Showing papers in "European Physical Journal C in 1985"

Exclusive Semileptonic Decays of Heavy Mesons

Abstract: Exclusive semileptonic decays of heavy mesons provide interesting information on systems consisting of quarks of unequal mass. We express the formfactors of the hadronic current in terms of relativistic bound state wave functions for which we take the solutions of a relativistic harmonic oscillator potential. The wave function overlap is determined by the quark mass dependent longitudinal momentum distribution and differs from results based on non relativistic wave functions. The semileptonic widths and lepton spectra are calculated using in addition nearest pole dominance for the momentum transfer dependence of the formfactors. We compare our results with recent experimental data. The formfactor calculation also allows an estimate of special nonleptonic transitions. From the CLEO results on\(\bar B^0 \to \pi ^ + \pi ^ -\) and\(\bar B^0 \to D^{* + } + \pi ^ -\) we find for the corresponding Kobayashi-Maskawa matrix element ratio the limit |V ub /V cb |≲0.3.

A basis independent formulation of the connection between quark mass matrices, CP violation and experiment

Abstract: In the standard eletroweak model, with three families, a one-to-one correspondence between certain determinants involving quark mass matrices (m andm′ for charge 2/3 and −1/3 quarks respectively) and the presence/absence of CP violation is given. In an arbitrary basis for mass matrices, the quantity Im det [mm+,m′m′+] appropriately normalized is introduced as a measure of CP violation. By this measure, CP is not maximally violated in any transition in Nature. Finally, constraints on quark mass matrices are derived from experiment. Any model of mass matrices, with the ambition to explain Nature, must satisfy these conditions.

Similarity of parton and hadron spectra in QCD jets

Abstract: A possible existence of the local correspondence between parton and hadron distributions in hard processes (local parton-hadron duality) is discussed. First comparison is made to check up local duality at modern energies. It is shown, in particular, that an account of essential single-logarithmic corrections to leading double-logarithmic approximation proves sufficient to fit π± spectra ine+e− annihilation atW≳20GeV by theoretical perturbative spectra of QCD partons. Rapidity spectra versus the normalized rapidity appear to be similar for π,K, p. Further tests of local duality as well as effects of chromodynamical coherence are suggested.

Parametrizations of the photon structure and applications to supersymmetric particle production at HERA

Abstract: We presentQ2-dependent parametrizations for the parton distributions within real photons obtained from full solutions of the corresponding leading order evolution equations. We show that our results differ appreciably from fits of the “asymptotic” solutions. Furthermore we discuss the production of heavy quarks as well as squarks and gluinos at the HERA collider using our parametrizations. The production rates are very promising especially in the case of gluino production.

Statistical thermodynamics in relativistic particle and ion physics: Canonical or grand canonical?

Abstract: We consider relativistic statistical thermodynamics of an ideal Boltzmann gas consisting of the particlesK, N, Λ, Σ and their antiparticles. Baryon number (B) and strangeness (S) are conserved. While any relativistic gas is necessarily grand canonical with respect to particle numbers, conservation laws can be treated canonically or grand canonically. We construct the partition function for canonicalB×S conservation and compare it with the grand canonical one. It is found that the grand canonical partition function is equivalent to a largeB approximation of the canonical one. The relative difference between canonical and grand canonical quantities seems to decrease like const/B (two numerical examples) and from this a simple thumb rule for computing canonical quantities from grand canonical ones is guessed. For precise calculations, an integral representation is given.

Excited lepton production at LEP and HERA

Abstract: General expressions for single and pair production cross sections of excited leptons (e *,µ*,v *) are presented. Specific results are shown for a realisticSU(2)×U(1) invariant model. Pair production ine + e − annihilation can measure anomalous magnetic moments of excited leptons. Single production ofe * is dominated by thet-channel γ exchange contribution which makes its detection feasible up to masses just below thee + e − c.m. energy. Due to this small |t| enhancement effect, contributions from elastic and resonance scattering inep production ofe * are substantial. Realistic estimates of the excited lepton production cross section at HERA are given

Q 2 dependence of the proton and neutron structure functions from neutrino and antineutrino scattering in deuterium

Abstract: 12,100 νD and 10,500\(\bar vD\) charged current interactions in deuterium measured in the BEBC bubble chamber were used to obtain the complete set of structure functions of proton and neutron. Thex andQ2 dependence of the structure functions of up and down valence quarks and antiquarks are presented and discussed. The Adler and Gross-Llewellyn Smith sum rules have been tested at differentQ2 values. A QCD analysis of the four non singlet structure functionsxF3νN,xuv,xdv andF2νn−F2νp has been performed yielding values ofΛLO between 100 and 300 MeV.

Observation of anomalous scaling violation in muon pair production by 194 GeV/c π−-tungsten interactions

Abstract: The differential cross-section for dimuon production by 194 GeV/c π− onW, as measured by the NA10 Collaboration, is compared with theoretical models. The wide kinematical range of the data, extending well above the ϒ resonances, provides the opportunity of a comparison with ‘realistic’ Drell-Yan models, i.e. with those allowing for scaling violation in the hadronic structure functions. The data in fact clearly indicate the failure of the ‘naive’ Drell-Yan model, while the available ‘realistic’ versions (leading logarithm approximation and next-to-leading logarithm approximation in first order QCD), although giving a better description of the data, still disagree in thexF and\(\sqrt \tau \) dependences of the cross-section at high dimuon masses. This disagreement is referred to here as ‘anomalous’ scaling violation. The dependence of the results on external inputs (nucleon and pion-sea structure functions) is analysed; it is shown that in the next-to-leading logarithm approximation the value 〈K〉=1.03±0.03 (stat.) can be obtained for the ratio experimental/theoretical cross-section.

q $$\bar q$$ g Hybrid mesons in ψ → γ+hadrons

Abstract: We study the hadronic decay of q\(\bar q\)g hybrid mesons. To that aim we establish the connection between the diatomic-molecule like wave functions and the standard q\(\bar q\)g wave functions. We show that inSU(6) approximation TE hybrids cannot decay intoPP, PV, VV channels while TM hybrids are weakly coupled to ψγ. Hence only TE-TM mixed hybrids are easy to see in ψ → γX. We show that hydrids are weakly mixed with quarkonia. We discuss the possible nature of the ξ(2.2) resonance and the ways of detecting exotic 1−+ q\(\bar q\)g bound states.

Experimental estimation of the sum of pion electrical and magnetic polarizabilities

Abstract: The pion radiative scattering πZ→πZγ at 40 GeV was investigated. Coulomb scattering-i.e. pion Compton-effect-dominates for small fourmomentum transfers in this reaction. In our previous paper we found the pion polarizability to beβ π =(−6.8±1.4)·10−43, cm3, where we assume following the theory that the sum of electrical and magnetic polarizabilities (α π +β π )≃0. More complete analysis of our data is done in order to test this assumption. The result for (α π +β π ) is in agreement with theoretical predictions.

Strong P, CP, T violations in heavy-ion collisions

Abstract: We consider the local excitation of the vacuum into an excited state which has the possibility of being CP violating. This gives rise to a dramatic effect: P, CP and T symmetries violated in high energy heavy-ion collisions at the level of a few percent.

Real-time Feynman rules for gauge theories with fermions at finite temperature and density

Abstract: We derive Feynman rules for gauge theories with fermions at finite temperature and density which use thermal propagators with real time arguments.

D^0 - bar D^0 mixing: A possible test of physics beyond the Standard Model

Abstract: It is shown that the\(D^0 - \bar D^0 \) mixing is strongly suppressed in the Standard Model and is smaller by several orders of magnitude than the current experimental upper-bound. The detection of a stronger\(D^0 - \bar D^0 \) mixing in the future experiments might indicate the existence of a new physics beyond the Standard Model. As an example, it is shown that in a class of simple super-symmetric theories\(D^0 - \bar D^0 \) mixing could be substantially larger than the Standard Model prediction. If on the other hand the Standard Model prediction is confirmed by future experiments that will require that the super-symmetric extension of the standard model should have a much larger SUSY breaking scale than that indicated by the phenomenology of the neutral kaon system.

Bose Einstein symmetrisation, coherence and chaos; with particular application toe + e − annihilation

Abstract: The phenomenon of Bose-Einstein correlation within the debris of hadronic final states is discussed in simple terms, with particular attention to the nature of coherent and chaotic sources. The Artru-Mennessier string is taken as a model for the pion source ine+e− annihilation and the predicted Bose-Einstein correlations between like pion pairs evaluated. The results are in good accord with such data as exist.

Measurement of the magnetic formfactor of the deuteron for Q 2 =0.5 to 1.3 (GeV/c) 2 by a coincidence experiment

Abstract: Elastic electron deuteron scattering was measured at the Bonn 2.5 GeV Electron-Synchrotron using a two spectrometer coincidence technique. Data were taken at values of the four momentum transfer squaredQ2=0.50, 0.60, 0.78, 1.00, and 1.3 (GeV/c)2 at electron scattering angles θ e =77.5° to 139.0° in order to separate the magnetic dipole formfactorF M (Q2) from the electric formfactorF E (Q2). Experimental cross sections are compared to theoretical predictions and to measurements of other laboratories. The results indicate that contributions from meson exchange currents are not negligible in thisQ2 region.

Large PT Double Photon Production in Hadronic Collisions Beyond Leading Logarithm QCD Calculation

Abstract: We calculateO(α s ) corrections to largepT double photon production in hadronic collisions We find that these corrections to the basic\(q\bar q \to \gamma \gamma \) subprocess are important, preventing to describe double photon production on the basis of the leading logarithm approximation only We give a phenomenological discussion of the results obtained at SPS, ISR and\(Sp\bar pS\) energies In particular, we investigate how the effect of the intrinsic parton may be disentangled from the perturbative contribution We also calculate the aplanarity distribution characteristic of 3 jet events

Hadronization model for quark-gluon plasma in ultra-relativistic collisions

Abstract: We propose a model for the expansion and hadronization of small droplets of quark-gluon plasma assumed to be produced in ultra-relativistic collisions of hadrons and/or nuclei, and we discuss its experimental consequences. The deconfinement transition is described in terms of formation of QCD strings in the expanding plasma droplet, the string tension stopping the expansion and string breaking leading to possible subdivision of the droplet into smaller ones. The bulk of plasma hadronization is predicted to occur by deflagration of the plasma droplets at transition, through their outer surface and with ejection of low pressure hadron gas. In the rapidity distributiondn/dy of hadrons, this predicts isolated maxima of width δy∼1 or high bumpy regions a few units of rapidity wide, on an event-by-event basis, the corresponding particles having larger than normal transverse momentum. It is in these rapidity intervals that one expects the “traditional” signals for plasma formation (direct dileptons, direct photons, strange particles). We review possible evidence for plasma formation in existing cosmic ray and hadron collider data. Although it appears to be inconclusive, the observed features of the rapidity distribution and the estimated energy densities in the central region are quite encouraging for a systematic search using all proposed signals.

Electromagnetic properties of the Z boson. I

Abstract: The contribution of the fermion triangle diagram responsible for the ABJ anomaly to theZZγ vertex is calculated paying particular attention to the symmetries which must be satisfied. Contrary to previous calculations no static electric dipole moment of theZ is found. Two otherP-violating but CP-conserving couplings are demonstrated as is a new anomaly condition.

A Detailed Study of Strange Particle Production in $e^+ e^-$ Annihilation at High-energy

Abstract: Results onK0 and Λ production ine+e− annihilation at c.m. energies of 14, 22 and 34 GeV are presented. The shape of theK0 and Λ differential cross sections are very similar to each other and to those of π±,K± and\(p(\bar p)\). Scaling violations are observed forK0 production. We obtain a value for the probability to produce strange quark-antiquark pairs relative to that to produce up or down quark-antiquark pairs of 0.35±0.02±0.05. The value ofRh=σ(e+e-→hX)/σµµ is shown to rise steadily with c.m. energy for all particle species. At 34 GeV we find 1.48±0.05K0 and 0.31±0.03 Λ per event. We have searched for possible Λ polarization. The production ofK0's and Λ's in jets is examined as a function ofpT2 and rapidity and compared to that of all charged particles; the yields in two and three jets are also investigated. Results are presented from events with two baryons\((\Lambda ,\bar \Lambda ,por\bar p)\) observed.

Improved πN partial waves, consistent with analyticity and unitarity

Abstract: Partial wave dispersion relations in a new formulation and fixed-s dispersion relations are used to calculate the long range contributions to the real parts of πN amplitudes Recent results from a double spectral function calculation are applied for constraining the imaginary parts We propose to use the new partial waves as starting values in future phase shift analyses and to treat our prediction for the tail of high partial waves as part of the input — The differences between our new partial waves and the Karlsruhe-Helsinki 80 and CMU-LBL 80 solutions are discussed Concerning measurable quantities, the new parital waves lead to significant changes in the forward logarithmic slopes of differential cross sections — Thel-dependence of our partial waves is discussed up to large values ofl We find a systematic even-l, odd-l splitting at all energies

Exponential QCD-moments for charmonium3S1 up to order 〈G4〉

Abstract: In accordance with recent findings of Reinders, Rubinstein and Yazaki we show that for exponential QCD-moments of charmonium the corrections due to dimension six and eight operators are very small so that the ratio of moments used for mass determination remains remarkably stable.

Multiple parton processes in the TEV region

Abstract: We discuss the role of multiple parton interactions in the production of multijets at Collider and Tevatron energies and we analize in detail the kinematics of double parton collisions. We make also some remarks on the combined parton distributions and some qualitative estimates on the total rate of events to be expected.

Multiplicity, momentum and angular characteristics of π - mesons for pC, dC, αC and CC interactions at 4.2 GeV/c per nucleon

Abstract: Light ion collisions with carbon target at 4.2 GeV/c/N are studied. Pion multiplicity distributions, momentum and angular spectra are analysed. These data are described in terms of models assuming independent interactions of nucleons from the projectile nucleus with the target.

Charged particle spectra in αα and αp collisions at the CERN ISR

Abstract: Momenta of charged particles produced in inelastic αα, αp, andpp collisions were measured using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. Inclusive and semi-in-clusive spectra are presented as a function of rapidityy, Feynman-x, and transverse momentumpT. The inclusivey distributions agree well with predictions of the dual parton model; the highest particle densities are reached aty≃0 and the momenta of leading protons decrease significantly for increasing total multiplicity. ‘Temperatures’ are equal in αα, αp, andpp interactions. ThepT distributions depend weakly on the multiplicity.

A determination of the leptonic neutral current couplings

Abstract: An analysis is presented of the recent data which are sensitive to thee, μ and τ neutral current couplings. A fit combining all results (e+e−, μC,ve, eD, atoms) selects a unique solution in agreement with the standard-model expectation. Assuming lepton universality, the vector and axial-vector couplings are determined to bev=−0.013±0.048 anda=−0.520±0.014. Similarly we find (sin2θ=0.213±0.012,ρ=0.015±0.038) or (sin2θ=0.211α0.012, ρ≡1 which, combined with all other values, gives an average of sin2θ=0.216±0.006.

The Production and Decay of Tau Leptons in e+e - Annihilation at PETRA Energies

Abstract: We have observed τ pair production at average CM energies of 13.9, 22.3, 34.5 and 43.1 GeV. The cross-sections are consistent with QED, the cut off parameters beingΛ +>161 GeV andΛ −169 GeV (95% CL). The topological branching fraction of the τ to 1 charged particle,B 1, is 0.847±0.011 (stat) −0.013 +0.016 (syst) and no decays to 5 charged particles were observed resulting inB 5<0.007 (95% CL). Within the 3 charged track final stateB(τ −→π − π + π − v)/(B(τ −→π − π + π − v)+B(τ −→π − π + π − π 0 v))=0.37 −0.20 +0.35

Once more on search for q 2 q −2 -states in photon-photon collisions

Abstract: It is shown that the JADE group upper limits for σ(γγ→ρ0ω) do not lead to any serious conclusions about the\(q^2 \bar q^2 \)-resonance production in this reaction. The predictions for the processes\(\gamma \gamma \to q^2 \bar q^2 \to \rho ^0 \omega \) and\(\gamma \gamma \to q^2 \bar q^2 \to \rho ^0 \varphi \) are discussed in detail. It is noted that one of some assumptions, which are made to extract the processγγ→ρ0ρ0 from γγ→4π, is wrong from the theoretical point of view and the other appears to be unsound. It is shown that theq2q−2-resonance production can describe all features of the reactionsγγ→ρ0ρ0 andγγ→ρ+ρ- qualitatively and quantitatively. It is emphasized that the production of the exotic resonance withI=2 and the resonance (or a few ones) withI=0, having close masses, provides the enhancement in σ(γγ→ρ0ρ0) and the absence of the similar enhancement in σ(γγ→ρ+ρ-) in the vector meson dominance model frame.

Tests of models for quark and gluon fragmentation ine+e− annihilation at\(\sqrt s = 29 GeV\)

Abstract: Three currently used fragmentation models are tested by studying the distribution of particles between jet axes in the 3-jet events ofe+e− annihilation, using data collected by the Time Projection Chamber at PEP. These three models — the Lund String model, the Webber Cluster model and an Independent Fragmentation model (IF) — each implement different Lorentz-frame structures for the fragmentation process of quarks and gluons into hadrons. The Lund model provides a good description of the data, while the IF model does not. The Webber model, which is untuned, does not describe the absolute particle densities between jets, but correctly predicts the ratios of those densities, which are less sensitive to the tuning.

Hard photon effects in W ± and Z 0 decay

Abstract: The effects of QED radiative corrections to the processes\(p\bar p \to W^ \pm \to lv\) and\(p\bar p \to Z_O \to l\bar l\) are discussed. The purpose is twofold. On one hand the rate for radiative events in actual experimental situations is of immediate relevance. On the other hand, the effect of bremsstrahlung on the precise experimental determination of the boson masses will become of importance once higher statistics are available. The method uses Monte Carlo simulation techniques which are directly applicable to any experimental setup.

Nonlocal light-cone expansions and evolution equations

Abstract: A new variant of the nonlocal light-cone expansion in QCD is proposed. The anomalous dimension of the corresponding fermion flavour nonsinglet operator is calculated in the one-loop approximation and shown to coincide (up to a trivial diagonal factor) with the Brodsky-Lepage kernel. The connection of our approach with the standard local conformal light-cone expansion is briefly discussed. An exclusive light-cone dominated process is considered within the framework of our formalism. The evolution equation obtained earlier by different methods is recovered in a particularly straightforward and compact manner.