The special status ofη 1 in QCD

On the basis of the approximate vanishing of the singlet axial charge of the nucleon, it is argued that ₁ should decouple from all hadrons constructed out of the constituentu, d ors quarks in theU(3) _L ×U(3) _R chiral limit for largeN _c . Furthermore ₁ should dominate the processesJ/, . A phenomenological analysis of the and couplings to many hadronic states is consistent with these results.     

LargeP T P−P collisions to probe the gluonic and sea spin distribution in the proton

We parametrise the polarised gluon and sea distribution functions incorporating the interpretation of the EMC experiment that, due to the axial anomaly the observed quark contribution to proton spin at Q ²>=10.7 GeV². Typical processes to isolate the gluonic and sea content of the proton studied here are the largeP _T direct photon production processes (a) using single polarized protonPPX and (b) polarized beam and target protonPPX. In both the above process the dominant contribution comes from the Compton subprocess and so can be used as a clean probe of the gluonic content of the proton. LargeP _T muon pair production PP(^+–)X are also studied and we find that the annihilation subprocess dominates, but not much larger than the Compton subprocess and so may not be a clean probe of the sea content of the proton. The effect of two loop corrections to the parametrisation and asymmetries are also considered, and are found to be negligible.     

Deep inelastic compton-scattering with polarized beam and target

The helicity difference of the photon photoproduction process px is calculated using four different polarized proton structure functions. Also discussed are the contributions originating from the Compton cross-section and the subprocesses of induced by photon structure and fragmentation. Up-quark and gluondominance can be separated by choosing different regions of pseudorapidity and normalized transverse momentumX _T of the final-state photon. We show, that it is possible to distinguish between the two extreme models of proton spin: polarized gluon vice polarized strange-quark.     

Particle flow in a jet

The angular distribution of hadrons in a jet is evaluated in perturbative QCD. The predictions are restrictive in the sense they do no depend on the details of the non-perturbative process. The distribution depends on only one phenomenologically adjustable parameter, a cutoff massQ ₀ (in addition to the universal QCD mass-scale ). The fit of the leading order prediction to the TASSO data is obtained withQ ₀270 MeV.The low value ofQ ₀ supports the hypothesis of local partonhadron duality. The particle flow in a gluon jet is also analysed.     

Quantum correlations and three body decays at a ϕ factory

The decays of neutral kaons produced in decay, K _L K _S , exhibit interesting quantum mechanical interference. The effects of this phenomenon on searches for CP violation have been previously been worked out for two body decays where the decay amplitude is a simple constant. For three body modes where the matrix element varies across the kinematically allowed region, the quantum correlations with enhance or cancel certain terms in the decay distribution. We work out the results for two interesting modes ()() and (3)(3). In the former case, the quantum correlation allows the isolation of the direct emission component of the decay, while in the latter case the intensity asymmetry can uniquely pick out the direct CP violating amplitude.Research supported in part by the National Science Foundation     

High spin states in77Se populated by the74Ge(α,n γ) reaction

⁷⁷Se has been investigated by the reaction⁷⁴Ge(,n) at 14 MeV. Gamma singles spectra, gamma angular distributions and gamma-gamma coincidences have been taken. A level scheme has been established, spins and parities have been assigned. States of a rotational band on the 1/2^– ground state, a rotational band on the 5/2^– 249.7 keV state and an anormal band have been identified. Nuclear Reaction ⁷⁴Ge(,n )E =14 MeV; measuredE ,I ,--Coin.,-ang. distr.⁷⁷Se deduced levels,J, . Enriched target, Ge (Li).     

Hadronic structure from jet physics

We discuss some aspects of high p_T jet physics, which are particularly relevant to test QCD and to probe the quark and gluon structure of hadrons. These include the so-called minijets, the multiple parton process, and the hard diffractive production.Invited talk at the International Symposium Hadron interactions — Theory and Pnenomenology, Bechyn, Czechoslovakia, June 26–July 1, 1988.     

Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

The total photofission cross section _,F for²³⁵U and²³⁸U has been measured in the energy range 50E 800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4 arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section _F , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections _,F normalized to the atomic numberA for both isotopes coincide, and agree in the-resonance region, within the systematic errors, with the socalledUniversal Curve _,T /A of the total photon absorption cross section _,T . At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there isno resonance-like shape near the D₁₃ resonance (at 710 MeV) as observed for the free proton. This complete suppression of the D₁₃ resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.Excerpt from D26 Supported by the Deutsche Forschungsgemeinschaft, SFB 201 Mainz     

AssociateJ/ψ+γ production: a clean probe of gluon densities

Production of strange and charm particles by hadron-proton collisions is analyzed in terms of a fire-ball (FB) model assuming the multiplicity of secondaries of a given massm, to be proportional to the FB mass: n(m)M ^*, the FB kinematics being determined by the Feynman-Yang scaling, as in the case of production. It is found that (m)1/m ² and that, using this property together with the scaling, no-free-parameter fits to currently available data of strange and charm particles frompp and p collisions are satisfactory, as well as for the photoproduction of charm mesonD and charm hyperon _c .     

Investigation of nematic order by coherent neutron scattering

The mathematical relationship between the orientational order parameters and the coherent neutron scattering cross section for a nematic liquid crystal is given. For deuterated para-azoxyanisole the single-molecule part of the cross section is evaluated within the meanfield approximation and combined with experimental results to give information about molecular orientational order in terms of P ₂, P ₄ and P ₆. Both P ₂ and P ₄ are found necessary for describing the molecular order. Discrepancies between experimental and theoretical results are interpreted as possibly reflecting the inadequacy of the meanfield theory of Maier and Saupe.     

Unconventional large-N limit of the Gaussian effective potential and the phase transition in λφ 4 theory

In the conventional large-N limit the coupling constant is required to scale as 1/N. While the Gaussian effective potential (GEP) is known to contain the exact result in this limit, it shows a phase transition only when 1/N (in units of the renormalized mass in the symmetric vacuum). Here we determine the asymptotic behaviour, asN, of and other quantities at the phase transition of the GEP. We find _crit to be finite in 0+1 dimensions; of order 1/lnN in 1+1 dimensions; 1/N ^1/3 in 2+1 dimensions; and in 3+1 dimensions. The GEP's first-order phase transition is shown to become asymptotically second-order in 1+1 dimensions and below. We also discuss non-integer dimensions and the approach to the non-trivial autonomous theory in 3+1 dimensions.     

From the deuteron to deusons,an analysis of deuteronlike meson-meson bound states

A systematic study of possible deuteronlike twomeson bound states,deusons, is presented. Previous arguments that many such bound states may exist are elaborated with detailed arguments and numerical calculations including, in particular, the tensor potential. This tensor potential which is crucial for the deuteron binding is shown to be very important also in the mesonic case. Especially, in the pseudoscalar³ P ₀ pseudoscalar-vector and vector-vector channels the important observation is made that the centrifugal barrier from theP-wave can be overcome by the 1/r ² and 1/r ³ terms of the tensor potential. In the heavy meson sector one-pion exchange alone is strong enough to form at least deuteronlike and composites bound by approximately 50 MeV. Composites of and states bound by pion exchange alone are expected near the thresholds, while in the light meson sector one generally needs some additional short range attraction to form bound states. The quantum numbers of these states areI=0, andJ ^PC=0^–+, 1⁺⁺ for the states andI=0,J ^PC=0⁺⁺, O^–+, 1^+– and 2⁺⁺ for the composites. In the states: ^b (10545), _b1(10562) are predicted and in , one finds the states: ^b (10590), _bQ (10582),h _b(10608), _b2(10602). Near the threshold the states: ^c (3870), _c0(3870) are predicted, and near the threshold one finds the states: _b0(4015), ^c (4015),h _c(4015), _c2(4015). Within the light meson sector pion exchange gives strong attraction for and systems with quantum numbers where the best non- candidates exist, although pion exchange alone is not strong enough to support such bound states. Thus, although one cannot conclude with certainty it to be the case, this fact does favour the picture that the (1440) and thef ₁ (1420) are mainly composites and thef ₀(1710) mainly a bound state, while thef ₀(1515) andf ₂(1520) could be predominantly composites. If the predicted and states are found, these would support this interpretation of the light states. In channels with exotic flavour orCP quantum numbers pion exchange is generally repulsive or quite weak. Therefore one does not expect that such deuteronlike bound states exist, althoughB*B* may be an exception.     

Aspects of χ and ψ production in polarized proton-proton collisions

Several topics of relevance to low transverse momentum and _1,2(c ) production in polarized proton-proton collisions are discussed. The leadingO( _S ³ ) contributions to the lowp _{T 1} production cross-sections viagg, qg, andq initial states are calculated as well as the corresponding spin-spin asymmetries. We find that ₁ production increases relative to direct and ₂ production, providing up to 25% of the observablee ^* e ^– pairs arising from decays inpp collisions at s=500 GeV. The spin-dependence of ₁ production, however, is much smaller than for either direct or ₂ production and so will likely be far less useful than either process in probing the polarized gluon structure function of the proton. A subset of theO( _S ³ ) radiative corrections to ₂ production involving initial state quarks are also performed and compared to leading ordergg₂ predictions.     

The droplet in the tube: A case of phase transition in the canonical ensemble

We consider the 2-dimensional Ising model with ferromagnetic nearest neighbour interaction at inverse temperature. LetS _N = _t be the total magnetization inside anN×N square box, ^per be the Gibbs state in with periodic b.c., andm() be the spontaneous magnetization. We show the existence of the limit

A theoretical prediction for exclusive decaysB→K(K*)η c

The decay rates for the exclusiveB decaysBK _c andBK* _c are calculated in the context of the heavy quark effective theory. We obtain(BK _c )/ (BK)=1.6±0.2 and(BK* _c )/ (K*)=0.39±0.04. These results lead to estimates BR(BK _c )=(0.11±0.02)% and BR(BK* _c )=(0.05±0.01)% if we use the central current experimental values forB(K, K ^*) branching ratios.     

K s →π+π−γ: a laboratory for meson dynamics

We discuss the decayK _{s +–} in the framework of chiral perturbation theory. The direct emission in this decay can be an useful test of meson dynamics.     

A unified formalism for γγ→meson and ψ-γX with possible tests for hybrid and gluonic hadrons

The couplings of conventional and hybrid mesons to (real and virtual) and their production amplitudes in M are described in a unified manner. Existing results for heavy quarks are recovered, extensions to light quarks and to virtual couplings are made and phenomenological applications discussed. In particular we discuss relativistic corrections to 0⁺, 1⁺, 2⁺ for both real and virtual photons and offer a resolution to a long standing puzzle in perturbative QCD concerning the helicity structure of 2⁺⁺. We suggest that the production off ₂ (1720) involves gluons in an essential way or that this meson hasJ2.