arXiv subjects
Publications and source records attributed to Amand Faessler.
We apply a phenomenological Lagrangian approach to the radiative decay Y(4260) -> X(3872) + gamma. The Y(4260) and X(3872) resonances are considered as composite states containing both molecular hadronic and charmonium components. Having a leading molecular component in the X(3872) and a sole molecular configuration for the Y(4260) results in a prediction compatible with present data.
In present work the Y(4260) resonance is considered as a weakly bound state of a pseudoscalar D and an axial D1 charm meson. We consider the two-body decay Y(4260) -> Zc(3900) + pi where Zc(3900) is treated as hadron molecule as well. Moreover we compute the Y(4260) decay modes J/psi pi(+) pi(-), recently observed by the BESIII Collaboration, and psi(2S) pi(+) pi(-). In the last process both the contact diagram with D D1 -> psi(nS) pi(+) pi(-) and the resonance diagram with D D1 -> Zc(3900) + pi -> psi(nS) pi(+) pi(-) are taken into account.
A relativistic light-front quark model is used to describe both the elastic nucleon and nucleon-Roper transition form factors in a large Q2 range, up to 35 GeV2 for the elastic and up to 12 GeV2 for the resonance case. Relativistic three-quark configurations satisfying the Pauli exclusion principle on the light-front are used for the derivation of the current matrix elements. The Roper resonance is considered as a mixed state of a three-quark core configuration and a molecular N+sigma hadron component. Based on this ansatz we obtain a realistic description of both processes, elastic and inelastic, and show that existing experimental data are indicative of a composite structure of the Roper resonance.
The Generalized Coherent State Model, proposed previously for a unified description of magnetic and electric collective properties of nuclear systems, is extended to account for the chiral like properties of nuclear systems. To a phenomenological core described by the GCSM a set of interacting particles are coupled. Among the particle-core states one identifies a finite set which have the property that the angular momenta carried by the proton and neutron quadrupole bosons and the particles respectively, are mutually orthogonal. All terms of the model Hamiltonian satisfy the chiral symmetry except for the spin-spin interaction. The magnetic properties of the particle-core states, where the three mentioned angular momenta are orthogonal, are studied. A quantitative comparison of these features with the similar properties of states, where the three angular momenta belong to the same plane, is performed.
The spectrum of the Cosmic Microwave Background follows Planck's black body radiation formula and shows a remarkable constant temperature of T = 2.7. About 380 000 years after the Big Bang at a temperature of T = 3000 Kelvin in the matter dominated era the electrons combine with the protons and 4He and the photons move freely in the neutral universe. So the temperature and distribution of the photons give us information of the universe 380 000 years after the Big Bang. Information about earlier times can, in principle, be derived from the Cosmic Neutrino Background (relic neutrinos). The neutrinos decouple already about 1 second after the Big Bang at a temperature of around 1 MeV or 10^{10} Kelvin. Today their temperature is about 1.95 Kelvin. Registration of these neutrinos is an extremely challenging experimental problem, which can hardly be solved with the present technologies. On the other hand it represents a tempting opportunity to check one of key elements of the Big Bang Cosmology and to probe the early stages of the universe evolution. The search for the Cosmic Neutrino Background with the induced beta decay: relic neutrino + 3H --> 3He + e-, is the topic of this contribution. The signal would show up as a peak in the electron spectrum by an energy with the neutrino mass above the Q value. We discuss the prospects of this approach and argue that it is able to set limits on the Cosmic Neutrino density in our vicinity. We also discuss critically ways to increase with modifications of the present KATRIN spectrometer the Tritium source intensity by a factor 100, which would yield about 170 counts of relic neutrino captures per year. Presently such an increase of the Tritium source intensity seems not to be possible. But one should be able to find an upper limit for the local density of the relic neutrinos in our galaxy.
The determination of the absolute scale of the neutrino masses is one of the most challenging present questions in particle physics. The most stringent limit, $m(\barν_{\mathrm{e}})<2$eV, was achieved for the electron anti-neutrino mass \cite{numass}. Different approaches are followed to achieve a sensitivity on neutrino masses in the sub-eV range. Among them, experiments exploring the beta decay or electron capture of suitable nuclides can provide information on the electron neutrino mass value. We present the Electron Capture $^{163}$Ho experiment ECHo, which aims to investigate the electron neutrino mass in the sub-eV range by means of the analysis of the calorimetrically measured energy spectrum following electron capture of $^{163}$Ho. A high precision and high statistics spectrum will be measured with arrays of metallic magnetic calorimeters. We discuss some of the essential aspects of ECHo to reach the proposed sensitivity: detector optimization and performance, multiplexed readout, $^{163}$Ho source production and purification, as well as a precise theoretical and experimental parameterization of the calorimetric EC spectrum including in particular the value of $Q_{\mathrm{EC}}$. We present preliminary results obtained with a first prototype of single channel detectors as well as a first 64-pixel chip with integrated micro-wave SQUID multiplexer, which will already allow to investigate $m(ν_{\mathrm{e}})$ in the eV range.
The two newly observed hidden-charm mesons Zc(+)[3900] and a possible partner state Zc'(+)[3950] with quantum numbers J(P) = 1(+) are considered as hadronic molecules composed of bar(D)D* and bar(D)* D*, respectively. We give predictions for the decay widths of the strong two-body transitions Zc(+) -> H + pi(+) and Zc' -> H + pi(+) with H = Psi(nS), hc(mP) in a phenomenological Lagrangian approach.
An exactly solvable model for a description of the two-neutrino double beta decay transition of the Fermi type is considered. By using perturbation theory an explicit dependence of the two-neutrino double beta decay matrix element on the like-nucleon pairing, particle-particle and particle-hole proton-neutron interactions by assuming a weak violation of isospin symmetry of Hamiltonian expressed with generators of the SO(5) group. It is found that there is a dominance of double beta decay transition through a single state of the intermediate nucleus. Then, an energy weighted sum rule connecting Delta Z=2 nuclei is presented and discussed. It is suggested that this sum rule can be exploited to study the residual interactions of the nuclear Hamiltonian.
In view of recent measurements of the mixing angle θ_{13} a possibility to determine the difference of two CP Majorana phases of the neutrino mixing matrix from the study of neutrinoless double-beta decay is investigated. We show that in the case of the inverted hierarchy of neutrino masses it might be possible if neutrinoless double-beta decay will be observed. The required experimental accuracies and uncertainty in the calculated nuclear matrix elements of the process are discussed.
Within QRPA we achieve partial restoration of the isospin symmetry and hence fulfillment of the requirement that the $2νββ$ Fermi matrix element $M^{2ν}_F$ vanishes, as it should, unlike in the previous version of the method. This is accomplished by separating the renormalization parameter $g_{pp}$ of the particle-particle proton-neutron interaction into the isovector and isoscalar parts. The isovector parameter $g_{pp}^{T=1}$ need to be chosen to be essentially equal to the pairing constant $g_{pair}$, so no new parameter is needed. For the $0νββ$ decay the Fermi matrix element $M^{0ν}_F$ is substantially reduced, while the full matrix element $M^{0ν}$ is reduced by $\approx$ 10%. We argue that this more consistent approach should be used from now on in the proton-neutron QRPA and in analogous methods.
In a previous article [Phys. Rev. D 79, 053001 (2009)] we estimated the correlated uncertainties associated to the nuclear matrix elements (NME) of neutrinoless double beta decay (0 nu beta beta) within the quasiparticle random phase approximation (QRPA). Such estimates encompass recent independent calculations of NMEs, and can thus still provide a fair representation of the nuclear model uncertainties. In this context, we compare the claim of 0 nu beta beta decay in Ge-76 with recent negative results in Xe-136 and in other nuclei, and we infer the lifetime ranges allowed or excluded at 90% C.L. We also highlight some issues that should be addressed in order to properly compare and combine results coming from different 0 nu beta beta decay candidate nuclei.
The two newly observed hidden-bottom mesons Zb(10610) and Zb'(10650) with quantum numbers J(P) = 1(+) are considered as hadronic molecules composed of BB(*) and B(*)B(*), respectively. We give predictions for the widths of the strong two-body decays Zb(+) to Upsilon(nS) + pi(+) and Zb'(+) to Upsilon(nS) + pi(+) in a phenomenological Lagrangian approach.
A new generation of neutrinoless double beta decay experiments with improved sensitivity is currently under design and construction. They will probe inverted hierarchy region of the neutrino mass pattern. There is also a revived interest to the resonant neutrinoless double-electron capture, which has also a potential to probe lepton number conservation and to investigate the neutrino nature and mass scale. The primary concern are the nuclear matrix elements. Clearly, the accuracy of the determination of the effective Majorana neutrino mass from the measured 0νββ-decay half-life is mainly determined by our knowledge of the nuclear matrix elements. We review recent progress achieved in the calculation of 0νββand 0νECEC nuclear matrix elements within the quasiparticle random phase approximation. A considered self-consistent approach allow to derive the pairing, residual interactions and the two-nucleon short-range correlations from the same modern realistic nucleon-nucleon potentials. The effect of nuclear deformation is taken into account. A possibility to evaluate 0νββ-decay matrix elements phenomenologically is discussed.
A novel approach is developed to find the three-body breakup amplitudes and cross sections within the modified Faddeev equation framework. The method is based on the lattice-like discretization of the three-body continuum with a three-body stationary wave-packet basis in momentum space. The approach makes it possible to simplify drastically all the three- and few-body breakup calculations due to discrete wave-packet representations for the few-body continuum and simultaneous lattice representation for all the scattering operators entering the integral equation kernels. As a result, the few-body breakup can be treated as a particular case of multi-channel scattering in which part of the channels represents the true few-body continuum states. As an illustration for the novel approach, an accurate calculations for the three-body breakup process $n+d\to n+n+p$ with non-local and local $NN$ interactions are calculated. The results obtained reproduce nicely the benchmark calculation results using the traditional Faddeev scheme which requires much more tedious and time-consuming calculations.
The Neutrinoless double beta Decay allows to determine the effectice Majorana electron neutrino mass. For this the following conditions have to be satisfied: (i) The neutrino must be a Majorana particle, i. e. identical to the antiparticle. (ii) The half life has to be measured. (iii)The transition matrix element must be reliably calculated. (iv) The leading mechanism must be the light Majorana neutrino exchange. The present contribution studies the accuracy with which one can calculate by different methods: (1) Quasi-Particle Random Phase Approach (QRPA), (2) the Shell Model (SM), (3) the (before the variation) angular momentum projected Hartree-Fock-Bogoliubov method (PHFB)and the (4) Interacting Boson Approach (IBA). In the second part we investigate how to determine experimentally the leading mechanism for the Neutrinoless Double Beta Decay. Is it (a) the light Majorana neutrino exchange as one assumes to determine the effective Majorana neutrino mass, ist it the heavy left (b) or right handed (c) Majorana neutrino exchange allowed by left-right symmetric Grand Unified Theories (GUT's). Is it a mechanism due to Supersymmetry e.g. with gluino exchange and R-parity and lepton number violating terms. At the end we assume, that Klapdor et al. have indeed measured the Neutrinoless Double Beta Decay(, although contested,)and that the light Majorana neutrino exchange is the leading mechanism. With our matrix elements we obtain then an effective Majorana neutrino mass of: = 0.24 [eV], exp (pm) 0.02; theor. (pm) 0.01 [eV]
Partial decay widths of various decay channels of the X(1835) are evaluated in the 3P0 quark model, assuming that the X(1835) is a nucleon-antinucleon bound state. It is found that the decays to rho+rho, omega+omega and pion+a0(1450) dominate over other channels, and that the product branching fractions of J/psi to pion+pion+eta and J/psi to pion+pion+eta' are in the same order. We suggest that the X(1835) may be searched in the pion+a0(1450) channel.
The mean values of a many-body Hamiltonian including a proton-neutron pairing term and matrix elements of one-, two- and four-body operators within a basis of particle number projected BCS states, are analytically expressed in terms of a single function Q(N) depending on the number of particles, $N$. The function Q(N) is calculated using a recursion in $N$ in which the shells and the BCS angles are kept the same for any step of iteration. An illustrative example is numerically considered in a restricted single particle space. Some specific features for the standard BCS, the projection after variation approach as well as for the variation after projection formalism, are pointed out.
We specify conditions under which the nucleon-nucleon interaction, based on the t-channel meson-exchange mechanism, is equivalent to an interaction generated via an s-channel exchange of six-quark bags. The duality is possible provided the alternation of zeros and poles of the non-dispersive part of D function takes place in the normalization where the imaginary part of D is non-negative and the CDD poles are the only poles of D.