Roper resonances in chiral quark models

We derive a method to calculate the multi-channel K -matrix applicable to a broad class of models in which mesons linearly couple to the quark core. The method is used to calculate pion scattering amplitudes in the energy region of low-lying P11 and P33 resonances. A good agreement with experimental data is achieved if in addition to the elastic channel we include the and N ( channels where the -meson models the correlated two-pion decay. We solve the integral equation for the K -matrix in the approximation of separable kernels; it yields a sizable increase of the widths of the (1232) and the N(1440) resonances compared to the bare quark values.     

Radiative corrections to pion-nucleus bremsstrahlung

We calculate the one-photon loop radiative corrections to virtual pion Compton scattering → , that subprocess which determines in the one-photon exchange approximation the pion-nucleus bremsstrahlung reaction Z → Z . Ultraviolet and infrared divergencies of the loop integrals are both treated by dimensional regularization. Analytical expressions for the O() corrections to the virtual Compton scattering amplitudes, A(s, u, Q) and B(s, u, Q) , are derived with their full dependence on the (small) photon virtuality Q from 9 classes of contributing one-loop diagrams. Infrared finiteness of these virtual radiative corrections is achieved (in the standard way) by including soft photon radiation below an energy cut-off . In the region of low center-of-mass energies, where the pion-nucleus bremsstrahlung process is used to extract the pion electric and magnetic polarizabilities, we find radiative corrections up to about -3% for = 5 MeV. Furthermore, we extend our calculation of the radiative corrections to virtual pion Compton scattering → by including the leading pion-structure effect in the form of the polarizability difference - . Our analytical results are particularly relevant for analyzing the data of the COMPASS experiment at CERN which aims at measuring the pion electric and magnetic polarizabilities with high statistics using the Primakoff effect.     

Equation of state and symmetry energy within the stability valley

We apply the direct variational method to derive the equation of state for finite nuclei within the stability valley. The extended Thomas-Fermi approximation for the energy functional with Skyrme forces is used. Applying the leptodermous expansion for the profile nucleon densities, we have studied the neutron coat and the isospin symmetry energy for neutron-rich nuclei. Using the equation of state for the pressure, we derive the region of spinodal instability of finite nuclei and its dependence on the mass number, the asymmetry parameter and the Skyrme force parameters. We suggest the procedure of derivation of the isospin symmetry energy from the analysis of the isospin shift of the chemical potential = - beyond the beta-stability line. We show that both the structure of the neutron coat and the position of the drip line depend significantly on the Skyrme force parameters.     

K-forbidden allowed $ \beta$ transitions in heavy nuclei

The role of the band quantum number K in influencing the character of allowed transitions in heavy deformed nuclei is examined. The conditions for the occurrence of K -forbidden decays in this region are explored. Specific cases of “allowed” decays proceeding via K = 2 to K = 6 channels are presented to illustrate the phenomenon. The listed K = 2 transitions, which by themselves contribute over 10% of all the presently known allowed transitions for A 228 nuclei, are seen to have an average , which is clearly outside the normal range for allowed transitions. It is concluded that, wherever the -connected states can be confidently labelled using the quantum numbers, the K -forbiddenness is in general as significant as that involving the other two (spin and parity) quantum numbers.     

Thermal neutron capture cross-section of <Superscript>76</Superscript>Ge

The thermal neutron capture cross-sections of the ⁷⁶Ge(n,)⁷⁷Ge and the ⁷⁶Ge(n,)^77m Ge reactions have been measured by activating targets of isotopically enriched GeO₂ through cold neutrons. The -decay spectra after the -decay of ⁷⁷Ge and ^77m Ge were measured with HPGe detectors. From these spectra the cross-sections for the ⁷⁶Ge(n,) reactions were derived relative to the cross-section of ¹⁹⁷Au using the absolute emission probabilities of the observed -ray energies. The methods used in this work result in smaller systematic uncertainties than those obtained in previous experiments.     

Single-pion production in pp collisions at 0.95 GeV/c (II)

The single-pion production reactions pp d , pp np and pp pp were measured at a beam momentum of 0.95GeV/c ( T _p 400 MeV) using the short version of the COSY-TOF spectrometer. The central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements from other detector parts. Thus all pion production channels were recorded with 1-4 overconstraints. The main emphasis is put on the presentation and discussion of the np channel, since the results on the other channels have already been published previously. The total and differential cross-sections obtained are compared to theoretical calculations. In contrast to the pp channel we observe in the np channel a strong influence of the excitation. In particular, the pion angular distribution exhibits a (3 cos² + 1) -dependence, typical for a pure s -channel excitation and identical to that observed in the d channel. Since the latter is understood by a s -channel resonance in the ¹ D ₂ pn partial wave, we discuss an analogous scenario for the pn channel.     

Dirac magnetic monopole production from photon fusion in proton collisions

We calculate the lowest-order cross-section for Dirac magnetic monopole production from photon fusion ( in p collisions at = 1.96 TeV, pp collisions at = 14 TeV, and we compare with Drell-Yan (DY) production. We find the total cross-section is comparable with DY at = 1.96 TeV and dominates DY by a factor > 50 at = 14 TeV. We conclude that both the and DY processes allow for a monopole mass limit m > 370 GeV based upon the null results of the recent monopole search at the Collider Detector at Fermilab (CDF). We also conclude that production is the leading mechanism to be considered for direct monopole searches at the Large Hadron Collider (LHC).     

Neutral pion photoproduction at high energies

A Regge model with absorptive corrections is employed in a global analysis of the world data on the reactions p p and n n for photon energies from 3 to 18GeV. In this region resonance contributions are expected to be negligible so that the available experimental information on differential cross-sections and single and double polarization observables at - t 2 GeV²allows us to determine the reaction amplitude reliably. The model amplitude is then used to predict observables for photon energies below 3GeV. A detailed comparison with recent data from the CLAS and CB-ELSA Collaborations in that energy region is presented. Furthermore, the prospects for determining the radiative decay width via the Primakoff effect from the reaction p p are explored.     

Improved bounds on the radius and curvature of the K$ \pi$ scalar form factor and implications to low-energy theorems

We obtain stringent bounds in the 〈r ² -c plane where these are the scalar radius and the curvature parameters of the scalar K form factor, respectively, using analyticity and dispersion relation constraints, the knowledge of the form factor from the well-known Callan-Treiman point , as well as at , which we call the second Callan-Treiman point. The central values of these parameters from a recent determination are accomodated in the allowed region provided the higher loop corrections to the value of the form factor at the second Callan-Treiman point reduce the one-loop result by about 3% with . Such a variation in magnitude at the second Callan-Treiman point yields 0.12 fm² 〈r ² 0.21 fm²and 0.56 GeV^-4 c 1.47 GeV^-4and a strong correlation between them. A smaller value of shifts both bounds to lower values.     

High-spin excitations of 81, 82, 83, 85Se : Competing single-particle and collective structures around N = 50

The ^{81, 82, 83, 85}Se nuclei have been produced as fission fragments in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. Their high-spin level schemes have been built from the triple -ray coincidence data and - angular correlations have been analyzed in order to assign spin and parity values to many observed states. The lowest-spin states of the two-neutron and three-neutron configurations are strongly mixed with two-proton excitations among the fp orbits. On the other hand, the highest-spin states of these neutron configurations are found to remain almost pure. Neutron excitation across the N = 50 gap is observed both in ⁸³Se₄₉ and in ⁸⁵Se₅₁ .     

Linearly polarised photon beams at ELSA and measurement of the beam asymmetry in \pi^{0}_{} photoproduction off the proton

At the electron accelerator ELSA a linearly polarised tagged photon beam is produced by coherent bremsstrahlung off a diamond crystal. Orientation and energy range of the linear polarisation can be deliberately chosen by accurate positioning of the crystal with a goniometer. The degree of polarisation is determined by the form of the scattered electron spectrum. Good agreement between experiment and expectations on the basis of the experimental conditions is obtained. Polarisation degrees of % are typically achieved at half of the primary electron energy. The determination of is confirmed by measuring the beam asymmetry, , in photoproduction and by a comparison of the results to independent measurements using laser backscattering.     

Ultra-sensitive in-beam \gamma -ray spectroscopy for nuclear astrophysics at LUNA

Ultra-sensitive in-beam -ray spectroscopy studies for nuclear astrophysics are performed at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator, deep underground in Italy’s Gran Sasso laboratory. By virtue of a specially constructed passive shield, the laboratory -ray background for < 3 MeV at LUNA has been reduced to levels comparable to those experienced in dedicated offline underground -counting setups. The -ray background induced by an incident -beam has been studied. The data are used to evaluate the feasibility of sensitive in-beam experiments at LUNA and, by extension, at similar proposed facilities.     

Dual parametrization of GPDs versus the double distribution Ansatz

We establish a link between the dual parametrization of GPDs and a popular parametrization based on the double distribution Ansatz, which is in prevalent use in phenomenological applications. We compute several first forward-like functions that express the double distribution Ansatz for GPDs in the framework of the dual parametrization and show that these forward-like functions make the dominant contribution into the GPD quintessence function. We also argue that the forward-like functions with 1 contribute to the leading singular small-x_Bj behavior of the imaginary part of DVCS amplitude. This makes the small-x_Bj behavior of independent of the asymptotic behavior of PDFs. Assuming analyticity of Mellin moments of GPDs in the Mellin space we are able to fix the value of the D -form factor in terms of the GPD quintessence function N(x, t) and the forward-like function Q ₀(x, t) .     

Single heavy flavour baryons using Coulomb plus a power law interquark potential

Properties of single heavy flavor baryons in a non-relativistic potential model with colour Coulomb plus a power law confinement potential have been studied using a simple variational method. The ground-state masses of single heavy baryons and the mass difference between the J ^P = ⁺ and J ^P = ⁺ states are computed using a spin-dependent two-body potential. Using the spin-flavour structure of the constituting quarks and by defining an effective confined mass of the constituent quarks within the baryons, the magnetic moments are computed. The masses and magnetic moments of the single heavy baryons are found to be in accordance with the existing experimental values and with other theoretical predictions. It is found that an additional attractive interaction of the order of -200 MeV is required for the antisymmetric states of (Q c, b) . It is also found that the spin-hyperfine interaction parameters play a decisive role in hadron spectroscopy.     

Photoproduction of $ \eta$ -mesons off neutrons from a deuteron target

A formalism is developed for the partial-wave analysis of data on meson photoproduction off deuterons and applied to photoproduction of and mesons. Different interpretations of a dip-bump structure of the photoproduction cross-section in the 1670MeV region are presented and discussed. Helicity amplitudes for two low-mass S₁₁ states are determined.     

Intermediate energy elastic scattering of protons on 24Mg in the $ \alpha$ -cluster model with dispersion

The -cluster model with dispersion has been developed for the case of the ²⁴Mg nucleus. The ²⁴Mg nucleus is considered as composed of the core ( ¹⁶O nucleus) and two -clusters that form a dumbbell configuration and are arranged with the most probability inside the core. In the calculations the -cluster structure of the core has been taken into account. On the basis of the multiple diffraction scattering theory the differential cross-section and the polarization observables for the elastic p - ²⁴Mg scattering at 800 and 250MeV have been calculated. The results obtained are in agreement with the existing experimental data.     

Final remarks to our study of $ \eta$ -photoproduction on protons in the resonance region

The properties of previously discovered nucleon resonances are amended basing on the recent and more detailed experimental data about the photoproduction of -mesons on protons.     

Topos-Theoretic Extension of a Modal Interpretation of Quantum Mechanics

This paper deals with topos-theoretic truth-value valuations of quantum propositions. Concretely, a mathematical framework of a specific type of modal approach is extended to the topos theory, and further, structures of the obtained truth-value valuations are investigated. What is taken up is the modal approach based on a determinate lattice , which is a sublattice of the lattice of all quantum propositions and is determined by a quantum state e and a preferred determinate observable R. Topos-theoretic extension is made in the functor category of which base category is determined by R. Each true atom, which determines truth values, true or false, of all propositions in , generates also a multi-valued valuation function of which domain and range are and a Heyting algebra given by the subobject classifier in , respectively. All true propositions in are assigned the top element of the Heyting algebra by the valuation function. False propositions including the null proposition are, however, assigned values larger than the bottom element. This defect can be removed by use of a subobject semi-classifier. Furthermore, in order to treat all possible determinate observables in a unified framework, another valuations are constructed in the functor category . Here, the base category includes all ’s as subcategories. Although has a structure apparently different from , a subobject semi-classifier of gives valuations completely equivalent to those in ’s.     

Lifetime measurement in 195Po

The lifetime of the 17/2⁺ yrast state in ¹⁹⁵Po has been measured using the recoil distance Doppler-shift technique to be = 43(11) ps. The lifetime was extracted from the singles -ray spectra obtained by using the recoil-decay tagging method. The present work provides more information of the coupling schemes, shapes and configuration mixing in neutron-deficient odd-mass Po nuclei.