119441340
Relationship between the Quark-Meson Coupling Model and Quantum Hadrodynamics
Using the quark-meson coupling (QMC) model, we study nuclear matter from the point of view of quark degrees of freedom. Carrying out a re-definition of the scalar field in matter, we transform the QMC into a QHD-type model with a non-linear scalar potential. The potentials obtained from the QMC are compared with those of relativistic mean-field models. Since at present, rigorous studies of quantum chromodynamics (QCD) are limited to matter systems with high temperature and zero baryon density, it is important to build models that help to bridge the discrepancy between nuclear phenomenology and QCD. We have proposed a relativistic quark model for nuclear matter and finite nuclei that consists of non-overlapping nucleon bags bound by the self-consistent exchange of isoscalar, scalar (σ) and vector (ω) mesons in the mean-field approximation (MFA). This model is called the quark-meson coupling (QMC) model. 1) It has also been found in recent theoretical studies that various properties of finite nuclei can be described very well by relativistic mean-field (RMF) models, i.e., quantum hadrodynamics (QHD). 2) In this Letter, we consider the relationship between the QMC and the QHD and study howthe internal structure of the nucleon plays a role in effective nuclear models. In our previous works, 1) the MIT bag model has been used to describe the quark structure of the nucleon. Because the confined quarks interact with the scalar field σ in matter, the effective nucleon mass M � N in the QMC is given by a function of σ through the quark model of the nucleon. (Although the quarks also interact with the ω meson, it has no effect on the nucleon structure, except for a shift in the nucleon energy. 1) ) The (relativistic) constituent quark model (CQM) is an alternative model for the nucleon. Recently, Shen and Toki 3) have proposed a newversion of the QMC — the quark mean-field (QMF) model, in which the CQM is used to describe the nucleon. In the present study, in addition to the bag model (BM), we use the relativistic CQM with confining potentials V (r) of a square well (SW) and harmonic oscillator (HO) type to see the dependence of the matter properties on the quark model. It is assumed that the light (u or d) quark mass mq is 300 MeV in the CQM and 0 MeV in the BM. Furthermore, we introduce a Lorentz vector-type confining potential that is proportional to γ0, in addition to one of the scalar type, as
15022310
A Deformable Bag Model of Hadrons. I
As a generalization of the MIT spherical bag model, we construct the spheroidal bag model of hadron with an arbitrary eccentricity. This generalization is made by slightly modifying the MIT linear boundary condition: The linear boundary condition is examined in detail. Our model always satisfies two necessary requirements of the MIT bag model --i. e., n-j=O, no quark colour flux leaves the bag, and ijq =0, the scalar density of quark should vanish on the bag surface-- and it reduces to the MIT spherical bag model in the limit of zero-eccentricity. Lagrangian formalism of our model is briefly described. The eigenfrequencies of a single massless quark confined in this spheroidal bag are numer­ ically calculated. We obtain the level-splitting of the excited quark orbits, which is just analogous to the well-known Nilsson's splitting of single particle orbits in deformed nuclei. By using the numerical results of the lowest orbit, the effect of the bag-deformation on the mass of low-lying hadrons is estimated. It is found that, although the spherical bag is stable, tbe quark bag is extremely soft against the quadrupole deformation. Brief discussions are added on the mechanisms which make the spherical bag more stable.
119162077
The quark-meson coupling model and chiral symmetry
We extend the quark‐meson coupling (QMC) model to incorporate chiral symmetry. The relationship between the QMC model and chiral perturbation theory is also discussed. The nuclear central potential is modified by the effect of internal structure of the nucleon.
11540608
The Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter
Abstract The quark-meson coupling model which we have developed previously is extended to incorporate the δ meson. It is then used to study the Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter. We find that, in combination with the u - d mass difference, the difference between quark scalar densities in protons and neutrons generates an effective neutron-proton mass difference of the right magnitude. Finally we find that isospin symmetry breaking in the quark condensates can be directly related to the δ meson field.
20298579
Relativistic hydrodynamics of quark-gluon plasma and stability of scaling solutions.
The scaling solutions of the relativistic hydrodynamics are expected to play an important role in describing the expansion stage of a quark-gluon plasma which may be formed in nucleus-nucleus collisions at high energies. After summarizing some general properties of the scaling solutions, we study in detail their stability against small perturbations. In some typical cases of the two-dimensional scaling solution it is found that (i) the scaling solution is stable if the Reynolds number {ital R} defined in terms of the viscosity coefficients is larger than a critical value {ital R}{sub {ital c}} (=1), (ii) it is also stable for a long-wavelength perturbation if {ital R} is small enough, and (iii) it becomes unstable when {ital R} approaches {ital R}{sub {ital c}} from below. It is also shown that these results are related to the time dependence of the Reynolds number, the entropy density, and the temperature, and the point {ital R}={ital R}{sub {ital c}} corresponds to a critical instant when the heating due to the dissipative processes balances with the cooling due to the expansion of the fluid. The stability of the scaling solution of the quark-gluon plasma is examined for typical ranges of the relevant parameters.
10938062
Composite nucleons in scalar and vector mean fields.
We emphasize that the composite structure of the nucleon may play quite an important role in nuclear physics. It is shown that the momentum-dependent repulsive force of second order in the scalar field, which plays an important role in Dirac phenomenology, can be found in the quark-meson coupling (QMC) model, and that the properties of nuclear matter are well described through the quark-scalar density in a nucleon and a self-consistency condition for the scalar field. The difference between theories of pointlike nucleons and composite ones may be seen in the change of the {omega}-meson mass in nuclear matter if the composite nature of the nucleon suppresses contributions from nucleon-antinucleon pair creation.
97830649
Detailed spatial measurements and Monte Carlo analysis of the transportation phenomena of thermal and epithermal neutrons from the 12-GeV proton transport line to an access maze
Abstract In order to investigate the neutron transportation from a beam-line tunnel to an access maze at a 12-GeV proton accelerator, we measured the spatial distribution of thermal and epithermal neutrons by using the Au activation method in detail. Gold foils were placed at about 70 positions in the maze in the case of the insertion (or extraction) of a copper target of 1 mm thickness into (or from) the beam axis in front of the maze. After the end of accelerator operation, relative activities of the Au foils were simultaneously measured by using an imaging plate technique and the radioactivity of one reference foil was also measured with a HPGe detector to convert to the absolute activities of all foils. It was found that the neutrons reach to the depth of the maze in the case of the insertion of the copper target. This result reflects higher proportion of high-energy particles from the copper target to that from other beam loss points and high-energy particles become the successive source of low-energy neutrons. Furthermore, it was found that several circumstances such as door walls and electric wire cables obviously affect the absorption effect of thermal neutrons. The reaction rates obtained in this study were also used for the benchmark of the Monte Carlo simulation code, MARS15 (version of February 2008). The results of the MARS15 calculations precisely reproduced experimental results and significant effects of the electric wire cables and door walls.
56462111
Performance of 1300 Mhz KEK-type single cell niobium cavities
Four single cell niobium cavities fabricated from Tokyo-Denkai material of RRR=200 have been tested repeatedly with the purpose to evaluate different fabrication and processing techniques used at KEK and Jefferson Lab, respectively. Two cavities--K-15 and K-16--have been manufactured completely at KEK prior to shipment to Jefferson Lab. In addition, K-16 had received a barrel polishing treatment at KEK, resulting in the removal of 40 {mu}m of material from the surface. Cavity K-17 was electron-beam welded at Jefferson Lab; the deep drawing of the half cells and the trimming of the cups for electron-beam welding were done at KEK, however. Cavity JL-1 was completely fabricated at Jefferson Lab. Often, some processing field levels related to electronic activity in the cavities, possibly multipacting, have been seen at KEK and the purpose of this investigation is a verification of such observations. In addition, a comparison of different fabrication procedures and surface treatments are of interest for optimizing cost and performance for larger scale application. In several cavities, accelerating gradients between 20 MV/m {<=} E{sub acc} {<=} 27 MV/m have been measured with only little field emission loading. In one of the cavities, resonant electron loading was ''provoked'' by rinsing it with oil contaminated acetone. The observed multipacting levels at E{sub acc}=13 MV/m and 25 MV/m could be identified with the help of simulation calculations as 1-point and 2-point multipacting across the equator of the cavity. There is - as previously reported - a rather strong dependence of the quench field levels on the amount of material removed from the surface, confirming a picture of a surface damage layer which becomes depleted of defects as more and more of it is removed.
55610926
EVALUATION OF MAGNETIC ALLOYS FOR JHF RF CAVITY
A new type of rf accelerating cavity using a high permeability magnetic alloy (MA) has been developed for the high intensity JHF proton synchrotrons. Compared with ordinary ferrites, the MA cores are very stable at high rf magnetic field and thus very high accelerating gradient (=accelerating voltage per cavity length) is available. We have measured several magnetic alloys in order to find a proper material for the cavity. In this paper, the test results are summarized and the evaluation of these materials is presented.
7147715
Design of a Low Loss SRF Cavity for the ILC
An international team comprising SLAC, KEK, FNAL, JLAB and DESY is collaborating on the design, fabrication and test of a low loss, 1.3 GHz 9-cell SRF structure as a potential improvement for the ILC main linac. The advantages of this structure over the TESLA structure include lower cryogenic loss, shorter rise time, and less stored energy. Among the issues to be addressed in this design are HOM damping, Lorentz force detuning and multipacting. We will report on HOM damping calculations using the parallel finite element eigenmode solver Omega3P and the progress made towards an optimized design. Studies on multipacting and estimates of the Lorentz force detuning will also be presented.
54939600
PROTON LINAC ACTIVITIES IN JAERI