73685731
Flux tube model for glueballs
We calculate the mass spectra and decay widths of glueballs in the flux tube model. The glueball is assumed to be a flux tube ring. The breathing and the rotational motions are investigated using the WKB approximation. The calculated spectrum is consistent with those obtained by lattice QCD. The decay widths are also computed using the Schwinger mechanism, and it is shown that they have rather large values. It is widely believed that the strong interaction is de- scribed by quantum chromodynamics ~QCD !@ 1#. It is, how- ever, very difficult to solve QCD, so that several effective models have been devised to explain the physical properties of many hadrons. The flux tube model @2#, or hadron string model @3,4#, is one such model. According to this model, mesons are made up of a quark and antiquark connected by a color flux tube and baryons are described by a quark and diquark connected by the same flux tube. We showed in a previous paper @5# that various excited states of the hadrons can be explained systematically using such a simple model. On the other hand, recent lattice QCD simulations @6# predict the existence of glueballs, which are composed of only gluons. It is the purpose of this paper to present an intuitive and analytic approach to glueballs using a flux tube model. We assume that the glueball is a closed color flux tube ~flux tube ring !. Moreover, the flux tube that constitutes the ring is assumed to have the same properties as the flux tube that constitutes a meson or a baryon. Consequently, our model has no free parameter. We study the relativistic motion of the closed string and obtain the mass spectrum of the glueballs. This simple picture has already been considered by several authors. In particular, Koma, Suganuma, and Toki @7# studied the relativistic breathing motion analytically with the use of the dual Ginzburg-Landau theory @ 8-1 0#. We study not only the vibrational motion but also the rotational one. Moreover, the decay widths in @7# are also calculated by taking into account qqpair production inside the flux tube ~Schwinger mechanism!. This paper is organized as follows. In the next section, the flux tube model for the glueballs is formulated. Section III is devoted to calculation of the mass spectra and the decay widths of the glueballs. In Sec. IV, the numerical results are presented and some discussion is given.
120691222
Superconductivity of Quark Matter at Finite Temperature
121686024
Excited baryons in the MIT bag model
Abstract The Johnson-Thorn bag model which explains the rotational motion of the elongated MIT bag is extended so as to describe the longitudinal vibration along the elongated bag. Our model is a kind of string model for baryons but it reduces to the ordinary spherical MIT bag model in the ground states. It is shown that the mass spectra of the P 11 and P 33 resonances of baryons can be reproduced by the present model as well as the Regge trajectories.
25502171
Rotating Bag Model for Hadrons
The MIT bag model!) has been quite successful in reproducing the observed masses and other static properties of the low-lying hadrons. It is very important to discuss whether or not excited states of the hadrons (resonances) can be explained in the framework of the bag model. A number of excited states have been described successfully by considering collective excitations of the bag.) In particular, Johnson and Thorn) investigated a series of excited states known as the Regge trajectory by using the rotating bag model. They assumed that the rotating bag has stringlike shape with two ends by the centrifugal force and the transverse length is negligible compared with its longitudinal one. From this onedimensional bag model, they succeeded in reproducing the experimental value of the Regge slope very well. Furthermore it was showt: by Wakimaru and one of the present authors (M. I.) that this simple model can explain not only the Regge slope but also the energy spectra of the trajectories.) On the other hand, Eguchi and Migdal et aJ.5) also discussed the excited states by using their string models 'which are independent of the bag model. Any string model which has been proposed is based on the assumption that the shape is stringlike or one-dimensional. Is the assumption of the stringlike shape, however, surely true? section of the stringlike bag, which we call tube, can be given by
117897053
Shear viscosity and spectral function of the quark matter
We discuss the shear viscosity of the quark matter by using the Kubo-Mori formula. It is found that the shear viscosity is expressed in terms of the quark spectral function. If the spectral function is approximated by a modified Bright-Wigner type, the viscosity decreases as the width of the spectral function increases. We also discuss dependence of the shear viscosity on the temperature and the density.
123223657
A Vibrational Bag Model for Baryons
Surface monopole vibration of baryons is investigated on the basis of the soliton bag model. We derive a relativistic Lagrangian for the surface motion whose mass parameter is proportional to square of the bag radius. With the use of the WKB approximation, the energy spectra of Pl1 and F" resonances are reproduced by our model fairly well. The static properties of the nucleon are alsO studied in our vibrational bag model and compared with those of the static bag model. Our model predicts that the nucleon consists of the central high·density part and the surrounding low-density part. It is also shown that our model is capable to predict the experimental data as well as the static bag model.
117791711
Radioactive Muonic Atom Studies with Intense Muon Beams
New intense muon beams with flux several orders of magnitude higher than at present muon facilities would allow many novel experimental studies that were until now statistically not feasible. The investigation of the nuclear properties of short‐lived nuclei using muonic atom spectroscopy would become possible. In this paper, the recent progress of a feasibility study at RIKEN‐RAL muon facility using the cold hydrogen film method to produce radioactive muonic atoms is being reported. The first experimental results have just been obtained with stable argon ions implanted in solid deuterium films.
18057139
Measurements of Parity-Violation Parameters at SLD
We present direct measurements of the parity-violation parameters A{sub b}, A{sub c}, and A{sub s} at the Z{sup 0} resonance with the SLD detector. The measurements are based on approximately 530 k hadronic Z{sup 0} events collected in 1993-98. Obtained results are A{sub b} = 0.914 {+-} 0.024 (SLD combined: preliminary), A{sub c}, = 0.635 {+-} 0.027 (SLD combined: preliminary), and A{sub s} = 0.895 {+-} 0.066(stat.) {+-} 0.062(sys.).
119990534
Muon density enhancement with a tapered capillary method
The focusing effect of a muon beam with a tapered capillary method has been investigated in a range from 4.2 MeV to 9.2 MeV (i.e. from 30 MeV/c to 45 MeV/c in momentum). We injected the muon beam into a pair of narrowing (tapered) plates and tubes made of glass, copper and gold‐coated copper, and measured the energy distribution of the muon leaving from the outlet. The plates were tilted from an inlet of 40 mm to an outlet of 20 mm. The density enhancement was more prominent with the plates made of heavier elements. The largest beam density enhancement at 10 mm downstream of the outlet was 1.3 with the gold‐coated copper narrowing plates. The enhancement was composed of muons scattered with a small angle. Their energy was slightly less than that of the initial beam. This effect did not depend on the surface roughness. The result strongly suggests a simple and effective way to increase the muon beam density for a small target.
125753081
Magnetic Field Measurement System for the SuperKEKB Final Focus Superconducting Magnets
SuperKEKB final beam focusing system consists of different types of superconducting magnets: 8 quadrupole magnets, 4 solenoids and 43 corrector coils. In order to measure the field performances of the magnets and the coils, KEK prepared one set of harmonic coil system during the production stage in a factory, and two sets of harmonic coil systems for the cold tests at 4K for the vertical cryostat test stand in KEK. In this paper, we report these magnetic field measurement systems
13435498
Study of top-quark production and decay vertices with LCD fast simulation
We report a study of top-quark reconstruction in e+e−→tt events at a 500 GeV linear collider using the LCD Fast simulator. The initial study of top-quark anomalous couplings is also reported. The final states of 4 jets and lepton as well as 6 jets are used. Using the 4 jets and lepton final state, we estimate the preliminary sensitivities for form factors at the γ/Z0tt vertex. In the 6 jets reconstruction, we show abilities of the top-quark charge identification and the c-quark tagging in W decays.