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.

Phys.Lett.B

In four-jet events from e + e − →Z 0 →multihadrons one can separate the three principal contributions from the triple-gluon vertex, double gluon-bremsstrahlung and the secondary quark-antiquark production, using the shape of the two-dimensional angular distributions in the generalized Nachtmann-Reiter angle θ NR ∗ and the opening angle of the secondary jets. Thus one can identify directly the contribution from the triple-gluon vertex without comparison with a specific non-QCD model. Applying this new method to events taken with the DELPHI-detector we get for the ratio of the colour factor N c to the fermionic Casimir operator C F : N c C F = 2.55 ± 0.55 ( stat. ) ± 0.4 ( fragm. + models ) ± 0.2 ( error in bias ) in agreement with the value 2.25 expected in QCD from N c =3 and C F = 4 3 .

AIP Conf. Proc.

A 0° facility is being developed for the study of meson production in proton‐nucleus collisions and other investigations at intermediate bombarding energies at an internal target position (TP2) of COSY. A set of three laminated magnets will provide a closed orbit bump for the proton beam and deflection as well as momentum analysis for ejectiles with p0/30= p=p0/2 (p0=projectile momentum). this facility will enable the spectroscopy of rare ejectiles like K+ mesons with a momentum resolution of =1%. It also allows studies of ejectiles emitted under 180° like protons from deuteron breakup.

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.

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 .

Nucl.Phys.B Proc.Suppl.

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.

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.

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.

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.

Phys.Lett.B

We present a search for the third generation up type quark t and a possible fourth down type quark b' in hadronic Z 0 decays observed in DELPHI at the LEP collider. For any scenario with a decay through the charged current or into a charged Higgs with a mass at least 6 GeV/ c 2 below the t and 3 GeV c 2 below the b' mass, we set a lower limit for the t quark mass at 44.0 GeV/ c 2 and for the b' mass at 44.5 GeV/ c 2 . For specific scenarios the mass limits are slightly higher, e.g. for charged current decays the limits are 44.5 and 45.0 GeV/ c 2 respectively, where all limits are given at a 95% confidence level.

Nucl. Phys. B

A search for the neutral Higgs boson in Z 0 -decays has been performed using the DELPHI detector at the large Electron Positron collider (LEP) at CERN. We looked for the decay of Z 0 into a neutral Higgs particle and a pair of fermions. No events fulfilled the criteria for H 0 -production. Our results, which are based on an integrated luminosity of 530 nb −1 , exclude a minimal Standard Model Higgs boson with a mass in the range 210 MeV/c 2 to 14 GeV/c 2 at 95% confidence level.

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,

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.

Phys.Lett.B

Using a sample of Z 0 's corresponding to about 12 000 events, we have searched for the production of charged scalars, primarily charged Higgs particles, decaying into c sc s , τν + jets, and τντν. The average detection efficiency is 20%. No candidate was found in the leptonic modes. Masses in the range up to 30–36 GeV/ c 2 are excluded, extending the mass domain covered by previous e + e − machines.

Yad. Fiz.

Pion pair production from the proton-tantalum nuclear interaction at proton energy 70 GeV has been studied. Pion correlations as a function of the relative momentum in a pair CMS have been measured at the relative momentum region below 40 MeV/ c . The experimental data agree with the calculation that takes into account the Coulomb factor in the differential cross section of pion pairs production.

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.

Nucl.Phys.A

The pionic annihilation of antiprotons stopped on 3 He nuclei in a self-shunted streamer chamber exposed to the antiproton beam of LEAR is studied. The data concern charged-particle multiplicity distributions, branching ratios for different final states, the probability of final-state interaction, π − , π + , p and d momentum spectra, like and unlike pion angular correlations, π and other charged-particle angular correlations. The comparison of the 3 He data with those obtained on 1 H, 2 H and 4 He does not reveal relevant effects due to the increase of the nucleon number; the small differences can be seen as due to a weak final-state interaction.

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.