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.     

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.     

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.     

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.     

Backward pion photoproduction

We present a systematic analysis of backward pion photoproduction for the reactions p p and p n . Regge phenomenology is applied at invariant collision energies above 3GeV in order to fix the reaction amplitude. A comparision with older data on - and -photoproduction at = 180^° indicates that the high-energy limit as given by the Regge calculation could be reached possibly at energies of around ≃ 3 GeV. In the energy region of 2.5 GeV, covered by the new measurements of p p differential cross-sections at large angles at ELSA, JLab, and LEPS, we see no clear signal for a convergence towards the Regge results. The baryon trajectories obtained in our analysis are in good agreement with those given by the spectrum of excited baryons.     

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.     

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.     

Nuclear structure of 189Tl states studied via \beta^{{+}}_{} /EC decay and laser spectroscopy of 189m+gPb

The /EC decay of ^{189m, g}Pb has been studied at the ISOLDE facility using nuclear spectroscopy and in-source laser spectroscopy. A level scheme of ¹⁸⁹Tl has been built from - coincidence relationships and information on the feeding of some excited levels of ¹⁸⁹Tl provided by the hyperfine spectra obtained from laser ionization. The half-lives of both the 13/2⁺ and 3/2^{- 189}Pb isomers have been estimated to be T _1/2 = 50±3 s and T _1/2 = 39±8 s, respectively. Calculations have been performed for different oblate and prolate nuclear deformations using an axial-rotor coupled to one-quasiparticle model, a structure has been suggested for the low-lying levels of the ¹⁸⁹Tl nucleus.     

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 .     

Nonadditive entropy: The concept and its use

The thermodynamical concept of entropy was introduced by Clausius in 1865 in order to construct the exact differential dS = Q/T , where Q is the heat transfer and the absolute temperature T its integrating factor. A few years later, in the period 1872-1877, it was shown by Boltzmann that this quantity can be expressed in terms of the probabilities associated with the microscopic configurations of the system. We refer to this fundamental connection as the Boltzmann-Gibbs (BG) entropy, namely (in its discrete form) , where k is the Boltzmann constant, and {p _i} the probabilities corresponding to the W microscopic configurations (hence ∑^W _i=1 p _i = 1 . This entropic form, further discussed by Gibbs, von Neumann and Shannon, and constituting the basis of the celebrated BG statistical mechanics, is additive. Indeed, if we consider a system composed by any two probabilistically independent subsystems A and B (i.e., , we verify that . If a system is constituted by N equal elements which are either independent or quasi-independent (i.e., not too strongly correlated, in some specific nonlocal sense), this additivity guarantees S_BG to be extensive in the thermodynamical sense, i.e., that in the N ≫ 1 limit. If, on the contrary, the correlations between the N elements are strong enough, then the extensivity of S_BG is lost, being therefore incompatible with classical thermodynamics. In such a case, the many and precious relations described in textbooks of thermodynamics become invalid. Along a line which will be shown to overcome this difficulty, and which consistently enables the generalization of BG statistical mechanics, it was proposed in 1988 the entropy . In the context of cybernetics and information theory, this and similar forms have in fact been repeatedly introduced before 1988. The entropic form S_q is, for any q 1 , nonadditive. Indeed, for two probabilistically independent subsystems, it satisfies . This form will turn out to be extensive for an important class of nonlocal correlations, if q is set equal to a special value different from unity, noted q_ent (where ent stands for entropy . In other words, for such systems, we verify that , thus legitimating the use of the classical thermodynamical relations. Standard systems, for which S_BG is extensive, obviously correspond to q _ent = 1 . Quite complex systems exist in the sense that, for them, no value of q exists such that S_q is extensive. Such systems are out of the present scope: they might need forms of entropy different from S_q, or perhaps --more plainly-- they are just not susceptible at all for some sort of thermostatistical approach. Consistently with the results associated with S_q, the q -generalizations of the Central Limit Theorem and of its extended Lévy-Gnedenko form have been achieved. These recent theorems could of course be the cause of the ubiquity of q -exponentials, q -Gaussians and related mathematical forms in natural, artificial and social systems. All of the above, as well as presently available experimental, observational and computational confirmations --in high-energy physics and elsewhere-- are briefly reviewed. Finally, we address a confusion which is quite common in the literature, namely referring to distinct physical mechanisms versus distinct regimes of a single physical mechanism. This paper is part of the Topical Issue Statistical Power Law Tails in High-Energy Phenomena.     

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.     

A 3-quasiparticle isomer in neutron-rich <Superscript>183</Superscript>Ta

Excited states in neutron-rich ¹⁸³Ta have been studied using a two-neutron transfer reaction of ¹⁸¹Ta(¹⁸O,¹⁶O) . In-beam -rays were measured in coincidence with scattered ions detected by a high-resolution E -E Si telescope for reaction channel selection. Previously known 1-quasiparticle bands are extended to higher spins, and several levels including a T _1/2 = 0.9(3) μs 3-quasiparticle isomer are identified.     

On the fluctuations of the force exerted by a lipid nanotubule

After deriving the projected stress tensor in cylindrical geometry for a fluid membrane described by the Helfrich Hamiltonian, we calculate the average force f exerted by a thermally fluctuating nanotubule of radius R , and its standard deviation f . We obtain f and f in terms of the internal membrane tension , the bending rigidity , the temperature k _B T and a molecular cutoff . We find for f a shift ∼ 1/ with respect to the mean field behavior ∼ . We obtain ( f )² ∼ R ln(R/b) where b is a molecular length, f being typically small compared to f . Taking into account the difference between the internal tension and the actual mechanical tension applied to the membrane from which the tubule is drawn, we discuss the amplitude of the fluctuation-induced corrections to the average force. Our results, obtained in the harmonic approximation, hold for tubules with aspect ratio not larger than 200 , of radius significantly smaller than 100nm, that are connected to a large membrane reservoir, e.g., a giant vesicle.     

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.     

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.     

$ \Phi$ -variable calculated for the mixture of thermal sources

The -variable, a measure of statistical correlation of particle momenta, introduced by Mrówczyński and Gaździcki, has been calculated for the events simulated with a simple thermal toy model. It is shown that mixing two thermal sources of unequal temperature can result in negative values of .     

Microwave propagation parameters in magnetic fluids

Complex dielectric permittivity and complex magnetic permeability measurements of two magnetic fluids (as microwave propagation media), in the approximate range 0.2-5GHz were performed. The two samples consisted of magnetite nanoparticles, dispersed in kerosene and in water, respectively. Based on the dielectric and magnetic measurements, the frequency (f ) dependence of the attenuation parameter, , the phase constant, , the propagation constant, , the intrinsic impedance, Z_m, the refractive index, n , the reflection coefficient, R , the wavelength, and the skin depth, , of the investigated samples were determined.     

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.