Z. Phys. C

This paper presents an analysis of the multiplicity distributions of charged particles produced inZ0 hadronic decays in the DELPHI detector. It is based on a sample of 25364 events. The average multiplicity is =20.71±0.04(stat)±0.77(syst) and the dispersionD=6.28±0.03(stat)±0.43(syst). The data are compared with the results at lower energies and with the predictions of phenomenological models. The Lund parton shower model describes the data reasonably well. The multiplicity distributions show approximate KNO-scaling. They also show positive forward-backward correlations that are strongest in the central region of rapidity and for particles of opposite charge.

Z.Phys.C

The analytic formulae for the bremsstrahlung photon spectra in the processeslN→γlN andlN→γlX (taking into account γ-andZ-boson exchange diagrams) are derived. The energy and angular distributions of photons are computed at HERA energies. The very large sensitivity of spectra for the deep inelastic channel to the choice of the structure functions is revealed in the region of small angles and large energies of the emitted photons.

Nucl. Instrum. Meth. A

DELPHI is a 4π detector with emphasis on particle identification, three-dimensional information, high granularity and precise vertex determination. The design criteria, the construction of the detector and the performance during the first year of operation at the large electron positron collider (LEP) at CERN are described.

Nucl.Phys.B Proc.Suppl.

Nucl. Instrum. Meth. A

A method for calculation of the momentum of a charged particle in magnetic spectrometers in high energy experiments with fixed targets is proposed. It is compared with the widely used method of Lechanoine, Martin and Wind [Nucl. Instr. and Meth. 69 (1969) 122]. The method gives an improvement in the number of coefficients by more than one order and in the number of computer instructions by approximately two orders and is much simpler. The method is tested on the magnetic spectrometers of experimental setups ISTRA-M and HYPERON at IHEP (Serpukhov, USSR).

Class.Quant.Grav.

The investigation of the Dirac equation by the WKB-Maslov method (complex sprout method) in Minkowski-Cartan space with an arbitrary external electromagnetic field is carried out. The Ehrenfest-type complete set of quasi-classical trajectory-coherent states (TCS) for the Dirac equation up to the order of O(h(cross)32/) at to 0 is constructed. These states have the form of wavepackets moving along the worldline of the charged particle. From the Dirac equation a classical relativistic spin equation is derived by the use of the TCS which coincides with the generalization of the well known Bargmann-Michel-Telegdi equation in the case of an arbitrary external torsion field.

Z.Phys.C

The dependence of distribution functions of quarks, antiquarks, diquarks and their fragmentation into hadrons on the transverse momentumkt is discussed in the frame of the quark-gluon string model. We then discuss the division ofkt between 2n-quark-antiquark chains, orn-pomeron showers. Hadron and hadron-nuclear processesp−p,p−A,K+−p,K+−A are analysed. A strong dependence of the observed values on the numbern is derived by this method, which is of special importance for the analysis of hadron-nucleus collisions. Our method is compared with the regularkt division method.

Nucl. Instrum. Meth. A

We have studied the achievable spatial resolution of a plastic streamer tube with pickup strips perpendicular to the anode wire. Making use of the fact that low cathode resistivity and/or large integration time broaden the induced charge distribution, we have obtained a spatial resolution better than 400 μm for ∼ 3 cm wide strips. This value is comparable with the best results ( ∼ 350–450 μm) obtained with the usual ∼ 1 cm wide strips.

Phys.Lett.B

The ratio of the number of ultrarelativistic positronium atoms ( A 2e ) to the photon number in the momentum interval 800–2000 MeV/ c has been measured in pC interactions at E p =70 GeV and at an angle of 8.4° in the laboratory frame. The branching ratio ϱ π =(1.84±0.29)×10 -9 for π 0 decay into a photon and A 2e has been obtained. The parameter ϱ π is determined by the conversion probability ϱ A of a time-like photon into A 2e in radiative decays of elementary particles.

Phys. Lett. B

A search has been made for pairs oade for pairs of scalar quarks (squarks) produced in e + e − annihilations at LEP ( s ≅M z 0 ) , and decaying into a standard quark and a neutral, non-interacting, stable, massive particle (the lightest supersymmetric particle, LSP). The search has been conducted for differences in the mass of the squark and LSP of 2 GeV/ c 2 and above. Up squarks with masses below 42 GeV/ c 2 and down squarks below 43 GeV/ c 2 were excluded. Six squark flavours degenerate in mass were excluded below 45 GeV/ c 2 .

Phys.Lett.B

The correlations in rapidity in hadron production from e + e − annihilation near the Z 0 resonance were studied by means of the method of factorial moments, using data taken with the DELPHI detector at LEP. The parton shower hadronization model was found to be in quantitative agreement with the data, in contrast with previous results at lower energies.

Phys.Lett.B

The production rates for 2-, 3-, 4- and 5-jet hadronic final states have been measured with the DELPHI detector at the e + e − storage ring LEP at centre of mass energies around 91.5 GeV. Fully corrected data are compared to O(α 2 s ) QCD matrix element calculations and the QCD scale parameter Λ MS is determined for different parametrizations of the renormalization scale ω 2 . Including all uncertainties our result is α s ( M 2 Z )=0.114±0.003[stat.]±0.004[syst.]±0.012[theor.].

Phys. Lett. B

Using a data sample corresponding to 10 000 hadronic Z 0 decays, we have searched for the production of sleptons and gauginos in the two-prong decays of Z 0 . No candidate remains after straightforward selections. For neutralinos, we use selection methods developed in our previous search for neutral Higgs particles. The negative results are translated into improved mass limits and parameter constraints on the minimal supersymmetric extension of the standard model.

Sov. Phys. J.

The spin properties of an electron due to quantization of its motion in a focusing electromagnetic field are studied. Within the framework of the complex Maslov WKB method, an explicit dependence is obtained for the quasiclassical particle energy spectrum on the spin. It is shown that for electrons in an axial channeling regime this will result in a different degree of states' stability depending on the value of the projection of the spin on the moment of rotation.

Nucl. Phys. A

Using a liquid hydrogen bubble chamber of the ITEP, 80 cm in diameter, a study was made of the 3 H + p → p + n + d reaction with an incident momentum of 5 GeV/c for the tritium nuclei. The reaction cross section was 20.4 ± 0.2 mb. The angular, momentum and mass distributions of the reaction products in the 4π geometry have been obtained. We have separated the phase-space regions corresponding to quasi-free pn scattering and to the final-state Nd interaction. In the region of quasi-free pn scattering various experimental spectra are compared with the theoretical predictions, by using pole diagrams with nuclear vertex functions for three NN potentials: the Yamaguchi potential, the RSC potential and the potential in the quark-compound bag model. In the mass spectra of pn, pd and nd systems no evidence for the exhibition of two- and three-baryon resonances has been obtained.

Nucl.Phys.A

The basic characteristics of the quasi-elastic charge exchange reaction p 3 He→ n F ppp are investigated using the 80 cm ITEP liquid-hydrogen bubble chamber, which is exposed to beams of 3 He nuclei with momenta of 2.5 and 5 GeV/ c (the kinetic energy of primary protons in the rest system of the nucleus are, respectively, T p = 0.318 and 0.978 GeV). The experimental data are compared with the predictions of the Glauber-Sitenko multiple scattering theory and of the pole model, taking into account the interaction between spectator nucleons in the final state. In the mass spectrum of the 3p system at 3.05 GeV a clearly denned structure has been revealed, which is not described within the pole model. A possible resonance origin of the given structure is discussed.

Phys.Lett.B

A single-spin asymmetry in the inclusive π 0 production at small x F was measured. In the experiment 40 GeV/c π − mesons were incident on transversely polarized protons and deutrons. An asymmetry of (40–50)% has been revealed in the hard scattering region.

Phys.Lett.B

Hadronic decays of Z 0 bosons are studied in the Delphi detector. Global event variables and singel particles inclusive distributions are compared with QCD-based predictions. The mean charged multiplicity is found to be 20.6±1.0 (stat+syst). The mean values of the sphericity, aplanarity, thrust, minor value, p in T and p out T are compared with values found at lower energy e + e − colliders.

Phys.Lett.B

We have studied the energy-energy angular correlations in hadronic final states from Z 0 decay using the DELPHI detector at LEP. From a comparison with Monte Carlo calculations based on the exact second order QCD matrix element and string fragmentation we find that Λ (5) MS =104 +25 -20 ( stat. ) +25 -20( syst. ) +30 00 ) theor. ) . MeV, which corresponds to α s (91 GeV)=0.106±0.003(stat.)±0.003(syst.) +0.003 -0.000 (theor). The theoretical error stems from different choices for the renormalization scale of α s . In the Monte Carlo simulation the scale of α s as well as the fragmentation parameters have been optimized to described reasonably well all aspects of multihadron production.

Phys. Lett. B

A determination of the partial width Γ c c ̄ of the Z 0 boson into charm quark pairs is presented, based on a total sample of 36 900 Z 0 hadronic decays measured with the DELPHI detector at the LEP collider. The production rate of cc̄ events is derived from the inclusive analysis of charged pions coming from the decay of charmed meson D ∗+ → D 0 π + and D ∗− → D ̄ 0 π − where the π ± is constrained by kinematics to have a low p T with respect to the axis. The probability to produce these π ± from D ∗± decay in cc̄ events is taken to be 0.31 ±_0.05 as measured at √ s =10.55 GeV. The measured relative partial width Γ c c ̄ Γ h = 0.162± 0.030 ( stat. ) ±0.050 ( syst. ) is in good agreement with the standard moel value of 0.171. Together with our previous measurement of the total hadronic width Γ h this implies Γ c c ̄ = 282±53 ( stat. )±88( syst. ) MeV .

Phys. Lett. B

The pair production of the lightest scalar Higgs boson, h, and a pseudoscalar Higgs boson, A, was searched for in a data sample containing 10 000 hadronic Z 0 decays. The search involved both leptonic and purely hadronic decay channels of each Higgs boson. No signal was found, and limits on the Higgs boson masses, in the framework of the minimal supersymmetric extension of the standard model, ar reported up to 35 GeV/ c 2 at 95% CL, for both tan β 1 and tan β <1, where tan β is the ratio of the vacuum expectation values of the two Higgs doublets.

Phys.Lett.B

A measurement of the cross section for e + e - → hadrons using 11 000 hadronic decays of the Z boson at ten different center-of-mass energies is presented. A three-parameter fit gives the following values for the Z mass M z , the total width Γ z , the product of the electronic and hadronic partial widths Γ e Γ h , and the unfolded pole cross section σ 0 : M Z =91.171±0.030(stat)±0.030 (beam) GeV, Γ Z =2.511±0.065 GeV, Γ e Γ h =0.148±0.006 (stat.)±0.004 (syst.) GeV 2 , σ 0 =41.6±0.7(stat.)±1.1 (syst.) nb,

Nucl.Instrum.Meth.A

A silicon one-coordinate detector made on the basis of a continuous position-sensitive counter and an external system of readout strips is described. The resistive layer of the detector, which is necessary for obtaining the charge distribution from the incident particles, was formed by a thin undepleted region of the detector. The active area of the detector was 21 × 5 mm 2 and its thickness was 812 μm. The possibility to obtain a position precision (using centroid finding of the charge) of σ ≈ 25 μ m for a strip pitch of 0.5 mm is shown.

Phys.Lett.B

The radiative decay of the τ -lepton is described in the quark model of the superconducting type. The decay width is estimated to be Br( τ → ν τ πγ ) = 0.15% (at the minimal registered photon energy 50 MeV). The contribution of the structural component is 10% of the total radiation. The angular and energy spectra of the decay products are obtained. The methods of extracting information on the axial and vector form factors are discussed.

Phys.Lett.B

Measurements are presented of the cross section ratios R ℓ = σ ℓ ( e + e − →ℓ + ℓ − ) σ h ( e + e − →hadrons) for ℓ=e, μ and τ using data taken from a scan around the Z 0 . The results are R e =(5.09± o .32±0.18)%, R μ =(0.46±0.35±0.17)% and R τ =(4.72±0.38±0.29)% where, for the ratio R e , the t -channel contribution has been subtracted. These results are consistent with the hypothesis of lepton universality and test this hypothesis at the energy scale s ∼8300 GeV 2 . The absolute cross sections σ ℓ (e + e − →ℓ + ℓ − ) have also been measured. From the cross sections the leptonic partial widths Γ e =(83.2±3.0±2.4) MeV, (Γ e Γ μ ) 1 2 =(84.6±3.0±2.4) MeV and (Γ e Γ τ ) 1 2 =(82.6±3.3±3.2) MeV have been extracted. Assuming lepton universality the ratio Γ ℓ Γ h =(4.89±0.20±0.12) × 10 −2 w was obtained, together with Γ ℓ =(83.6±1.8±2.2) MeV. The number of light neutrino species is determined to be N v =3.12±0.24±0.25. Al the data are consistent with the predictions of the standard model.