Showing papers in "European Physical Journal C in 1982"

Lepton-hadron processes beyond leading order in quantum chromodynamics

Abstract: We present a summary of QCD formulae describing the effects of scaling violation in leptonhadron processes, with the inclusion of recently derived higher order corrections. Deep inelastic leptoproduction, one-hadron inclusive distributions in leptoproduction and ine + e − annihilation and Drell-Yan processes are discussed in detail. Higher order corrections to parton densities, fragmentation functions and to lepton-parton cross-sections in the above processes are presented in a common factorization scheme, so that a comparative analysis of various processes as well as an independent analysis of each of them is possible. A discussion of the various scheme dependences at next-to-leading level is also included.

The Dirac-Kahler Equation and Fermions on the Lattice

Abstract: The geometrical description of spinor fields by E. Kahler is used to formulate a consistent lattice approximation of fermions. The relation to free simple Dirac fields as well as to Susskind's description of lattice fermions is clarified. The first steps towards a quantized interacting theory are given. The correspondence between the calculus of differential forms and concepts of algebraic topology is shown to be a useful method for a completely analogous treatment of the problems in the continuum and on the lattice.

Scaling Violations and the Gluon Distribution of the Nucleon

Abstract: Using recent data on deep inelastic lepton-nucleon scattering an attempt is made to extract the gluon distributionG(x, Q 2=4 GeV2) from the observed scaling violations of structure functions. The accuracy of the data allows only for a rough determination of the gluon distribution. In particular it is found that a hard gluon distributionis consistent with present measurements. Implications of the hard gluon distribution for charm production in the gluon fusion model and for the perturbative contributions to σ L /σ T are further discussed. Finally, analytic parametrizations of the QCDx- andQ 2-dependence of quark and gluon distributions are presented facilitating further possible applications.

Experimental-study of opposite-sign dimuons produced in neutrino and antineutrino interactions

Abstract: A large sample of opposite-sign dimuons, produced by the interaction of neutrinos and antineutrinos in iron, is analysed. The data agree very well with the hypothesis that the extra muon is the product of charm decay. They yield information on the strength and space-time structure of the charmproducing weak current. The strange-sea structure functionxs(x) is determined. The difference between neutrino and antineutrino dimuon production is analysed to provide a value of the Kobayashi-Maskawa weak mixing angleθ2.

A new determination of the π N sigma term using hyperbolic dispersion relations in the (ν 2 ,t) plane

Abstract: Dispersion relations in the (ν2,t) plane along hyperbolas are used in order to extrapolate the invariant isospin-even πN amplitude D+(ν2,t) to the Cheng-Dashen point, ν=0, t=2μ. The fluctuation of the results obtained with different hyperbolas gives a realistic estimate of the errors, except for errors of the partial wave solution and of the ππ $$ - N\bar N$$ amplitudes assumed at t < 4μ2 —If our ππ $$ - N\bar N$$ partial waves are used, which are based on the ππs-wave scattering length a 0 0 =0.28 μ-1, the result for the sigma term is 64±8 MeV, in agreement with earlier determinations.—The discrepancy with the theoretical prediction σπN≈ 30 MeV is smaller by only 8 MeV, if our $$ - N\bar N$$ amplitudes are modified in such a way that the threshold behaviour of the ππs-wave agrees with Weinberg's prediction a 0 0 =0.16 μ-1. Further progress depends on new accurate experimental π±p scattering data in the Coulomb interference region at low energies.

Higher order perturbative QCD calculation of jet cross sections ine + e − annihilation

Abstract: We present in detail the analytic calculation of the Sterman-Weinberg type 3-jet cross section to order αs2 The fit to recent PLUTO data gives in the\({MS}\) scheme αs which corresponds to Λ=0.24 GeV in the 1-loop approximation.

Coulombic-hadronic interference in an eikonal model

Abstract: The problem of extracting the phase of the hadronic proton-proton scattering amplitude from its interference with the Coulombic amplitude near the forward direction is re-examined using an eikonal model. The results are in accord with the Feynman diagrammatic calculation of West and Yennie, with some small corrections. An especially compact forms is derived for the electromagnetic shift in the hadronic amplitude's phase, which includes the effect of the electromagnetic form factor. The largest modification of the previous results comes from the effect of the form factor on the phase of the electromagnetic amplitude itself.

Hadronic mass-relations from topological expansion and string model

Abstract: Simple relations among intercepts and slopes of Regge trajectories based on the topological expansion and\(q\bar q\)-string picture of hadrons are derived. It is shown that the corresponding mass relations for bosons with different quark content are satisfied with a very high accuracy.

To search for four-quark states in γγ-collisions

Abstract: It is shown that the reactions γγ into hadrons is a rather effective means of searching for fourquark states. We predict the suppression ofS *(980,0+) and δ(980,0+) in γγ→ππ and γγ→π0 η respectively, if they are four-quark states from (9.0+). The well-known anomaly in γγ→ρ 0 ρ 0 is interpreted as the production of the tensor four-quark resonances with the isospin 0 and 2. We predict the absence of similar enhancement in γγ→ρ + ρ −. The bright anomalies are predicted near thresholds of γγ→ρ 0 ω and γγ→ρ 0 ϕ

Double logs of perturbative QCD for parton jets and soft hadron spectra

Abstract: The influence of coherence in a soft parton bremsstrahlung on hadron spectra in jets is discussed. We present a simple functional method for calculation of different inclusive parton distributions in the “plateau” region. Inclusive parton cross sections, spectra, multiplicities, energy and angular correlations, etc. are derived in the Double Logarithmic approximation.

Renormalization of the axial anomaly operators

Abstract: The renormalization of the three pseudoscalar gauge invariant operators which appear in the Adler-Bell-Jackiw anomaly is studied in the back-ground field gauge, where it is simplest. We analyse questions concerning renormalization-group invariance, mixing, the γ5-perscription inD dimensions, as well as the meaning of the nonrenormalization of the axial anomaly in the context of the renormalization of composite operators.

High-p T direct photon production inpp collisions

Abstract: Direct photon and neutral-pion production have been measured inpp collisions at the CERN ISR for 30< $$\sqrt s $$ <63 GeV and transverse momenta up to 12 GeV/c. The direct photon signal relative to neutral-pion production increases withp T and shows little $$\sqrt s $$ -dependence. Results are reported from a variety of running conditions, and details are given on the method of analysis and on the evaluation of systematic errors for the inclusive cross-section of single-photon and neutral-pion production.

Neutral Strange Particle Production in Proton Proton Collisions at $\sqrt{s}=63$-{GeV}

Abstract: The inclusive cross section for the production ofK 0 mesons, Λ and $$\bar \Lambda$$ particles in proton-proton interactions at $$\sqrt s = 63$$ GeV is presented. The produced particles have been detected in the full phase space. Behaviour of the longitudinal and transversal depandences of the cross sections are discussed. The total production cross sections for 0 mesons and Λ particles was determined to $$\sigma _{{\rm K}_S^0 } = (25.5 \pm 1.4)$$ mb andσ Λ =(7.8±1.2) mb respectively. A strong energy dependence of the production cross sections is observed.

Comments on massive and massless Yang-Mills lagrangians with a quartic coupling of Faddeev-Popov ghosts

Abstract: The complicated Lagrangians for massless as well as massive Yang-Mills fields and their BRS and anti-BRS transformations proposed by Curci and Ferrari are simplified by the help of an auxiliary field. In the massive non-Abelian case, the mechanism of the breakdown of physicalS-matrix unitarity is clarified and contrasted to the situation in the Abelian case.

Determination of the gluon distribution in the nucleon from deep inelastic neutrino scattering

Abstract: The observed scaling violations of the nucleon structure functionF 2 and $$\bar q$$ have been analysed in the framework of perturbative QCD to determine the shape and magnitude of the gluon distribution. The data are in good agreement with leading order QCD, and the simultaneous use ofF 2 and $$\bar q$$ structure functions permits, for the first time, a reliable determination of the gluon structure function.

Gluonic corrections to quark vacuum condensate contributions to two-point functions in QCD

Abstract: We present the αs corrections to quark vacuum condensate contributions to various types of current correlation functions. Their relevance to the first Weinberg sum rule is discussed. A new derivation of the relation between theA1-mass and the ϱ-mass is presented. The higher order corrections to the socalled non-perturbative quark mass are also discussed.

A test for the gluon selfcoupling in the reactionse+e−→4 jets andZ0→4 jets

Abstract: We consider the reactionse+e−→γ*→4 jets andZo→4 jets with the 4 jets coming in two pairs of essentially back to back jets of high and low energy. We calculate the angular distribution of the low energy jet axis with respect to the high energy jet axis in QCD, in an abelian gluon model “QED” and a phase space model (PS). Using simple helicity arguments we show that our angular distribution is very sensitive to the triple gluon coupling in QCD. This is then confirmed by a complete calculation. Our correlation offers, therefore, a direct test for QCD as a non-abelian gauge theory.

Z2 Monopoles in the Standard SU(2) Lattice Gauge Theory Model

Abstract: The standardSU(2) lattice gauge theory model without fermions may be considered as aZ2 model with monopoles and fluctuating coupling constants. At low temperatures β−1 (=small bare coupling constant) the monopoles are confined.

Angular correlations in γγ→ρ 0 ρ 0 near threshold

Abstract: We present an analysis ofρ0ρ0 production by two photons in theρ0ρ0 invariant mass range from 1.2 to 2.0 GeV. From a study of the angular correlations in the process γγ→ρ0ρ0→π−π+π− we exclude a dominant contribution fromJP=0− or 2− states. The data indicate sizeable contributions fromJP=0+ for four pion massesM4π 1.7 GeV. The data are also well described by a model with isotropic production and uncorrelated isotropic decay of theρ0,s. The cross section stays high below the nominalρ0ρ0 threshold, i.e.M4π<1.5 GeV. The matrix element forρ0ρ0 production is found to decrease steeply with increasingM4π. Upper limits for the couplings of the ι(1440) and Θ(1640) to γγ andρ0ρ0 are given:Γ(ι→γγ)·B(ι→ρ0ρ0)<1.0 keV andΓ(Θ→γγ)

Rare decay of a pseudoscalar meson into a lepton pair—A way to detect new interactions?

Abstract: The rare electromagnetic decay of a neutral pseudoscalar meson into a lepton pair is calculated in a bound state quark model. For heavy mesons, the leading QCD diagram is argued to be dominant allowing higher order QCD corrections to be neglected for the branching ratio of this decay to the two-photon decay. The experimentally interesting case of pion decay is treated separately, and the rates for competing processes (weak neutral currents, axions, technicolour ...) are estimated. We conclude that existing data may well allow for such contributions.

Spin Spin Asymmetries in Inclusive Muon Proton Charm Production

Abstract: Spin-spin asymmetries have been calculated in the inclusive process\(\mu ^ + p \to \mu c\bar cX\) with reference to photon gluon events only. The resulting asymmetries are small and relatively insensitive to the exact form of the structure functions used.

A new diquark model for deep inelastic structure functions

Abstract: The bulk of data from deep inelasticep, eD, μp, μN, νp and νN scattering is fitted with a new diquark model of nucleons. The proton is found to be mostly in au(ud)0 state, where the (ud)0 diquark has spin and isospin zero. There is hence no trace ofSU(6) symmetry among diquarks in nucleons.

On the Laplace Transform of the Weinberg Type Sum Rules and on the Properties of Pseudoscalar Mesons

Abstract: We reanalyse the Weinberg type sum rules in the light of the Laplace transform sum rule and including the leading non-perturbative effects. We then estimate the light quark invariant masses\(\hat m_s /\hat m_d ,\hat m_u \hat m_d \); the pion decay amplitudefπ and theA1 coupling and mass. Using other type of sum rules, we derive bounds on the pseudoscalar decay amplitudesf p (P≡π, K, D, F) as well as on the gluon component of theU(1) A meson mass. Our main results are summarized in Sect. 4.

Energy dependence of jet measures in e + e − annihilation

Abstract: The jet character of the hadronic final states produced ine+e− annihilations is studied in terms of jet measures such as thrust, sphericity, jet opening angle and jet masses, in the energy range 7.7 to 31.6 GeV. All distributions and averages have been corrected for detector effects and initial state radiation. The energy dependence of the averages of these jet quantities is used to estimate the contributions due to perturbative QCD and fragmentation effects. Correlations between the jet measures and the multiplicity of charged hadrons are also presented.

A study of elastic photoproduction of low mass K + K − pairs from hydrogen in the energy range 2.8–4.8 GeV

Abstract: The results of an experiment to study elasticK + K − photoproduction are presented. Differential cross sections and spin density matrix elements for ϕ(1.019) production are stddied as a function of incident photon energy and over a wide range of momentum transfer,t (t min >t>−1.5(GeV/c)2). Helicity conserving amplitudes are observed to dominate ϕ production throughout this range and the differential cross sections exhibit a forward diffractive peak which cannot be understood in terms of a simple exponential dependence. A new value of the photon ϕ coupling constant is determined and shown to be consistent withe + e − annihilation measurements. A detailed study of the energy dependence of the differential cross sections is made, including other experimental data, and the extracted effective Regge trajectory compared with other diffractive processes. A study of the dependence of theK + K − decay angular distribution on invariant mass reveals evidence for ans wave contribution interfering with thep wave ϕ which may be attributable to theS * meson.

Phenomenology of photon-e± collisions

Abstract: The physical interest ofγe ± collisions is examined. A basic formalism is established. Crosssections are computed with general couplings and polarization states. Illustrations are given for QED tests, Z0 andW ± production, various electro-weak processes including γγ collisions and the search for new currents and particles.

The ? function in the 1/N f expansion

Abstract: The Callan-Symanzik γ-function is studied in the large number of lepton (in QED) or flavour (in QCD) limit. We have computed analytically 7 terms and they show a striking factorization. We have computed numerically 19 terms and they show a large radius of convergence and two unambiguous zeros within the region of convergence.

Gauge covariance in lattice field theories

Abstract: We consider in detail the gauge invariance constraints in Hamiltonian lattice gauge theories, focusing mainly on pureSU(2) Yang-Mills theory in 2+1 dimensions. We present matrix and partial differential representations of the Hamiltonian in which all gauge constraints have been taken fully into account. The applicability of this formulation is demonstrated on small lattices.

Evidence for a newK*\(\bar K\) state at a mass of 1,530 MeV withIJPC=01++ observed inK−p interactions at 4.2 GeV/c

Abstract: Evidence is presented for a newK*\(\bar K\)+c.c. resonance with a mass of (1,526±6) MeV, a width of (107±15) MeV and quantum numbersIJPC=01++. We call itD′ meson. Initially it is observed as aK*\(\bar K\)+c.c. enhancement in the reactionsK−p→(K s 0 K±π∓)Λ at 4.2 GeV/c. The isospin assignmentI=0 comes from its further observation in the reactionsK−p→(K s 0 K±π∓)Σ0 andK−p→(K s 0 K±π∓)Σ(1,385)0 but not inK−p→(K+K−π−)Σ+ orK−p→(K s 0 K±π∓)Σ(1,385)+. A maximum likelihood analysis of the (K\(\bar K\)π) decay Dalitz plots in the reactionsK−p→(K s 0 K±π∓) determines theJPC of theD′ meson to be 1++. A satisfactorySU(3) fit is obtained to a 1++ nonet composed of theI-1A1, theI=1/2QA with theD(1,285) and theD′(1,526) as theI=0 members having a mixing angle close to the magic one.

Muon pair production in very high energy nucleus-nucleus collisions

Abstract: Characteristics of muon pair production in very high energy nucleus-nucleus collisions are discussed. Particular attention is given to comparing the rate of muon pairs produced from thermalized quark-gluon matter to that of pairs produced via the usual Drell-Yan mechanism. The thermal rate is at least of the same order of magnitude as the direct Drell-Yan rate and will certainly dominate whenxF for the pair approaches 1. BeyondxF=1 the thermal rate is also substantial. This region is particularly easily accessible in fixed target experiments.