Inclusive Pomeron-Pomeron interactions at the CERN ISR

Data are presented for the first time on inclusive Pomeron-Pomeron interactions which produce a central systemX (composed mainly of multimeson states) in proton-proton collisions at \(\sqrt s \) at the CERN ISR. The systemX has a Feynman-x distribution which is sharply peaked atx _f=0, is inconsistent with any significant contributions from Reggeon exchange processes, and has an invariant mass dependence in good agreement with the predicted formM _x ^?2 . Kaon production is about 15% of pion production, nearly independent ofM _x, while proton-antiproton production averages about 5% of pion production and increases withM _x. The structure of the central systemX develops into a jetlike shape, asM _x increases, as would be expected from a model of Pomeron fragmentation. The shape of thex _f(π) distribution in the center of mass of theX system (although not proving existence) is consistent with asoft partonic substructure of the Pomeron.     

Exclusive semi-leptonic decays of bottom mesons in the spectator quark model

We calculate the exclusive semileptonic bottom meson decays \(B \to D(D*) + l^ - + \bar v_l \) in the spectator quark model. The helicity structure of the mesonic current transitionsB→D(D ^*) is matched to the helicity structure of the free quark current transitionsb→c at minimum momentum transferq ²=0. The results are continued toq ²≠=0 by pole-dominated form factors. Our results are compared to recent calculations that use quark model dynamics at maximum momentum transferq _max ² = (M ₁ ?M ₂)². We find agreement atq _max ² . Atq ²=0 there are significant differences between the predictions of the two approaches leading to marked differences in the predictions for the shape of the lepton energy spectrum, the shape of theq ²-distribution, and the helicity composition of the transition measurable in the angular distributions of the decaysD ^*→Dπ and \(W_{virtual}^ - \to l^ - + \bar v_l \) .     

A study of meson-baryon couplings in the constituent quark model

Within the framework of the constituent quark model we discuss the effects of different types of meson-baryon-baryon vertex operators on the form factors and the coupling strengths of the lowest-lying positive and negative parity non-strange baryons. We compare the quark pair creation model (³P₀-model) with the SU(6)-model in which mesons are treated as elementary fields that directly couple to the quarks. The latter model is employed both in the so-called static limit and in a modification motivated by Galilei invariance. It is demonstrated that the inclusion of non-static effects simulates some features of the³P₀ vertex. Especially the reaction πN→ππN is found to be very sensitive to the different assumptions on the dynamics of theq¯q pair creation process. More indirect hints for the internal structure of the mesons might be obtained from the predicted asymmetry for the two form factors ofN→Δ+π andΔ→N+π, which occurs in the³P₀-model, only.     

Instantons and meson correlation functions in QCD

Various QCD correlators are calculated in the instanton liquid model in zeromode approximation and 1/N _c expansion. Previous works are extended by including dynamical quark loops. In contrast to the original “perturbative” 1/N _c approximation, not all quark loops are suppressed. Renormalization of the instanton density allows the identification of the density with the gluon condensate even in presence of dynamical quark loops. In the flavor singlet meson correlators a chain of quark bubbles survives the N _c → ∞ limit causing a massive η′ in the pseudoscalar correlator while keeping massless pions in the triplet correlator. The correlators are plotted and meson masses and couplings are obtained from a spectral fit. They are compared to the values obtained from numerical studies of the instanton liquid and to experimental results.     

SU(2N f) ⊗O(3) light diquark symmetry and current-induced heavy baryon transition form factors

We study the current-induced bottom baryon to charm baryon transitions in the Heavy Quark Symmetry limit asm _q→∞. Our discussion involvess-wave tos-wave as well ass-wave top-wave transitions. Using a constituent quark model picture for the light diquark system with an underlyingSU(2N _f)?O(3) symmetry and the heavy quark symmetry we arrive at a number of new predictions for the reduced form factors that describe these transitions.     

The BFKL Pomeron in deep inelastic diffractive dissociation neart=0

The small-t behaviour of the deep inelastic diffractive dissociation cross section in the triple Regge region is investigated, using the BFKL approximation in perturbative QCD. We show that the cross section is finite att=0, but the diffusion in lnk _t ² leads to a large contribution of small momenta at the triple Pomeron vertex. We study the dependence upon the total energy and the invariant mass. Att=0, there is a decoupling of the three BFKL singularities which is a consequence of the conservation of the conformal dimension. For large invariant masses, the four gluon state in the uppert-channel plays an important role and cannot be neglected.     

NMR investigations of dynamical processes in orientationally ordered and disordered NaCN,RbCN and CsCN

The nuclear spin lattice relaxation timeT ₁ of the²³Na,⁸⁵Rb,⁸⁷Rb,¹³³Cs,¹⁴N nuclei is measured in NaCN, RbCN and CsCN as a function of temperature below and above the ferroelastic phase transition temperatureT _c. BelowT _c the behaviour ofT ₁ of the alkali nuclei renders possible to determine the flip frequency of the CN molecules and its temperature dependence. AboveT _c from the¹⁴NT ₁ the correlation time τ_c of the rotational motions of the CN molecules and its temperature dependence is determined. An empirical rule is verified demonstrating that atT _c the correlation times take nearly the same values for all cyanides. For the high and low temperature phases one obtains atT _c about τ_c=5·10^?13s and τ_c=5·10^?11s, respectively. The results are discussed with respect to the mechanism of the phase transition.     

Experimental study on the 3p size-resonance in thep- wave neutron strength function

Using a silicon filtered fission neutron beam of an energy width of 20 keV around 143 keV we measured the total cross sections for 37 nuclides and elements having mass numbers between 87 and 140 and determined thep-wave strength functions. The 3P-resonance atA=98 shows no splitting into theP _3/2?P _1/2 doublet. The narrow resonance peak and the following broad distribution of thep-strength function (A=103 to 140) can approximately be reproduced by deformed optical model calculations. The spin-orbit term in the optical potential is consistent with the spin orbit force in the shell model. For nuclei around the closed (N=50) neutron shell a shell effect in thep-wave strength function is indicated.     

Predictions of QCD fragmentation models ine + e − annihilation up to\sqrt s = 200 GeV

Results on event and single particle characteristics are presented for the three most successful perturbative QCD+fragmentation models in the c.m. energy range 12.0≦W≦200 GeV. The models were optimised to describe the properties of the large sample of hadronic events obtained by TASSO atW=35 GeV. The energy evolution of the observables across the range spanned by the PETRA and PEP data, 12.0≦〈W〉≦41.5 GeV, is reasonably well described by all the models. However, for some quantities the predictions of the different models diverge at higher energies; distributions of observables are shown at c.m. energies of 93 and 200 GeV, where data are expected from thee ⁺ e ^? colliders currently under construction. The ability to describe simultaneously, with the same parameter values, hadronic event features both at PETRA/PEP and LEP/SLC energies will provide a severe test of the models. The effects of top quark production on the event properties are illustrated for a top mass of 60 GeV/c². Predictions are given for the rates of multijet events up toW=200 GeV, where ≧4-jet events dominate the cross section and will form a background to events containing heavy states which decay into hadron jets.     

TheN=83 nucleus149Dy from Gamow-Teller decay of its 11/2− and 1/2+ 149Ho parents

A high-sensitivityγ-spectroscopic study of the¹⁴⁹Hoπh _11/2 andπs _1/2 β-decays using mass separated sources has located dominant 0⁺ → 1⁺ GT decay strength associated with decay of pairedh _11/2 protons, leading to 3п-states in the¹⁴⁹Dy daughter nucleus. In theirγ-decay low-lying¹⁴⁹Dy levels characteristic of anN=83 nucleus are excited. They include theνf _7/2,νp _3/2,νh _9/2 andνp _1/2 single particle- and theνs ₁ ^2/?1 andνd ₃ ^2/?1 two-particle one-hole states, as well as the νf _7/2 × 3^? andνf _7/2 × 2⁺ particle-phonon multiplets. A synopsis is given of these excitations in theN=83 isotones from¹⁴⁹Nd to¹⁵³Yb. The¹⁴⁹Dy GT decay strength is discussed in terms of the¹⁴⁷Tb₈₂ and¹⁴⁸Dy₈₂ decays. The strength function results are also compared with independent¹⁴⁹Ho 11/2^? decay data from the literature based on totalγ-ray absorption measurements.     

Valence and inner proton hole states in119in via the (d,3He) reaction

Proton holes states have been studied up toE _x=17 MeV andE _x=3.5 MeV in the¹¹⁹In nucleus via the¹²⁰Sn(d,³He)¹¹⁹In reaction respectively atE _d=108.4 MeV andE _d=51 MeV. DWBA analysis of angular distributions has allowedl attributions for a large number of new levels and the determination of valence and inner hole strength distributions. The first 1g _9/2, 2p _1/2 and 2p _3/2 levels only exhaust 40%, 60% and 32% of their respective sum rule limits. The missing strengths are shared among several low lying levels and significant higher lying contributions. The 1f strength, not identified in the previous experiments is spread fromE _x=1 MeV to about 17 MeV. The low lying levels aroundE _x=2.4 MeV could exhaust some 40% of the 1f _5/2 sum rule. The higher lying strength with a flat maximum aroundE _x=7.5 MeV could account for the 1f _7/2inner hole strength and the missing 1f _5/2 valence strength. The experimental strength functions compare rather well with the predictions of the quasiparticle-phonon model.     

QCD sum rules and the Skyrme model at large Nc

We study the large-N_c behaviour of the baryon spectrum using QCD duality sum rules. A comparison of our results with the ones of the Skyrme model gives a determination of the Skyrme parameter e and a relation between the pion decay constant f_π and the quark condensate. As a consequence, we show that f_π is the only scale which controls the hadron dynamics. An extrapolation of our large-N_c results into the real world N_c = 3 yields a good agreement with phenomenological estimates.     

L 2 andL 3 subshell fluorescence and Coster-Kronig yields forZ=96 from the decay of249Cf

TheL ₂ andL ₃ subshell fluorescence and Coster-Kronig yields forZ=96 have been measured by theK-L x-ray coincidence method with high resolution Si(Li) and Ge(Li) x-ray detectors. The results ν₂=0.650±0.036, ω₂=0.552±0.032, ω₃=0.515±0.034, andf ₂₃=0.188±0.019 agree fairly well with theory. New measurements of theL x-ray singles spectra of²⁴⁴Cm and²³⁸Pu with a high resolution Si(Li) detector permitted reevaluation of the values of ω₂ andf ₂₃ forZ=92 and 94 reported by Byrneet al. The revised values atZ=92 are ω₂=0.529±0.035 andf ₂₃=0.23±0.12, and atZ=94, ω₂=0.523±0.023 andf ₂₃=0.24±0.08. These revised values are in much better agreement with theory and with current experiments.     

Correlations in inhomogeneous Ising models

Using general methods developed in a previous treatment we study correlations in inhomogeneous Ising models on a square lattice. The nearest neighbour couplings can vary both in strength and sign such that the coupling distribution is translationally invariant in diagonal direction. We calculate correlations parallel to the layering in the diagonally layered model with periodv=2, the so-called “general square lattice” model (GS). If the model has a finite critical temperature,T _c>0, we have a spontaneous magnetization belowT _c vanishing atT _c with the Ising exponent β=1/8. AtT _c correlations decay algebraically with critical exponnet η=1/4 and exponentially forT>T _c. In the frustrated case we have oscillatory behaviour superposed on the exponential decay where the wavevector of the oscillations changes at some “disorder temperature”T _D(>T _c) from commensurate to temperature-dependent in commensurate periods. If the critical temperature vanishes,T _c=0 we always have exponential decay at finite temperatures, while atT=T _c=0 we encounter either long-range order or algebraic decay with critical index η=1/2, i.e.T=0 is thus a critical point.     

Quark masses and their hierarchies

Electroweak symmetry breaking is attributed to dynamical generation of quark masses. Quarksq (and leptonsl) are assumed to be produced by hypercolor confinement of preons at an intermediate scaleΛ _hc. Hierarchies observed in theq mass spectra can be explained by a BCS mechanism if the color interaction is enough asymptotically free and if residual ones emerging by the confinement are medium strong. The former assumption claims thatN≦4, whereN is the family number ofq andl. Dynamical equations to determineq masses and mixings are given, but they require knowledge on the physics atΛ _hc. A phenomenological approach is also made on the basis of anSU(7)×SU(7) chiral preon model withN=4. The mass ratiom _t/mb is related to (m _c/m _s)^ηB withη _B?1.1 andm _t'/mb' to (m _u/m _d)^ηA withη _A?1.4. In this scheme the fourth down quark is the heaviest (～ 110 GeV) and contributes dominantly toF ², whereF is the Fermi scale.     

Three-nucleon yrast states in145Sm

In-beamγ-ray and conversion electron measurements with (α, xn) reactions have established the¹⁴⁵Sm highspin states up toI ^π=25/2⁺ at 3.5 MeV excitation. A shell model analysis using empirical two- and one-body energies from neighbouring nuclei classifies the low-lying odd-parity levels as 3-quasiparticle states formed by the¹⁴⁴Sm two-proton-hole excitations and thef _7/2 valence neutron. The higher-lying positive-parity states involve particle-hole core excitations with one proton inh _11/2.     

Radiative decays of scalar mesons σ(600), f 0(980) and a 0(980) in the local Nambu-Jona-Lasinio model

The two-photon decay widths of scalar mesons σ(600), f ₀(980) and a ₀(980) as well a ₀ → ju(ω)γ and f ₀ → ju(ω)γ are calculated in the framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hartree-Fock approximation) and the meson loops (next 1/N _c -approximation where N _c is the number of colors) are taken into account. The values of these contributions, as we show, are of the same order of magnitude. For the f ₀ decay the K-loop contribution plays the dominant role. The results for two-gamma decays are in satisfactory agreement with modern experimental data. The predictions for a ₀ → ju(ω)γ and f ₀ → ju(ω)γ widths are given.     

Infrared behaviour and the bare Pomeron intercept in a Reggeon Field Theory including the Pomeron and thef-pole

An extension of the critical Reggeon Field Theory that includes both the Pomeron and thef-Reggeon fields is constructed. The quantum numbers of thef-Reggeon allows specific Reggeon-Pomeron couplings that have not been considered previously in standard works on secondary trajectories. We show the existence of a single fully stable fixed point among a total of 11 points. Unfortunately this point does not satisfy the factorization requirements imposed by thef-dominance of the Pomeron hypothesis and, in consequence, the critical Pomeron can not bef-dominated in aP+f model. We have also evaluated the value of the intercept of the bare critical Pomeron, using the method of integral representations of the propagators. The value obtained is clearly higher than the one previously obtained without thef-Pomeron interplay. With an adequate choice of the values of the bare coupling constants its value is in good agreement with the phenomenological one.