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Amand Faessler

Publications and source records attributed to Amand Faessler.

At least 73 records · Page 4Linked to original sources
arXiv2010

On the possibility to measure nuclear matrix elements of neutrinoless double beta decay in charge-exchange reactions

As shown in Ref.\cite{Rod09}, the Fermi nuclear matrix element $M^{0ν}_F$ of neutrinoless double beta ($0νββ$) decay can be reconstructed if one is able to measure the isospin-forbidden single Fermi transition matrix element from the ground state of the final nucleus to the isobaric analog state (IAS) of the initial nucleus, for instance by means of charge-exchange reactions of the $(n,p)$-type. Here, simple estimates for $^{82}$Se are made which show that indeed the tiny cross section $σ_{np}(0_f^+\to IAS)$ is dominated by the admixture of the double IAS in the ground state of the final nucleus provided that the isospin mixing is weak and can be treated perturbatively. A measurement of such a cross section would definitely be a very difficult task, but it can advance a lot our knowledge of the $0νββ$ nuclear matrix element.

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arXiv2010

Relation between the $0νββ$ and $2νββ$ nuclear matrix elements revisited

We show that the dominant Gamow-Teller part, $M^{0ν}_{GT}$, of the nuclear matrix element governing the neutrinoless $ββ$ decay is related to the matrix element $M^{2ν}_{cl}$ governing the allowed two-neutrino $ββ$ decay. That relation is revealed when these matrix elements are expressed as functions of the relative distance $r$ between the pair of neutrons that are transformed into a pair of protons in the $ββ$ decay. Analyzing this relation allows us to understand the contrasting behavior of these matrix elements when $A$ and $Z$ is changed; while $M^{0ν}_{GT}$ changes slowly and smoothly, $M^{2ν}$ has pronounced shell effects. We also discuss the possibility of phenomenological determination of the $M^{2ν}_{cl}$ and from them of the $M^{0ν}_{GT}$ values from the experimental study of the $β^{\pm}$ strength functions.

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arXiv2010

J/psi gamma and psi(2S) gamma decay modes of the X(3872)

The X(3872) with quantum numbers J(PC) = 1(++) is considered as a composite state containing both molecular hadronic and a c bar(c) component. Based on this structure assumption we first constrain model parameters in order to reproduce the predictions for the radiative decay widths of X(3872) to J/psi gamma and X(3872) to psi(2S) gamma as obtained in c bar(c) potential models. Depending on these predictions we find that further inclusion of the molecular component can in principle lead to an improved description of the radiative X(3872) decays. We also show that strong decay modes of the X(3872) and in particular the ratio of radiative (J/psi gamma) to strong (J/psi pi(+) pi(-)) decays hint towards a subleading role of the c bar(c) component in the X(3872).

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arXiv2010

Neutrinoless double beta decay of $^{150}$Nd with account for deformation

A microscopic state-of-the-art calculation of the nuclear matrix element for neutrinoless double beta decay of $^{150}$Nd with an account for nuclear deformation is performed. The proton-neutron quasiparticle random phase approximation (QRPA) with a realistic residual interaction [the Brueckner $G$ matrix derived from the charge-depending Bonn (Bonn-CD) nucleon-nucleon potential] is used as the underlying nuclear structure model. The present calculated matrix element is suppressed by about 40% as compared with our previous QRPA result for $^{150}$Nd obtained with neglect of deformation. By making use of this newest nuclear matrix element, one may conclude that neutrinoless double beta decay of $^{150}$Nd, to be measured soon by the SNO+ collaboration, provides one of the best probes of the Majorana neutrino mass.

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arXiv2010

B_s(d) - bar B_s(d) mixing constraints on flavor changing decays of t and b quarks

We study those dimension 6 effective operators which generate flavor-changing quark-gluon transitions of the third generation quarks, with t -> g + u(c) and b -> g + d(s), and which could be of interest for LHC experiments. We analyze the contribution of these operators to B_s(d) - bar B_s(d) mixing and derive limits on the corresponding effective couplings from the existing experimental data. The Standard Model gauge invariance relates these couplings to the couplings controlling t -> g + u(c). On this basis we derive upper limits for the branching ratios of these processes. We further show that forthcoming LHC experiments might be able to probe the studied operators and the physics beyond the Standard Model related to them.

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arXiv2010

Radiative decay of Lambdac(2940)+ in a hadronic molecule picture

The Lambdac(2940)+ baryon with quantum numbers J(P) = 1/2(+) is considered as a molecular state composed of a nucleon and D* meson. We give predictions for the width of the radiative decay process Lambdac(2940)+ to Lambdac(2286)+ gamma in this interpretation. Based on our results we argue that an experimental determination of the radiative decay width of Lambdac(2940)+ is important for the understanding of its intrinsic properties.

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arXiv2010

Contributions of different neutron pairs in different approaches for neutrinoless double beta decay

The methods used till now to calculate the neutrinoless double beta decay matrix elements are: the Quasiparticle Random Phase Approximation (QRPA), the Shell Model (SM), the angular momentum projected Hartee-Fock-Bogoliubov approach (HFB) and the Interacting Boson Model (IBM). The different approaches are compared specifically concerning the the angular momenta and parities of the neutron pairs, which are changed into two protons by the $0νββ$ decay. The QRPA and SM involve about the same angular momentum and parity neutron pairs, while the HFB is restricted to $0^{+}, 2^{+}, 4^{+}, ...$, and IBM to $0^{+}$ and $2^{+}$ nucleon pairs. The differences in the seniority contributions for the QRPA and the SM are discussed.

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arXiv2010

Few active mechanisms of the neutrinoless double beta-decay and effective mass of Majorana neutrinos

It is well known that there exist many mechanisms that may contribute to neutrinoless double beta decay (0nbb-decay). By exploiting the fact that the associated nuclear matrix elements are target dependent we show that, given definite experimental results on a sufficient number of targets, one can determine or sufficiently constrain all lepton violating parameters including the mass term. As a specific example we show that, assuming the observation of the 0nbb-decay in three different nuclei, e.g., 76Ge, 100Mo and 130Te, and just three lepton number violating mechanisms (light and heavy neutrino mass mechanisms as well as R-parity breaking SUSY mechanism) being active, there are only four different solutions for the lepton violating parameters, provided that they are relatively real. In particular, assuming evidence of the 0nbb-decay of 76Ge, the effective neutrino Majorana mass |m_bb| can be almost uniquely extracted by utilizing other existing constraints (cosmological observations and tritium beta-decay experiments). We also point out the possibility that the non-observation of the 0nbb-decay for some isotopes could be in agreement with a value of |m_bb| in sub eV region. We thus suggest that it is important to have at least two different 0nbb-decay experiments for a given nucleus.

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arXiv2010

Charmed baryon Sigmac(2800) as a ND hadronic molecule

The isotriplet Sigmac(2800) baryon with possible quantum numbers J(P) = 1/2(+), 1/2(-) or 3/2(+), 3/2(-) is considered as a hadronic molecule composed of a nucleon and a D meson. We determine the strong two-body decay widths Sigmac to Lambdac + pi which are shown to be consistent with current data for the J(P) = 1/2(+) and J(P) = 3/2(-) assignments.

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arXiv2010

Semiclassical features of rotational ground bands

A time dependent variational principle is used to dequantize a second order quadrupole boson Hamiltonian. The classical equations for the generalized coordinate and the constraint for angular momentum are quantized and then analytically solved. A generalized Holmberg-Lipas formula for energies is obtained. A similar $J(J+1)$ dependence is provided by the coherent state model (CSM) in the large deformation regime, by using an expansion in powers of $1/x$ for energies, with $x$ denoting a deformation parameter squared. A simple compact expression is also possible for the near vibrational regime. These three expressions have been used for 44 nuclei covering regions characterized by different dynamic symmetries or in other words belonging to the all known nuclear phases. Nuclei satisfying the specific symmetries of the critical point in the phase transitions $O(6)\to SU(3)$, $SU(5)\to SU(3)$ have been also considered. The agreement between the results and the corresponding experimental data is very good. This is reflected in very small r.m.s. values of deviations.

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arXiv2010

Running sums for $2νββ$-decay matrix elements within the QRPA with account for deformation

The $2νββ$-decay running sums for $^{76}$Ge and $^{150}$Nd nuclei are calculated within a QRPA approach with account for deformation. A realistic nucleon-nucleon residual interaction based on the Brueckner G matrix (for the Bonn CD force) is used. The influence of different model parameters on the functional behavior of the running sums is studied. It is found that the parameter $g_{pp}$ renormalizing the G matrix in the QRPA particle-particle channel is responsible for a qualitative change in behavior of the running sums at higher excitation energies. For realistic values of $g_{pp}$ a significant negative contribution to the total $2νββ$-decay matrix element is found to come from the energy region of the giant Gamow-Teller resonance. This behavior agrees with the results of other authors.

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arXiv2010

Relativistic constituent quark model with infrared confinement

We refine the relativistic constituent quark model developed in our previous papers to include the confinement of quarks. It is done, first, by introducing the scale integration in the space of alpha-parameters, and, second, by cutting this scale integration on the upper limit which corresponds to an infrared cutoff. In this manner one removes all possible thresholds presented in the initial quark diagram. The cutoff parameter is taken to be the same for all physical processes. We adjust other model parameters by fitting the calculated quantities of the basic physical processes to available experimental data. As an application, we calculate the electromagnetic form factors of the pion and the transition form factors of the omega and eta Dalitz decays.

hep-ph↗
arXiv2010

Theoretical mean field and experimental occupation probabilities in the double beta decay system 76Ge to 76Se

Usual Woods-Saxon single particle levels with BCS pairing are not able to reproduce the experimental occupation probabilities of the proton and neutron levels 1p_{3/2}, 1p_{1/2}, 0f_{5/2}, 0g_{9/2} in the double-beta decay system 76Ge to 76Se. Shifting down the 0g_{9/2} level by hand can explain the data but it is not satisfactory. Here it is shown that a selfconsistent Hartree-Fock+BCS approach with experimental deformations for 76Ge and 76Se may decisively improve the agreement with the recent data on occupation probabilities by Schiffer et al. and Kay et al. Best agreement with available data on 76Ge and 76Se, as well as on neighbor isotopes, is obtained when the spin-orbit strength for neutrons is allowed to be larger than that for protons. The two-neutrino double-beta decay matrix element is also shown to agree with data.

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arXiv2010

Quasielastic rho0 electroproduction on the proton at intermediate energy: Role of scalar and pseudoscalar meson exchange

We present a detailed analysis of rho(0) electroproduction at intermediate energy for quasi-elastic knockout kinematics. The approach is based on an effective Lagrangian which generates exchanges of scalar, pseudoscalar, axial-vector and tensor mesons. The specific role of mesons with different values for J(PC) is analyzed. We show that the pi(0) exchange amplitude and its interference terms with eta(eta') and f1 exchanges dominate in the transverse part of the cross section sigmaT. The main role plays the pi(0) to rho(0) M1 spin transition when coupling the virtual photons to the nucleon. In contrast, the longitudinal cross section sigmaL is generated by a series of scalar meson exchanges. To extract the dominant term more detailed information on the inner structure of scalar mesons is required. It turns out that recent data of the CLAS Collaboration on sigmaL and sigmaT can be described with reasonable accuracy if one proposes the quarkonium structure for the heavy scalar mesons (M > 1.3 GeV). On this basis the differential cross sections dsigmaL/dt and dsigmaT/dt are calculated and compared with the latest CLAS data.

hep-ph↗
arXiv2010

Hadron Molecules

We discuss a possible interpretation of the open charm mesons $D_{s0}^*(2317)$, $D_{s1}(2460)$ and the hidden charm mesons X(3872), Y(3940) and Y(4140) as hadron molecules. Using a phenomenological Lagrangian approach we review the strong and radiative decays of the $D_{s0}^* (2317)$ and $D_{s1}(2460)$ states. The X(3872) is assumed to consist dominantly of molecular hadronic components with an additional small admixture of a charmonium configuration. Determing the radiative ($γJ/ψ$ and $γψ(2s)$) and strong ($J/ψ2π$ and $ J/ψ3π$) decay modes we show that present experimental observation is consistent with the molecular structure assumption of the X(3872). Finally we give evidence for molecular interpretations of the Y(3940) and Y(4140) related to the observed strong decay modes $J/ψ+ ω$ or $J/ψ+ ϕ$, respectively.

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arXiv2010

Strong two-body decays of the Lambdac(2940)+ in a hadronic molecule picture

The Lambdac(2940)+ baryon with possible quantum numbers J(P) = 1/2+ and 1/2- is studied as a molecular state composed of a nucleon and D* meson. We give predictions for the strong two-body decay channels Lambdac(2940)+ to p D0, Sigmac(++) pi(-) and Sigmac(0) pi(+) where the sum of partial widths is consistent with current data for the case of J(P) = 1/2(+). The case of J(P) = 1/2(-) is shown to be ruled out.

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