A fresh look at exotics

Simple quark model considerations suggest that the least massive oxotic mesons and baryons may occur close to the nucleon-antinucleon and nucleon-nucleon-antinucleon thresholds respectively. The fact that such channels are energetically open for the decay of these exotics means that both production and decay can proceed via allowed duality diagrams. We suggest three specific reactions which may permit their detection.     

A fresh look at neutrino oscillations

We analyze the present experimental situation on neutrino oscillations in the standard weak interaction theory with three neutrinos. Sizeable oscillations ν_e ? ν_τ are compatible with, and perhaps indicated by, present data.     

A fresh look at generalized Veneziano amplitudes

The dual resonance model, which was a precursor of string theory was based upon the idea that two-particle scattering amplitudes should be expressible equivalently as a sum of contributions of an infinite number of s channel poles each corresponding to a finite number of particles with definite spin, or as a similar sum of t channel poles. The famous example of Veneziano [Nuovo Cimento A 57 (1968) 190] satisfies all these requirements, and is additionally ghost free. We recall other trajectories which provide solutions to the duality constraints, e.g. the general Mobiüs trajectories and the logarithmic trajectories, which were thought to be lacking this last feature. We however demonstrate, partly empirically, the existence of a regime within a particular deformation of the Veneziano amplitude for logarithmic trajectories for which the 4-point amplitude remains ghost free.     

A fresh look at the electric-field dependence of surface-atom binding energy

This paper aims to clarify the theoretical concepts associated with the field dependence of surface-atom binding energy. The various coefficients involved are defined, and orbital-polarization and charge-transfer effects are distinguished. It is demonstrated that the latter, as well as the former, may have an F² form. A new empirical method of estimating the polarization-energy coefficient for a field-evaporating surface atom is described: this is based on the joint measurements of activation energy and onset appearance energy made by Ernst. His data for rhodium are reanalysed to give the value 1.05 ± 0.3 meV V^?2 nm². This value is then used to show that polarization-type effects will influence the interpretation of field-sensitivity data. Further experiments are called for.     

The size of Bose-Einstein effects in the statistical bootstrap model

We have determined the shift in Hagedorn temperature due to Bose statistics and calculated explicitly the cluster expansions of fireball level densities. This enabled us to investigate Bose effects in one-particle spectra and integrated correlations. Apart from the low secondary energy region of the one-particle distributions, the nonasymptotic behaviour of these quantities is little affected.     

Multiplicity distributions in hadron interactions derived from the statistical bootstrap model

We give a self-contained (though sketchy) derivation of the charged multiplicity distribution of final hadrons in a simplified (only pions) version of the statistical bootstrap model (SBM). The analytical form of this distribution is determined by two prominent features of SBM: a singularity at some temperatureT ₀ (related to the phase transition hadrons → quark-gluon plasma) and the production of Poisson-distributed hadron clusters with well-defined decay structure. The multiplicity distribution of final hadrons has two free parameters: an average temperatureT and the mean number \(\bar N\) of clusters, both depending on the collision energy √s such that for √s→∞, the temperature tends to the limitT ₀ while \(\bar N\) may grow (very slowly) without bound. With these two free parameters we obtain reasonable to good fits to experimental data at energies ranging from √s=7.87 to 900 GeV (full and in some cases cut pseudorapidity). The average cluster sizes found in our fits are compatible with those inferred from (pseudo) rapidity correlations in the data. We discuss the relation of this model to the negative binomial distribution (NBD).     

A fresh look at diffraction from a nonabsorbing perfect crystal in the Bragg-Laue configuration

The Bragg diffraction from a thick, nonabsorbing perfect crystal theory of dynamical diffraction. The intensities of two beams, one in the incident and the other in the diffracted direction, exciting the side face of the crystal are characterised. The implications of such beams for neutron diffraction experiments are indicated.     

An explicit solution of the statistical bootstrap

An explicit solution of the statistical bootstrap proposed by Frautschi is exhibited and discussed. The associated density of states is shown to be linked to the solution of a one-dimensional partition problem, arising from the infinite compositeness of hadrons in the statistical world. A configuration-space interpretation of the compositeness condition is given, and the possibility that a field-theoretic analogue of such a system exists is raised in in the context of non-polynomial Lagrangians.     

A fresh look into the neutron EDM and magnetic susceptibility

We reexamine the estimate of the neutron electric dipole moment (NEDM) from chiral and QCD spectral sum rules (QSSR) approaches. In the former, we evaluate the pion mass corrections which are about 5% of the leading Log results. However, the chiral estimate can be affected by the unknown value of the renormalizaton scale ν  . For QSSR, we analyze the effect of the nucleon interpolating currents on the existing predictions. We conclude that previous QSSR results are not obtained within the optimal choice of these operators, which lead to an overestimate of these results by about a factor 4. The weakest upper bound |θ|?2×¹⁰⁻⁹$|\theta |?2\times {10}^{\mathrm{-9}}$ for the strong CP  -violating angle is obtained from QSSR, while the strongest upper bound |θ|?1.3×¹⁰⁻¹⁰$|\theta |?1.3\times {10}^{\mathrm{-10}}$ comes from the chiral approach evaluated at the scale ν=MN$\nu =M_N$. We also re-estimate the proton magnetic susceptibility, which is an important input in the QSSR estimate of the NEDM.     

Violation of KNO scaling and the NBD phenomenon in the framework of the statistical bootstrap model

The connection is considered of multiplicity distributions in three stages: partonic, hadronization, and hadronic. An interpretation of the LoPHD parameter is found. It is shown that under specific hypotheses on the form of the mass spectrum, the statistical bootstrap model leads to the negative binomial distribution (NBD) at the hadronic stage of development of the multiple production process with specific analytic dependences of the parameters of the NBD.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 28–32, May, 1991.One of the authors (V. I. Kuvshinov) is thankful to R. Hagedorn and G. Burgers for numerous discussions.     

A fresh look at hadronic light-by-light scattering in the muon g - 2 with the Dyson-Schwinger approach

Using the Dyson-Schwinger and Bethe-Salpeter equations, we calculate the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon a_m\ensuremath a_\mu , using a phenomenological model for the gluon and quark-gluon interaction. We find a_m=(84 ±13)×10^-11\ensuremath a_\mu=(84 \pm 13)\times 10^{-11} for meson exchange, and a_m = (107 ±2 ±46)×10^-11\ensuremath a_\mu = (107 \pm 2 \pm 46)\times 10^{-11} for the quark loop. The former is commensurate with past calculations; the latter much larger due to dressing effects. This leads to a revised estimate of a_m=116 591 865.0(96.6)×10^-11\ensuremath a_\mu=116 591 865.0(96.6)\times 10^{-11} , reducing the difference between theory and experiment to ≃ 1.9s \sigma .     

New techniques for new sources: A fresh look at energy-dispersive diffraction for high-pressure studies

Abstract

Energy-dispersive diffraction is the most frequently used technique for high-pressure studies with synchrotron radiation. For optimum performance it requires high-energy radiation and few existing sources are able to meet this requirement. This is also important with large volume devices which demand even higher energies in order to obtain sufficient transmission. When working with diamond-anvil cells, the main experimental difficulties arise from the very small sample sizes. The use of a conical diffraction geometry increases the diffracted intensities, improves the signal-to-noise ratio and largely overcomes the crystallite statistics problem. This technique can also be used to greatly simplify high-pressure single-crystal studies. Combining these developments with recent progress in detectors and electronics will open up the field of high-pressure kinetics, but it is only with the operation of third generation synchrotron sources such as the ESRF that the present experimental limitations will be overcome.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’. Daresbury Laboratory 20-21 July 1991     

Pairing-plus-quadrupole model and nuclear deformation: A look at the spin-orbit interaction

The pairing-plus-quadrupole model, realized in the framework of the Elliott SU(3) scheme, is used to study the combined effects of the quadrupole-quadrupole, pairing, and spin-orbit interactions on ground state shapes of nuclear systems. Relevant measures for nuclear deformation are reviewed. Representation mixing induced by the symmetry-breaking pairing and spin-orbit forces is shown to soften the deformation. The angular momentum dependence of the results is discussed.     

A statistical model of the electrostatic field at a dielectric surface

A method is proposed for determination of electric-field intensity distribution on a plane over which charges of random magnitude and sign are distributed. The distribution functions for normal and tangent components of electric field intensity in this plane are obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 95–99, June, 1975.     

A new look at the PPAC

The Parallel Plate Avalanche Counter (PPAC) has been used mostly for measuring the energy loss of single, heavily ionizing particles. A PPAC is even more effective with high-energy showers for which a single event causes hundreds of electrons to pass through it. For operation at reduced pressures, the alkanes such as isobutane, C₄H₁₀ are excellent PPAC gasses with the quality of performance increasing with the size of the molecule. Under some circumstances the perfluoroalkanes such as perfluoropropane, C₃F₈, may be preferred. For operation at atmospheric pressure, CF₄ and mixtures containing Ar and CO₂ work well.     

Large transverse momenta from statistical bootstrap with spin

We show that statistical bootstrap models (SBM) with their prediction of exponentially decreasing p distributions (equivalently: constant maximal temperature τ₀ ≈ m_π) are not ruled out by the large p_⊥ observed above ≈ 100 GeV lab energy in hadron collisions. Usual SBM sum over all spin angular momenta of the decaying fireball; if a particular spin is fixed, SBM leads to large p_⊥. We discuss in this paper (after having justified a classical approach) several mechanisms yielding high-mass, high-spin fireballs, select arbitrarily one of these (single fireball excitation) and calculate in SBM with fixed spin the decay structure. The cross section $\text{d}\text{σ}\text{d}\text{M}$ is taken to be an empirical function, fitted to existing p_⊥ data at one energy and then calculable at other energies. We can easily reproduce the p_⊥ distribution. Further results concern multiplicities rising with p_⊥, anisotropy of the single-particle inclusive distribution and various correlations. Unexpectedly, but a posteriori rather naturally a jet-like structure is found in the spin-orthogonal plane.     

Remark on the production cross section of J particles in hadron-hadron collisions according to the statistical bootstrap model

Heavy J particles decaying into e⁺e^? were recently found in p-Be collisions [1] as well as in e⁺e^? annihilations [2, 3], where also the decay into hadrons with a branching ratio of about $\text{σ(}\text{J}\text{→}\text{h}\text{)}\text{σ(}\text{J}\text{→}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{) = 15}$ was observed.