First dark matter limits from a large-mass, low-background, superheated droplet detector

We report on the fabrication aspects and calibration of the first large active mass ( approximately 15 g) modules of SIMPLE, a search for particle dark matter using superheated droplet detectors (SDDs). While still limited by the statistical uncertainty of the small data sample on hand, the first weeks of operation in the new underground laboratory of Rustrel-Pays d'Apt already provide a sensitivity to axially coupled weakly interacting massive particles (WIMPs) competitive with leading experiments, confirming SDDs as a convenient, low-cost alternative for WIMP detection.     

The CASPAR recoil discrimination detector for WIMP searches with calcium and fluorine

We present the results of development work on the CASPAR (‘Cocktail with Alkali-halide Scintillating PARticles’) WIMP Dark Matter detector. The results of Monte Carlo simulations and neutron-scattering tests indicate that even a modest sized detector should provide improved spin-dependent WIMP sensitivity.     

Perturbation theory for the effective interaction in nuclei

Starting from a decomposition of the Hamiltonian H(x) of the nuclear many-body problem in the form H(x) = H₀ + xV, where H₀ is a shell-model Hamiltonian, V the residual interaction, and x a strength parameter, we introduce a general effective interaction W(x) describing the interaction of nucleons within a shell, and the associated effective operators $\text{A}\text{?}\text{(x)}$. We display some properties of these operators. From a particular choice of W(x) we obtain the expressions introduced earlier by several authors. The convergence of the expansions for W(x) and $\text{A}\text{?}\text{(x)}$ in powers of x is investigated. It is shown that W(x) and $\text{A}\text{?}\text{(x)}$ are holomorphic in a domain of the complex x-plane including the point x = 0. With the help of a generalization of the von Neumann-Wigner noncrossing rule, we exhibit the nature of the common singularity of W(x) and $\text{A}\text{?}\text{(x)}$ which is closest to the origin and thus defines the radius r₀ of convergence of the expansions of W and $\text{A}\text{?}$. It is shown that r₀ is unaffected by the cancellation of unlinked diagrams. A criterion of consistency is established, which shows that most of the practical calculations of W lead to results which are inconsistent with the definition of W.     

Properties of universal functions in the Wigner mass formula for nuclei

The properties of the empirical functions in the Wigner mass formula for nuclei, which is based on SU(4) spin-isospin symmetry, are considered. It is shown that the origin of the odd-even effect in nuclei can be explained on the basis of an explicit analytic form of the second-degree Casimir operator for even-even and odd-odd nuclides and for nuclei of odd mass number. Experimental data in support of the proposed Wigner origin of the odd-even effect are presented.     

Nonperturbative approximation schemes for the effective interaction in nuclei

Several methods are investigated to deal with the singularities of the effective interaction which cause the perturbation series to diverge. Some of these methods, which are found to be quite useful, are based upon a semiphenomenological treatment of the “intruder” states. One method, based upon the use of Padé approximants, seems to be free of such semiphenomenological input data and appears to yield a particular effective interaction which has as eigenvalues those levels of the system for which the corresponding eigenfunctions have maximum overlap with the model space. The methods are investigated with the help of simple examples. Those methods which are found to be useful are applied to the 0⁺ and 2⁺ levels of ¹⁸O.     

Electromagnetic interactions in a chiral effective lagrangian for nuclei

Electromagnetic (EM) interactions are incorporated in a recently proposed effective field theory of the nuclear many-body problem. Earlier work with this effective theory exhibited EM couplings that are correct only to lowest order in both the pion fields and the electric charge. The Lorentz-invariant effective field theory contains nucleons, pions, isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields. The theory exhibits a nonlinear realization of SU(2)_L × SU(2)_R chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the currents and the strong-interaction dynamics, it satisfies the symmetries of the underlying QCD, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. It has been verified that for normal nuclear systems, the effective lagrangian can be expanded systematically in powers of the meson fields (and their derivatives) and can be truncated reliably after the first few orders. The complete EM lagrangian arising from minimal substitution is derived and shown to possess the residual chiral symmetry of massless, two-flavor QCD with EM interactions. The uniqueness of the minimal EM current is proved, and the properties of the isovector vector and axial-vector currents are discussed, generalizing earlier work. The residual chiral symmetry is maintained in additional (non-minimal) EM couplings expressed as a derivative expansion and in implementing vector meson dominance. The role of chiral anomalies in the EM lagrangian is briefly discussed.     

Nucleation efficiency of R134a as a sensitive liquid for superheated drop emulsion detector

Superheated emulsion detector is known to detect neutrons, γ-rays and other charged particles. The present work includes the study of nucleation efficiency of superheated drops of one of the CFC-free liquids, R134a (C₂H₂F₄), to fast neutrons, its response to γ-rays from ²⁴¹Am and ¹³⁷Cs and compare its nucleation efficiency with that of R12. The observation indicates that because of the presence of hydrogen, the nucleation efficiency is less in R134a than in R12 in the present neutron energy range of consideration. R134a is one of the most environment-friendly, commercially available liquid that is suitable for superheated drop detector, specially in neutron dosimetry and one needs to investigate it in detail.     

Semi-microscopic model for the effective pairing interaction in atomic nuclei

A model has been proposed in which the ab initio effective pairing interaction in atomic nuclei is supplemented by a small phenomenological term containing one parameter universal for all intermediate-mass and heavy nuclei. The neutron and proton pairing gaps have been calculated for several chains of semimagic nuclei; these calculations demonstrate the applicability of this model.     

Ab initio shell model calculations with three-body effective interactions for p-shell nuclei

We present a qualitative improvement of the ab initio no-core shell model (NCSM) approach by implementing three-body interaction capability for p-shell nuclei. We report the first calculations using three-body effective interactions derived from realistic nucleon-nucleon potentials for 6Li, 8Be, and 10B and demonstrate that the use of three-body effective interactions speeds up the convergence of the NCSM approach. For 10B, we predict JpiT = 1(+)0 ground state, contrary to the experimental observation of 3(+)0, when the AV8(') potential is used, indicating the need for true three-body forces.     

Evidence for nucleosynthesis in the supernova gamma process: universal scaling for p nuclei

Analyzing the solar system abundance, we find two universal scaling laws concerning the p and s nuclei. They indicate that the gamma process in supernova (SN) explosions is the most probable origin of the p nuclei that has been discussed with many possible nuclear reactions and sites in about 50 years. In addition, the scalings lead to new concepts: a universality of the gamma process and a new nuclear cosmochronometer. We carry out gamma-process nucleosynthesis calculations for typical core-collapse SN explosion models, and the results satisfy the observed scalings.     

Two-body and three-body effective interactions in nuclei

Finite-range two-body and zero-range three-body effective forces for use in spin unsaturated systems are determined so as to reproduce the total binding energies, rms radii, and single-particle energies of ¹⁶O, ⁴⁰Ca, ⁴⁸Ca and ⁹⁰Zr; the saturation of nuclear matter; and experimental two-body matrix elements extracted by Schiffer and True. In addition to the Skyrme three-body force which acts only in spatially even states, a spatially odd force is introduced to obtain sufficient generality. The Landau parameters and the effective mass specified by this force are also discussed.     

Consistency of effective,relativistic four-point interactions for nuclei

We derive consistency conditions for effective field theoretic models for nuclei with four-fermion couplings. The transformation properties of these consistency conditions under the renormalization group are discussed.Supported by Gesellschaft für Schwerionenforschung (GSI)     

Liquid xenon as a dark matter detector. Prospects for nuclear recoil discrimination by photon timing

Two mechanisms lead to liquid xenon scintillatlon, and are excited differently by incident electrons and by heavy charged nuclei. This could be used to discriminate nuclear recoil events from radioactive background in a search for hypothetical Galactic dark matter particles. To achieve low energy threshold a likelihood analysis is proposed using the time intervals between detected photons. Results are presented of Monte Carlo simulations, showing the background rejection achievable as a function of the number of detected photons. Some comments are included on background discrimination by simultaneous measurement of scintillation and ionization signals.     

A generalization of the algebraic approach for effective interactions in nuclei

We generalize the algebraic approach of Schucan and Weidenmüller for effective interactions in nuclei and show that in general one obtains an effecti to that of Brandow by an arbitrary similarity transformation. We then show how this arbitrariness can be utilized to obtain hermitian effective interac     

Spin-tensor decomposition of effective interactions for 0p shell nuclei

The spin-tensor decomposition of effective interactions is carried out in the 0p shell region. As effective interactions, we adopt two different types: one is the Cohen-Kurath interaction and the other is the Hauge-Maripuu interaction. Non-central components of these interactions have natures different to each other. Moreover, it is shown that different kinds of mechanism for determining the energy levels occur in the Cohen-Kurath and Hauge-Maripuu calculations.     

A comparison between various expressions for effective interactions and operators in nuclei

Different choices of effective interactions and operators are related to each other and to definitions given in the literature. Perturbation expansions are given, and the degree of complexity in evaluating terms of a given order is exhibited. The application of Padé approximants to different choices of effective interactions and to effective operators is investigated numerically.     

MCT探测器Franz-Keldysh效应有效强度的一种表征方法

通常只有使用较为昂贵、精密的实验设备才能获得 MCT探测器响应波长的偏移量 ,才可确定 MCT探测器 Franz- Keldysh(以下简写为 F- K)效应的强度。提出一种表征 MCT探测器 F- K效应有效强度的简易方法 ,即用 MCT探测器在零偏压及反偏压时的输出电压比来表征其 F- K效应有效强度的强弱。实验结果证实了这种方法有效、可行。     

Searching critical-point nuclei in Te- and Xe-isotopic chains using sextic oscillator potential

We have identified the nuclei in the Te- and Xe-isotopic chains lying close to the critical point, through which the shape phase transition occurs, by using the sextic oscillator potential formalism. It has been found that ¹¹⁰Te, ¹²⁴Te, and ¹²⁴Xe isotopes are the most promising candidates for the critical-point nuclei slightly above the Z = 50 proton shell closure.     

The effective neutron—proton interaction in rare-earth nuclei

The available experimental information concerning the low-lying rotational-band energies in rare-earth nuclei with odd neutron and proton numbers is analysed within the framework of the unified model. We extract 69 empirical values for 51 two-particle matrix elements of the effective neutron—proton interaction in 16 nuclei. This information deals with 43 two-quasi-particle configurations. Strength and range parameters for various types of effective interaction are determined from least-squares fits of calculated matrix elements to the empirical values. We find a significant improvement in the fit when spin-polarized and long-range components are included in the effective force, indicating the importance of core-polarization effects. We investigate the sensitivity of the calculation to the choice of experimental information, to the single-particle model, and to the radial shape of the force. Some predictions are made concerning as yet unconfirmed or unobserved configurations.