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.

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.

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

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 widthParseError: KaTeX parse error: Invalid size: '-' at position 100: …} \right. \kern-̲\nulldelimiters… 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.

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.

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.

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 .

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.

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. 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.

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

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.

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.

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 .

Nucl. Phys. A

A search for superheavy hydrogen isotopes and multineutrons in the two- and three-body channels of π − absorption at rest on a 9 Be target has been carried out. The 5 H system revealed a broad resonance with E r = 7.4±0.7 MeV and Γ = 8±3 MeV. An indication has been obtained for the resonance in the 3n system with E r = 3±1 MeV. The measured parameters for 4 H are close to the results of previous experiments.

Z.Phys.C

The possibility of the experimental investigation of the radiative tau decay into pion is discussed including background conditions. The decay width is estimated to be Br(τ→vτπγ)=0.15% (at the minimal registered photon energy 50 MeV). The contribution of the structural component is 10% of the total radiation. The main background is produced by photons from the τ→vτπ−π0 decay. We investigate the angular and energy spectra of the decay products and analyse the background conditions. The kinematic region was found where the structural radiation dominates over background.

Nucl.Phys.A

A new technique has been developed for investigation of the spin-neutrino angular correlation in electron capture. The technique is based on measurement of Doppler shifts in the energy of gamma-quanta resulted from the decay of polarized nuclei. This technique was used to investigate the decay of 56 Co nuclei polarized by the magnetic field of the Fe host at the temperature 17 mK. A Doppler shift + 12 ± 1 eV has been obtained for the 2598.5 keV gamma-line. It allows to admit that the magnetic moment of the 56 Co nucleus has a positive sign and to estimate the behaviour of the recoil ion of 56 Fe in the Fe crystal lattice.

Nucl.Instrum.Meth.A

The procedure and results of mass testing of plastic streamer tubes for the DELPHI hadron calorimeter are described in detail. The mass testing includes three stages: high voltage test and conditioning, X-ray test on radiation load capability and wire tension control in ready detectors. The productivity of the test workshop was 240 detectors per day at maximum. After testing of about 25 000 streamer tubes, 8% have been rejected on the ground of severe rejection criteria which exceed significantly the working conditions in the DELPHI experiment.

J. Phys. G

A status report is given on an experiment started in 1987 at PSI to search for the lepton flavour violating muon to electron conversion process. The motivation for this experiment, the design and performance of the detector (SINDRUM II), and results of a first run are presented. No candidate of the process mu -Ti to e-Ti was found, and, using two independent determinations of the muon stop rate, an upper limit for the branching ratio relative to muon capture Bmu e<4.4.10-12 (90% C.L.) was obtained. This result confirms the current best value for the upper limit found at TRIUMF (4.6.10-12).

Phys.Lett.B

The ( 3 He, t) charge-exchange reaction on carbon nuclei and protons, accompanied by the excitation of Δ isobars in a target, has been studied at beam momenta from 4.40 to 18.3 GeV/ c . The analysis is performed to explain why the Δ-peak in the inclusive A( 3 He, t) and A ( p , n ) measurements is shifted towards lower energy transfers (in comparison with the reactions on free nucleons) but in the exclusive ones it is shifted towards higher transfers. An attempt is undertaken to determine the characteristics of Δ excitation in nuclei by a ( 3 He, t) reaction that is free of the admixture of quasifree Δ production.