10.2172/10158865

Phys. Lett. B

New experimental results for polarization transfer, κ 0 and the analyzing power, T 20 , in 12 C ( d , p ) X at 0° are present. The measurements have been performed at the Dubna polarized deuteron facility. At high intrinsic momenta of the proton in the deuteron ( k ⩾300 MeV/ c ) the behaviour of these observables is in disagreement with the impulse approximation predictions based on realistic NN-potentials. The data are compared with calculations of some other models predicting the high k behaviour of κ 0 and T 20 .

Z.Phys.C

The study of the properties of inclusive production ofDs mesons and of events in which a ϕ and a muon are present in the same jet provides two independent measurements of the probability,fsw, for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ0 decays. The combined value of these measurements isfsw=0.19±0.06±0.08. From the flight distance distributions ofDs and of (ϕ-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theBs0 meson lifetime. Combining these measurements with a previous result based on the study ofDs-μ events, theBs0 meson lifetime is measured to be: 0.96±0.37 ps.

Phys.Lett.B

An analysis of the production of the Λ baryon in the hadronic decays of the Z 0 is presented, based on about 993K multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. The differencial cross section of the Λ and the correlations between Λ and Λ produced in the same event are compared to current models, based both on string fragmentation and on cluster decay. The predictions of the string fragmentation model are found to give satisfactory agreements with the data, clearly better than those of the cluster model.

Nucl.Instrum.Meth.A

A calorimeter module was fabricated using profiled lead plates and scintillating fibers with diameter 1 mm and attenuation length about 80 cm. The absorber-to-fiber volume ratio was 1.17 and the module average radiation length X 0 ⋍ 1.05 cm . The energy resolution of the module was investigated using the electron beams of U-70 at Serpukhov and of the SPS at CERN in the energy range 5–70 GeV. The energy resolution at θ = 3° (the angle between the fiber axis and the beam direction) may be expressed by the formula σ E (%) = 13.1 E ⊕ 1.7 . The energy resolution was also simulated by Monte Carlo and good agreement with the experiment has been achieved.

Phys.Lett.B

A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392 000 Z 0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/ c 2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit abd its results exclude first and second generation leptoquarks D 0 with masses below 65 GeV/ c 2 and 73 GeV/ c 2 respectively, at 95% confidence level, assuming that the D 0 lq Yukawa coupling α λ is equal to the electromagnetic one. An upper limit is also given on the coupling α λ as a function of the leptoquark mass m D

10.2172/10124115

Nucl. Instrum. Meth. A

A new method of function minimization is developed and a new code (called FUMIVI) is created. Its main features are: i) regular functions of arbitrary structure can be minimized, ii) when minimizing χ 2 -like functions or functionals of a more general case one can use the linearization method, and in case of degeneration FUMIVI may automatically switch to accurate calculation of the second derivatives matrix, iii) nonlinear regular constraints of arbitrary type can be used, iv) both analytical and numerical calculation of the derivatives are possible. The new code was extensively tested both with model and real events of the experiment on rare K-meson decays.

Nucl. Instrum. Meth. A

A number of long scintillator counters employing UPS 923A and NE 114 plastic scintillators seen by a single photomultiplier were tested using cosmic muons. These counters have suitable dimensions to be used in large arrays in a proton supercollider experiment. The efficiency for m.i.p. was excellent in all cases. The yield of UPS 923A was found to be by about 25% higher than NE 114, while the attenuation length was approximately the same.

Phys.Lett.B

A search for Ks0→e+e− decay was performed by means of a 624-channel lead glass shower hodoscope and a set of proportional chambers. Neutral kaons were obtained in the quasibinary charge exchange reaction. A new upper limit of 2.8×10 −6 at 90% C.L. for the branching ratio is obtained.

J.Phys.A

Based on the Maslov complex germ theory, a method of constructing the quasi-classical spectral series for the Dirac operator is proposed. The case when the corresponding relativistic Hamiltonian system is non-integrable and it admits a family of invariant two-dimensional stable Lagrangian tori containing the focal points is considered. The resulting quantization conditions for the above family generalize the Bohr-Sommerfeld-Maslov conditions and include new additional characteristics. The quasi-classical asymptotics obtained are regular over the full classically allowed domain. They also form an asymptotically complete and orthonormal set. Examples which use the proposed technique of the quasi-classical quantization are analysed.

Mod.Phys.Lett.A

We present the first measurement of the left-right cross-section asymmetry (ALR) in Z-boson production observed at the SLAC Linear Collider. In 1992 the SLD detector recorded 10 224 Z events produced by the collision of longitudinally polarized electrons with an unpolarized positron beam at a center-of-mass energy of 91.55 GeV. The average electron beam polarization during the run was (22.4 ± 0.6)%. We measure ALR to be 0.100 ± 0.0440 (stat.) ±0.004 (syst.), which determines the effective weak mixing angle to be $\sin^2\theta_W^{\rm {eff}} = 0.2378\pm 0.0056\, ({\rm stat.})\pm 0.0005\, ({\rm syst.})$.

Phys.Lett.B

The decays of B -hadrons have been reconstructed using the charged particles recorded in the DELPHI silicon microstrip detector. The sum of the charges of the secondaries determines the charge of the B -hadron parent. Some 232 114 multihadronic Z 0 decays recorded during the 1991 run of LEP at centre-of-mass energies between 88.2 GeV and 94.2 GeV yield 253 B -hadron candidates with well-measured charge. From these the mean lifetimes of neutral and charged B -hadrons are found to be 1.44±0.21 (stat.)±0.14(syst.) ps and 1.56±0.19(stat.)±0.13(syst.) ps respectively. The ratio of their lifetimes is 1.09 −0.23 +0.28 (stat.) ± 0.11(syst.). Under some assumptions on the abundance and lifetime of the Λ b 0 and B s 0 states, the B 0 and B + lifetimes are inferred.

Nucl.Phys.B

Based on a sample equivalent to 365 000 hadronic Z 0 decays, the search in DELPHI data for pairs of leptons accompanied by a pair of charged particles is described. A total of 11 events were found in the electron channel, 9 in the muon channel and 7 in the tau channel. Results on lepton pairs with a radiated photon are also presented. The data from all channels are compatible with the expectations from standard processes. However, one event was found in the tau channel with an unusually high mass of the charged particle pair.

Phys.Lett.B

A determination of the hadronic fragmentation functions of the Z 0 boson is presented from a study of the inclusive hadron production with the DELPHI detector at LEP. These fragmentation functions were compared with the ones at lower energies, thus covering data in a large kinematic range: 196 ⩽ Q 2 ⩽ 8312 GeV 2 and x (= P h E beam ) > 0.08 . A large scaling violation was observed, which was used to extract the strong coupling constant in second order QCD: α s ( M Z ) = 0.118 ± 0.005. The corresponding QCD scale for five quark flavours is: Λ (5) MS = 230 ± 60 MeV .

Z. Phys. C

A study of the fragmentation properties of charm and bottom quarks intoD mesons is presented. From 263 700Z0 hadronic decays collected in 1991 with the DELPHI detector at the LEP collider,D0,D+ andD*+ are reconstructed in the modesK−π+,K−π+K+ andD0π+ followed byD0→K−π+, respectively. The fractional decay widths\(\Gamma {{(Z^0\to {D \mathord{\left/ {\vphantom {D {\bar D}}} \right. \kern-\nulldelimiterspace} {\bar D}}X)} \mathord{\left/ {\vphantom {{(Z^0\to {D \mathord{\left/ {\vphantom {D {\bar D}}} \right. \kern-\nulldelimiterspace} {\bar D}}X)} {\Gamma _h }}} \right. \kern-\nulldelimiterspace} {\Gamma _h }}\) are determined, and first results are presented for the production ofD mesons from\(c\bar c\) and\(b\bar b\) events separately. The average energy fraction ofD*± in charm quark fragmentation is found to be 〈XE(D*)〉c=0.487±0.015 (stat)±0.005 (sys.). Assuming that the fraction ofDs and charm-baryons produced at LEP is similar to that around 10 GeV, theZ0 partial width into charm quark pairs is determined to beΓc/Γh=0.187±0.031 (stat)±0.023 (sys). The probability for ab quark to fragment into\(\bar B_s \) orb-baryons is inferred to be 0.268±0.094 (stat)±0.100 (sys) from the measured probability that it fragments into a\(\bar B^0 \) orB−.

Nucl.Phys.A

The double strangeness production has been observed in two final states of annihilation of antiprotons at momentum less than 0.9 GeV/ c on Xe nuclei: K + K + X (8 events) and K + K 0 ΛX (6 events). The probabilities of the reaction p Xe → K + K + X vary from 2 · 10 −5 (at rest) up to 7 · 10 −5 (in flight). The reaction p Xe → K + K 0 ΛX is observed only in flight with probability 3 · 10 −4 . The properties of the observed reactions are similar to those resulting from the cascade process with production of Ξ hyperon: p N → K ∗ −K ∗ , K ∗ → Kπ, −K ∗ N → ΞK, ΞN → ΛΛ . The new upper limit on the production probability of the stable H ( S = −2) dibaryon in the reaction Xe → K + K + H(H → Σ − p)X was obtained to be < 2 · 10 − (90% C . L .).

Z.Phys.C

A new measurement of αs is obtained from the distributions in thrust, heavy jet mass, energy-energy correlation and two recently introduced jet broadening variables following a method proposed by Cata

Phys. Lett. B

The strong coupling constant for b quarks has been determined, and its flavour independence, as predicted by QCD, investigated. The analysis involved events with lepton candidates selected from approximately 356 000 hadronic decays of the Z 0 , collected by the DELPHI detector at LEP in 1990 and 1991. A method based on a direct comparison of the three-jet fraction in a b enriched sample, selected by requiring leptons with large momenta, to that of the entire hadronic sample, illustrated the significant effect of the b quark mass on the multi-jet cross section, and verified the flavour independence of the strong coupling constant to an accuracy of ±6%. A second procedure based on a fit to the momentum and transverse momentum spectra of the lepton candidates in both two-jet and three (or more)-jet event samples simultaneously determined the b content in each, and, using second order QCD calculations, gave an absolute measurement of α s for b quarks of 0.118±0.004 (stat.)±0.003 (syst.)±0.008 (scale). A comparison with α s for all quark flavours, as measured from the three-jet fraction in all hadronic events, further allowed the coupling strength for b quarks to be expressed in terms relative to that for udsc quarks, thereby cancelling certain common systematic uncertainties, and yielded α s b α s udsc = 1.00 ± 0.04 ( stat. ) ± 0.03 ( syst. ) .

Z.Phys.C

This constitutes a convincing model-independent proof of the existence of the triple-gluon vertex, since its contribution is directly proportional toCA/CF. The results are in agreement with the values expected from QCD:CA/CF=2.25, andNC/NA=3/8.

Phys. Lett. B

Evidence for the production of b -flavoured baryons in Z 0 decays is reported from the analysis of 365 000 hadronic events collected by the DELPHI detector. Assuming that most of the weakly decaying b flavoured baryons produced by the Z 0 are Λ b , the observed signal of (Λ − + Λ l + ) pairs, where l is a high transverse momentum lepton in the same jet as the Λ, leads to a production rate: f ( b → Λ b )×Br( Λ b → Λlν X ) = (0.41±0.13±0.09)%. Using a sample of 18 reconstructed Λ b decay vertices, the lifetime is determined to be τ ( Λ b ) = (1.04 +0.48 −0.38 ±0.10) ps.

Phys.Lett.B

In the experiment 272±49 atoms consisting of π + and π + − mesons were observed. The atoms were produced in a Ta target by 70 GeV protons and π + and π − mesons were detected from the atom break-up in the same target.

Phys. Scripta

A universal facility is in preparation for the study of particle production in proton-nucleus reactions below the nucleon-nucleon threshold. The device will be located at the internal target position TP2 at COSY-J?lich and will consist of three dipole magnets. This 0? Facility will separate ejectiles from the circulating proton beam and allow momentum and angle analysis both for positively and negatively charged particles. A major goal of the experimental program is the investigation of the K+-meson production at projectile energies below the NN threshold. The detector concept for these studies is described and also an overview over further planned experiments is given.

Phys. Lett. B

The tau lepton lifetime is measured using four different methods with the DELPHI detector. Three measurements using one prong decays are combined, accounting for correlations, resulting in τ τ =298 ±7 (stat.)±4 (syst.) fs while the decay length distribution of three prong decays gives π π =298±13 (stat)±(syst.) fs. The combined result is τ τ =298±7 fs. The ratio of the Fermi coupling constant from tau decay relative to that from muon decay is found to be 0.985±0.013, compatible with lepton universality.

Phys.Lett.B

Total cross sections for the reaction π + d → pp have been measured for incident pion energies T π =26.5, 28.5, 30.5, 32.5 and 39.5 MeV. The data are in good agreement with previous experiments. There is some indication of a peculiarity in the energy dependence of the total cross section near incident pion energy T π =30 MeV.