12942853
Calculation of strongly-coupled rotational bands in terms of the tilted axis cranking model
Abstract Recently observed strongly-coupled rotational bands associated with the ν[505] 11 2 − quasiparticle state are studied by means of a microscopic tilted axis cranking (TAC) model. The results of calculation for the routhians and the B (M1)/ B (E2) ratios are investigated in the light of other existing models, i.e., the strong-coupling model and the conventional cranking model. It is demonstrated that only the TAC model can successfully reproduce these two observables at the same time. The reason of the success is clarified by making connections between these models.
199673909
Nuclear moments of inertia and wobbling motions in triaxial superdeformed nuclei
The wobbling motion excited on triaxial superdeformed nuclei is studied in terms of the cranked shell model plus random phase approximation. Firstly, by calculating at a low rotational frequency the \gamma-dependence of the three moments of inertia associated with the wobbling motion, the mechanism of the appearance of the wobbling motion in positive-\gamma nuclei is clarified theoretically -- the rotational alignment of the \pi i_{13/2} quasiparticle(s) is the essential condition. This indicates that the wobbling motion is a collective motion that is sensitive to the single-particle alignment. Secondly, we prove that the observed unexpected rotational-frequency dependence of the wobbling frequency is an outcome of the rotational-frequency dependent dynamical moments of inertia.
119426197
Nuclear wobbling motion and electromagnetic transitions
Abstract The nuclear wobbling motion is studied from a microscopic viewpoint. It is shown that the expressions not only of the excitation energy but also of the electromagnetic-transition rate in the microscopic RPA framework can be cast into the corresponding forms of the macroscopic rotor model. Criteria to identify the rotational band associated with the wobbling motion are given. Examples of realistic calculations are investigated and some theoretical predictions are presented.
119187180
Microscopic study of tetrahedrally symmetric nuclei by an angular-momentum and parity projection method
We study the properties of the nuclear rotational excitations with hypothetical tetrahedral symmetry by employing the microscopic mean-field and residual-interaction Hamiltonians with angular-momentum and parity projection method; we focus on the deformed nuclei with tetrahedral doubly-closed shell configurations. We find that for pure tetrahedral deformation the obtained excitation patterns satisfy the characteristic features predicted by group-representation theory applied to the tetrahedral symmetry group. We find that a gradual transition from the approximately linear to the characteristic rigid-rotor, parabolic energy-vs.-spin dependence occurs as a function of the tetrahedral deformation parameter. The form of this transition is compared with the similar well-known transition in the case of quadrupole deformation.
119098407
Microscopic Calculation of the Wobbling Excitations Employing the Woods-Saxon Potential as a Nuclear Mean-Field
The wobbling excitations of the triaxial superdeformed (TSD) bands in the Lu and Hf region are studied by the microscopic framework of the cranked mean-field and the randomphase approximation (RPA). In contrast to the previous works, where the Nilsson potential was used, the more realistic Woods-Saxon potential is employed as a nuclear mean-field. It is pointed out that the original formulation should be slightly modified for general meanfield like the Woods-Saxon potential. The wobbling-like RPA solutions have been found systematically in the nuclei studied and their characteristic properties are investigated in detail. This confirms the wobbling phonon excitations in TSD nuclei from the microscopic calculations. The result of B(E2) values indicates that the triaxial deformation is increasing as a function of spin in the observed TSD bands in 163 Lu. Subject Index: 210, 211, 212
121954152
The role of spin-orbit potential in nuclear prolate-shape dominance
Abstract It is confirmed, in terms of the Woods–Saxon–Strutinsky method, that the spin–orbit potential plays a decisive role in the predominance of prolate deformation, which has been a long standing problem in nuclear physics. It is originated from the combined effects of the spin–orbit coupling and the diffused surface of the potential, in agreement with the previous work based on a more schematic Nilsson–Strutinsky method. The degree of prolate-shape dominance exhibits an oscillatory behavior with respect to the strength of spin–orbit potential and, the prolate-shape dominance is realized at the proper strength of the spin–orbit potential together with the standard surface diffuseness; this oscillatory behavior disappears in case of small diffuseness corresponding to ellipsoidal cavity. The calculated energy differences between oblate and prolate minima in this Letter are consistent with those of our extensive self-consistent calculations of the Hartree–Fock + BCS method with the Skyrme interaction.
120050590
Numerical Approach to One-Loop Integrals
Two numerical methods are proposed for the calculation of one-loop scalar integrals. In the first method, the singularity is cancelled by the symmetrization of the integrand and the integration is done by a Monte-Carlo method. In the second one, after the transform of the integrand into a standard form, the integral is reduced into a regular numerical integral. These methods provide us practical tools to evaluate one-loop Feynman diagrams with desired numerical accuracy. They are extended to the integral with numerator and the treatment of the one-loop virtual correction to the cross section is also presented
96206265
Production cross section measurements of radioactive isotopes by BigRIPS separator at RIKEN RI Beam Factory
Abstract We have measured the production rates and production cross sections for a variety of radioactive isotopes which were produced from 124 Xe, 48 Ca, and 238 U beams at an energy of 345 MeV/nucleon using the BigRIPS separator at the RIKEN Nishina Center RI Beam Factory (RIBF). Proton-rich isotopes with atomic numbers Z  = 40–52 and neutron-rich isotopes with Z  = 5–16 were produced by projectile fragmentation of the 124 Xe and 48 Ca beam on Be targets, respectively. Neutron-rich isotopes with Z  = 20–59 were produced by in-flight fission of the 238 U beam, in which both Be and Pb were used as production targets. The measured production rates and production cross sections were compared with those of the LISE ++ calculations, and overall fairly good agreement has been obtained. Furthermore, in the measurements with the 124 Xe beam, we have discovered four new isotopes on the proton-drip line, 85,86 Ru and 81,82 Mo, and obtained the clear evidence that 103 Sb is particle unbound with an upper limit of 49 ns for the half-life. The measurements of projectile-fragment momentum distributions have been also performed with the 124 Xe beam, in which the low-momentum tails of the distributions have been measured for the first time at the energy of 345 MeV/nucleon.
28690711
Deviations from tri-bimaximality and quark-lepton complementarity
We study deviations from tri-bimaximality (TBM) and quark-lepton complementarity (QLC) in a model-independent way. The current neutrino experimental data is well approximated by tri-bimaximal generation mixing but the QLC relations are not satisfied with each data of 1σ level. This means that there exist deviations from the complementarity. The same fact for the TBM might be checked in the future neutrino experiments. We discuss such deviations from the TBM and QLC, simultaneously. A new ratio between the deviations is introduced, and some interesting points are presented. We also show predicted correlations among leptonic mixing angles at the points.
117897043
Automatic calculations in high energy physics and GRACE at one-loop
Abstract We describe the main building blocks of a generic automated package for the calculation of Feynman diagrams. These blocks include the generation and creation of a model file, the graph generation, the symbolic calculation at an intermediate level of the Dirac and tensor algebra, implementation of the loop integrals, the generation of the matrix elements or helicity amplitudes, methods for the phase space integrations and eventually the event generation. The report focuses on the fully automated systems for the calculation of physical processes based on the experience in developing GRACE-loop which is a general purpose code applicable to one-loop corrections in the Standard Model. As such, a detailed description of the renormalisation procedure in the Standard Model is given emphasizing the central role played by the non-linear gauge fixing conditions for the construction of such automated codes. These new gauge-fixing conditions are used as a very efficient means to check the results of large scale automated computations in the Standard Model. Their need is better appreciated when it comes to devising efficient and powerful algorithms for the reduction of the tensorial structures of the loop integrals and the reduction of the N > 4 point-function to lower rank integrals. A new technique for these reduction algorithms is described. Explicit formulae for all two-point functions in a generalised non-linear gauge are given, together with the complete set of counterterms. We also show how infrared divergences are dealt with in the system. We give a comprehensive presentation of some systematic test-runs which have been performed at the one-loop level for a wide variety of two-to-two processes to show the validity of the gauge check. These cover fermion–fermion scattering, gauge boson scattering into fermions, gauge bosons and Higgs bosons scattering processes. Comparisons with existing results on some one-loop computation in the Standard Model show excellent agreement. These include e + e - → t t ¯ , W + W - , ZH ; γ γ → t t ¯ , W + W - ; e γ → eZ , ν W and W + W - → W + W - . We also briefly recount some recent development concerning the calculation of one-loop corrections to 3 body final states cross sections in e + e - with the help of an automated system.
122420983
Monte Carlo Approach to Radiative Processes in e+ e- Annihilation
We present a new approach to radiative processes in e+ e- annihilation based on a Monte Carlo method. This is nothing but the QED version of the parton shower model studied extensively in QCD. It is applicable to both initial and final state radiation but without the interference between these two. To examine the validity of the model, we compare it with the results of the exact calculations up to OCa) and OCa 2 ). Comparison of several distributions shows that the model can give reliable results for practical use. Study of radiative corrections in e+ e- collisions has a long history!) since its importance was recognized in the discovery of ]/CP.2) Until now, most efforts have concentrated on the calculation of O(a) corrections to weak interactions. Precise measurements of properties of the ZO boson, however, required the detailed study of higher order QED corrections. Techniques of calculating some contributions in all order have been developed, such as soft photon summation 3 ) and collinear photon summation. 4 ) Generally speaking, these are methods suitable only for inclusive distributions, and they can hardly be applied to exclusive processes or event genera­ tions. It is obvious that the collinear photon summation has an exact correspondence with the collinear parton summation based on the Altarelli-Parisi equation in pertur­ bative quantum chromodynamics (QCD). The parton shower model was originally proposed to deal with exclusive processes in QCD. 5 ) In this paper we apply this technique to QED and examine its validity for radiative processes. We shall call this new model QED parton shower (QEDPS). Although the development of the model is not difficult in the technical sense, study of its validity is a nontrivial task because a much higher accuracy of calculation is required than in QCD. Recently one of the authors calculated exact O(a 2 ) QED corrections to the initial state of e+ e- annihila­ tion. 6 ) With the help of this calculation, we are able to test the validity of QEDPS in a systematic and quantitative way. The purposes of this paper are to present the formulation of QEDPS in a Monte Carlo method and to show that it is really a practical method to describe radiative processes. Since the parton shower model is applied to the final q, q and gluon system in e+ e- annihilation, QEDPS can also be used to estimate QED radiative corrections to the charged particles in the final state. Thus it is equally applicable to both initial and final state radiation, though the interference between these two states cannot be included at present. In the next section we will give the algorithm of QEDPS. In § 3, comparison will