Nucl. Instrum. Meth. A

The structure of traditional data processing systems looks approximately like this: space coordinates of events C i are searched, parameters X j (angles, momenta and so on) are estimated together with their covariance matrix and then kinematical analysis is performed within some hypothesis about the physical event. In the case of the Lagrange multipliers method it means minimization of the functional M=(X−X m ) T S (X−X m )+2ƒα , where X is the parameter vector, X m is its measured value, S −1 the covariance matrix of parameter X, ƒ the vector of constraints, and α the vector of Lagrange multipliers.

Nucl. Instrum. Meth. A

The problem of minimization of the functional χ 2 = ∑ i, j nf, nf [C i (X)−C m i ]G ij [C j (X)−C m j ]; i, j=1… nf , with the constraints ƒ λ (X)=0; λ=1…nc , is considered. Here: X is the vector of the parameters to be estimated, C i ( X ) = ( C ( X )) i is the vector of functions, C i m are their measured values, and G −1 the covariance matrix.

Phys. Lett. B

A strong increase of the mean transverse momentum 〈 p t 〉 with the number of charged particles n ch is observed in e + e − annihilations into hadrons at LEP energies. The effect resembles correlations observed in hadron-hadron interactions. In e + e − annihilations the 〈 P t 〉 and n ch correlations can be accounted for by gluon radiation.

Phys.Lett.B

The weak mixing angle has been measured from the charge asymmetry of hadronic events with two different approaches using the DELPHI detector at LEP. Both methods are based on a momentum-weighted charge sum to determine the jet charge in both event hemispheres. In a data sample of 247 300 multihadronic Z 0 decays a charge asymmetry of 〈 Q F 〉 − 〈 Q B 〉 = −0.0076±0.0012(stat.)±0.0005(exp. syst.)±0.0014(frag.) and a raw forward-backward asymmetry of A raw FB = −0.0109±0.0020(stat.)±0.0010(exp. syst.)±0.0017(frag.) have been measured. This result corresponds to a value of sin θ eff =0.2345±0.0030(exp.)±0.0027(frag.), sin 2 θ MS =0.2341±0.0030( exp. )±0.0027( frag. ) and to sin 2 θ W =1− m 2 W / m 2 Z =0.2299± 0.0030(exp.)±0.0027(frag.)±0.0028(theor.). The experimental error is the quadratic sum of the statistical and the experimental systematic error and the theoretical error originates from a value of m t =130±40 GeV/ c 2 and a range of m H from 45 GeV/ c 2 to 1000 GeV/ c 2 .

Phys.Lett.B

An analysis of the production of strange particles from the decays of the Z 0 boson into multihadronic final states is presented. The analysis is based on about 90 000 selected hadronic Z 0 decays collected by the DELPHI detector at LEP in 1990. K s 0 , K ∗± , Λ( Λ ) and Ξ − ( Ξ + ) have been identified by their characteristic decays. The measured production cross sections are compared with predictions of the Lund Monte Carlo tuned to data at PEP/PETRA energies.

Teor.Mat.Fiz.

For the Schrödinger and Dirac equations in an external gauge field with symmetry groupSU(2), we construct to any degree of accuracy in powers ofh1/2,h→0, approximate dynamical states in the form of wave packets—semiclassical trajectory-coherent states. For the quantum expectation values calculated with respect to these semiclassical states we obtain for the operators of the coordinates, momenta, and isospin of the particle Hamiltonian equations of motion that are equivalent (in the relativistic case after transition to the proper time) to Wong's well-known equations for a non-Abelian charge with isospin 1/2.

Phys. Lett. B

We have searched for possible fourth family heavy neutrinos, pair produced in Z 0 decays, in a sample of about 112 000 hadronic Z 0 final states collected with the DELPHI detector. For all mixing matrix elements we exclude a new Dirac neutrino lighter than 44.5 GeV at a 95% confidence level, if the neutrino couples to the electron or muon family, and lighter than 44.0 GeV, if the neutrino couples to the tau family. Depending on the values of the mixing element and to which lepton family the neutrino couples, we obtain mass limits up to 46.2 GeV. For all mixing matrix elements we exclude a new Majorana neutrino lighter than 39.0 GeV, if it couples to the electron or the muon family, and lighter than 38.2 GeV, if it couples to the tau family. Depending on the values of the mixing matrix element and to which lepton family the neutrino couples, we obtain mass limits up to 44.7 GeV. We also exclude stable new Dirac neutrinos lighter than 45.0 GeV and new Majorana neutrinos lighter than 39.5 GeV.

Z. Phys. C

The differential cross section for final state radiation from primary quarks is obtained from a study of isolated energetic photons produced in the reactione+e

Phys.Lett.B

We have searched for pair produced scalar leptoquarks each decaying to a quark and a charged lepton in a sample of 116 000 hadronic Z 0 events produced at LEP. No candidate was detected and cross section and branching ratio limits are set for the above process at 95% CL. Mass limits are found to be about 42 GeV/ c 2 depending only slightly on the models used and a coupling times branching ratio exclusion line is drawn for a scalar leptoquark with a free coupling. We have also probed the mass region above 45 GeV/ c 2 for a singly produced scalar leptoquark and set limits on the cross section and the coupling λ 2 /4 π up to 60 GeV.

Nucl.Phys.B

The search in DELPHI data for neutral Higgs bosons is described. No candidate for the Standard Model Higgs is seen in Z 0 decays to H 0 ν ν , H 0 μ + μ − or H 0 τ + τ − after selections that proved efficient for finding simulated H 0 . One remaining candidate for Z 0 → H 0 e + e − is consistent with background. Together with our earlier studies, these results restrict the H 0 mass to be above 38 GeV/ c 2 at the 95% confidence level. No signal is found for decays of Minimal Supersymmetric Standard Model neutral Higgs bosons to τ + τ − . Limits are obtained for their decays to produce four jets.

Z.Phys.C

The average lifetime ofB hadrons produced in hadronicZ0 decays has been measured with the DELPHI detector at LEP. The measurement is based on the analysis of the impact parameter distributions of highpt muons and hadrons. The resulting meanB lifetimes are τB=(1.30±0.10±0.08)ps and τB=(1.27±0.04±0.12)ps respectively, giving a combined value of τB=(1.28±0.10)ps. The hadronic sample was also used to measure the partialZ0 width\({{\Gamma _{b\bar b} } \mathord{\left/ {\vphantom {{\Gamma _{b\bar b} } {\Gamma _h }}} \right. \kern-\nulldelimiterspace} {\Gamma _h }}\) and gave a value of 0.222−0.031+0.033±0.017.

Int. J. Mod. Phys. A

A search has been performed for weakly interacting neutral light scalar and pseudoscalar particles in a proton-iron beam dump experiment via the Bethe-Heitler process. No positive signal was observed. Limits are derived on the masses of these particles in the framework of the Standard Model and its minimal supersymmetric extension (MSSM) comparing the experimental results with expectations for Bethe-Heitler e+e− and μ+μ− pair production. The Higgs particle of the SU2L×U1 Standard Theory is excluded for masses in the range mH<0.9 MeV at 95% CL. Limits on light Higgs particles of the MSSM and Peccei-Quinn like axions are derived.

Phys.Lett.B

The total and differential cross-sections for the reaction e + e − → γγ ( γ ) are measured at centre of mass energies around 91 GeV using an integrated luminosity of 4.7 pb −1 . The aggreement with QED prediction is good. Consequently there is no evidence for non-standard channels which would have the same experimental signature. The lower limits on the QED cuttoff parameters are Λ + > 113 GeV and Λ − > 95 GeV. An upper limit on the effective coupling between a possible excited electron and the gamma is derived. At 95% confidence level the branching ratios for Z 0 decay into π 0 γ, ηψ and γγγ are below 1.5 × 10 −4 , 2.8 × 10 −4 and 1.4 × 10 −4 respectively.

Phys.Lett.B

The lifetime of the tau lepton has been measured by two independent methods using a silicon microvertex detector installed in the DELPHI detector. The signed impact parameter distribution of the one prong decays yielded a lifetime of τ τ = 321 ± 36 (stat.) ± 16 (syst.) fs, while the decay length distribution of three prong decays gave the result τ τ = 310 ± 31 (stat.) ± 9 (syst.) fs. The final value of the combined result was τ τ = 314 ± 25 fs. The ratio of the Fermi coupling constant from tau decay relative to that from muon decay was found to be 0.95 ± 0.04, compatible with the hypothesis of lepton universality.

Z. Phys. C

Using a data sample of 115000 hadronicZ0 decays, a search was performed for the production of excited charged leptons decaying into an ordinary lepton and one photon. Pair production of excited leptons of mass below 45 GeV/c2 is excluded. From an analysis of the lepton-photon mass spectra this experiment is also able to exclude single production of these particles for masses that reach up to 85 GeV/c2, if the compositeness scale is below 1 TeV.

Nucl. Phys. B

From measurements of the cross sections for e + e − → hadrons and the cross sections and forward-backward charge-asymmetries for e e −→ e + e − , μ + μ − and π + π − at several centre-of-mass energies around the Z 0 pole with the DELPHI apparatus, using approximately 150 000 hadronic and leptonic events from 1989 and 1990, one determines the following Z 0 parameters: the mass and total width M Z = 91.177 ± 0.022 GeV, Γ Z = 2.465 ± 0.020 GeV , the hadronic and leptonic partial widths Γ h = 1.726 ± 0.019 GeV, Γ l = 83.4 ± 0.8 MeV, the invisible width Γ inv = 488 ± 17 MeV, the ratio of hadronic over leptonic partial widths R Z = 20.70 ± 0.29 and the Born level hadronic peak cross section σ 0 = 41.84±0.45 nb. A flavour-independent measurement of the leptonic cross section gives very consistent results to those presented above ( Γ l = 83.7 ± 0.8 rmMeV ). From these results the number of light neutrino species is determined to be N v = 2.94 ±0.10. The individual leptonic widths obtained are: Γ e = 82.4±_1.2 MeV, Γ u = 86.9±2.1 MeV and Γ τ = 82.7 ± 2.4 MeV. Assuming universality, the squared vector and axial-vector couplings of the Z 0 to charged leptons are: V ̄ l 2 = 0.0003±0.0010 and A ̄ l 2 = 0.2508±0.0027 . These values correspond to the electroweak parameters: ϱ eff = 1.003 ± 0.011 and sin 2 θ W eff = 0.241 ± 0.009. Within the Minimal Standard Model (MSM), the results can be expressed in terms of a single parameter: sin 2 θ W M ̄ S = 0.2338 ± 0.0027 . All these values are in good agreement with the predictions of the MSM. Fits yield 43< m top < 215 GeV at the 95% level. Finally, the measured values of Γ Z and Γ inv are used to derived lower mass bounds for possible new particles.

Phys.Lett.B

The study of the orientation of three-jet events from e + e − → Z 0 → multi-hadrons is presented, in particular the polar angle distributions of the thrust axis and of the normal to the three-jet plane, and the azimuthal correlations between the hadron plane and the one defined by the beam and thrust axes. The data are compared with results at lower energy and with QCD predictions. Good agreement with QCD predictions is observed. The scalar gluon theory is excluded by the data.

AIP Conf. Proc.

Information recently obtained by the PS179 (STREAMER) collaboration at LEAR on p̄4He elastic scattering, strangeness production in antiproton annihilation at rest and p̄ annihilation in nuclear photo‐emulsion is presented.

AIP Conf. Proc.

A confirmation of the resonance AX(1565), a precision measurement of the Pontecorvo reaction p̄d→π− p and the first antineutron annihilations are the preliminary results obtained by the OBELIX Spectrometer.

Phys. Lett. B

Measurements of the cross section and forward-backward asymmetry for the reaction e + e − → μ + μ − using the DELPHI detector at LEP are presented. The data come from a scan around the Z 0 peak at seven centre of mass energies, giving a sample of 3858 events in the polar angle region 22° < θ < 158°. From a fit to the cross section for 43° < θ < 137°, a polar angle region for which the absolute efficiency has been determined, the square root of the product of the Z 0 → e + e − and Z 0 → μ + μ − partial widths is determined to be (Γ e Γ μ ) 1 2 = 85.0 ± 0.9( stat. ) ± 0.8( syst. ) MeV . From this measurement of the partial width, the value of the effective weak mixing angle is determined to be sin 2 ( θ w ) = 0.2267 ± 0.0037 . The ratio of the hadronic to muon pair partial widths is found to be Γ h / Γ μ = 19.89 ± 0.40(stat.) ± 0.19(syst.). The forward-backward asymmetry at the resonance peak energy E CMS = 91.22 GeV is found to be A FB = 0.028 ± 0.020(stat.) ± 0.005(syst.). From a combined fit to the cross section and forward-backward asymmetry data, the products of the electron and muon vector and axial-vector coupling constants are determined to be V e V μ = 0.0024 ± 0.0015(stat.) ± 0.0004(syst.) and A e A μ = 0.253 ± 0.003(stat.) ± 0.003 (syst.). The results are in good agreement with the expectations of the minimal standard model.

Class. Quant. Grav.

Using Maslov's complex sprout method the complete set of quasiclassical trajectory-coherent quantum states (TCS) for the Klein-Gordon equation in a curved spacetime in the presence of external electromagnetic and background scalar fields up to the order of O(32/) at to 0 was constructed. The approximate solutions Psi v are strongly peaked around the worldline neighbourhood of the charged particles. The method of reducing the initial Klein-Gordon equation to the Schrodinger type equation for which Psi v are exact solutions has been developed. In the quasi-classical trajectory-coherent approximation based on the ' gamma -reconstruction' technique the concept of the local time for a quantum scalar particle in a curved spacetime has been suggested. In general it has been stated that the constructed TCS Psi v permit the standard quantum-mechanical interpretation.

Phys.Lett.B

The q 2 dependence of the vector form factor has been investigated using 3.2 × 10 4 K + → π 0 e + ν decays. The usual linear parametrization. ƒ + (q 2 ) = ƒ(0)(1+λ + q 2 /m π 0 0 ) gives λ + = 0.0284±0.0027. An analysis of the Dalitz plot density distribution for K e3 + decays yields the values for the scalar and tensor couplings ƒ s and ƒ t , and their relative phase angle ø st .

Nucl. Instrum. Meth. A

In this article a simple method for making multiwire chambers is described. The chamber design does not involve any frame structure, which permits the

Phys. Rev. C

The vector analyzing power iT11 of the reaction πd→pp was measured at Tπ=350, 400, and 450 MeV. The results obtained at Tπ=350 MeV are in agreement with earlier measurements of iT11 at 325 MeV. With increasing energies our results show a marked increase in the vector analyzing power up to a value close to its theoretical limit at Tπ=450 MeV (√s =2.40 GeV). In this energy region broad structure has been found in earlier measurements of dσ/dΩ and Ay0.

Z.Phys.C

The multiplicity distributions of charged particles in restricted rapidity intervals inZ0 hadronic decays measured by the DELPHI detector are presented. The data reveal a shoulder structure, best visible for intervals of intermediate size, i.e. for rapidity limits around ±1.5. The whole set of distributions including the shoulder structure is reproduced by the Lund Parton Shower model. The structure is found to be due to important contributions from 3-and 4-jet events with a hard gluon jet. A different model, based on the concept of independently produced groups of particles, “clans”, fluctuating both in number per event and particle content per clan, has also been used to analyse the present data. The results show that for each interval of rapidity the average number of clans per event is approximately the same as at lower energies.