitions in 15 neuron-rich nuclei with mass numbers 101≦A≦106 have been measured with a plastic scintillator telescope in coincidence with a large Ge(Li)-detector at the on-line mass separator LOHENGRIN. From theQ β -values obtained in these experiments, nuclear structure effects in this region of the nuclear chart are deduced. Finally, nuclear masses derived from theseQ β -values are compared with the predictions of different theoretical mass calculations.  相似文献   

8.
Delayed neutron emission probabilities,P n , have been calculated using usual nuclear statistical model considerations. The influence of the incident parameters on the calculatedP n -values is discussed. The observed systematic deviation from the experimental neutron emission probabilities may be explained by the persistence of nuclear structure effects not contained in a simple statistical model.  相似文献   

9.
《Nuclear Physics A》1987,462(4):791-802
We investigate suggestions that quark matter with strangeness per baryon of order unity may be stable. We model this matter at nuclear matter densities as a gas of close packed Λ-particles. From the known mass of the Λ-particle we obtain an estimate of the energy and chemical potential of strange matter at nuclear densities. These are sufficiently high to preclude any phase transition from neutron matter to strange matter in the region near nucleon matter density. Including effects from gluon exchange phenomenologically, we investigate higher densities, consistently making approximations which underestimate the density of transition. In this way we find a transition density ρtr≳7ρ0, where ρ0 is nuclear matter density is not far from the maximum density in the center of the most massive neutron stars that can be constructed. Since we have underestimated ρtr and still find it to be ∼7ρ0, we do not believe that the transition from neutron to quark matter is likely in neutron stars. Moreover, measured masses of observed neutron stars are ≅1.4 M, where M is the solar mass. For such masses, the central (maximum) density is ρc<5ρ0. Transition to quark matter is certainly excluded for these densities.  相似文献   

10.
The nuclear spin-lattice relaxation times of protons in a low-dimensional Ising-like system [(CH3)3NH]CoCl3 · 2H2O were measured from 1.2 to 4.2 K in zero field and in an external magnetic field applied along the spin easy-axis. The calculation for the two-magnon Raman process was carried out with respect to a ferromagnetic layer of the bc-plane. By taking the gap energy to be 14.0 K, the best fit of the theoretical curves with the data was obtained from 1.2 K to about 2.0 K. The experimental results at high temperatures deviate seriously from the prediction of this process, which is discussed in terms of a tentative model for the nuclear relaxation process associated with magnon bound states.  相似文献   

11.
《Physics Reports》1999,319(3):85-144
The liquid drop model (LDM) expansions of energy and incompressibility of finite nuclei are studied in an analytical model using Skyrme-like effective interactions to examine, whether such expansions provide an unambiguous way to go from finite nuclei to nuclear matter, and thereby can yield the saturation properties of the latter, from nuclear masses. We show that the energy expansion is not unique in the sense that, its coefficients do not necessarily correspond to the ground state of nuclear matter and hence, the mass formulas based on it are not equipped to yield saturation properties. The defect is attributed to its use of liquid drop without any reference to particles as its basis, which is classical in nature. It does not possess an essential property of an interacting many-fermion system namely, the single particle property, in particular the Fermi state. It is shown that, the defect is repaired in the infinite nuclear matter model by the use of generalized Hugenholtz–Van Hove theorem of many-body theory. So this model uses infinite nuclear matter with well defined quantum mechanical attributes for its basis. The resulting expansion has the coefficients which are at the ground state of nuclear matter. Thus a well defined path from finite nuclei to nuclear matter is found out. Then using this model, the saturation density 0.1620 fm−3 and binding energy per nucleon of nuclear matter 16.108 MeV are determined from the masses of all known nuclei. The corresponding radius constant r0 equal to 1.138 fm thus determined, agrees quite well with that obtained from electron scattering data, leading to the resolution of the so-called ‘r0-paradox’. Finally a well defined and stable value of 288±20 MeV for the incompressibility of nuclear matter K is extracted from the same set of masses and a nuclear equation of state is thus obtained.  相似文献   

12.
The study of nuclear effects for J/ψ production in proton–nucleus collisions is crucial for a correct interpretation of the J/ψ suppression patterns experimentally observed in heavy-ion collisions. By means of three representative sets of nuclear parton distribution, the energy loss effect in the initial state and the nuclear absorption effect in the final state are taken into account in the uniform framework of the Glauber model. A leading order phenomenological analysis is performed on J/ψ production cross-section ratios R W/Be (x F) for the E866 experimental data. The J/ψ suppression is investigated quantitatively due to the different nuclear effects. It is shown that the energy loss effect with resulting in the suppression on R W/Be (x F) is more important than the nuclear effects on parton distributions in high x F region. The E866 data in the small x F keep out the nuclear gluon distribution with a large anti-shadowing effect. However, the new HERA-B measurement is not in support of the anti-shadowing effect in the nuclear gluon distribution. It is found that the J/ψ–nucleon inelastic cross section $\sigma^{J/\psi}_{\mathrm{abs}}$ depends on the kinematical variable x F, and increases as x F in the region x F>0.2.  相似文献   

13.
《Physics letters. [Part B]》1988,207(2):222-226
Results are presented from a calorimeter study on the production of jets in large-ET proton-nucleus collisions at 400 GeV/c. Jet-like large-pT events from eight nuclear targets are seen with a special jet trigger. As previously observed, the cross section for such events increases slightly faster than the atomic number, much like in the production of large-pT single hadrons. Data on energy flows and multiplicities suggest that a heavy nucleus does not significantly widen the angular distribution of the beam remmants. In the central region the particle flow in hard nuclear collisions is similar to that in soft nuclear collisions.  相似文献   

14.
This work studies the relevance of nuclear structure in the nonmesonic weak decay of Λ-hypernuclei, with the mechanism of ΛN → NN transition being restricted to one pion exchange (OPE) only. As an application, for the hypernucleus Λ 12 C a comparison between the L-S coupling and the j-j coupling gives an estimate of the range of nuclear structure effects. A considerable dependence is found of the total decay rate and the ratio Г n /qG p on the single particle properties of nuclear models. The possible contribution from the ΔI = 3/2 channel is investigated in a phenomenological manner.  相似文献   

15.
General kinetic equations are derived for nuclear reactions in dense plasmas by taking into account first-order collective plasma effects. We show that, apart from the corrections proportional to the product of the charges Z i and Z j of two reacting nuclei i and j, new corrections comparable in magnitude and proportional to the squares of the nuclear charges Z i 2 and Z j 2 arise. The Salpeter corrections [1] to the nuclear reaction probabilities due to the plasma screening of the interaction potential are shown to be at least a factor of r/d (r is the nuclear size and d is the Debye screening length) smaller than those assumed previously. These are zero in the approximation where the terms of order r/d are disregarded. The correlation corrections proportional to Z iZj have a different physical meaning than those in [1], can have a different sign, and arise for reactions with zero Salpeter corrections. For the correlation corrections that substitute for the previously used Salpeter corrections, strong correlations are difficult to describe analytically. The interpolation formulas between weak and strong Salpeter screenings previously used in many astrophysical applications are inapplicable, because the interpolation formulas between weak and strong correlations cannot yet be obtained. We found a new type of corrections that are proportional to the squares of the charges of reacting nuclei. These are attributable to a change in the collective electrostatic self-energy of the plasma system during nuclear reactions. Plasma corrections for the hydrogen-cycle nuclear reactions are numerically calculated for the temperature, density, and abundances in the solar interior.  相似文献   

16.
This paper presents the most recent nuclear k T measurements from STAR derived from multi-particle jet reconstruction of d+Au and p+p collisions at √s=200 GeV. Since jets reconstructed from multiple particles are relatively free of fragmentation biases, nuclear k Tcan be measured with greater certainty in this way than with traditional di-hadron correlations. Multiparticle jet reconstruction can also be used for a direct measurement of the fragmentation function.  相似文献   

17.
Hadroprduction ofJ/ψ in π? nucleus collisions is studied in the context of the colour singlet model using nuclear structure functions from three different models of the EMC effect. We conclude that it is possible to understand the data on the large transverse momentum (p T ) and small Feynmanx (x F ) of theJ/ψ in terms of the nuclear dependence of structure functions alone. We further show that these data can be used to distinguish between different models of the EMC effect, and that a study of distributions in various kinematic variables in photoproduction ofJ/ψ should be able to very effectively supplement the information obtained from hadroproduction experiments.  相似文献   

18.
Two superfluid states of nuclear matter, which are supposed to play an important role in neutron stars, are discussed: the first one due to the proton-proton 1 S 0 pairing in β-equilibrium nuclear matter; the second one due to the anisotropic neutron-neutron 3 PF 2 pairing in neutron matter. Since the two phases appear at high density of nuclear matter, the three-body forces were added to the pairing interaction and the strong correlation effects in the single-paricle spectrum. The energy gaps, obtained solving the extended BCS equations, significantly deviate from the values without medium effects so as to limit the role of these two superfluid states in the interpretation of phenomena occurring in the neutron-star core.  相似文献   

19.
Measurements of the tensor analyzing power T20 are presented for deuteron elastic scattering from 208Pb at energies below the Coulomb barrier. It is found that, for energies below about 7 MeV, T20 arises primarily from the interaction of the deuteron quadrupole moment with the nuclear electric field gradient. Contributions to T20 from nuclear interactions with the target are shown to be very small for Ed ? 5 MeV. Measurements of T20 at Ed = 4 MeV, accurate to ± 8 × 10?5, are presented. After correcting for deuteron stretching and a number of additional small effects, the data are used to make a new determination of the quadrupole moment. The result, Q = 0.282 ± 0.019 fm2, is in good agreement with the conventional value deduced from molecular hyperfine structure data.  相似文献   

20.
The 1H nuclear spin-lattice relaxation behavior was characterized in the perovskite-type layered structure quasi-two-dimensional Heisenberg paramagnets, (CnH2n+1NH3)2MnCl4,with different chain lengths (n=8, 10, and 12). In contrast to the case of the short-chain compound with n=8, the nuclear spin diffusion to the electron spin system alone is not able to fully account for the spin-lattice relaxation in the compounds with longer chain lengths. Our results are discussed in light of the nuclear magnetic relaxation by the regularly distributed dense paramagnetic ions.  相似文献   

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