Dynamical selection rules from $p \bar p$ annihilation at restin three meson final states

The hadronic annihilation branching-ratios in quasi-two-body final states have been obtained from the observation of the reactions , at rest in hydrogen targets at different densities. The enhancement or suppression of specific hadronic channels connected to dynamical selection rules is observed in the production of different resonances both in protonium S and P-waves, systematically investigated for the first time. Besides the well known and enhancement from ³S₁ and ¹S₀ partial waves, the dominance of one isospin source in production, well established from S-waves, is confirmed also in P-waves (¹S₀, I = 0; ³S₁, I = 1; ¹P₁, I = 0; ³P₁, I = 0; ³P₂, I = 1). In addition, the experimental data clearly show a strong suppression of and final states from P-wave which has a remarkable coincidence with pattern production.Received: 4 February 2004, Published online: 5 May 2004     

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.     

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.     

Non-hermitian quantum mechanics in non-commutative space

A recent investigation of the possibility of having a -symmetric periodic potential in an optical lattice stimulated the urge to generalize non-hermitian quantum mechanics beyond the case of commutative space. We thus study non-hermitian quantum systems in non-commutative space as well as a -symmetric deformation of this space. Specifically, a -symmetric harmonic oscillator together with an iC(x ₁+x ₂) interaction are discussed in this space, and solutions are obtained. We show that in the deformed non-commutative space the Hamiltonian may or may not possess real eigenvalues, depending on the choice of the non-commutative parameters. However, it is shown that in standard non-commutative space, the iC(x ₁+x ₂) interaction generates only real eigenvalues despite the fact that the Hamiltonian is not -symmetric. A complex interacting anisotropic oscillator system also is discussed.     

Two-Parameter Deformed SUSY Algebra for Fibonacci Oscillators

We construct a two-parameter deformed SUSY algebra for the system of n ordinary fermions and n(q ₁,q ₂)-deformed bosons called Fibonacci oscillators with -symmetry. We then analyze the Fock space representation of the algebra constructed. We obtain the total deformed Hamiltonian and the energy levels together with their degeneracies for the system. We also consider some physical applications of the Fibonacci oscillators with -symmetry, and discuss the main reasons to consider two distinct deformation parameters.     

Transmission of information through mesoscopic scattering systems

The storage and transmission of information is well defined using the notions of entropy, mutual information and channel capacity as formalized by Shannon. These quantities are calculated for a quantum mesoscopic system in terms of scattering parameters. For a one-dimensional system, the mutual information is related to the thermal conductance. This relation allows to show that for an incident signal of power P, the channel capacity C has a universal upper bound given by C independent of quantum statistics. A general framework is proposed which makes use of a natural underlying symplectic structure, to relate the entropy of a quantum mesoscopic system to the scattering matrix.     

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.     

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.     

Electroweak precision constraints on vector-like fermions

We calculate the oblique electroweak corrections and confront them with the experiments in an extension of the standard model. The new fields added are a vector-like weak doublet and a singlet fermion. After electroweak symmetry breaking there is a mixing between the components of the new fields, but there is no mixing allowed with the standard fermions. Four electroweak parameters, , , W and Y, are presented in the formalism of Barbieri et al.; these are the generalization of the Peskin–Takeuchi S, T and U. The vector-like extension is slightly constrained. requires the new neutral fermion masses not to be very far from each other, allowing for higher mass differences for higher masses and smaller mixing. , W and Y give practically no constraints on the masses. This extension can give a positive contribution to , allowing for a heavy Higgs boson in electroweak precision tests of the standard model.     

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 unparticles: a new form of energy density in the universe

An unparticle with scaling dimension has peculiar thermal properties due to its unique phase space structure. We find that the equation of state parameter , the ratio of pressure to energy density, is given by providing a new form of energy in our universe. In an expanding universe, the unparticle energy density evolves dramatically differently from that for photons. For , even if at a high decoupling temperature T _D is very small, it is possible to have a large relic density at present photon temperature T _γ ⁰, large enough to play the role of dark matter. We calculate T _D and using photon–unparticle interactions for illustration.     

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.     

Critical dynamics of lateral and transversal phase separations in bilayer biomembranes and surfactants

We consider bilayer biomembranes or surfactants made of two chemically incompatible amphiphile molecules, which may laterally or transversely phase separate into macrodomains, upon variation of some suitable parameter (temperature, lateral pressure, etc.). The purpose is an extensive study of the dynamics of both lateral and transverse phase separations, when the bilayer is suddenly cooled down from a high initial temperature towards a final one very close to the spinodal point. The critical dynamics are investigated through the partial dynamic structure factors of different species. Using a two-order parameter field theory, where the two fields are the composition fluctuations of one component in the leaflets of the bilayer, combined with an extended van Hove approach that is based on two coupled Langevin equations (with noise), we exactly compute these dynamic structure factors. We first find that the dynamics is governed by two time scales. The longest one, , can be related to the thermal correlation length, | T - T _c|^-1/2 , by , with the dynamic critical exponent z = 4 , where is an atomic length scale, T the absolute temperature, and T_c its critical value. The characteristic time can be interpreted as the time required for the formation of the final macrophase domains. The second time scale is rather shorter, and can be viewed as the short time during which the unlike phospholipids execute local motion. Second, we demonstrate that the dynamic structure factors obey exact scaling laws, and depend on three lengths, namely the wavelength q^-1 (q is the wave vector modulus), the correlation length , and a length scale R(t) t ^1/z (z = 4representing the size of macrophase domains at time t . Of course, the two lengths and R(t) coincide at the final time at which the bilayer reaches its final equilibrium state. Finally, the present work must be considered as a natural extension of our previously published one dealing with the study of lateral and transverse phase separations from a static point of view.     

Measurement of charm fragmentation ratios and fractionsin photoproduction at HERA

The production of , D⁰, D ⁺ , D_s ⁺ and charm hadrons and their antiparticles in e p scattering at HERA was measured with the ZEUS detector using an integrated luminosity of . The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality and for photon-proton centre-of-mass energies in the range . The charm hadrons were reconstructed in the range of transverse momentum and pseudorapidity . The production cross sections were used to determine the ratio of neutral and charged D-meson production rates, , the strangeness-suppression factor, , and the fraction of charged D mesons produced in a vector state, . The measured and values agree with those obtained in deep inelastic scattering and in e ⁺ e^- annihilations. The measured value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron, , were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous results, although the measured is smaller and is larger than those obtained in e ⁺ e^- annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process. Received: 12 August 2005, Revised: 8 September 2005, Published online: 6 October 2005     

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.     

An experimental test of the scaling prediction for the spatial distribution of water during the drying of colloidal films

A Peclet number, Pe, for the drying of colloidal films can be used as a predictor of the uniformity of water concentration in the direction normal to the film. Uniform drying is predicted to occur when Pe < 1, whereas with , a layer of packed particles is expected to develop above a more dilute layer. Routh and Zimmerman have more recently proposed that the particle concentration gradient between the packed and dilute layers, , will scale as . Here, this scaling relation is tested experimentally with magnetic resonance profiling data obtained from waterborne colloidal films dried under conditions to yield a range of Pe. It is found that increases with Pe but scales as . This disagreement with the prediction can be attributed to an underestimate of Pe when there are greater non-uniformities of drying, because of an unquantified slowing down of the evaporation rate.     

The Invariant Eigen-Operator Method for?N?Harmonically Coupled Identical Oscillators

In this paper, we apply the method of “invariant eigen-operator” to study the Hamiltonian of arbitrary number of coupled identical oscillators and derive their invariant eigen-operator. The results show that, (1) for the system of arbitrary number of identical harmonic oscillators by coordinate coupling or momentum coupling, the invariant eigen operator of system always has the form of or ; (2) the energy level gap of the system has two kinds of possibilities: one is that gap only related to ω that the frequency of oscillators; another one is that gap not only related to ω that the frequency of oscillators, but also related to the number of the coupling oscillators.     

Finite- N effects for ideal polymer chains near a flat impenetrable wall

This paper addresses the statistical mechanics of ideal polymer chains next to a hard wall. The principal quantity of interest, from which all monomer densities can be calculated, is the partition function, G _N(z) , for a chain of N discrete monomers with one end fixed a distance z from the wall. It is well accepted that in the limit of infinite N , G _N(z) satisfies the diffusion equation with the Dirichlet boundary condition, G _N(0) = 0 , unless the wall possesses a sufficient attraction, in which case the Robin boundary condition, G _N(0) = - G _N ^′(0) , applies with a positive coefficient, . Here we investigate the leading N ^-1/2 correction, G _N(z) . Prior to the adsorption threshold, G _N(z) is found to involve two distinct parts: a Gaussian correction (for z aN ^1/2 with a model-dependent amplitude, A , and a proximal-layer correction (for z a described by a model-dependent function, B(z) .     

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).